WO1991011030A1

WO1991011030A1 - IONIC SUPERCONDUCTOR OBTAINED BY INTRODUCTION OF LITHIUM ATOMS IN THE LATTICE OF HIGH TEMPERATURE SUPERCONDUCTOR MATERIALS OF THE Ba2YCu3O7-x TYPE

Info

Publication number: WO1991011030A1
Application number: PCT/ES1991/000004
Authority: WO
Inventors: Miguel Angel Alario Franco; Emilio Moran Miguelez; Alejandro Varez Alvarez; Jacobo SANTAMARÍA SÁNCHEZ-BARRIGA; Francisco SÁNCHEZ QUESADA
Original assignee: Universidad Complutense De Madrid
Priority date: 1990-01-17
Filing date: 1991-01-17
Publication date: 1991-07-25
Also published as: ES2021491A6; AU7074591A

Abstract

The invention discloses a new ceramic superconductor material of formula LizBa2TRCu3O7-x wherein TR is an element or mixture of elements of rare earthes and wherein copper may be partially substituted by Fe, Co, Ni or Al. This material whose the transition temperature is equal to that of ''Ybacuo'' (Ba2TRCu3O7-x) from which it was obtained, has nonetheless the particularity of presenting at higher temperature (≈ 340 K) a cationic conductivity. In order to obtain this material, the ''ybacuo'' is first prepared by sintering, in an oxigen atmosphere, a stoichiometric mixture of the oxides or salts of Cu, Ba and Y (or other lanthanide). Once the ''ybacuo'' is obtained, it is treated with a solution of an organolithium (butyl-lithium) in an appropriate organic solvent (cyclohexane), the amount of lithium introduced in the lattice depending essentially on the duration of the reaction.

Description

Title

Ionic superconductor obtained by introducing lithium atoms in the network of high temperature superconducting materials type

Field of the Invention

The present invention relates to the preparation of a new family of materials of enormous interest in that it brings together electronic (superconductivity) and ionic (ionic conductivity) properties.

State of the art

From the discovery of superconductivity in 1911 until 1986 the known superconducting materials were metals, alloys or intermetallic compounds. On this date a new type of superconducting materials based on metal oxides appears for the first time [J.G. Bednorz and K.A. Müller, Zeitschr. F. Physik B - Condensed Matter, 64, 189 (1986)].

Shortly after, and in various laboratories around the world, it was confirmed that the materials type Balacuo (Ba _x La _> _ _x Cu0 ₄ ) are superconductors with critical temperatures between 25 and 30 K.

Subsequently, Chu, Wu et al. [Phys. Rev. Letters, 58 (4), 405-407 (1987)], found a mixture of superconducting oxides above the boiling temperature of liquid nitrogen at normal pressure, identifying R. Cava et al. [Phys. Rev. Letters, 58 (4), 408-410, (1987)] Ba ₂ YCu ₃ 0 ₇ as responsible for superconductivity. This product, which is known as Ybacuo, has, on the other hand, the characteristic of being non-stoichiometric in terms of its oxygen content [see, for example, references of MA Alario-Franco et al. in Mat. Res. Soc. Symp. Proc, 99, 41-47 (1988) and C. Chaillout, MA Alario-Franco et. al in Solid State Communications, 65 (4), 283-286 (1988)], and this influences the value of the critical temperature of transition to the superconducting phase, T _c .

As regards the ionic conductivity in the solid state, it is a phenomenon known since the time of Faraday, who observed it in silver sulfide, Ag ₂ S, and refers to displacement, under the influence of a electric field, of some or some of the ions of a solid. The ionic conductivity is, therefore, a phenomenon clearly distinct from the electronic superconductivity referred to above and which consists in the transport of electric current without resistance. However, in some ionic conductors the conductivity is very high, as in the so-called β-alumina [JT Kummer, Progress in Solid State Chemistry, 7, 141 (1977)] or in the silver iodide [K. Funke, Progress in Solid State Chemistry, 11 (4), 345-407 (1976)]. Therefore, said materials receive different names such as fast ionic conductors (fast ionic conductors), superionic conductors (superionic conductors) or ionic superconductors (ionic superconductors). Reference is made in this field to A. Hooper, Contemporary Physics, 19 (2), 147-168 (1978).

So far there are very few documents in which lithium is mentioned in relation to Ybacuo type metal superconductors (BaaYCU _to Ov- _x ). In this regard, European patents PE-284438 and PE-323178 stand out; the first describes a procedure to minimize the content of alkali metals (Li, Na, K), so that the content of these in the final product is not greater than 0.2% by weight, in order to achieve higher values of the transition temperature. PE-323178 describes a method to achieve an improvement in oxygen-ion mobility, reaching the desired stoichiometry of oxygen in a short time; for this, it makes a partial or total replacement of the alkaline earth elements by some of the alkali metals (Li, Na, K, Rb or Cs).

One document, in some way related to the present invention, is US-3,933,688 (June 20, 1976) where a process for introducing lithium into the network of chalcogenides of elements of Groups IVB and VB is described. Of course, the relationship with the present invention is only insofar as a technique of introducing lithium atoms into a crystalline lattice (totally foreign to the present invention) is described, which is otherwise described in previous documents: J. Chem. Phys ., 58, 697 (1970); J. Less Comm. Met., 20, 121 (1970); Science, 175, 884 (1972); C.R. Acad. SC. Paris, 5., 276C, 1283 (1973), etc.

The present invention relates to the insertion of lithium in electronic superconductors of Ybacuo type giving materials of formula

[0 <z <2, O≤x≤l], which we will hereinafter briefly call Liybacuo, characterized in that three transport phenomena generally coexist, with cationic conductivity prevailing for 340 <T <675 K, electronic conductivity for 95 <T <340 K and finally the superconductivity at T <95 K. This type of material, according to the bibliographic search carried out is completely new, because although materials with any of these types of conductivity are known , this is the first time that a material is obtained in which these three phenomena coexist. It should be noted, however, that when x> 0.6 disappears, as is known, the phenomenon of superconductivity. Nevertheless, even these materials with x> 0.6, being lithiated also show the phenomenon of cationic conductivity.

In the X-ray diffraction study of these materials, diffraction maxima characteristic of the orthorhombic phase Ba ₂ YCU ₃ 0v-- _{x are} observed with reticular parameters slightly different from those of the starting superconductor. As an example, table I shows the parameters corresponding to the starting sample and one with a lithium content of approximately 0.5 atoms per formula

TABLE I Sample

On the other hand, by measuring the variation of magnetic susceptibility with temperature, in the range of 300 to 4 K, a paramagnetic-diamagnetic transition around 90-95 K is observed, which is indicative of the super¬ conductive character of these materials.

The measurements of the real and imaginary part of the permittivity of these materials between 100 and 500 K reveal the existence of two well differentiated sections in conductivity, with activation energies of the order of 0.5 to 0.01 eV. Said activation energy values correspond to a cationic and metallic conduction process respectively. The temperature at which both sections differ is approximately 340 K («70 ° C). It should be noted that due to the difficulty of separating the ionic conductivity from the electronics, it is possible that the conductivity above 70 ° C is not pure ionic but mixed. It should be noted that the activation energy of the ion conduction process is within the range found for lithium in β-alumina and other ions in fast ionic superconductors (those referred to in the Anglo-Saxon literature "Fast Ionic Conductors").

The present invention, in accordance with the foregoing, is not intended simply to obtain a new superconductor which, in the best case, could mean an increase in its _^ -, which, on the other hand, does not take place in the material we claim. It is a new material that, while maintaining the characteristics in terms of superconductivity of the materials that we could call conventional, adds to them the characteristic of converting them, at practically room temperature, into ionic conductors.

Detailed description of the invention

The introduction of lithium atoms into the network of a superconductor Ybacuo type gives rise to the new material that we call Liybacuo characterized because, although it has a transition temperature practically equal to that of the starting Ybacuo and something above it presents metallic conductivity up to approximately 340 K, said material manifests a new transition, becoming cationic conductivity.

Obtaining this Liybacuo comprises a sequence of stages, which are individually known, but which together constitute a new procedure to obtain the desired material. These stages, whose detailed description will be made later, are the following:

a) Preparation of a homogeneous mixture of oxides, hydroxides or oxisals of barium, copper and one or more rare earth elements in the weighted proportions appropriate to the stoichiometry of the Ybacuo to obtain.

b) Sintering of the mixture between 900 and 950 ° C in air or oxygen.

c) Treatment of the product obtained in b) in an oxygen-rich atmosphere between 350 and 500 ° C.

d) Ybacuo grinding obtained up to <100 μm

e) Preparation of an organic solution of a suitable organo lithium.

f) Reaction in the organic medium of the organolithium with the Ybacuo.

g) Separation of the Liybacuo from the organic solution

g) Compaction and conditioning of the Liybacuo powder obtained.

Ybacuo Preparation

In everything that follows we will refer to the simplest Ybacuo corresponding to the formula YBa ₂ Cu ₃ θ7- »:. The substitution of the ytrium for some or some of the other rare earth elements does not affect at all the characteristics of the material claimed in terms of its electrical properties. You can also substitute small amounts of Cu for other metals such as Fe, Co, Ni, Al, Zn and even Ga; Although the introduction of these elements deteriorates the superconducting properties of ybacuo, the products are still suitable for subsequent lithiation and the obtained libacuo has cationic conductivity. As has been repeatedly stated, the present invention is based on modifying a conventional Ybacuo by introducing it, by means of a claimed technique, lithium atoms. The starting point can be either a commercial Ybacuo or the one obtained following conventional techniques for obtaining ceramic powders.

A typical sequence consists of mixing BaC0 _{3 /} Y_ »0 ₃ and CuO, calcining the mixture for six hours at 800 ° C, grinding in dry acetone for one hour, compacting the powder, sintering at 950 ° C for twelve hours, making a treat Oxygenation at 400-450 ° C for another twelve hours, repeating the grinding-oxygenation treatment again.

The sintering operation can be done by supporting the compacted sample on a crucible of an appropriate nature, for example sintered alumina.

There are other chemical-type Ybacuo preparation techniques that of course can be used; such as sol-gel [K.C. Goretta et al., Mater Lett., 7, 161 (1988)] or the mixture-liquid [S.E. Trolier et al., Am. Ceram. Soc. Bull, 67, 759 (1988)] that, although they allow a better quality of the Ybacuo obtained, are not essential for obtaining the product in question.

Ybacuo grinding

An important stage of the process of obtaining Lybacuo is the milling process of Ybacuo.

Once this is obtained, as described in the previous section, it is subjected, under the same conditions of step a) to a grinding (step c) so that the product obtained has a size smaller than about 100 μm. The conditions under which the grinding is carried out are the same as those indicated for the preparation of the Ybacuo.

Ybacuo lithiation

Once the Ybacuo powder has been obtained, lithium atoms are introduced into its crystalline network. This operation is performed by contacting the Ybacuo with a solution of a lithium organ in an appropriate solvent. The reaction that takes place can be expressed by the following equation:

zR-Li + Ba_, YCu ₃ 0 _v -__>

+ ^Z / ₂ RR

where 0 <z <2 and 0 <x <l and R is an alkyl radical.

The reaction is normally carried out at room temperature, the boiling and solidification points of the solvent being set as extreme limits (69 ° C and -94 ° C respectively for n-hexane).

Since organolithium is available in the trade, of which the most common is n-butyllithium, C ₄ H ₉ Li, hereinafter we will refer to it. Its commercial form is its solution in n-hexane, a solvent that has proven to be an appropriate means to carry out the reaction; The most common concentration is 1.6 M although there are also more concentrated solutions.

According to the characteristics that are sought for Liybacuo, related to the lithium content introduced into the Ybacuo network, different organolithium concentrations that are normally between 1 and 2 M (which are reached by dilution or evaporation of the solution), as well as a greater excess or less than the compound required by the stoichiometry of the reaction.

The reaction is verified by suspending, by stirring, the ground Ybacuo in the reagent solution, maintaining at all times an inert atmosphere (for example nitrogen), avoiding contact especially with oxygen, water and carbon dioxide.

The reaction time depends on the proportion of lithium to be introduced into the network, the excess of reagent, its concentration and the temperature at which it is carried out.

Product handling Once the reaction is complete, the majority of the excess reagent is removed by decantation or filtration, the rest being removed by successive washing operations with pure solvent (n-hexane). Given the need to verify these operations under an inert atmosphere, the most advisable thing is to carry out the separation by decantation, verifying both this and the successive washes in the reactor itself or in another closed container to which the suspension is transferred after the reaction.

Once the excess organolithium has been removed, the solvent that soaks the product obtained is removed. This operation is carried out by the usual drying techniques taking into account the precaution, repeatedly indicated, of always operating under an inert atmosphere, at room temperature. In this sense, a simple way to perform the operation is, using the container itself where the decantation and washing has been carried out, evaporate the solvent in vacuo.

The washed and dried product, given its reactivity, must Continue to be protected from air and moisture.

Examples

In the examples that we present below, we started with a commercial Ybacuo whose composition corresponded to the formula Ba ₂ YCu ₃ 0 ₆ _ «, _».

The parameters of its crystalline network were 3,815 (5) Á b 3,890 (6) Á c 11.60 (2) Á V 172.2 (8) Á ³ with a transition temperature of 92.5 K.

No ionic conductivity below 573 K (300 ° C) is detected in this material.

The material is milled, in agate mill, until all of it passes the N2 150 sieve of the Tyler series (0.105 mm mesh opening).

Example 1 5 g of this material are introduced into a 50 ml capacity flask, the air being dislodged by successive vacuum operations (<5 Pa) and 3N nitrogen purity sweeping with which the flask is filled. 5 ml of a 1.6 M commercial solution of n-butyllithium in n-hexane are added. After cutting off the gas flow and closing the mouths of the flask, the mixture is subjected to strong agitation by means of a teflon magnetoagitator that rotates at 1000 rpm; Stirring is maintained for 48 hours. After this time the stirring is cut off and the solid is allowed to settle, then the supernatant is siphoned creating a slight nitrogen overpressure. Without removing the solid from the flask, it is washed several times by adding 10 ml portions of n-hexane which, after stirring for about 15 minutes, is removed by siphoning through a small nitrogen overpressure. Finally, the n-hexane that is soaking the sample is removed by evaporation under vacuum at room temperature (~ 25 ° C).

The chemical analysis of the sample allows you to assign the formula Li. _3β Ba ₂ YCu ₃ 0 _β . ₉ ; The measure of its magnetic susceptibility, X _m , shows a clear transition to the superconducting phase at approximately 92 K. This material now has cationic conductivity.

Example 2 The experiment is repeated under the same conditions as in Example 1 but maintaining stirring for 72 h.

The chemical analysis of the sample allows you to assign the formula Li ₀ . _3Ba ₂ YCu ₃ O _β .85; The measure of its magnetic susceptibility, X _m , shows a clear transition to the superconducting phase at approximately 90 K. As in Example 1, this Liybacuo has cationic conductivity.

Example 3 The experiment is repeated under the same conditions as in Example 2 but varying the amount and concentration of n-butyllithium; In this case, it is based on a 1.0 M solution, obtained by diluting the commercial solution with hexane, and using 10 ml instead of 5 ml.

The chemical analysis of the sample allows you to assign the formula Li _or .____ Ba ₂ YCu ₃ 0s. ₈ ; The measure of its magnetic susceptibility, X _m , shows a clear transition to the superconducting phase at approximately 90 K, and as in the two previous examples, the Liybacuo obtained presents also cationic conductivity.

Example 4

In order to reduce the oxygen content of the commercial Ybacuo, 2 g of it was heated at 400 ° C for 14 days in a vacuum glass ampoule (<5 Pa) in which 0.14 g of metal zirconium was also placed powder [technique of Cava et al., Physica C, 153-155, 560-565 (1988)]. As a result of this treatment, a new semiconductor material was obtained whose formula was Ba ₌ YCu ₃ O _β .is, of tetragonal structure [a = 3,859 (2) A, c = 11.80 (7) A, V = 175.8 (3) A ³ ].

The lithiation was carried out under the same conditions of example 1 resulting in a material of formula

Li ₀ . ₃ _.Ba ₂ YCu ₃ 0 ₆ . and that, although it showed no superconducting transition, it presented, as in the previous examples, cationic conductivity.

Claims

1. A new type of conductive material of general formula Li _^ BasTRCUaO - _^ and its obtaining by lithiation of a conventional Ybacuo of formula Ba ₂ TRCu ₃ 0 ₇ _- _<: characterized by presenting in general, in addition to the superconductivity of Ybacuo, always a cationic conductivity above 340 K.

2. A new type of conductive material according to claim 1 characterized in that the values of xyz appearing in its chemical formula, Li _z Bas RCU _at O ^ - _x , are within the ranges: 0 <z <2; O≤x≤l

3. A new type of conductive material according to claims 1 and 2 characterized in that the symbol TR that appears in its chemical formula, Li-.Ba ₌ .TRCu ₃ O _v _- _ϊt , is an element of the so-called rare earths or lanthanides, and in particular La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, or Lu or combinations of 2 or more of them in fixed or variable proportions of the type

Li _z Ba ₂ (TR _x .TR ' ₁ - _r ) Cu ₃ 0 ₇ . _x where TR and TR 'are any two of the aforementioned elements of the rare earths and [O≤r≤l].

4. A new type of conductive material according to claims 1 to 3, characterized in that in its crystalline network, trace elements already existing in the original Ybacuo Fe, Al, Ni, Co and Zn can appear as isomorphically replacing Cu in a percentage with respect to this element never exceeding 10% and preferably less than 2%.

5. A procedure for the preparation of a new type of conductive material of the formula Li _^ BaaTRCu _s Ov-- _* , according to claims 1 to 4 characterized by using a commercial Ybacuo of chemical composition Ba ₂ TRCu ₃ 0 ₇ _ _x , wherein the symbols are the same as defined in claims 2 to 3, or simply the product obtained by conventional reaction methods in solid state of stoichiometric amounts of oxides, hydroxides and / or oxisals of Ba, Y and Cu.

6. A process for the preparation of a new type of conductive material of formula Li _^ Ba _at RCU _at O- _x , according to claims 1 to 5, characterized in that the lithiation, consisting of the insertion of lithium into the Ybacuo, is verified by the reaction of said Ybacuo with an excess solution of an organolithium, R-Li, where R is an alkyl radical, preferably butyl, and where the concentration of the organolithium will preferably be between 1 and 2 mol per liter.

7. A procedure for the preparation of a new type of conductive material of formula

according to claims 1 to 6, in which the lithiation is verified by stirring a suspension of ground Ybacuo preferably at less than 100 μ in said organolithium solution at a temperature between the melting and boiling of the solution, preferably between and 30 ° C.

8. A process for the preparation of a new type of conductive material of the formula Li_.Ba2TRCu ₃ O.7-_ _* , according to claims 1 to 7, characterized in that the lithiation operations, washing and drying the product obtained as well as its Handling should be done under an inert atmosphere such as 99.9% pure nitrogen.