JP2009538948A - Preparation and production of coating solutions - Google Patents

Abstract

  Concentrated produced from a hygroscopic precursor solution via a hydrolysis reaction using a microemulsion containing a cationic surfactant, optionally mixed with a metal organic CSD-solution in a proportion of less than 50% with respect to the metal oxide Coating solution for producing a dense mesoscopic ceramic film composed of oxide nanoparticle dispersion. The challenge of mixed CSD-solutions also arises by lowering the sintering temperature required therefor, and also by using ceramic composite membranes combined with other metals with nanoscale inhomogeneities or doping, increasing density It is to let you.

Description

  The present invention relates to a method for preparing a coating solution for obtaining a particularly dense ceramic film, and a product thereof.

  Electroceramic thin films are increasingly being used in microelectronics, memory building blocks (DRAM, FRAM) and microwave resonators for miniaturizing capacitors. This trend toward ultra-miniaturization is due to the discrete multilayer capacitors (MLCC) that have been fabricated by typical thick film methods such as “Tape Casting” (foil drawing method) having a film thickness of about 1 to 100 μm. Etc. This type of capacitor is constituted by a layer in which a ceramic dielectric film made of, for example, barium titanate and a metal electrode film made of nickel, palladium, or the like, which are alternately joined, are arranged in order. The film thickness lower limit value of the dielectric made of barium titanate achieved so far has been raised and lowered in the range of 1 μm.

Further reduction of the film thickness in the range between the typical film thickness and the thick film to a mesoscopic film thickness range of about 50 nm to 1 μm requires additional costs. This relates in a special way to so-called X7R-materials having a Core-Shell structure (X7R: EIA, Electronic Industry Association regulations). In this material, ferroelectric nuclei (“cores”) are present inside the particles with a temperature coefficient of −15% to + 15% ε _r (Δε _max / ε _r (25 ° C.)) in the temperature range of −55 ° C. to 125 ° C. _Presents a high value of the dielectric constant ε _r (eg, ε _r (25 ° C.) ≈3000), which is a result of the heterogeneity of the structure with a dielectric surface layer (“shell”). The required coating of small particles of about 100 nm is particularly difficult when further film thickness reduction to the range of 0.8-1 μm is required. Currently, the thinnest film of 0.8 μm is made by Murata of Japan. The 100 nm diameter barium titanate particles used are manufactured by NCI in Japan.

  Ensuring the temperature stability of dielectric properties is a special challenge, besides the reduction in film thickness so far. However, this requirement can be fulfilled by purposely producing nanocomposites in which two phases with different temperature courses of dielectric constant are present side by side on the nanometer scale (nanoscale inhomogeneity). It will be possible. On the other hand, functional ceramic thin films (about 3 nm to 300 nm) made of barium titanate (BT) are preferred materials when they are stable at the same time for a long time due to their high dielectric constant, their small dielectric loss and their small leakage current. It is made with very good quality by different methods. R. W. Schwartz, T.W. Schneller, and R.C. From Waser, “Chemical Solution of Electronic Oxide Films”, C.R. Chimie, 2004, p. 433-461, etc. The known so-called “Chemical Solution Deposition” (CSD) method of wet chemistry has several advantages such as having high flexibility with respect to stoichiometry and relatively low investment costs. Have In order to advance into the target mesoscopic range, in addition to the further reduction of the film thickness, which is very laborious by the tape casting method by reducing the particle size in the slurry, CSD- The use of the law can be considered in principle. The latter is described in the literature R.I. Waser, T.W. Schneller, S.M. Hoffmann-Elfert, P.M. Ehrhart, “Advanced Chemical Deposition Techniques from Research to Production”, Integrated Ferroelectrics, Vol. 1, Integrated Ferroelectrics, Vol. 36, 200, pp. 36, 200. As can be seen, all methods known as sol-gel processes and metalorganic deposition (MOD) are included. In that case, the reaction method can be adjusted within the wide limits between the two extreme cases “sol-gel” and “MOD” by chemically modifying the molecular precursor.

In addition to the advantages already described above, the CSD-method has the advantage that it can cover large areas with relatively little effort compared to other methods. In that case the production of a relatively thick film can be achieved on the one hand by explicitly increasing the number of coating steps, which is relatively laborious [C. A. OHLY, “Nanocrystalline Alkaline Earth Titanates and the Thermistors of the Electrical Conductors, and the Electrical Conductivity of the Environmental Conductors of the United States.” RWTH Aachen, D82, 2003; Baborowski, P.A. Muralt, N.M. Leadermann, S.M. Petit grand, A.M. Bosebeeuf, N.M. Setter, Ph. Gaucher, “PZT Coated Membrane Structured Micromachined Ultrasonic Transducers”, ISAF 2002, 13th Japan International Symposium on Ferroelectrics, ISAF 2002, IE Japan May 28-June 1 ^* Piscataway, New Jersey, USA, IEEE, 2002, p. 483-486], on the other hand, achieved by chemical modification of the precursor solution (extract and viscosity increasing solvent) .

Chemical modification CSD- law, for the ultrasonic transducers and other electromechanical _{applications, Pb (Zr x, Ti 1} - x) O on the ₃ (PZT) of lead-based system such as a relatively thick piezoelectric ceramics Also used to make membranes.

Thus, for example, 1,2-ethylenediol [G. Yi, Z. Wu, M.M. Thayer (Sayer) Author, Pb by "sol-gel process (Zr, Ti) O ₃ thin film preparation of; electrical, optical and electro-optical properties (Preparation of Pb (Zr, Ti ) O 3 thin films by sol gel processing; Electrical, optical, and electro-optical properties), Journal of Applied Physics 64, 2005, p. 2717-2724] or 1,3-propanediol [Y. L. Two, Tu. J. et al. Milne, “Characterization of single layer PZT (53/47) films pre-prepared from the air-stable route, air-stable sol-gel route. ) ", Journal of Materials Research, Vol. 10, 1995, p. 3222-3231], by replacing polyhydric alcohols with commonly used simple alcohols, a comparison of about 1 μm per coating process In principle, a thick film can be produced. Due to the relatively high content of sintered organics in the film, there is often a relatively high porosity that leads to functional limitations of the ceramic film. In addition, care must be taken to crack formation.

Multi-layer coating with such a solution can yield films up to 10 μm thick [R. Kurchania, S.A. J. et al. Milne, “Characterization of sol-gel Pb (Zr _0.53 Ti _0.47 ) O ₃ films in the thickness,” sol-gel Pb (Zr _0.53 Ti _0.47 ) O ₃ film in a thickness range of 0.25 to 10 μm. range 0.25-10 μm) ”, Journal of Materials Research Vol. 14, 1999, p.1852-1858]. Besides the platinum-plated silicon substrate which has been mainly used, the PZT film having the above-mentioned film thickness range is a Hastelloy-metal thin plate [S. Seelfeld, D.C. Sporn, T .; Hauke, G .; Mueller, H.M. Belge, “Dielectric and electromechanical properties of sol-gel prepared PZT thin films on metallic subs. (See Ceramic Society, Vol. 24, 2004, p.2553-2566). On the copper foil, a PZT film with or without doping was further placed in a thickness range of 0.8 to 1.2 μm [T. Kim, A.A. I. Klingon, J.A. -P-Maria, R.M. T.A. By Croswell, "Ca-doped lead zirconate titanate thin base capacitors on base nickel on copper foil", Journal of -See Materials Research Vol. 19, 2004, p.2841-2848].

Regarding alkaline earth titanate films (SrTiO ₃ , BaTiO ₃ or corresponding mixed crystals), nickel [R. J. et al. Ong, J.A. T.A. Dawley, P.M. G. Klemm (Clem) Author, "biaxially oriented on <100> Ni [Ba, Sr ] TiO 3 thin film chemical solution deposition (Chemical solution deposition of biaxially oriented [ Ba, Sr] TiO 3 thin films on <100> Ni) "Journal of Materials Research Vol. 18, 2003, p. 2310-2317] and copper electrodes [J. F. Ihlefeld, A.M. I. Klingon, W.M. Borland, J.A. -P. Maria, “Cu-compatible ultra-high permittivity for embedded passive components”, Materials Research Society 3 Symposium 78 Vol., 2004, p.145-150] Some work up is known. However, the film thickness achieved in this case (0.3 to 1.2 μm) is usually equivalent to a multilayer coating [J. T.A. Dawley, P.M. G. Clem, "Dielectric properties of random an <100> oriented SrTiO3 and <100> randomly oriented SrTiO3 and [Ba, Sr] TiO3 thin films made on <100> nickel tape. [Ba, Sr] TiO3 thin films fabricated on <100> nickel tapes) ", Applied Physics Letter 81, 2002, reported in 8 coatings for p. 3028-3030-0.8 μm]. The main research on CSD on nickel can then be done to make the second generation of high-temperature superconductors, so-called “coated conductors”, consisting of YBa ₂ Cu ₃ O _7- δ (YBCO) [F. F. Lange, “Microstructure and mechanisms of superconductor epitaxy via the chemical solution deposition. United States Ministry of Energy, United States Ministry of Energy, United States Ministry of Energy.” Lecture at the conference “Superconductivity for Electric Systems 2004 Annual Peer Review”; Pitan, D.C. Hennings, R.A. Vazeru (Waser) al., "Advances in MCLL for nano-crystal BaTiO ₃ powder synthesis (Progress in the Synthesis of Nano- crystalline BaTiO 3 Powders for MCLL) ", International Journal of Applied Ceramic Technology, Volume 2, 2005 P. 1-14; Hoffmann and R.H. Vazeru (Waser) al., "CSD produced [Ba, Sr] TiO ₃ thin film of form control (Control of the morphology of CSD- prepared [Ba, Sr] TiO 3 thin films) ", Journal of the European ceramic Society 19 (1999), p. 1339; Kaydanova, A.M. Miedaner, C.I. Curtis, J.M. Alleman, J.M. D. Perkins, D.C. S. Ginley, L.M. Sengupta, X. et al. Zhang, S.H. He, L. Chiu, “Direct ink jet printing of composite thin titanium titanate films,” Journal of Materials Research, Vol. 18, 2003, p. 2820; . Curtis, T.W. Rivkin, A.R. Miedaner, J.M. Alleman, J.M. Perkins, L.A. Smith, D.C. Ginley, “Metalizations by direct-write ink jet printing”, Proceedings NCPV Program Revised Meeting, Lakewood, CO, 2001, CD ROM.

  Generally speaking, by producing a composite metal oxide film on a semi-noble metal, various capacitors such as capacitors embedded between different positions on a sheet bar, so-called “printed wiring boards” (PWB), etc. Interest in new applications increases.

  When coating this electrode material, the parameter to be carefully adjusted is always the oxygen partial pressure. If this is adjusted too high, the semi-noble metal Cu or Ni will be oxidized, while if the oxygen partial pressure is too low, the quality of the oxide ceramic film will be impaired. In addition to the classic CSD method, a ceramic thin film or a mesoscope thin film is basically formed into a composite nanoparticle having a dispersed primary particle size of less than 100 nm as known from US Patent Application Publication No. 2005/0194573. It can also be produced using a corresponding colloidal solution.

Such dispersions or colloidal solutions can in principle be produced by a series of different methods. A very energy and costly process is the so-called mixed oxide process [C. Pitan, D.C. Hennings, R.A. Vazeru (Waser) al., "Advances in MCLL for nano-crystal BaTiO ₃ powder synthesis (Progress in the Synthesis of Nano- crystalline BaTiO 3 Powders for MCLL) ", International Journal of Applied Ceramic Technology, Volume 2, 2005 , P. 1-14], the coarsely grained (> 1 μm) oxide ceramic powder obtained using an organic dispersion medium. For example, redispersion of nanopowder aggregates with addition of organic stabilizers is also known according to hot water or oxalate methods using high performance stirrers or high performance grinders. These two methods usually give a suspension with a polydisperse size distribution whose primary particles rarely become smaller than 50 nm. Using such a solution, a usable functional ceramic thick film having only a film thickness in the micrometer range can be produced.

  However, in order to produce mesoscopic ceramic films with adjustable film thicknesses in the range of 50-1000 nm, narrow particle sizes, such as obtained by hydrolyzing hygroscopic precursors in the use of microemulsions, are used. A colloidal solution with a distribution and an average primary particle size of at least less than 50 nm, particularly preferably less than 10 nm is required. A microemulsion is a transparent, optically isotropic, thermodynamically stable liquid-liquid dispersion. Microemulsions typically have <100 nm droplets or domains and are composed of polar and non-polar solvents, typically water or oil-containing aqueous solutions. The microemulsion is stabilized by the addition of a surfactant, which is polar and nonpolar based on its amphiphilic nature (structure; lipophilic CH-chain on the head of the hydrophilic group). It adsorbs favorably at the interface between the organic solvents, and the interfacial tension is lowered. The size of the formed nanodomains is related to the temperature and the elastic nature of the surface-active film to be separated, in addition to the composition of the microemulsion. Each is divided into three types of microemulsions according to the relative ratio of oil to water, which are oil-in-water microemulsions with low oil content (o / w-microemulsions), approximately equal proportions of water and Bicontinuous microemulsions in the case of oils, as well as water-in-oil microemulsions with high oil content (w / o-microemulsions). The boundary between different types is fluid and related to the system. In the special case of w / o-microemulsions containing hydrous reverse micelles of spherical nanoscopes typically <50 nm dispersed in oilmatics, the aqueous droplets are used to synthesize ceramic nanoparticles. It acts as a nanoreactor for hydrolyzing hygroscopic compounds. However, bicontinuous microemulsions having a spongy structure in which water is already present as a continuous medium can also be used to synthesize the nanoparticles. The typical size of the sponge structure is in the range of 100 nm.

  By confining the reaction within such an isolated microspace (nanoreactor), the nucleation rate of the resulting spherical nanoparticles can be adjusted so that a monodisperse particle size distribution having a particle size of less than 50 nm can get.

  For example, when trying to produce barium titanate nanoparticles, the necessary hygroscopic barium-titanium precursor is obtained by dissolving free barium in alcohol and adding a stoichiometric amount of titanium alcoholate accordingly. It can occur easily. The resulting metal alcoholate molecules react with the water in the microemulsion droplets, producing barium titanate particles, and the remainder of the organic molecules are separated as alcohol.

  After the addition of a stoichiometric amount of water, first an anhydrous dispersion, ie an organosol, is obtained, the nanoparticles of which have a diameter of less than 20 nm, but even less than 10 nm, Surrounded by a cover made of surfactant molecules. This organic “coating” is responsible for the solution nature of the nanoparticles, and by selecting the composition of the surfactant in the microemulsion used, an almost monodisperse particle size distribution on the primary structure surface. The polarity of the solvent can be adapted to produce a substantially colorless and transparent dispersion having. If this is not possible in exceptional cases, the colloidal solubility of the nanoparticles in the solvent can also be achieved by adding a dispersion medium in the form of organic acids, amines and ketones into the microemulsion or into the precursor solution. Can be raised.

  If a dispersion having an appropriate amount of solid content, that is, a high content of ceramic nanoparticles is successfully provided, this solution can be used to obtain 1 by a conventional method such as centrifugal rotation, immersion or spraying. In the process step, a mesoscopic film with a film thickness range of 50 nm to 1 μm, which is homogeneous and free of cracks, can be produced. However, this is not possible with conventional technology. Thus, the solids content according to US Patent Application No. 2005/0194573 is only 0.2% by weight. It is impossible according to the prior art to adapt the corresponding rheological properties of this colloidal solution to the intended coating thickness.

  Due to the low particle concentration of the solutions used according to the prior art, multiple coating steps are required to reach the desired film thickness. This makes this process more laborious and thereby more expensive. As known from US 2005/0194573, a 240 nm thick dielectric film is produced when a colloidal solution having a maximum mass ratio of 1.5% by weight oxidized nanoparticles is used. This requires up to 20 coating steps. In order to produce the coating dispersions described there, a synthesis based on microemulsions was also used and the hygroscopic precursor solution was added to the microemulsion so that the water droplets were anionic or nonionic. A microemulsion stabilized with a surfactant was used. In that case, a colloid coating dispersion having a mass proportion of dispersed barium titanate nanoparticles of up to 1.5% by weight and a mass ratio of oxidized nanoparticles to non-volatile organic components (annealed organics) of 0.11 Occurred.

C. Beck, W.M. Haerti, R.A. Henperuman (Hempelmann) Author, "Sizing synthesis of nanocrystalline BaTiO ₃ due to the sol-gel type hydrolyzed in microemulsion feed nano reactor (Size-Controlled Synthesis of Nano- crystalline BaTiO 3 by a Sol -From Gel Type Hydrolysis in Provided Nanoreactors) Journal of Materials Research Vol. 13, 1998, p. 3174-3180, containing nonylphenol ethoxylate as a nonionic surfactant and relatively high water content By using a microemulsion of a quantity and a relatively advantageous water / surfactant ratio, acid to non-volatile organic substances Nanoparticle dispersions are known in which the ratio of the compounds is relatively advantageous. In the most advantageous case (for Tergitol NP-7), the water / surfactant mass ratio is 1: 1 and the oxide / surfactant mass ratio is 4: 1.

US 2005/0194573, paragraph [0018] describes that dispersions with too high surfactant content are unstable. The nonionic surfactant NP-10 described in the examples of US Patent Application Publication No. 2005/0194573 is (among other things) C.I. Beck, W.M. Haerti, R.A. Henperuman (Hempelmann) Author, "Sizing synthesis of nanocrystalline BaTiO ₃ due to the sol-gel type hydrolyzed in microemulsion feed nano reactor (Size-Controlled Synthesis of Nano- crystalline BaTiO 3 by a Sol -Gel Type Hydrolysis in Microprovisioned Nanoreactors) "Journal of Materials Research Vol. 13, 1998, p. 3174-3180, was also used to form microemulsions. Thus, in US 2005/0194573, using the described surfactants, the oxide / surfactant ratio is greater than 0.11 and the barium titanate-nanoparticle content is 1.5 wt. It was not possible to produce dispersions greater than% that were sufficiently stable to processing.

  To remove this technical disadvantage, as in US 2005/0194573, the mass concentration of the metal in such a coating dispersion is increased using a correspondingly synthesized CSD-solution. It has been known. From the coating test carried out and subsequent tempering at 700 ° C. for 10 minutes, with a mixing ratio of 1 part dispersion to 1 part CSD-solution (relative to barium titanate mass), 240 nm barium titanate It has been found that 10 coating steps are required to produce the film thickness. The lowest number of 6 coating steps was achieved with a mass ratio of 1 part dispersion to 30 parts CSD-solution when the film thicknesses produced were equal. At 1:30 or more, since the CSD-solution is excessively large, the lack of crystallinity of the produced film causes the functional failure of the ceramic film, so that a usable dielectric ceramic film could not be obtained. Below a 1: 1 ratio, this film showed a relatively high dielectric constant when the crystallinity was sufficient. However, the lack of storage stability of the solution could not be used for technical processes as well as the required number of coating steps (20).

  Therefore, a composition range of 1: 1 to 1:30 represents a compromise for minimizing the number of coating steps when the functionality of the resulting ceramic film is sufficient. However, it has been found that even the most advantageous reported 1:30 mixing ratio still requires six process steps to produce a 240 nm ceramic film.

  C. Beck, W.M. Haerti, R.A. Nonionic surfactants of the type cyclohexane, water, nonylphenol ethoxylate, from Hempelmann, Journal of Materials Research Vol. 13, No. 11, 1998, p. 3174-3180 Also known are nanoparticle dispersions prepared by hydrolysis with w / o-microemulsions composed of 1-octanol as co-surfactant. The stability of this dispersion was not tested due to precipitation of this material. The maximum oxide / surfactant mass ratio was 4.1.

  US Patent Application Publication No. 2005/0194573 describes that a sufficiently stable dispersion cannot be obtained if the alkoxide is hydrolyzed with a microemulsion with too high water and surfactant content. ing. The solution described in this print has a nanoparticle content of up to 1.5% by weight and an oxide / surfactant ratio of up to 0.11.

  From US 2005/0194573 a hybrid solution is also known which consists of a nanoparticle dispersion and a CSD-solution. In that case, the proportion of nanoparticles in the total amount of metal oxide is 50% by weight at maximum, and 3.2% by weight when coating is performed with the smallest number of coating steps.

  German Patent Application No. 10237915 discloses a method for producing a coating dispersion, whereby a solution containing alcohol as a solvent is prepared, in which a hygroscopic metal compound is at least partially dissolved. The solution is then mixed with the microemulsion for producing the dispersion. Nonionic surfactants should be used so that the surfactant can be removed by pyrolysis without residue. It is speculated that this printed matter will also take into account cationic surfactants. However, this printed matter does not disclose a method for obtaining a sufficiently stable dispersion having a high solid content exceeding 5% by weight using such a surfactant. This is not related to the production of a coating solution, but to the production of nanoparticle powders that can be sintered to dense ceramics under high pressure.

  US Patent Application No. 5703002 is involved in the production of nanoparticle powders. In fact, this printed matter uses the concept of microemulsion. However, this printed product indicates that in order to produce a “microemulsion”, it should be vigorously stirred under ultrasound. This represents the first suggestion that the mixture is not thermodynamically stable and therefore not a microemulsion in the sense of the present invention. The 30: 1 water / surfactant mass ratio listed in column 4, lines 62-67 also indicates that this is not a microemulsion in the sense of the present invention. Because such ratios require extremely effective surfactants. However, the surfactants specifically disclosed in this print are rather ineffective. Thus, US Pat. No. 5,703,002 is not really concerned with microemulsions in the sense of this application, but rather with so-called miniemulsions. Miniemulsions are kinematically stable enough for use in particle synthesis only under energy supply. Accordingly, the water content is low, less than 0.5%. Cationic surfactants are listed as possible surfactants for producing emulsions known from this. However, the possibility that a stable dispersion can be obtained using this material cannot be read from this printed matter because there is no example.

  US Pat. No. 5,770,172 is involved in the production of nanoparticles. To that end, the microemulsion used according to the examples contains an anionic surfactant. Neither the hygroscopic metal compound is at least partially dissolved, and the synthesis described here is always based on precipitation from a metal salt solution. Always talk about water-soluble metal compounds. However, this process mode generally limits the solubility of the starting compound, so that only a fraction of the mass of the aqueous phase (water + metal salt) is replaced for the particles, so generally the solid content This leads to a small dispersion. Whether the particle dispersion obtained according to the examples is sufficiently stable to be used as a coating solution cannot be read from this printed matter and appears to be questionable.

  Accordingly, an object of the present invention is to provide a solution that makes it possible to easily produce a dense ceramic film or film of a mesoscope having a film thickness range of 50 nm to 1 μm.

  In order to solve this problem, at least one solution having alcohol as a solvent is provided, and at least one hygroscopic metal compound is at least partially dissolved in the solution. This solution is mixed with a microemulsion containing a cationic surfactant. In that way, stable dispersions with a solids content of 5 to 10% by weight with a narrow particle size distribution are produced. The maximum value of the particle size distribution is usually at least less than 50 nm, on the contrary, usually less than 10 nm. When the substrate is coated with this dispersion and subsequently sintered, a dense ceramic film with a film thickness of 50 nm to 1 μm is produced in only one coating process due to the high solids content.

It is an electron micrograph of a barium titanate film.

  The metal compound is hygroscopic when it is reacted with water. Therefore, the dissolved metal compound reacts by adding a microemulsion containing water. Since this solution is essentially free of water, the metal compound reacts only after the water-containing microemulsion is added.

One expert used a microemulsion made from a nonionic surfactant to prepare the coating solution because it is composed of carbon, oxygen and hydrogen. This is sintered at a temperature in excess of 600 ° C. to produce the desired film. Carbon, oxygen and hydrogen are removed from the ceramic film in the form of carbon dioxide and water without residue when air is introduced at this temperature. In contrast, cationic surfactants include, for example, bromide or chloride as a counter ion. For example, chlorine is not sufficiently removed so that the membrane becomes contaminated and loses its function. The expert therefore did not expect to be able to consider cationic surfactants to obtain a sufficiently stable dispersion with sufficient solids content.
Even if an expert seriously considers a cationic surfactant, in any case, the expert should use a microemulsion containing a cationic surfactant and be sufficiently stable at a high concentration of over 5% by weight. I don't know how to get the coating dispersion.

As the cationic surfactant, an alkyl ammonium salt, dialkyl ammonium salt, trialkyl ammonium salt or tetraalkyl ammonium salt of the composition R ₁ R ₂ R ₃ R ₄ N ⁺ X ⁻ can be used, in which case R ₁ Represents an alkyl residue, R ₂ , R ₃ and R ₄ represent an alkyl residue or a proton, and X ⁻ represents an anion. This anion can also be multivalent.

  Commercially available in large quantities cetyltrimethylammonium bromide (hexadecyltrimethylammonium bromide; CTAB) has proven to be a particularly advantageous surfactant for the production of microemulsions with a high water content. In the application example, when the barium titanate film is produced, a sufficiently low conductivity of sintered ceramics can be obtained despite the inclusion of bromine ions in the surfactant. You can get ceramics. Other advantageous surfactants are dioctadecyldimethylammonium chloride and hexadecylpyridinium chloride if the halide ion does not significantly impair the desired functionality. For surfactants that do not contain elements other than H, C, N and O, hexadecyltrimethylammonium acetate, hexadecylammonium acetate, hexadecylammonium propionate and hexadecylpyridinium salicylate are particularly well suited for the production of microemulsions. . However, the selection of the cationic surfactant is not limited to the compounds mentioned.

  Methanol is particularly well suited for producing a sufficiently stable desired dispersion. Experts have shown that the solubility of these metals or metal compounds is N.I. Y. Tarova, E .; P. Turevskaya V.V. G. Kessler, M.C. I. Nanoparticle synthesis depending on at least microemulsion, as known from Yanovskaya, “The Chemistry of Metal Alkoxides” Klufer Academic Publishing, Dordrecht, The Netherlands, 2002, etc. Is considered to be impossible, so methanol is not considered a suitable solvent for metal alkoxides, especially alkaline earth metals and alkaline earth alkoxides, and it is judged impossible to use methanol. did.

  The expert therefore thought that, for example, one should start with a solution in which the precursor, ie the hygroscopic metal compound, is completely dissolved. For this reason, for example, US Patent Application Publication No. 2005/0194573 discloses in paragraphs [0056] and [0057] that benzene is mixed into the solvent to improve the solubility of the barium-titanium precursor. ing. The knowledge underlying the needed theory is that the degree of solubility is not capable of compromising the desired outcome.

  Judging from the tests done so far, higher alcohols are not suitable for obtaining a sufficiently stable dispersion. Judging from the tests performed, isopropanol is no longer suitable. On the other hand, when dissolved in methanol, a stable dispersion is produced that is necessary for the production of the membrane. In many cases, ethanol is still suitable for obtaining a stable dispersion.

By this process, for example, a mesoscopic Al ₂ O ₃ -film is made suitable for use, in which case it then starts from a solution in which the hygroscopic aluminum compound is dissolved.

When a solution is prepared in which two or more hygroscopic metal compounds are dissolved, the stoichiometric composition is selected as desired in the subsequent ceramic. For example, if a mesoscopic BaTiO ₃ -film is to be made, an equal molar proportion of barium and titanium is prepared in the solution.

To prepare this solution, the elemental metal is dissolved in the alcohol, preferably directly or in the form of a metal alcoholate. In this way it is ensured that no unwanted material reaches the solution. Thus, for example, elemental barium as well as titanium alcoholate can be dissolved in alcohol to obtain mesoscopic BaTiO ₃ -films.

  When making a functional ceramic film to take advantage of the magnetic, electrical, or optical properties of the produced film, the selection of a cationic surfactant should be taken into consideration. When a cationic surfactant is used together with an anion containing an element other than hydrogen, carbon, nitrogen and oxygen, such as a halide, a hetero element remains in the produced film, and the functionality of the film Can be damaged. In that way, even a trace amount of halide ions in the electronic ceramic film can increase the conductivity so much that the functionality is significantly impaired. However, for the hexadecyltrimethylammonium bromide (cetyltrimethylammonium bromide, CTAB) mentioned in the examples, it has surprisingly been found that the conductivity is in an acceptable range. Accordingly, the dielectric film can also be fabricated according to the claimed method.

  Such functional infringement due to the heteroelements remaining in the film is, in one embodiment, only the elements hydrogen, carbon, nitrogen and oxygen that are removed in gaseous form when the film is calcined and sintered. This is addressed by using an anion containing in the cationic surfactant. Corresponding cationic surfactants, in the case of quaternary ammonium salts, can be prepared by suitable synthetic methods or ion exchange. In the case of alkylammonium, dialkylammonium and trialkylammonium salts, this compound can be prepared by simply mixing the amine with the corresponding acid. Examples of such halogen-free cationic surfactants are nitrates and carboxylates containing alkylammonium ions, dialkylammonium ions, trialkylammonium ions or tetraalkylammonium ions. However, possible choices are not limited to the examples given. In general, as the salt, all alkylammonium compounds and dialkylammonium compounds whose anion does not contain an element different from H, C, N and O, such as azide, cyanide, cyanate, isocyanate, hydroxide, etc. Trialkylammonium compounds or tetraalkylammonium compounds can be envisaged. The pH-value in the microemulsion can be adjusted by mixing the alkylammonium salt, dialkylammonium salt and trialkylammonium salt with the acid in the correct mixing ratio. Thereby, the rate of hydrolysis during particle synthesis can be changed, thereby making it possible to produce products that are altered with respect to particle size distribution, composition and morphology.

  The chain length of the individual alkyl chains is usually between C1 and C20 for the cationic surfactant used. The total carbon number of the alkylammonium ion, dialkylammonium ion, trialkylammonium ion or quaternary ammonium ion is typically between C8 (octylammonium salt) and C38 (distearyldimethylammonium salt). Resize droplets in microemulsions to suit your needs by using a mixture of the aforementioned alkylammonium, dialkylammonium, trialkylammonium or tetraalkylammonium salts with nonionic surfactants can do. Replacing 10-25% of the cationic surfactant CTAB with the non-ionic surfactants Lutensol ON 110 and Lutensol ON 50 (Lutensol is a trademark of BASF) results in somewhat larger droplet microemulsions.

  The microemulsion in the embodiment is preferably added dropwise to the precursor solution. In contrast to the method known from US 2005/0194573, where the precursor solution is dropped into the microemulsion, the reverse sequence is always in the presence of an excess of water in the precursor solution during synthesis. Therefore, it has an advantage of countering the formation of metal hydroxide. This hydroxide may reduce the functionality of the ceramic film produced after coating.

  Complete dispersion of the nanoparticles is definitely improved in certain embodiments of the present invention, in which case, after performing the hydrolysis reaction, surfactant molecules are adsorbed on the resulting nanoparticle surface, resulting in solution properties. The type and composition of the cationic surfactant in the microemulsion used is adapted to the polarity of the solvent as it has a significant effect. For example, the use of cetyltrimethylammonium bromide CTAB has proven to be a suitable cationic surfactant in producing stable barium titanate dispersions. This results in a directly concentrated colloidal solution containing dispersed nanoparticles having a monodisperse particle size distribution with a maximum particle size of less than 50 nm on the primary structure surface. As such, a colloidal solution or dispersion having a mass concentration of metal oxide exceeding 5% by weight can be easily prepared. If the viscosity is low, the storage stability is at least 6 months. As disclosed for concentrated dispersions in US Patent Application Publication No. 2005/0194573, no aggregation of the formed nanoparticles and thereby no precipitation of barium titanate powder, for example during the manufacturing process or during storage .

  In exceptional cases, if sufficient storage stability of the concentrated colloidal solution or dispersion is not achieved, the initial dispersion is further dispersed in the form of a low molecular volatile organic acid, amine or ketone. By adding an agent, this storage stability could be guaranteed.

  The microemulsion is preferably added to the alcohol containing the precursor therein until the water contained in the microemulsion is completely replaced. Thereafter, further addition of the microemulsion is stopped so as to ensure that the proportion of cationic surfactant is kept as low as possible and is further improved to produce a dense ceramic film.

  In order to further reduce the proportion of surfactant, unlike the prior art known from US 2005/0194573, microemulsions with a high water content, in particular with a water content of at least 5 percent by weight, are advantageous. Used for. In contrast, the moisture content according to US 2005/0194573 is only 2 to 3 percent by weight. A moisture content greater than 10 weight percent has proven suitable. In order to ensure process functionality, the moisture content should not exceed 15 weight percent.

  The low surfactant content results in a very low proportion of organic molecules (not volatile organics) that have a negligible vapor pressure in the standard state in the nanoparticle dispersion. The mass ratio of oxidized nanoparticles to cationic surfactant is greater than 4.2 without problems. On the contrary, it is usually greater than 10. When the dispersion is applied onto a substrate and subsequently sintered at 700 ° C. or higher, a mesoscopic film having a dense and uniform thickness is immediately formed.

  If the sintering temperature is less than 700 ° C., the membrane produced from the dispersion still has residual porosity, which creates the risk of impairing the functionality of the ceramic membrane.

  In order to reliably obtain a dense mesoscope film directly even at a sintering temperature of less than 700 ° C., it has been proved preferable to mix a molecular organometallic CSD-solution with a colloidal solution. This so-called hybrid solution has a proportion of CSD-solution of equal stoichiometric metal ion composition of less than 50% by weight relative to the total mass of the metal oxide when producing a one-phase pure metal oxide film. Including. Lowering the sintering temperature leads to various advantages. In particular, costs can be saved.

  When producing a one-phase pure metal oxide film, it is preferable to use a proportion of metal oxide consisting of a CSD-solution of less than 50% by weight having an equal stoichiometric metal ion composition.

  Using this hybrid solution, a multiphase composite film having nanoscale inhomogeneity (core-shell structure) for adjusting its physical properties while controlling it also has a metal composition different from that in the nanoparticle dispersion. Obtained by using a CSD-solution. In that case, the proportion of CSD solution can be less than 50% by weight, preferably less than 20% by weight, particularly preferably less than 10% by weight, based on the total metal mass of the resulting oxide. However, when using hybrid solutions to make mesoscopic membranes, it is also possible to dope in a particularly easy way, in which one or a number of doping agents are incorporated with respect to the mixed CSD-solution. . The proportion of this doping is preferably less than 5%, particularly preferably less than 1%, based on the total mass of the oxide. It is also possible to use simultaneously a CSD-solution containing the same metal as the particles and a metal different from the particles. Doped homogeneous or heterogeneous films can also be produced by adding doping substances to any of the aforementioned hybrid solutions.

  Using this hybrid solution, a dense mesoscopic ceramic thin film can be obtained on a different substrate even at a sintering temperature of 700 ° C. or lower. The metal oxide concentration in this hybrid solution used in each case is adapted to the targeted film thickness and the preferred coating method of the resulting thin film. For example, with a concentrated solution, a ceramic film of less than 250 nm can be obtained directly in one process step by using a relatively easy centrifugation technique.

In order to produce a suitable CSD-solution, carboxylates, simple alkoxides, methoxy ethoxides and amino ethoxides can be used as starting materials. These are converted into stable CSD-precursor solutions by simple dissolution in simple alcohols, ether alcohols, amino alcohols and carboxylic acids or appropriate mixtures or by reflux and distillation steps. In addition, the solvent is selected such that optimal coating behavior results. Optimal coating behavior is achieved when the solution has good wetting behavior that allows for a homogeneous dispersion on the substrate and not too rapid volatilization behavior of the solvent. Furthermore, it is preferable that chemical compatibility with the microemulsion is guaranteed. In order to protect the metal alkoxide used against hydrolysis and condensation before the expected time, chelate complexing agents such as β-diketonates, polyhydric alcohols or aminoethanol are added as stabilizers. The upper limit of the solution concentration which can be adjusted in this case is determined by the solubility product for each given precursor combination and is typically 0.05 to 1.5 mol / l. A solution having a concentration in the range of 0.1 to 0.5 mol / l is preferably used. S. Hoffmann and R.H. Vazeru (Waser) al., "CSD produced [Ba, Sr] TiO ₃ thin film of form control (Control of the morphology of CSD- prepared [Ba, Sr] TiO 3 thin films) ", Journal of the European ceramic As shown in Society Vol. 19, 1999, p. 1339, changing the concentration often allows for adjustment of the morphology as well as control of the film thickness per individual coating step.

  For coating, all methods known from the CDS-technique, such as centrifugation, dipping and various forms of spraying, are basically suitable. This method is selected in relation to the targeted application or the shape of the substrate. In the case of simple centrifugation, a defined amount of solution is applied onto the substrate, possibly in a dry protective gas environment, to avoid hydrolysis before the scheduled time and condensation reactions during the centrifugation process. , And centrifugally rotated at a rotational speed of 1000 to 6000 U / min until the film thickness becomes constant. The film thickness that can be achieved in that case is related to the concentration of the solution, the viscosity of the solution, the vapor pressure of the solvent used and the rotational speed. In the case of the dipping method, the substrate to be coated is dipped in the solution and pulled up while adjusting the speed. In that case, the film thickness can be adjusted by viscosity and dipping speed, with relatively high speeds generally resulting in a relatively thick film, while slow dipping results in a relatively thin film. Various methods are known for spraying. Whether the ultrasonic nebulizer produces small droplets in the micrometer range from the solution and then directs it onto the substrate with a dry argon stream and deposits on it, or transfers the solution to the aerosol through a fine nozzle Or C.I. Curtis, T.W. Rivkin, A.R. Miedaner, J.M. Alleman, J.M. Perkins, L.A. Smith, D.C. Published by Ginley, "Metalizations by direct-write ink jet printing", Proceedings NCPV Program Revised Meeting, Lakewood, CO, 2001, CD ROM) As is done, the solution is applied onto the substrate by inkjet printing. The latter method allows the structuring of the membrane at the same time if the viscosity and vapor pressure of the solvent are commensurate. In order to make mesoscopic membranes economically with respect to the MCLL-technology, preferably an ink jet printing method which is also usable in principle for intermediate metallization is suitable [C. Curtis, T.W. Rivkin, A.R. Miedaner, J.M. Alleman, J.M. Perkins, L.A. Smith, D.C. Ginley, “Metalizations by direct-write ink jet printing”, Proceedings NCPV Program Revised Meeting, Lakewood, CO, 2001, CD ROM.

Example 1
160 g of the coating solution of the present invention having a mass concentration of 6.25 wt% dispersed oxide nanoparticles for producing a mesoscopic barium titanate film can be easily synthesized as follows.

  5.888 g of metal barium is dissolved in 153 ml of methanol under protective gas and at room temperature, and 12.187 g of titanium isopropoxide is added dropwise. Subsequent hydrolysis with a stoichiometric amount of water resulted in 12.21% by weight 1-pentanol, 3.74% by weight CTAB (cetyltrimethylammonium bromide), 12.23% by weight water and 72.% by weight. This is done by slowly dropping 20.634 g of a cationic microemulsion composed of 82% by weight of cyclohexane. Immediately after complete addition of the microemulsion, an optically isotropic, almost colorless and transparent barium titanate dispersion is obtained, which has a practical monodisperse particle size distribution and an average particle size of 5 nm ± 0.5 nm ( It has a viscosity of 1.5 mPa s and a proportion of non-volatile organic matter of 0.48 wt%. This corresponds to a mass ratio of 13 barium titanate nanoparticles to cationic surfactant.

  Using this coating solution, a simple crystalline barium titanate film with a thickness of about 200 nm is directly formed by simple centrifugation on a platinum silicon substrate at 3000 U / min and subsequent deposition at a temperature above 700 ° C. Obtainable.

Example 2
150 ml of the hybrid coating solution of the present invention composed of a molecular ZirO ₂ -precursor solution and a barium titanate nanoparticle dispersion can be prepared as follows.

  First, 1.9487 g of zirconium tetrabutoxide was dissolved in 5 ml of n-butanol under a protective gas, and a transparent yellow solution was formed by slowly dropping acetylacetone twice as much substance corresponding to 1.0158 g under stirring. Mix until done. Then replenish with butanol until a 5% solution is obtained. Then 30 ml of CSD-solution corresponding to 20% by volume is combined with 120 ml of the solution prepared according to Example 1 to produce a clear, colorless optically isotropic hybrid coating solution with a total solids content of 5%. Occurs. Using this hybrid solution, a crystalline dense mesoscope film with a thickness of about 570 nm is produced by simple centrifugation at 3000 U / min on a platinum silicon substrate and subsequent deposition at temperatures above 700 ° C. be able to.

Example 3
200 g of the coating solution of the present invention having a mass concentration of 5 wt% dispersed oxidized KNaNb ₂ O ₆ -nanoparticles for producing a mesoscopic piezoelectric ceramic potassium-sodium niobate film is easily synthesized as follows. can do.

18.507 g of niobium ethoxide, 2.065 g of potassium methoxide and 1.570 g of sodium methoxide are dissolved in 137 g of methanol under protective gas and at room temperature with stirring. Subsequent hydrolysis with a stoichiometric amount of water resulted in 12.21% by weight 1-pentanol, 3.74% by weight CTAB (cetyltrimethylammonium bromide), 12.23% by weight water and 72.% by weight. This is done by slowly dropping 27.967 g of a cationic microemulsion composed of 82% by weight of cyclohexane. An optically isotropic orange potassium-sodium niobate dispersion is obtained immediately after complete addition of the microemulsion and is stored by mixing 5.82 g acetylacetone and 6.98 g acetic anhydride. Stability could be improved over 6 months. With respect to this dispersion, a monodisperse particle size distribution with an average particle size of 7 nm ± 0.8 nm was calculated at a non-volatile organic matter ratio of 0.52% by weight (dynamic light scattering using a Malvern zeta sizer). Measured by). This corresponds to a mass ratio of potassium-sodium niobate nanoparticles to cationic surfactant of 9.56.

  Using this coating solution, for example, by simple centrifugation at 3000 U / min on a platinum silicon substrate and subsequent deposition at a temperature in excess of 700 ° C., a dense crystalline potassium-niobic acid with a thickness of about 180 nm directly. A sodium membrane can be obtained.

Example 4
100 g of the halogen-free coating solution of the present invention having a mass concentration of 2.5% by weight dispersed zirconium dioxide-nanoparticles for making a mesoscopic zirconium dioxide film can be easily synthesized as follows. Can do.

  6.551 g of zirconium tetraisopropoxide was dissolved in 78.815 g of absolute ethanol under protective gas and at room temperature and, for hydrolysis, 5.09% cetyltrimethylammonium octoate (CTAO), 1.17. Mix slowly by dropwise addition of 14.634 g of a halogen-free microemulsion composed of 4% acetic acid, 4.92% water, 77.06% cyclohexane and 11.76% pentanol. Immediately after complete addition of the microemulsion, an optically isotropic, almost colorless and transparent zirconium dioxide dispersion with a practical monodisperse particle size distribution and an average particle size of 4 nm ± 0.8 nm was obtained ( (Measured by dynamic light scattering using a Moulburn zeta sizing machine).

  Using this coating solution, a dense crystalline zirconium oxide film with a thickness of about 70 nm is directly formed by, for example, simple centrifugation at 3000 U / min on a platinum silicon substrate and subsequent deposition at a temperature exceeding 700 ° C. Obtainable.

Halogen-free surfactant (CTAO) was easily prepared by replacing the bromine ion of CTAB (cetyltrimethylammonium bromide) with octoate ion using ion exchange.
In this regard, plenty of water was placed in a column containing 100 ml of the ion exchanger DOWEX ™ 1 × 8 in chloride form with an ion exchange capacity of 1.2 meq / ml. 133 ml of a mixture of 2M caustic soda solution (266 mmol) and 38.4 g octanoic acid (266 mmol) was placed in the column and the chloride was quantitatively exchanged for octanoate. The column was then washed with 200 ml water followed by 200 ml methanol. Finally, 14.3 g of CTAB (39.2 mmol) in 100 ml methanol was added to the column. The eluent was collected in fractions and analyzed for bromine using an acidic silver nitrate solution. Bromine was not detected in all collected fractions. Octanoic acid-N-cetyl-N, N, N-trimethylammonium (CTAO) precipitated as a viscous paste after removal of the solvent. The residual amount of bromine was below the detection limit of 10 ppm.

  According to a paper by Heinz Rehage [Rheology of Unstugengen an viskoelastischen Tensidloesungen, Bayreuth University, 1982], quaternary ammonium salts of such organic acids It can also be produced by replacing quaternary ammonium chloride with silver oxide and replacing the hydroxide with the corresponding organic acid. Thus, for example, hexadecylpyridinium salicylate (CPySal) was produced from hexadecylpyridinium bromide and salicylic acid.

  The mass fraction of oxidized nanoparticles is less than 5% by weight in this example. The surfactant used (CTAO) is advantageously distinguished from that of the other examples (CTAB). This is preferably a halogen-free surfactant (as main or subcomponent). The coating solution does not contain halogen. The CTAO used is a carboxylate. Its production takes place by the described ion exchange.

Example 5
Hybrid coating of the present invention comprising a molecular bismuth precursor solution and a strontium titanate nanoparticle dispersion for making a mesoscopic Bi ₂ O ₃ / SrTiO ₃ -binding material film with a solid mass ratio of 1: 4 100 g of the solution can be synthesized as follows.

  In order to produce 80 g of a 5% by weight strontium titanate nanoparticle dispersion, 1.909 g of strontium metal was first dissolved in 61.422 g of methanol under protective gas and at room temperature to give 6.188 g of titanium isopropoxide. Is mixed dropwise. Subsequent hydrolysis with a stoichiometric amount of water resulted in 12.21% by weight 1-pentanol, 3.74% by weight CTAB (cetyltrimethylammonium bromide), 12.23% by weight water and 72.% by weight. This is done by slowly dropping 10.481 g of a cationic microemulsion composed of 82% by weight cyclohexane. Immediately after complete addition of the microemulsion, an optically isotropic, almost colorless and transparent strontium titanate dispersion with a practical monodisperse particle size distribution and an average particle size of 5 nm is obtained.

To this dispersion is added 20 g of a colorless molecular bismuth precursor solution (content 1 g Bi ₂ O ₃ equivalent), which is prepared by previously dissolving 0.828 bismuth acetate in 19.172 g propionic acid with stirring. Can be produced by gentle heating.

Using this hybrid solution, in particular by simple centrifugation at 3000 U / min on a platinum silicon substrate, followed by deposition at a temperature above 600 ° C., a dense crystalline Bi ₂ O ₃ / SrTiO with a thickness of about 240 nm is obtained. _{3- A} binding material film is obtained.

Example 6
From a 0.2 molar lead titanate nanoparticle dispersion and a 0.2 molar molecular barium titanate precursor solution with a mixing ratio of 60:40 to produce a mesoscopic BaTiO ₃ / PbTiO ₃ -binding material film The other 100 ml of the hybrid coating solution of the present invention that is constructed can be synthesized as follows.

  In order to produce the required 60 ml of 0.2 mol lead titanate dispersion, first, 3.9033 g of anhydrous lead acetate and 3.3107 g of titanium isopropoxide are dissolved in butanol under protective gas. . The resulting reaction product in the form of isopropyl acetate is subsequently distilled off continuously and the reaction mixture is evaporated to dryness. In order for the white solid so obtained to be absorbed in 53 ml of methanol and fully hydrolyzed, 12.21 wt% 1-pentanol, 3.74 wt% CTAB (cetyltrimethylammonium bromide), 3.846 g of cationic microemulsion composed of 12.23 wt% water and 72.82 wt% cyclohexane is added dropwise and mixed. After the addition is complete, an optically isotropic yellow lead titanate dispersion having an average particle size of about 4 nm is obtained.

  To this dispersion is added 40 ml of a 0.2 molar barium titanate solution of molecules.

  First, 1.5786 g of high-purity barium carbonate is dissolved in 8 ml of propionic acid by reflux boiling for several hours. In order to capture the liberated water, 1.0416 g of propionic anhydride (corresponding to 1.19 ml of propionic acid liberated after the reaction) is mixed. In the second flask, 2.7189 g of titanium tetrabutoxide was dissolved in 5 ml of n-butanol under a protective gas, and with stirring, twice the amount of acetylacetone corresponding to 1.6019 g was added to a clear light yellow solution. Mix by slowly dropping until formed. Pre-manufactured so that the solvent ratio for propionic acid / n-butanol in the finished barium titanate precursor solution is 1: 1.5 after corresponding filling with propionic acid and n-butanol to 40 ml Quantitatively mix the barium propionate solution into the stabilized titanium tetrabutoxide solution.

With this coating solution, for example, by simple centrifugation at 3000 U / min on a platinum silicon substrate followed by deposition at a temperature above 700 ° C., the dense crystalline BaTiO ₃ / PbTiO with a thickness of about 320 nm is immediately _{3- A} membrane is obtained.

  To define the concepts of “dispersion”, “solution” and “suspension”, the Lemp Chemical Dictionary, 9th edition, editor: J. Am. Falbe, M .; Reference is made to Regitz, Georgtimeme Publishing, Stuttgart, 1989, ISBN: 3-13-734609-6.

According to dispersion DIN 53900 (July 1972) one system (dispersion system) consisting of a plurality of phases, one persistent (dispersion medium) and at least one more finely dispersed (dispersion phase, dispersoid) ) Name

Solution In the broadest sense, a solution is a homogeneous mixture of different substances, where the smallest partial volume of this solution has a similar composition. With respect to the solution in the narrow sense, it is understood as a liquid mixture of at least two components, in which the partners are present in molecular dispersion in different quantity ratios. Colloidal solutions such as sols, suspensions and emulsions are distinguished from this true solution.

A name representing the dispersion of insoluble solid particles having a particle size up to the size of colloids (<10 ^-5 cm) in the suspension liquid ... in the case of a relatively coarse suspension, the suspended particles are delayed If it settles to the bottom sooner (deposition), on the other hand, if the particle has reached the size of the colloidal particle, it is floating in the liquid.

  Basically the suspension is thermodynamically unstable. However, such a colloidal solution is sufficiently stable to processing, as kinetic stability can be improved by a suitable peptizer. The surfactant present in the reaction mixture during synthesis in the microemulsion causes the resulting nanoparticles to stabilize against aggregation or agglomeration. The surfactant thus allows sufficient kinetic stability to the process, and this kinetic stability can optionally be further improved by adding a peptizer.

  It is therefore possible to obtain a sufficiently stable coating dispersion using microemulsions. This (colloidal) coating solution, optionally added with a CSD-solution, is suitable for the production of dense mesoscopic membranes.

  A stable dispersion in the sense of the present invention is achieved especially when the particle size distribution in such a colloidal solution does not change for at least 3 days, preferably at least 10 days, particularly preferably at least 30 days. The dispersion obtained according to the examples is usually kept for several months.

  There are numerous ways to produce nanoparticles. The actual problem is to use this particle to make a stable dispersion with a high solids ratio. This was successful with the present invention. A submicron film can be produced economically in one step.

  In addition to a pure coating solution consisting of a stable dispersion, a hybrid coating solution can also be produced according to the invention, which consists of incorporation of an organometallic compound into the dispersion. The great advantage of this hybrid solution is that it makes it possible to fabricate mesoscopic bonding material films with nano-scale inhomogeneities, mechanical properties (such as expansion coefficient) and electrical properties (such as temperature course of dielectric constant) of ceramics Can be adjusted for the purpose.

  Nanoscale heterogeneity means that the nanoparticles are embedded in a different ceramic substrate than that formed from the organometallic compound mixed after heating (sintering) the separation membrane.

  The figure shows an electron micrograph of a mesoscopic barium titanate film produced according to the process and having a dielectric constant greater than 1000. Since this film was made with only one coating process, this film has no boundaries caused by sintering. When such a film is produced by multiple application and sintering processes, a boundary is created that can be seen with an electron microscope. A dielectric constant in excess of 1000 has been achieved with the method of the present invention. As regards comparable film thicknesses, only a dielectric constant of 760 has been achieved with the method known from US 2005/0194573. Therefore, not only the film produced according to the present invention but also clearly improved in this respect.

  The various membrane applications mentioned at the beginning of the specification and the materials alone or in combination with each other belong to the present invention.

Claims (21)

In a method for producing a coating dispersion, a solution containing alcohol as a solvent and at least partially dissolving a hygroscopic metal compound is prepared, and the solution is mixed with a microemulsion for producing a dispersion.
A method for producing a coating dispersion, wherein the microemulsion comprises a cationic surfactant.   The method of claim 1, wherein the proportion of hygroscopic metal compound is selected so as to produce a dispersion having a proportion of solids of at least 5% by weight.   The process according to claim 1 or 2, wherein methanol is used as the solvent.   A method according to one of the preceding claims, wherein the solution comprises an alkaline earth metal.   The process according to one of the preceding claims, wherein the metal is dissolved directly in the alcohol or in the form of a metal alcoholate to produce the solution.   A process according to one of the preceding claims, wherein barium and titanium alcoholate are dissolved in methanol to prepare the solution.   A process according to one of the preceding claims, wherein only cationic surfactants containing no halogen are used, or cationic surfactants containing bromine are used.   A method according to one of the preceding claims, wherein the type and composition of the cationic surfactant in the microemulsion used is adapted to the polarity of the solvent.   A method according to one of the preceding claims, wherein the microemulsion is dropped onto the hygroscopic precursor until the water present in the microemulsion is completely replaced.   A process according to one of the preceding claims, wherein the microemulsion has a water content of at least 5% by weight.   A process according to one of the preceding claims, wherein hexadecyltrimethylammonium bromide is selected as the cationic surfactant.   A method according to one of the preceding claims, wherein the CSD-solution is added to the dispersion. The added CSD-solution has the same stoichiometric metal composition as the nanoparticles, in which case the proportion of the metal mass of this molecular organometallic compound is less than 50% by weight of the total metal mass in the hybrid solution Or
Or the added CSD-solution has a metal composition different from the nanoparticles, in which case the metal mass proportion of this metal organic compound is also less than 50% by weight of the total metal mass in the hybrid solution ,
Or the added CSD-solution contains one or a number of metals in the form of metal organic compounds, in which case the percentage of metal mass of the metal considered for doping is the total metal mass in the hybrid solution The method of any preceding claim, wherein the method is less than 5% by weight.   A method of making a film, wherein a coating dispersion according to one of the preceding claims is produced, the coating dispersion is applied onto a substrate and subsequently sintered.   A method according to the preceding claim, wherein the coating dispersion is applied to the substrate by printing, preferably using an ink jet printer.   A method according to one of the preceding two claims, wherein a film with a thickness of 50 nm to 1 μm is produced in only one application step.   A method according to one of the preceding three claims, wherein the burning of the non-volatile organic part and the compression of the mesoscopic ceramic film are carried out using a diffusion- or fast annealing furnace. -Having metal oxide nanoparticles dispersed in an organic solvent,
The dispersion for stabilization comprises one or many cationic surfactants,
A coating solution for producing a dense ceramic film, particularly a functional ceramic film having the above characteristics, wherein the mass ratio of the oxidized nanoparticles exceeds 5% by weight and / or the coating solution contains no halogen.   The solution of any preceding claim, wherein the mass ratio of oxidized nanoparticles to cationic surfactant is greater than 4.2.   The solution according to one of the preceding two claims, wherein the maximum value of the particle size distribution is at least less than 50 nm, preferably less than 10 nm.   Barium titanate film having a film thickness of 50 nm to 1 μm and a dielectric constant greater than 1000, produced by sintering and not including the boundaries visible with an electron microscope.

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