EP4662445A1 - Electrocaloric devices using ferroelectric nematic material - Google Patents

Abstract

An electrocaloric device based on a liquid material suitable for cooling and heat management. The liquid crystalline material designated for the device is operated in or in vicinity of the ferroelectric nematic phase. The device has broad operating temperature, high induced temperature change, while requiring modest electric field strengths.

Description

P23-010 - 1 - Electrocaloric devices using ferroelectric nematic material An electrocaloric device based on a liquid dielectric material suitable for cooling and heat management. The liquid crystalline material designated 5 for the device is operated in or in vicinity of the ferroelectric nematic phase. The device has a broad operating temperature, high induced temperature change, while requiring modest electric field strengths. The electrocaloric effect (EC effect) is the induction of a reversible 10 temperature change in a material via the adiabatic application and removal of an electric field. The EC effect, which is based on a change of the electric field on the active material, has long been regarded as having potential as a cooling technology. However, conventional electrocaloric materials (EC materials) offer only small induced temperature changes 15 (ΔT) or require application of relatively large voltages. Some EC materials with larger temperature changes are found in the class of ferroelectric ceramics and ferroelectric polymers, as reviewed in X. Moya et al, Nature Materials 2014, 13, 439-450. The most effective studies on 20 materials and applications were made using thin films of materials rather than bulk materials. Due to the mostly solid nature of the EC materials a heat exchange between the active material and surrounding material is necessary for building a real life heat pump. 25 It was found that also liquid crystals (LC) show an electrocaloric effect, which is increased by the choice of ferroelectric smectic LC materials (P. J. Tipping, H. F. Gleeson, Crystals 2022, 12, 809). Mostly the temperature range of highest EC efficiency is confined to the 30 vicinity of a certain temperature. The working temperature of different EC materials varies significantly, some of which are close to room temperature and others are far above or below room temperature. The working temperature range of different EC materials also varies significantly for different materials. The choice of material is crucial for the desired 35 temperature of the cooling application. P23-010 - 2 - In a typical cooling process (Fig.1) an electric field is adiabatically applied to the working material (electrocaloric material) while the material is isolated from the load. The temperature of the material increases as a result of being subject to the electric field (adiabatic temperature change 5 ΔT). The material is placed in thermal contact with a heat sink while the electric field is maintained, and the material transfers thermal energy to the heat sink, which causes a decrease in temperature and entropy in the material. The material is then isolated from the heat sink and the electric field is removed, which causes the temperature of the material to decrease 10 by ΔT. The material is then exposed to the cooling load, where the material will absorb thermal energy from the load and its temperature increases. The material is then isolated from the load and the process is repeated (reversed Brayton cycle). ΔS and ΔT are parameters for the performance of a dielectric material for use in a cooling process. 15 In previous years, the areas of application for liquid crystal compounds have been considerably expanded to various types of display devices. Most of these devices employ the enantiotropic nematic liquid crystal phase, including all common LCD television sets, LCD desktop monitors 20 and mobile LCD devices. Some alternative liquid crystalline phases are known, like ferroelectric smectic phases or blue phases. However, a ferroelectric nematic phase (Nf-LC phase) had been postulated by theory for decades only, without finding a suitable liquid crystalline material with such nematic and ferroelectric property. Only recently, a few chemical 25 structures have been reported to show ferroelectric nematic behavior. Exemplary, a ferroelectric nematic substance of formula C is published by Atsutaka Manabe, Matthias Bremer, Martin Kraska (2021): Ferroelectric phase at and below room temperature, Liquid Crystals, 48, 1079-1086 (DOI 10.1080/02678292.2021.1921867), which is described to have a 30 monotropic ferroelectric nematic liquid crystalline phase (Nf-LC phase) close to ambient temperature. 35 P23-010 - 3 - Disadvantages of conventional solid electrocaloric materials are their solid nature, causing immobility of the thermic effect, and breakdown of the effect in thicker layers. Solid materials are also prone to material fatigue 5 building up over repeated cooling cycles. Electrocaloric material undergoing a change in the electric field at a given starting temperature can be assayed by evaluation of the adiabatic temperature change (ΔT), isothermal entropy change ΔS and isothermal 10 heat Q. Direct measurement remains a challenge. Indirect measurements repeatedly use the Maxwell approach to determine the temperature change. An expression for the isothermal entropy change per unit volume, ΔS/V, as a function of electric field can be derived using the Maxwell relation between the electric field and temperature, 15 w^{here E1 and E2 are the initial and final field strengths and is the} 20 rate of change of spontaneous polarisation with respect to temperature at a constant field strength. The indirect measurement of Q is obtained by the relation Q = T∙ΔS. 25 Assuming that the initial temperature and the volumetric heat capacity do not vary with the applied field, an estimate of the induced temperature change, ΔT, is 30 T^{1: initial temperature at which the electric field is applied, ^(^,^^): volumetric heat capacity at E = 0,} 35 ^^{^^} ^_^^_^ ^{: change in dielectric polarisation with temperature, at a fixed electric} field. P23-010 - 4 - Temperature changes obtainable by the electrocaloric effect in conventional liquid crystals are usually small. In addition, in conventional LC materials the known working temperature range of the electrocaloric 5 effect is limited to 1 K or less and fixed around the isotropic-liquid crystal phase transition temperature. So far no material has been found which fulfills the minimum criteria for applicability in an electrocaloric device in each relevant parameter. 10 The current invention aims at reducing these drawbacks and combining all practical requirements in a single electrocaloric material and device. Short description of the invention 15 In a first aspect the current invention relates to an electrocaloric device comprising two or more electrodes for generating an electric field in a space volume distributed between at least two of the electrodes, a dielectric material positioned at least partly in said space volume, wherein the dielectric material comprises one or more liquid crystalline (LC) 20 materials having a ferroelectric nematic phase. Said ferroelectric nematic LC material preferably comprises at least two compounds with a molecular structure of formula I, 25 I 30 35 A² denotes P23-010 - 5 - 5 10 A³ denotes 15 R¹ is an alkyl radical having 1 to 12 C atoms, preferably 1 to 8, more 20 preferably 1 to 6 and most preferably 1 to 5 C atoms, where, in addition, one or more CH2 groups in these radicals may in each case be replaced, independently of one another, by -C≡C-, -CF2-O-, -OCF2-, -CH=CH-, , 25 such a way that O/S atoms are not linked directly to one another, and in which, in addition, one or more H atoms may be replaced by halogen, or denotes H, X is CN, F, CF3, -OCF3, -NCS, Cl, preferably CN or F, 30 L¹ is H or CH3, Z¹ is -CF2O- or -(CO)-O- or a single bond, and Z² is -CF2O- or -(CO)-O- or a single bond. P23-010 - 6 - The invention further relates to a process for cooling an object using the electrocaloric response of a ferroelectric nematic liquid crystal and to a process for cooling an object using the electrocaloric device as described throughout this disclosure. 5 The invention further relates to use of a liquid crystal material having a ferroelectric nematic liquid crystal phase as an electrocaloric dielectric material in a heat pump or cooling device and to use of a electrocaloric device as describes throughout this disclosure as a cooling device, namely 10 for electronic devices, preferably processors, transistors and integrated circuits. A further aspect of the invention is a method of preparation of an electrocaloric device comprising two or more electrodes for generating an 15 electric field in a space volume distributed between at least two of the electrodes, wherein the method comprises inserting a dielectric material comprising a ferroelectric nematic liquid crystalline material at least partly into said space volume. 20 In one aspect of the invention the electrocaloric device induces or can be configured to induce a temperature change in the dielectric material upon change of the electric field across the volume between the electrodes. An aspect of the invention relates to using liquid crystalline media 25 exhibiting a ferroelectric nematic liquid crystalline phase over a substantial range of temperatures, preferably at ambient temperature as the dielectric material. Ambient temperature, also sometimes called room temperature, means in 30 a narrower sense a temperature of 20°C here. More generally it means the starting temperature of an electrocaloric process. The disclosure includes stable compounds which are suitable as component(s) of ferroelectric nematic liquid crystal media, in particular 35 for application to the electrocaloric devices of the present invention. P23-010 - 7 - Surprisingly, it has been found that a ferroelectric nematic liquid crystalline material can achieve a strong electrocaloric behavior in an highly advantageous broad temperature range, preferably up to 10 K or more. The working range is located at the upper transition temperature 5 of the Nf-LC phase and may extend above and below this transition temperature (e. g. +/- 10 K or more). The electrocaloric response is distributed over this range. For narrow transition ranges the electrocaloric response is relatively higher. The ferroelectric nematic liquid crystalline material can be used as LC media with unprecedent 10 properties, including liquid crystal media for electrocaloric devices making use of the high spontaneous polarisation P_S and electrocaloric efficiency ΔTmax/ΔE of the materials. The media and compounds used according to the invention are sufficiently chemically stable. In particular, they are distinguished by 15 extraordinarily high dielectric constants and in particular by very high dielectric anisotropies (Δε). The compounds have reasonably good solubility for compounds having comparable properties and can be admixed with similar compounds. The compounds involved also have relatively low melting points, or can be stably kept below their melting 20 point as super-cooled melts. The invention enables the formation of the Nf-LC phase and any adjacent transitional phase(s) in an advantageous working range. The working range can be advantageously adapted to the temperature and range needed by varying the liquid crystal media. 25 The liquid crystalline phase is inherently stable at its preferred temperature range, unlike solid crystals, which macroscopic lattice is prone to mechanical decay and to material fatigue by accumulated irreversible disorder of the lattice. As damage sums up in a solid system, the liquid system may always return to its initial ordering as long its 30 molecules are stable. Surprisingly it is found that the Nf-LC materials respond to relatively small electric fields, typically between 0.5 V/µm and 5 V/µm. Compared to prior art material, e.g. polymers or ceramics, the polarisation saturates 35 already at very low electric fields. P23-010 - 8 - The moderate volumetric heat capacity enables outstanding physical performance. In addition, the media have very low electric conductivity, are insulators, and are unique over conventional high-εr materials (e.g. lead zirconate titanate ceramics). The combination of low electric 5 conductivity with low required electric fields result in low electric losses. The ferroelectric nematic materials are more fluid than the highly viscous smectic materials, which enables the current materials to move through pipes of a device as a thermal carrier. 10 Short description of the drawings: Fig.1 shows a schematic diagram of a typical electrocaloric cooling process of an electrocaloric device. The cooling process involves two constant entropy transitions, (a) to (b) and (c) to (d), and two constant field 15 transitions, (b) to (c) and (d) to (a). The arrows within the boxes denote the alignment of molecular dipoles in the system. The material starts at state (a) at ambient temperature, T1, with no field applied, E1=0, and an initial entropy, S_($^,%^). Adiabatically applying a field, E2, to the material (b) causes a caloric temperature increase by ΔT to T2. The excess heat is 20 allowed to transfer to the heat sink while the field is maintained, which causes the temperature to return to T1 (c), and consequently there is a decrease in entropy to S_($^,%^). Adiabatic removal of the field will cause a caloric temperature decrease of ΔT to T3, (d), at which point the material absorbs thermal energy from the heat load and is restored to the original 25 state (a). Fig.2 shows a graph representing the measurement of the spontaneous polarisation P_S in nC∙cm^-2 of a ferroelectric nematic LC mixture (M-9) over temperature (30 - 80°C) at a constant field strength (1.0 V/µm). Further 30 details are described in the related example. Fig.3 shows a first graph (dotted line) representing the electrocaloric temperature change ΔT (in K) of the ferroelectric nematic LC mixture M-9 over the reduced temperature T-TF (K), where ΔT is derived from 35 integration over dE of the slice functions of dP/dT at varying fields E (equation 2). A second graph (crosses) shows ΔT of a comparative P23-010 - 9 - ferroelectric smectic LC material “LC 1”. TF is the upper end transition temperature of the ferroelectric nematic phase. Fig.4 shows the graph of Fig.2 and two curves at lower field strengths (0.4 5 and 0.8 V/µm). Detailed description In one major aspect of the invention the electrocaloric device works as a heat pump or cooling device (electrocaloric cooling device, ECC device). 10 The invention therefore also relates to an electrocaloric heat pump or an electrocaloric cooling device. The electrocaloric device has means to dissipate heat from the medium (liquid dielectric material) to a heat sink (heat exchanger). The heat sink can be a conventional cooling system like a connection to open air, a second cooling medium, a heat guiding material 15 (preferably metal, e.g. copper, silver, etc.) or a combination thereof. The invention also relates to an electrocaloric device wherein the dielectric material is used as a heat-exchange fluid. In this preferred embodiment of the invention the dielectric material is liquid. The electrocaloric device 20 preferably comprises a channel for exchange of the liquid dielectric medium. Preferably the device further comprises a pumping mechanism for exchanging the dielectric medium in the space volume between the electrodes. The liquid dielectric medium may be guided in a loop through the electrocaloric device and other regions which are to be cooled or 25 warmed. Preferably the device according to the invention comprises a loop for the liquid medium, wherein the volume of the loop includes said space volume of said electric field between the electrodes. The loop preferably comprises one or more heat exchange zones. Preferably the volume of the loop is configured in a way to be or get thermally connected to a heat load, 30 i.e. an object that shall be cooled. This is usually attached to the loop via a heat exchange zone. In this embodiment optionally one or more pumps for the liquid medium are connected to the loop for circulation of the liquid medium. Optionally one or more heat exchangers are connected to the closed loop. In a preferred mode of operation a voltage between the 35 electrodes causes a temperature increase of the medium, which is absorbed by a heat sink corresponding with the electrode volume. - 10 - Preferably the electrocaloric device comprises a pumping mechanism for transporting the dielectric medium in the space volume between the electrodes. In a more preferred mode of operation the pump transports the volume of medium between the electrodes to another volume outside the 5 electrode volume, thereby removing the electric field from said first volume of medium, and thereby causing a temperature decrease. The transported volume of cooler medium may be used for cooling purposes, while a following volume of medium enters the electrode volume, transfers some of its heat to the heat sink, and so on. A continuous mode operation of the 10 cooling device results by a circulating medium. The devices may be cascaded, wherein the heat sink of one device is provided by the cooling medium of another. The optional spatial separation of heat sink and cooled medium is an advantage of this invention. Stacked multilayer electrocaloric devices of prior art inherently have only limited distance between the cool 15 and warm zone and are prone to detrimental heat flow between the zones. The electrocaloric device according to the invention preferably has a controlled voltage source connected to the electrodes. Electric voltage can be applied constantly or at intervals depending on the operation mode of 20 the device. The voltage control is preferably adapted for the pumping mechanism. Preferably the voltage and the pumping mechanism are in a continuous mode during operation. The interaction of voltage at the electrodes and pumping may be controlled by a microprocessor. 25 The liquid crystal medium for use in the devices according to the invention is preferably operated at and closely above temperatures in which the medium has a ferronematic phase. The preferred range above is up to 20 K above the upper transition temperature of the Nf-LC phase, more preferably 10 or 5 K above. The choice of medium determines the 30 temperature range where the electrocaloric effect is most efficient. The highest effect can be expected in a temperature range close to the upper temperature transition temperature of the ferroelectric nematic phase range, preferably in a range of +/- 3 K of the transition temperature. Often a transition from ferroelectric nematic to another ferrielectric phase or a 35 nematic phase (transitional phase) is observed at the upper transition temperature of the ferroelectric nematic phase. Preferably the - 11 - electrocaloric device is operated with a LC material which has a ferroelectric nematic phase within or in vicinity of the working temperature of the working range of the electrocaloric device. Also preferred is a medium having a spontaneous polarisation of greater than Ps of 1000 nC 5 cm^-2 or more within the working temperature range of the electrocaloric device. The suitable ferroelectric materials show a ferroelectric response to an applied electric field within the working temperature range of the device. A ferroelectric response means that the spontaneous polarisation P (or the relative dielectric permittivity εr) is modified (respectively increased), by a 10 change (respectively increase) of the electric field. Preferably the electrocaloric material increases in temperature upon application of a voltage thereto and decrease in temperature upon removal of a voltage. The electrocaloric device preferably has a working temperature of 15°C or 15 more, more preferably 20°C or more, most preferably 30°C or more, and preferably of 60°C or less, preferably 50°C or less and more preferably 45°C or less. The temperature of maximum electrocaloric efficiency can be tailored by use of suitable LC media with the appropriate transition temperatures of the ferroelectric nematic phase into the adjacent phases 20 (typically N2, N or isotropic phase). Accordingly, the preferred device has a working temperature range located inside the range of 15 to 60°C, more preferably 20 to 50°C. In the following the dielectric media comprising a ferroelectric nematic 25 liquid crystal medium are further described. The liquid crystalline (LC) materials having a ferroelectric nematic (Nf) phase which are comprised as the dielectric material (further also addressed as the liquid crystalline media) preferably comprise at least 30 20 % by weight or more, preferably 50 % by weight or more, more preferably 60 % by weight or more, and even more preferably 65 % by weight or more of compounds selected from compounds with a molecular structure of formula I. The material or the medium preferably comprises three, four, five or six or more of compounds of formula I. Preferably the 35 compounds of formula I are selected from compounds of the following formulae IA, IB and IC, preferably and independently for each formula in P23-010 - 12 - the percentages provided with each formula. Preferably the LC media comprise one or more compounds of formula I, more preferably of each of the formulae IA and IB and one or more of IC-1 to IC-3 as defined below. Alternatively the media comprise one or more compounds of each of 5 formula IB and of formula IC. Preferably the liquid crystalline medium used on the electrocaloric device has an enantiotropic ferroelectric nematic phase. The liquid crystalline medium preferably has a ferroelectric nematic phase at a temperature 10 within the working temperature of the electrocaloric device, this may be preferably at or below 30 °C. Preferably the liquid crystalline medium has a ferroelectric nematic phase at a temperature interval of at least 10 K. In a more preferred embodiment the invention uses liquid crystalline media 15 comprising 10 %, preferably 15 % by weight or more of one or more compounds of formula IA, 20 10% by weight, preferably 15 % by weight or more of one or more of 25 compounds of formula IB, 30 and 10% by weight, preferably 15% by weight, more preferably 20 % by weight or more of one or more compounds selected from formula IC-1 to 35 IC-3, P23-010 - 13 - 5 10 in which X^1B denotes -CN or -NCS, preferably -CN, 15 X^1C denotes -CN, F, CF3, -OCF3, -NCS, SF5 or O-CF=CF2, preferably -CN or F, most preferably CN, Z^1A and Z^1B independently of one another denote -(CO)-O- or -CF2-O- or 20 a single bond, preferably -(CO)-O- or -CF2-O-, Z^2A and Z^2B independently of one another denote a single bond, -(CO)-O- or -CF2-O-, 25 preferably a single bond, Z^1C and Z^2C one of the both groups denotes -(CO)-O- or -CF2-O- and the other a single bond, preferably Z^1C is -(CO)-O- or -CF2-O-and Z^2C is a single 30 bond, L^1A, L^1B and L^1C independently of each other denote H or CH3, preferably H, 35 L^2A is F or H, preferably F, P23-010 - 14 - L^2C is F or H, preferably F, A^1A denotes 5 10 15 most preferably 20 A^1B denotes 25 30 wherein L^8B denotes alkyl, alkoxy or alkoxyalkyl, each with 1 to 7 C atoms, preferably CH3, OCH3, OCH2CH3, CH2OCH3, CH2OCH2CH3, 35 CH2CH2OCH3, CH2CH2OCH2CH3 or CH2CH2CH2OCH3, P23-010 - 15 - A^1C independently denotes 5 10 15 20 25 A^2C denotes 30 preferably 35 P23-010 - 16 - 5 m, n 0, 1 or 2, where (m + n) is 1 or 2, preferably 2, R^1A, R^1B and R^1C independently of each another denote an alkyl radical 10 having 1 to 12 C atoms, preferably 1 to 8, more preferably 1 to 6 and most preferably 1 to 5 C atoms, where, in addition, one or more CH2 groups in these radicals may in each case be replaced, independently of one another, by -C≡C-, -CF2-O-, 15 a way that O/S atoms are not linked directly to one another, and in which, in addition, one or more H atoms may be replaced by halogen, or denotes H, 20 preferably R^1A, R^1B and R^1C independently are a halogenated or unsubstituted alkyl radical having 1 to 10 C atoms, where, in addition, one or more CH2 groups in these radicals may be replaced by -O- or -CH=CH- in such a way that O atoms are not 25 linked directly. The percentages are provided under the circumstance that the whole medium makes up 100% by weight of the medium. Usually the medium represents 100 % of the liquid part of dielectric material. 30 The radicals R^1A , R^1B and R^1C in the respective formulae IA, IB and IC-1 to IC-3 and their respective sub-formulae preferably denote alkyl having 1 to 8 carbon atoms, alkoxy having 1 to 8 carbon atoms or alkenyl having 2 to 8 carbon atoms. These alkyl chains are preferably linear or they, preferably 35 in case of R^1C, are branched by a single methyl or ethyl substituent, preferably in 2- or 3-position. R^1A, R^1B and R^1C particularly preferably P23-010 - 17 - denote a straight-chain alkyl radical having 1 to 7 C atoms or an unbranched alkenyl radical having 2 to 8 C atoms, in particular unbranched alkyl having 1 to 5 C atoms. 5 Alternative preferred radicals R^1A, R^1B and R^1C are selected from cyclopentyl, 2-fluoroethyl, cyclopropylmethyl, cyclopentylmethyl, cyclopentylmethoxy, cyclobutylmethyl, 2-methylcyclopropyl, 2- methylcyclobutyl, 2-methylbutyl, 2-ethylpentyl and 2-alkyloxyethoxy. 10 Compounds of the formula IA, IB and IC1 to IC-3 containing branched or substituted end groups R^1A, R^1B and R^1C, respectively, may occasionally be of importance owing to better solubility in the liquid-crystalline base materials. The groups R^1A, R^1B and R^1C, respectively, are preferably straight chain. 15 The radicals R^1A, R^1B and R^1C, respectively, particularly preferably selected from the moieties: CH3- C2H5- 20 n-C3H7- n-C4H9- n-C5H11- C2H5CH(CH3)CH2- n-C6H13- 25 n-C7H15- n-C3H7CH(C2H5)CH2- n-C8H17- c-C3H5- c-C3H5CH2- 30 c-C4H7- c-C5H7- c-C5H9- c-C5H9CH2- CH2=CH- 35 CH3CH=CH- CH2=CH(CH2)2- P23-010 - 18 - CH3O- C2H5O- n-C3H7O- n-C4H9O- 5 n-C5H11O- CH3OCH2- C2H5OCH2- CH3OCH2CH2- C2H5OCH2CH2- 10 c-C3H5CH2O- c-C5H9CH2O- wherein the following abbreviations for the end groups are used: 15 ^c-C3H5- c-C³H⁵CH²- c-C4H7- c-C5H7 20 c-C5H9- and c-C5H9CH2- . 25 In a preferred embodiment, the media according to the present invention preferably comprise one, two, three or more compounds of formula IA-1 30 35 preferably selected from the group of formulae IA-1 to IA-3, preferably of formula IA-1: P23-010 - 19 - 5 10 15 in which the parameters have the respective meanings given above and 20 preferably Z^1A denotes -CF2-O-. In a preferred embodiment, the media according to the present invention 25 preferably comprise one, two, three or more compounds of formula IB-1 and/or IB-2, preferably of formula IB-1, 30 35 P23-010 - 20 - R^1B denotes an alkyl radical having 1 to 12 C atoms, preferably 1 to 7, more preferably 1 to 6 and most preferably 1 to 5 C atoms, where, in addition, one or more CH2 groups in these radicals 5 may in each case be replaced, independently of one another, by in such a way that O/S atoms are not linked directly to one 10 another, and in which, in addition, one or more H atoms may be replaced by halogen, or denotes H, preferably R^1B is a halogenated or unsubstituted alkyl radical having 1 to 12 C atoms, where, in addition, one or more CH2 15 groups in these radicals may in each case be replaced, independently of one another, by -C≡C- or -CH=CH-, A^1B denotes 20 25 30 and Z^1B, Z^2B independently denote -(CO)-O- or -CF2-O-, 35 preferably selected from the group of the following formulae, formulae IB-1- 1 to IB-2-3,: P23-010 - 21 - 5 10 15 20 25 30 in which the parameters have the respective meanings given above and, in particular, in formula IB-1-1 to IB-1-3, Z^1B preferably denotes -CF2-O- 35 and, in particular, in formula IB-2-1 and IB-2-2, P23-010 - 22 - Z^2B denotes preferably -CF2-O-; and, in particular, in formula IB-2-3, Z^2B denotes preferably -C(O)O-. 5 In a preferred embodiment, the media according to the present invention preferably comprise one, two, three or more compounds selected of formulae IC-1-1 to IC-3-5: 10 15 20 25 30 35 5 wherein A^1C and A^2C are defined as above, preferably selected from the group of formulaeIC-1-1-1 to IC-3-5-2, preferably selected from the group of formulae IC-1-1-1, IC-1-1-2, IC-1-1- 10 3, IC-1-1-4, IC-3-1-1 and IC-3-2-1: 15 20 25 30 35 - 24 - P23-010 - 25 - 5 10 15 20 in which the parameters have the respective meanings given above and preferably 25 L^1C denotes H, Z^1C denotes -CF2-O- or -(CO)-O-, and X^1C denotes -CN or F, preferably -CN. 30 Particularly preferred compounds of the formula IC-1-1 to IC-1-4 used in the media are the compounds of the formulae below: 35 P23-010 - 26 - 5 10 15 20 wherein the parameters are defined as above, preferably L^1C is H. In a preferred embodiment of the present invention the media comprise up to 100 % by weight of one or more compounds, preferably of three, four, five, six or more, compounds selected from group 1 of compounds, the 25 group of compounds of formulae IA, IB and IC-1/-2/-3. In this embodiment the media and/or LC materials preferably predominantly consist of, more preferably they essentially consist of, and most preferably, they virtually completely consist of these compounds. 30 For the present invention, the following definitions apply in connection with the specification of the constituents of the compositions, unless indicated otherwise in individual cases: - "predominantly consist of": the concentration of the constituents in 35 question in the composition is preferably 50 % by weight or more, P23-010 - 27 - particularly preferably 55 % by weight or more and very particularly preferably 60 % by weight or more, - "essentially consist of": the concentration of the constituents in question 5 in the composition is preferably 80 % by weight or more, particularly preferably 90 % or more and very particularly preferably 95 % by weight or more, and - "virtually completely consist of": the concentration of the constituents in 10 question in the composition is preferably 98 % by weight or more, particularly preferably 99 % or more and very particularly preferably 100.0 % by weight. Preferably the LC media and/or the dielectric materials applied according 15 to the present application fulfil one or more of the following conditions. The LC materials, in particular the LC media, preferably comprise: - 20 % by weight or more of compounds of formula IA, more preferably 25 %, more preferably 27 % or more and most preferably 32 % by 20 weight by weight or more of compounds of formula IA, - 17 % by weight or more of compounds of formula IB, more preferably 20 % or more, more preferably 22 % or more and most preferably 25 % by weight or more of compounds of formula IB, 25 - 20% by weight or more, preferably 25 % or more of compounds selected of formula IC-1, IC-2 and IC-3, more preferably 28 %, more preferably 32 % or more and most preferably 34 % by weight or more, 30 - optionally 2 % by weight or more of compounds of formula ID (ID-1, ID- 2, ID-3, ID-4), more preferably 5 %, more preferably 10 % or more and most preferably 15 % by weight or more of compounds of formula ID, - one, two, three or more, preferably three or more, compounds of the 35 formula IA-1-1, preferably of formula DUUQU-n-F, most preferably P23-010 - 28 - selected from the group of the compounds DUUQU-2-F, DUUQU-3-F, DUUQU-4-F and DUUQU-5-F and DUUQU-6-F, - one, two, three or more, preferably three or more, compounds of the 5 formula IB-1, preferably of formulae GUUQU-n-N and/or DUUQU-n-N, most preferably selected from the group of the compounds GUUQU-2- N, GUUQU-3-N, GUUQU-4-N, GUUQU-5-N, GUUQU-6-N, GUUQU-7- N, DUUQU-2-N, DUUQU-3-N, DUUQU-4-N, DUUQU-5-N and DUUQU- 6-N, 10 - one, two, three or more compounds of the formula IA-1-3, preferably of formula GUUQU-n-F, more preferred selected from the group of the compounds GUUQU-3-F, GUUQU-4-F and GUUQU-5-F, 15 - one, two, three or more compounds of the formula IB-1-3, preferably of formula DUUQU-n-N, more preferred selected from the group of the compounds DUUQU-3-N, DUUQU-4-N and DUUQU-5-N, - one, two, three or more compounds of the formula IC-1-1, preferably of 20 formula MUZU-n-N or MUQU-n-N, more preferred selected from the group of the compounds MUZU-2-N, MUZU-3-N, MUZU-4-N and MUZU-5-N, - one, two, three or more compounds of the formula IC-3, preferably 25 selected from the formulae MUU-n-N or UMU-n-N, more preferably selected from the group of the compounds MUU-3-N, MUU-4-N, MUU- 5-F, UMU-3-N, UMU-4-N and UMU-5-N, - one, two, three or more compounds of the formula IC-1-1, preferably 30 selected from the formulae GUZU-n-N or GUQU-n-N, more preferably selected from the group of the compounds GUZU-3-N, GUZU-4-N, GUZU-5-F, GUQU-3-N, GUQU-4-N and GUQU-5-N, and/or 35 P23-010 - 29 - - one, two, three or more compounds of the group of formulae IC-1-1-3 and IC-1-1-4, preferably of formulae UUZU-n-N and/or UUQU-n-N, most preferably selected from the group of the compounds UUZU-2-N, UUZU-3-N, UUZU-4-N, UUZU-5-N, UUQU-2-N, UUQU-3-N and UUQU- 5 4-N, wherein n is 1, 2, 3, 4, 5, 6 or 7. Varying amounts of compounds of formula IA, IB and IC allow to achieve 10 different upper transition temperatures of the ferroelectric nematic phase, thus enabling different temperatures of the electrocaloric effect. In another preferred embodiment of the present invention said compounds of formulae IA, IB and IC-1/-2/-3 are a first group of compounds, group 1, 15 of compounds. In this embodiment the concentration of the compounds of this group 1 of compounds preferably is in the range from 70 % by weight or more, preferably 80 % or more, more preferably 90 % or more to 100 % by weight or less. 20 In addition to the compounds of formulae IA, IB and IC-1/-2/-3 the media according to the invention optionally, preferably obligatory, comprise one, two, three or more compounds selected from formula ID-1 to ID-4, 25 30 35 - 30 - 5 10 X^D denotes CN, F, CF3, -OCF3, NCS, SF5 or O-CF=CF2, preferably -CN, F, -CF3, -OCF3, -Cl or -NCS, most preferably F or CN, L^1D, L^2D, L^3D, L^4D, L^5D, L^6D and L^7D, independently denote F, H, alkyl, 15 alkoxy or alkoxyalkyl, each with 1 to 7 C atoms, preferably H, F, CH3, OCH3, OCH2CH3, CH2OCH3, CH2OCH2CH3, CH2CH2OCH3, CH2CH2OCH2CH3 or CH2CH2CH2OCH3, Z^1D andZ^2D independently of one another denote -(CO)-O-, -CF2-O-, a 20 single bond, and preferably both -(CO)-O-, R^1D denotes an alkyl radical having 1 to 12 C atoms, preferably 1 to 7, more preferably 1 to 6 and most preferably 1 to 5 C atoms, where, in addition, one or more CH2 groups in these radicals 25 may in each case be replaced, independently of one another, by 30 or -O-(CO)- in such a way that O/S atoms are not linked directly to one another, and in which, in addition, one or more H atoms may be replaced by halogen, or denotes H, preferably R^1D is a halogenated or unsubstituted alkyl radical 35 having 1 to 12 C atoms, where, in addition, one or more CH2 - 31 - groups in these radicals may in each case be replaced, independently of one another, by -C≡C- or -CH=CH-, R^2D denotes alkyl, alkoxy or alkoxyalkyl, each with 1 to 7 C atoms, 5 preferably CH3, OCH3, OCH2CH3, CH2OCH3, CH2OCH2CH3, CH2CH2OCH3, CH2CH2OCH2CH3 or CH2CH2CH2OCH3, A^1D denotes a single bond, 10 15 preferably a single bond, 20 wherein 25 L^8D denotes alkyl, alkoxy or alkoxyalkyl, each with 1 to 7 C atoms, preferably CH3, OCH3, OCH2CH3, CH2OCH3, CH2OCH2CH3, CH2CH2OCH3, CH2CH2OCH2CH3 or CH2CH2CH2OCH3, preferably it comprises one or more of formulae ID-1-1 to ID-3-1: 30 35 P23-010 - 32 - 5 10 wherein the variable groups R^1D and L^8D are defined as above. 15 Corresponding starting materials can generally be readily prepared by the person skilled in the art by synthetic methods known from the literature or are commercially available. The reaction methods and reagents used are in principle known from the literature. 20 In the present disclosure, the 2,5-disubstituted dioxane ring of the formula preferably denotes a 2,5-trans-configured dioxane ring, i.e., the two 25 substituents are preferably both in the equatorial position in the preferred chair conformation. The 2,5-disubstituted tetrahydropyran of the formula 30 likewise preferably denotes a 2,5-trans-configured tetrahydropyran ring, i.e., the two substituents are preferably both in the equatorial position in the preferred chair conformation. The liquid crystalline medium used according to the invention has a broad 35 temperature range of the ferroelectric nematic phase. It exhibits the ferroelectric nematic phase ranges at 20 ° and above and below (ambient P23-010 - 33 - temperature). It covers the technically most interesting range from at least 10 to 30°C and beyond to lower and/or higher temperatures. So it is highly suitable for a broad range of cooling operations in various applications. 5 The liquid crystal media used according to the invention preferably exhibit a temperature range of the ferroelectric nematic phase which is 20 degrees wide or more, preferably it extends over a range of 40 degrees or more, more preferably of 60 degrees or more. 10 Preferably the liquid crystal media used according to the invention exhibit the ferroelectric nematic phase from 10°C to 30°C, more preferably from 10°C to 40°C, more preferably from 10°C to 50°C, more preferably from 0°C to 50°C and, most preferably, from -10°C to 50°C. 15 In another preferred embodiment the liquid crystal media used according to the invention preferably exhibit the ferroelectric nematic phase from 10°C to 40°C, more preferably from 10°C to 50°C, more preferably from 10°C to 60°C and, most preferably, from 10°C to 70°C. 20 These advantageous electrocaloric properties are predominantly achieved at temperatures at which the media are in the ferroelectric nematic phase or above. The dielectric and thermotropic characteristics may occasionally show a hysteresis behavior, particularly under varying temperature, and in that case the values obtained at a certain temperature may depend on the history 25 of the material, i.e. whether the material is being heated up or cooled down. The liquid crystal media according to the invention preferably comprise 2 to 40, particularly preferably 4 to 20, compounds as further constituents besides one or more compounds according to the invention. In particular, these 30 media may comprise 1 to 25 components besides one or more compounds according to the invention. These further constituents are preferably selected from ferroelectric nematic or nematogenic (monotropic or isotropic) substances, 35 P23-010 - 34 - Prior art ferroelectric substances and similar compounds with high dielectric permittivity for combination with the current substances are selected from e.g. the following structures: 5 10 15 The media used for the invention preferably comprise 1 % to 100 % by weight, more preferably 10 % to 100 % and, particularly preferably, 50 % to 100% by weight, of the compounds of formulae IA and/or IB and/or IC-1/IC- 2/IC-3 preferably used according to the invention. 20 Preferred is an electrocaloric device according to the invention wherein the LC material exhibits a spontaneous polarisation Ps of 1000 nC∙cm^-2 or more at the upper end transition temperature of the ferroelectric nematic phase range, more preferably of 2000 nC∙cm^-2 or more, and most 25 preferably of 3000 nC∙cm^-2 or more. Further preferred is an electrocaloric device according to the invention wherein the LC material exhibits a relative dielectric permittivity εr of 15000 or more at 20 °C and 10 Hz, more preferably εr of of 20000, and most preferably εr of 30000 or more. 30 The expression "alkyl" encompasses unbranched and branched alkyl groups having 1 to 12 carbon atoms, preferably 1 to 10 carbon atoms, in particular and preferably the unbranched groups methyl, ethyl, n-propyl, n- butyl, n-pentyl, n-hexyl and n-heptyl and further, alternatively, the groups n- butyl, n-pentyl, n-hexyl and n-heptyl substituted by one methyl, ethyl or 35 propyl. Groups having 1-5 carbon atoms are generally preferred. P23-010 - 35 - The expression "alkenyl" encompasses unbranched and branched alkenyl groups having up to 12 carbon atoms, in particular the unbranched groups. Particularly preferred alkenyl groups are C2-C7-1E-alkenyl, C4-C7-3E- alkenyl, C5-C7-4-alkenyl, C6-C7-5-alkenyl and C7-6-alkenyl, in particular 5 C2-C7-1E-alkenyl, C4-C7-3E-alkenyl and C5-C7-4-alkenyl. Examples of pre- ferred alkenyl groups are vinyl, 1E-propenyl, 1E-butenyl, 1E-pentenyl, 1E- hexenyl, 1E-heptenyl, 3-butenyl, 3E-pentenyl, 3E-hexenyl, 3E-heptenyl, 4-pentenyl, 4Z-hexenyl, 4E-hexenyl, 4Z-heptenyl, 5-hexenyl, 6-heptenyl and the like. Groups having 2 to 5 carbon atoms are generally preferred. 10 The expression "halogenated alkyl radical" preferably encompasses mono- or polyfluorinated and/or -chlorinated radicals. Perhalogenated radicals are included. Particular preference is given to fluorinated alkyl radicals, in par- ticular CF3, CH2CF3, CH2CHF2, CHF2, CH2F, CHFCF3 and CF2CHFCF3. 15 The expression "halogenated alkenyl radical" and related expressions are explained correspondingly. The terms liquid crystal medium (LC medium) and liquid crystal material are used as synonyms throughout this disclosure. 20 Above and below, percentage data denote per cent by weight. All temperature values indicated in the present application, such as, for example, the melting point T(C,N), the smectic (Sm) to nematic (N) phase transition T(S,N) and the clearing point T(N,I), resp. T(Nf,I), are indicated in 25 degrees Celsius (°C) and all temperature differences are correspondingly indicated in differential degrees (° or degrees), unless explicitly indicated otherwise. Furthermore, C = crystalline state, N = nematic phase, Nf = ferroelectric nematic phase, Sm = smectic phase (more especially SmA, SmB, etc.), Tg = glass-transition temperature and I = isotropic phase. 30 The data between these symbols represent the transition temperatures. ^n denotes optical anisotropy (589 nm, 20°C), ^ ^ the dielectric anisotropy (1 kHz, 20°C). The physical, physicochemical and electro-optical parameters are deter- 35 mined by generally known methods, as described, inter alia, in the bro- chure "Merck Liquid Crystals - Licristal® - Physical Properties of Liquid P23-010 - 36 - Crystals - Description of the Measurement Methods", 1998, Merck KGaA, Darmstadt. The occurrence of the ferroelectric nematic phase of the materials is 5 identified using differential scanning calorimetry (DSC), via observation of the textures under a polarising microscope equipped with a hot-stage for controlled cooling resp. heating and additionally confirmed by temperature dependent determination of the dielectric properties. Transition temperatures are predominantly determined by detection of the optical 10 behaviour under a polarising microscope. The dielectric anisotropy ^ ^ of the individual substances is determined at 20°C and 1 kHz. To this end, 5 to 10 % by weight of the substance to be investigated are measured dissolved in the dielectrically positive mixture 15 ZLI-4792 (Merck KGaA), and the measurement value is extrapolated to a concentration of 100% by weight. The optical anisotropy ^n is determined at 20°C and a wavelength of 589.3 nm by linear extrapolation. The relative dielectric permittivity (εr) of the materials, especially in the 20 ferroelectric nematic phase is directly determined by measuring the capacitance of at least one test cell containing the compound and having cell thickness of 250 µm with homeotropic and with homogeneous alignment, respectively. Temperature is controlled by a Novocontrol Novocool system set to temperature gradients of +/-1 K/min; +/-2 K/min; +/- 25 5 K/min; +/- 10 K/min applied to the sample cell. Capacitance is measured by a Novocontrol alpha-N analyzer at a frequency of 1 kHz or 10 Hz with a typical voltage < 50 mV down to 0.1 mV in order make sure to be below the threshold of the investigated compound. Measurements are performed both upon heating and upon cooling of the sample(s). 30 In the present application, unless explicitly indicated otherwise, the plural form of a term denotes both the singular form and the plural form, and vice versa. Further combinations of the embodiments and variants of the inven- tion in accordance with the description also arise from the appended claims 35 or from combinations of a plurality of these claims. P23-010 - 37 - Examples The present invention is described in detail by the following non-restrictive examples and figures. 5 Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the 10 disclosure in any way whatsoever. From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications 15 of the invention to adapt it to various usages and conditions. This applies both to the media as compositions with their constituents, which can be groups of compounds as well as individual compounds, and also to the groups of compounds with their respective constituents, the 20 compounds. Only in relation to the concentration of an individual compound relative to the medium as a whole does the term comprise mean: the concentration of the compound or compounds in question is preferably 1% by weight or more, particularly preferably 2% or more, very particularly preferably 4% by weight or more. 25 For the present invention 30 denote trans-1,4-cyclohexylene, 35 denotes a mixture of both cis- and trans-1,4-cyclohexylene and P23-010 - 38 - denote 1,4-phenylene. 5 For the present invention, the expression "dielectrically positive com- pounds" means compounds having a ^ ^ of > 1.5, the expression "dielectri- cally neutral compounds" means compounds having -1.5 ^ ^ ^ ^ 1.5 and the expression "dielectrically negative compounds” means compounds 10 having ^ ^ < -1.5. The dielectric anisotropy of the compounds is determined here by dissolving 10% by weight of the compounds in a liquid-crystalline host and determining the capacitance of the resultant mixture in each case in at least one test cell having a cell thickness of 20 µm with homeotropic and with homogeneous surface alignment at 1 kHz. The measurement 15 voltage is typically 0.5 V to 1.0 V, but is always lower than the capacitive threshold of the respective liquid-crystal mixture (material) investigated. The liquid-crystal media and LC materials employed according to the invention may, if necessary, also comprise further additives, such as, for 20 example, stabilisers in the usual amounts. The amount of these additives employed is preferably in total 0 % or more to 10 % by weight or less, based on the amount of the entire mixture, particularly preferably 0.1 % or more to 6 % by weight or less. The concentration of the individual compounds employed is preferably 0.1 % by weight or more to 3 % or less. 25 The concentration of these and similar additives is generally not taken into account when specifying the concentrations and concentration ranges of the liquid-crystal compounds in the liquid-crystal media. For the purposes of the present invention, all concentrations are, unless 30 explicitly noted otherwise, indicated in per cent by weight and relate to the corresponding mixture as a whole or mixture constituents, again a whole, unless explicitly indicated otherwise. In this context the term “the mixture” describes the liquid crystalline medium. 35 The following symbols are used, unless explicitly indicated otherwise: T(N,I) resp. T(Nf,I) (or clp.) P23-010 - 39 - clearing point [°C], Dielectric properties at 1 kHz and preferably at 20°C or at the respective temperature specified: ^ ^ dielectric anisotropy and especially for the screening data of 5 single compounds. And, in particular for the data from the screening of the respective compounds in the nematic host mixture ZLI-4792,: ne extraordinary refractive index measured at 20°C and 589 nm, 10 no ordinary refractive index measured at 20°C and 589 nm and ^n optical anisotropy measured at 20°C and 589 nm. The following examples explain the invention without intending to restrict it. The person skilled in the art will be able to glean from the examples 15 working details that are not given in detail in the general description, generalise them in accordance with general expert knowledge and apply them to a specific problem. The examples show to the person skilled in the art preferred mixture concepts with compounds preferably employed and the respective concentrations thereof. In addition, the examples illustrate 20 the properties and property combinations that are accessible. Definitions of structural elements by abbreviations for use in acronyms for chemical compounds are provided in the following tables: 25 Table A: Ring elements 30 35 P23-010 - 40 - 5 10 15 20 25 30 35 P23-010 - 41 - Q -CF2-O- QI -O-CF2- Table C: End groups On the left individually or in combi- On the right individually or in com- 5 10 15 20 On the left only in combination On the right only in combination -…n…- -CnH2n- -…n… -CnH2n- -…M…- -CFH- -…M… -CFH- -…D…- -CF2- -…D… -CF2- -…V…- -CH=CH- -…V… -CH=CH- 25 -…Z…- -CO-O- -…Z… -CO-O- -…ZI…- -O-CO- -…ZI… -O-CO- -…K…- -CO- -…K… -CO- -…W…- -CF=CF- -…W… -CF=CF- in which n and m are each integers, and the three dots "…" are place- 30 holders for other abbreviations from this table. Besides the compounds of formulae IA, IB and IC-1/-2/-3 the mixtures used for the invention preferably comprise one or more compounds of the compounds mentioned below. 35 The following abbreviations are used: P23-010 - 42 - (n, m, k and l are, independently of one another, each an integer, pref- erably 1 to 9 preferably 1 to 7, k and l possibly may be also 0 and preferably are 0 to 4, more preferably 0 or 2 and most preferably 2, n preferably is 1, 2, 3, 4 or 5, in the combination “-nO-” it preferably is 1, 2, 3 5 or 4, preferably 2 or 4, m preferably is 1, 2, 3, 4 or 5, in the combination “- Om” it preferably is 1, 2, 3 or 4, more preferably 2 or 4. The combination “- lVm” preferably is “2V1”.) For the present invention and in the following examples, the structures of 10 the liquid-crystal compounds are indicated by means of acronyms, with the transformation into chemical formulae taking place in accordance with Tables A to C above. All radicals C_nH_2n+1, C_mH_2m+1 and ClH2l+1 or C_nH_2n, C_mH_2m and ClH2l are straight-chain alkyl radicals or alkylene radicals, in each case having n, m and l C atoms respectively. Preferably n, m and l 15 are independently of each other 1, 2, 3, 4, 5, 6, or 7. Table A shows the codes for the ring elements of the nuclei of the compound, Table B lists the bridging units, and Table C lists the meanings of the symbols for the left- and right-hand end groups of the molecules. The acronyms are composed of the codes for the ring elements with optional linking groups, followed by 20 a first hyphen and the codes for the left-hand end group, and a second hyphen and the codes for the right-hand end group. Table D shows illustra- tive structures of compounds together with their respective abbreviations. 25 30 35 P23-010 - 43 - Table D Exemplary, preferred compounds of formula IA 5 10 15 20 Exemplary, preferred compounds of formula IB 25 30 35 P23-010 - 44 - 5 Exemplary, preferred compounds of formula IC-1 10 15 20 25 30 35 P23-010 - 45 - 5 Exemplary, preferred compounds of formula IC-3 10 15 Further compounds optionally used 20 25 30 35 P23-010 - 46 - 5 10 15 20 25 CPZG-n-N 30 wherein n is 0, 1, 2, 3, 4, 5, 6, 7, etc., preferably 0, 1, 2, 3, 4 or 5. Mixture Examples In the following exemplary mixtures are disclosed. The preparation of the 35 compounds is made analogous to those of same or similar structure in earlier publications. The preparation of mixtures is made in a conventional P23-010 - 47 - way by combining the required materials and homogenizing them at a suitably high temperature. Mixture Example 1 5 The following mixture (M-1) is prepared. Mixture M-1 Composition Physical properties C^{ompound Concentration} 10 _{T(N, I) = 97 °C} N^{o. Abbreviation /% by weight} _{T(FerroN) c = 52 °C} 1 DUUQU-3-F 18.0 2 DUUQU-4-F 18.0 15 3 DUUQU-5-F 7.0 4 GUUQU-3-N 10.0 ε(20°C, 1 kHz) c = 3960 5 GUUQU-4-N 13.0 ε(20°C, 10 Hz) c = 42200 6 GUUQU-5-N 4.0 20 7 GUZU-4-N 15.0 8 GUQU-4-N 15.0 ^ 100.0 c) value upon cooling. 25 Mixture Example 2 The following mixture (M-2) is prepared. Mixture M-2 30 Composition Physical properties C^{ompound Concentration} _{T(N, I) = 97 °C} N^{o. Abbreviation /% by weight} _{T(FerroN) c = 49 °C} 1 DUUQU-3-F 16.0 35 2 DUUQU-4-F 16.0 P23-010 - 48 - 3 DUUQU-5-F 7.0 4 GUUQU-3-N 10.0 ε(20°C, 1 kHz) c = 3220 5 GUUQU-4-N 13.0 ε(20°C, 10 Hz) c = 42200 5 6 GUUQU-5-N 4.0 7 GUZU-4-N 13.0 8 GUZU-5-N 8.0 9 GUQU-4-N 13.0 10 ^ 100.0 c) value upon cooling. Mixture Example 3 The following mixture (M-3) is prepared. 15 Mixture M-3 Composition Physical properties C^{ompound Concentration} _{T(N, I) = 96 °C} 20 N^{o. Abbreviation /% by weight} _{T(FerroN)c = 41 °C} 1 DUUQU-3-F 15.0 2 DUUQU-4-F 14.0 no = t.b.d. 25 3 DUUQU-5-F 6.0 ne = t.b.d. 4 GUUQU-3-N 9.0 ε(20°C, 1 kHz) c = 4060 5 GUUQU-4-N 12.0 ε(20°C, 10 Hz) c = 42600 6 GUUQU-5-N 4.0 30 7 GUZU-4-N 15.0 8 GUZU-5-N 10.0 9 GUQU-4-N 15.0 ^ 100.0 35 ^c) value upon cooling. P23-010 - 49 - These is the highest value of the relative dielectric permittivity εr for any physical matter known to the authors so far. Mixture Example 4 5 The following mixture (M-4) is prepared. Mixture M-4 Composition Physical properties C^{ompound Concentration} 10 _{T(N, I) = 91 °C} N^{o. Abbreviation /% by weight} _{T(FerroN) c = 33 °C} 1 DUUQU-3-F 14.0 2 DUUQU-4-F 13.0 15 3 DUUQU-5-F 5.0 4 GUUQU-3-N 8.0 ε(20°C, 1 kHz) c = 5270 5 GUUQU-4-N 11.0 ε(20°C, 10 Hz) c = 40500 6 GUUQU-5-N 3.0 20 7 GUZU-4-N 17.0 8 GUZU-5-N 12.0 9 GUQU-4-N 17.0 ^ 100.0 25 ^c) value upon cooling. Mixture Example 5 The following mixture (M-5) is prepared. 30 Mixture M-5 Composition Physical properties C^{ompound Concentration} _{T(N, I) = 88 °C} N^{o. Abbreviation /% by weight} _{T(FerroN) c = 25 °C} 35 1 DUUQU-3-F 13.0 P23-010 - 50 - 2 DUUQU-4-F 11.0 3 DUUQU-5-F 4.0 4 GUUQU-3-N 7.0 ε(20°C, 1 kHz) c = 5010 5 5 GUUQU-4-N 10.0 ε(20°C, 10 Hz) c = 40200 6 GUUQU-5-N 3.0 7 GUZU-4-N 19.0 8 GUZU-5-N 14.0 10 9 GUQU-4-N 19.0 ^ 100.0 c) value upon cooling. 15 Mixture Example 6 The following mixture (M-6) is prepared. Mixture M-6 Composition Physical properties 20 C^{ompound Concentration} _{T(N, I) = 87 °C} N^{o. Abbreviation /% by weight} _{T(FerroN) c = 21 °C} 1 DUUQU-3-F 12.0 25 2 DUUQU-4-F 10.0 3 DUUQU-5-F 4.0 4 GUUQU-3-N 6.0 ε(20°C, 1 kHz) c = 5010 5 GUUQU-4-N 10.0 ε(20°C, 10 Hz) c = 39800 30 6 GUUQU-5-N 3.0 7 GUZU-4-N 20.0 8 GUZU-5-N 15.0 9 GUQU-4-N 20.0 35 ^ 100.0 c) value upon cooling. P23-010 - 51 - Mixture Example 7 The following mixture (M-7) is prepared. Mixture M-7 5 Composition Physical properties C^{ompound Concentration} _{T(N, I) = 88 °C} N^{o. Abbreviation /% by weight} _{T(FerroN) c = 35 °C} 1 DUUQU-3-F 12.0 10 2 DUUQU-4-F 12.0 3 DUUQU-5-F 4.0 4 GUUQU-3-N 7.0 ε(20°C, 1 kHz) c = 5580 15 5 GUUQU-4-N 11.0 ε(20°C, 10 Hz) c = 36000 6 GUUQU-5-N 3.0 7 GUZU-4-N 15.0 8 GUZU-5-N 10.0 20 9 GUQU-4-N 15.0 10 UUZU-4-N 3.0 11 UUZU-5-N 3.0 12 UUQU-5-N 5.0 25 ^ 100.0 c) value upon cooling. Mixture Example 8 The following mixture (M-8) is prepared. 30 Mixture M-8 Composition Physical properties C^{ompound Concentration} _{T(N, I) = 88 °C} 35 ^{No. Abbreviation /% by weight} _{T(FerroN) c = 39 °C} P23-010 - 52 - 1 DUUQU-3-F 12.0 2 DUUQU-4-F 12.0 3 DUUQU-5-F 4.0 5 4 GUUQU-3-N 7.0 ε(20°C, 1 kHz) c = 5300 5 GUUQU-4-N 11.0 ε(20°C, 10 Hz) c = 37800 6 GUUQU-5-N 3.0 7 GUZU-4-N 13.0 10 8 GUZU-5-N 8.0 9 GUQU-4-N 13.0 10 UUZU-4-N 5.0 15 11 UUZU-5-N 5.0 12 UUQU-5-N 7.0 ^ 100.0 c) value upon cooling. 20 Mixture Example 9 The following mixture (M-9) is prepared. Mixture M-9 Composition Physical properties 25 C^{ompound Concentration} _{T(N, I) = 89 °C} N^{o. Abbreviation /% by weight} _{T(FerroN) c = 44 °C} 1 DUUQU-3-F 12.0 T(N2,N1) = 58 °C 30 2 DUUQU-4-F 12.0 3 DUUQU-5-F 4.0 4 GUUQU-3-N 7.0 ε(20°C, 1 kHz) c = 5530 5 GUUQU-4-N 11.0 ε(20°C, 10 Hz) c = 36200 35 6 GUUQU-5-N 3.0 P23-010 - 53 - 7 GUZU-4-N 11.0 8 GUZU-5-N 6.0 9 GUQU-4-N 11.0 5 10 UUZU-4-N 7.0 11 UUZU-5-N 7.0 12 UUQU-5-N 9.0 ^ 100.0 10 ^c) value upon cooling. The nematic transitional phase (N2) is observed in a temperature range above the ferroelectric nematic phase until 58 °C, followed by the conventional nematic phase (N1). Mixture Example 10 15 The following mixture (M-10) is prepared. Mixture M-10 Composition Physical properties 20 ^{Compound Concentration} _{T(N, I) = 107 °C} N^{o. Abbreviation /% by weight} _{T(FerroN) c = 30 °C} 1 MUU-4-N 10.0 2 MUU-5-N 5.0 25 3 UMU-4-N 10.0 4 UMU-5-N 5.0 ε(20°C, 1 kHz) c = 5 UMU-6-N 5.0 ε(20°C, 10 Hz) c = 6 GUUQU-3-N 15.0 30 7 GUUQU-4-N 10.0 8 GUUQU-5-N 10.0 9 DUUQU-3-F 10.0 35 10 DUUQU-4-F 10.0 P23-010 - 54 - 11 DUUQU-5-F 10.0 ^ 100.0 c) value upon cooling. 5 Mixture Example 11 The following mixture (M-11) is prepared. Mixture M-11 10 Composition Physical properties C^{ompound Concentration} _{T(N, I) = 108 °C} N^{o. Abbreviation /% by weight} _{T(FerroN) c = 28 °C} 1 MUU-4-N 7.0 15 2 MUU-5-N 4.0 3 UMU-4-N 7.0 4 UMU-5-N 4.0 5 UMU-6-N 3.0 20 6 GUUQU-3-N 15.0 7 GUUQU-4-N 13.0 8 GUUQU-5-N 12.0 25 9 DUUQU-3-F 7.0 10 DUUQU-4-F 9.0 11 DUUQU-5-F 4.0 12 GUZU-4-N 5.0 30 13 GUZU-5-N 5.0 14 GUQU-4-N 5.0 ^ 100.0 c) value upon cooling. 35 P23-010 - 55 - Mixture Example 12 The following mixture (M-12) is prepared. Mixture M-12 5 Composition Physical properties C^{ompound Concentration} _{T(N, I) = 104 °C} N^{o. Abbreviation /% by weight} _{T(FerroN) c = 30 °C} 1 MUU-5-N 4.0 10 2 UMU-4-N 7.0 3 UMU-5-N 4.0 4 GUUQU-3-N 13.0 15 5 GUUQU-4-N 13.0 6 GUUQU-5-N 12.0 7 DUUQU-3-F 9.0 8 DUUQU-4-F 9.0 20 9 DUUQU-5-F 4.0 10 GUZU-4-N 10.0 11 GUZU-5-N 5.0 12 GUQU-4-N 10.0 25 ^ 100.0 c) value upon cooling. Mixture Example 13 The following mixture (M-13) is prepared. 30 Mixture M-13 Composition Physical properties C^{ompound Concentration} _{T(N, I) = 103 °C} 35 ^{No. Abbreviation /% by weight} _{T(FerroN)c = 20 °C} P23-010 - 56 - 1 MUU-5-N 6.0 2 UMU-4-N 8.0 3 UMU-5-N 6.0 5 4 GUUQU-3-N 13.0 5 GUUQU-4-N 13.0 6 GUUQU-5-N 12.0 7 DUUQU-3-F 7.0 10 8 DUUQU-4-F 7.0 9 DUUQU-5-F 3.0 10 GUZU-4-N 10.0 15 11 GUZU-5-N 5.0 12 GUQU-4-N 10.0 ^ 100.0 c) value upon cooling. 20 Mixture Example 14 The following mixture (M-14) is prepared. Mixture M-14 Composition Physical properties 25 C^{ompound Concentration} _{T(N, I) = 43 °C} N^{o. Abbreviation /% by weight} _{T(FerroN)c = 43 °C} 1 UUQU-2-N 10 % 30 2 UUQU-3-N 15 % 3 UUQU-4-N 35 % 4 UUQU-5-N 15 % 5 UUQU-6-N 5.0 % 35 6 UUZU-4-N 10 % P23-010 - 57 - 7 UUZU-5-N 10% ^ 100.0 c) value upon cooling. 5 The mixture has a narrow transition from the NF phase to the isotropic phase at about 43 °C. The maximum temperature change is ΔTmax = 3 K. Mixture Example 15 The following mixture (M-15) is prepared. 10 Mixture M-15 Composition Physical properties C^{ompound Concentration} _{T(N, I) = 90 °C} N^{o. Abbreviation /% by weight} 15 _{T(FerroN) c = 76 °C} 1 DUUQU-4-N 5% T(N2, N1) = 80 °C 2 GUUQU-3-N 8% 3 GUUQU-4-N 12% 20 4 GUZU-4-N 8% 5 UUZU-3-N 6% 6 UUZU-4-N 16% 7 UUZU-5-N 7% 25 8 UUQU-2-N 7% 9 UUQU-3-N 14% 10 UUQU-4-N 11% 11 AUUQU-2-N 6% 30 ^ 100.0 c) value upon cooling. The mixture has a high operating temperature (about 76 °C) and a maximum temperature change of ΔTmax = 1.5 K. 35 P23-010 - 58 - Reference materials: The ferroelectric materials FELIX-017/000 and OB4HOB [Bsaibess, E.; Sahraoui, A.H.; Boussoualem, Y.; Soueidan, M.; Duponchel, B.; Singh, D.P.; Nsouli, B.; Daoudi, A.; Longuemart, S. Study of the electrocaloric 5 effect in ferroelectric liquid crystals. Liq. Cryst.2019, 46, 1517–1526] were studied by Bsaibess et al. Klemenčič et al. induced a temperature change at the isotropic to SmA phase transition in 12CB [Klemencic, E.; Trcek, M.; Kutnjak, Z.; Kralj, S. 10 Giant electrocaloric response in smectic liquid crystals with direct smectic- isotropic transition. Sci. Rep.2019, 9, 1721]. PST-MLC: The ferroelectric ceramic, lead scandium tantalate (PST), [Nair, B.; Usui, T.; Crossley, S.; Kurdi, S.; Guzman-Verri, G.G.; Moya, X.; Hirose, S.; Mathur, N.D. Large electrocaloric effects in oxide multilayer capacitors 15 over a wide temperature range. Nature 2019, 575, 468–472] arranged in a multilayer capacitor (MLC) is included for reference. The temperature changes for 12CB and PST-MLC are direct measurements, and all other measurements are indirect. 20 SCE13 is a ferroelectric chiral smectic C (SmC*) liquid crystal mixture (Merck KGaA) for electrooptic applications with the following phase sequence (upon cooling, in °C)). I 100.8 N* 86.3 SmA 60.8 SmC* -20 Cr 25 LC 1 has the following structure: 30 LC 2 has the following structure: 35 P23-010 - 59 - The compounds LC1 and LC2 are reported to have a chiral smectic ferroelectric phase (SmC*) at certain temperatures (Tipping, P.J.; Gleeson, H.F., Crystals 2022, 12, 809). 5 12CB has the following structure: Results 10 The mixtures are characterized according to literature methods following Tipping, P.J.; Gleeson, H.F., Crystals 2022, 12, 809. Reference data is also obtained from this literature. The density and heat capacity of the mixtures were measured with conventional means. 15 The mixture of Mixture Example 9 is subjected to the indirect measurement method for obtaining the values of spontaneous polarisation Ps as a function of applied field (0.2 - 1.0 V µm^-1 in 0.2 V µm^-1 intervals , 87 Hz) and temperatures from 65°C down to 30°C. The transformation of data into 20 values of the rate of change of spontaneous polarisation ^^{^^^} ^_^ ^ and ΔT ^ followed the referenced method of Tipping. Exemplary measurement curves for mixture M-9 are detailed in Fig.2, 3 25 and 4. The results of evaluation of the materials and comparison to reference data are summarized in Table 1 below. 30 Table 1. The maximum spontaneous polarisation (PS), volumetric heat capacity (CE), maximum EC temperature change (Tmax), figure of merit Δ^Tmax^/ΔE, and temperature range over which the electrocaloric temperature change remains greater than 90% of the peak temperature change, for the current materials and other systems chosen for comparison. 35 P23-010 - 60 - Range where P_S C_E ΔT_max ΔT_max/ΔE Material ⁻² ΔT_EC/ΔT_ECmax ) (MJ K⁻¹ m⁻³ > (nC cm ) (K) (K m MV⁻¹) 0.9 K Comparative materials 5 SCE13 26 1.6 0.09 0.006 0.2 LC 1 71 2.3 0.37 0.022 0.9 LC 2 71 2.6 0.22 0.016 1.4 FELIX- 25 3.5 0.023 0.003 1.0 10 017/000 OB4HOB 60 7.1 0.17 0.021 0.1 12CB: I-SmA - - 6.5 0.80 <0.1 PST MLC (Ferroelectric 30,000 2.7 3.3 0.19 73 15 ceramic) Materials according to invention Mixture M-9, 5200 2.3 0.59 0.73 1.1 Example 9 20 M-14, 6800 2.2 3 3 3 Example 14 M-15, 7300 2.3 1.5 1.5 10 - 12 Example 15 25 Characterisation of Mixture Example 9 (Mixture M-9) Key results: • The peak electrocaloric (EC) efficiency and applicable temperature range are 50% larger than the best performing smectic ferroelectric LC. 30 • Efficiency improvement – 32 times the best performing smectic ferroelectric LC. • Over 3 times more efficient as PST ceramic multilayer with broadest applicable temperature range reported. • Peak electrocaloric temperature change ΔT is respectable at ~0.6 K. 35 • Being a liquid, the electrocaloric cooling process is not frequency limited as it is with solid electrocaloric materials. P23-010 - 61 - • Electrocaloric temperature range is very advantageous for technical applications e.g. microelectronic cooling. • Applicable temperature range can be broadened with mixture of NF LCs. 5 ^^ • Large implies large pyroelectric effect,which is useful for energy recovery. 10 15 20 25 30 35

Claims

P23-010 - 62 - Patent Claims 1. An electrocaloric device comprising two or more electrodes for generating an electric field in a space volume distributed between at 5 least two of the electrodes, a liquid dielectric material positioned at least partly in said space volume, wherein the dielectric material comprises one or more liquid crystalline (LC) material having a ferroelectric nematic phase. 10 2. Electrocaloric device according to claim 1, wherein said dielectric material shows a ferroelectric response to an applied electric field within the working temperature range of the device. 3. Electrocaloric device according to claim 1 or 2, wherein the device is 15 an electrocaloric heat pump or cooling device. 4. Electrocaloric device according to any of claims 1 to 3, wherein the device further comprises a pumping mechanism for transporting the dielectric material in the space volume between the electrodes. 20 5. Electrocaloric device according to any of claims 1 to 4, wherein said one or more LC material comprises at least two compounds with a molecular structure of formula I, 25 30 35 A² denotes P23-010 - 63 - 5 A3 denotes 10 15 R¹ is an alkyl radical having 1 to 12 C atoms, where, in addition, one or more CH2 groups in these radicals may in each case be 20 replaced, independently of one another, by -C≡C-, -CF2-O-, -OCF2-, -CH=CH-, , such a way that O/S 25 atoms are not linked directly to one another, and in which, in addition, one or more H atoms may be replaced by halogen, or denotes H, X is CN, F, CF3, -OCF3, -NCS, Cl, preferably CN or F, 30 L¹ is H or CH3, Z¹ is -CF2O- or -(CO)-O- or a single bond, and Z² is -CF2O- or -(CO)-O- or a single bond. 35 P23-010 - 64 - 6. Electrocaloric device according to one or more of claims 1 to 5 wherein the LC material exhibits a spontaneous polarisation Ps of 1000 nC cm^-2 or more at the upper end transition temperature of the ferroelectric nematic phase range. 5 7. Electrocaloric device according to one or more of claims 1 to 6 where the device comprises a loop for the liquid LC material, wherein the volume of the loop includes said space volume of said electric field between the electrodes and the volume of the loop is configured to be 10 thermally connected to a heat load. 8. Electrocaloric device according to one or more of claims 1 to 7 where the space volume between the electrodes corresponds with a heat sink. 15 9. Electrocaloric device according to one or more of claims 1 to 8, which comprises a controlled voltage source connected to the electrodes. 10. Electrocaloric device according to one or more of claims 1 to 9 which 20 has a working temperature range located inside the range of 15 to 60 °C. 11. Process for cooling an object using the electrocaloric response of a ferroelectric nematic liquid crystal. 25 12. Process for cooling an object using the electrocaloric device of any of claims 1 to 10. 13. Use of a liquid crystal material having a ferroelectric nematic liquid 30 crystal phase as an electrocaloric dielectric material in a heat pump or cooling device. 14. Use of a electrocaloric device according to any of claims 1 to 10 as a cooling device for an electronic device. 35 P23-010 - 65 - 15. A method of preparation of an electrocaloric device comprising two or more electrodes for generating an electric field in a space volume distributed between at least two of the electrodes, the method comprises inserting a dielectric material comprising one or more liquid 5 crystalline (LC) materials having a ferroelectric nematic phase at least partly into a said space volume. 10 15 20 25 30 35