DE2515874A1 - CRYSTALLINE COMPOUNDS WITH PEROWSKITE STRUCTURE - Google Patents

Description

Patent attorneys Dipl.-Ing. RVi ^ ckmann,

Dipl.-Ing. H.Weickmann, Dipl.-Phys. Dr. K. Fincke Dipl.-Ing. R A.Weickmann, Dipl.-Chem. B. Huber

8 MUNICH 86, DEN

PO Box 860 820

MÖHLSTRASSE 22, CALL NUMBER 98 39 21/22

HtM / th

Case 0125 75 B D.6827

AGENCE NATIONALE DE VALORIZATION DE LA RECHERCHE (ANVAR),

13, rue Madeleine Michelis, 92200 Neuilly-sur-Seine,

France

Crystalline compounds with a perovskite structure.

The invention relates to crystalline compounds having a structure of the perovskite type, magnetic or conductive Possess properties.

More precisely, these new compounds have the deformed perovskite structure described in the article "High Pressure Synthesis and Crystal Structure of NaMn ₇ O ₁₂ " by Marezio, Dernier, Chenavas and Joubert in the "Journal of Solid State Chemistry" No. 6 (1973 ) Pages 16 to 20, is described - a structure which contains Na ⁺ , Mn ³⁺ and Mn cations as cations, corresponds to ^{the following ionic formula Na 1+} Mn ³⁺ (Mn ³⁺ Mn ₂ ⁺ ) O _12, dodecahedrally coordinated lattice sites (i.e. lattice sites with 12 adjacent oxygen atoms), square-coordinated lattice sites (i.e. lattice sites that contain 4 adjacent

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have exposed oxygen atoms, which are arranged in the form of a square around the atom occupying this lattice site) and lattice sites with octahedral coordination - and correspond to the general formula AC ₃ B ₄ O ..- ^ in which A is a cation with a large ionic radius, the one dodecahedral

can occupy coordinated lattice site, C a cation described in more detail below with a

Preference for square coordinated lattice sites and B a medium-sized cation explained in more detail below, which can easily occupy octahedrally coordinated lattice sites, ■ mean.

The crystalline compounds of the invention are by Fact marked that

on the one hand, the square coordinated lattice sites (the

2+ cations C) are occupied by copper cations (more precisely with Cu cations), which have unpaired electrons, and on the other hand the octahedrally coordinated lattice sites (of the cations B) are occupied by ions of transition elements such as Ni ³⁺ , Co ³⁺ , Mn ^{3 +} , Fe ³⁺ , Cr ³⁺ , Rh ³⁺ , Ru ³⁺ , In ³⁺ , Cr ⁴⁺ , Mn ⁴⁺ , Ru ⁴⁺ , Pt ⁴⁺ , Ir ⁴⁺ , Pd ⁴⁺ , Rh ⁴⁺ and / or U ⁵⁺ , which have unpaired electrons, are occupied.

When the unpaired electrons of the the octahedral lattice sites occupying transition metal ions are localized, they have a spin that corresponds to the spin of the electrons of the Copper interacts magnetically, being when the concentration of localized moments (localized unpaired Electrons) at the octahedral lattice sites is sufficient, the crystalline compounds according to the invention extremely Have useful magnetic properties analogous to those of garnet or spinel type ferrites. If on the other hand the unpaired electrons of the transition metal ions that make up the Occupy octahedral sites, are not localized, these electrons give the crystalline compounds according to the invention a electronic conductivity, so that these compounds in the

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Act possess metallic properties. As it is with the connections When it comes to oxides, due to their ability to withstand various attacks, especially for Fuel cells are used.

The dodecahedrally coordinated lattice sites (the lattice sites of the A cation) can be occupied by one of the following cations: Na ⁺ , Ca ⁺ , Cd ⁺ , Sr, Ln ⁺ (rare earth cations, Y ³⁺ ), Th ⁴⁺ , U ^{4 +} , Ce ⁴⁺ , Pr ⁴⁺ ^ cations of tetravalent

4+ 4+ ^ - ^ actinide elements, such as Am, Po, or can be unoccupied sexn (Gap connection or gap connection).

The invention therefore includes crystalline compounds having deformed perovskite structure, the lattice positions with dodecahedral, square and octahedral coordination, of the general formula AC ₃ B ₄ O ₁₂ / i ⁿ OCE
A is a cation with a large ionic radius that can occupy a dodecahedrally coordinated lattice site that is also unoccupied

can be (gap connection),
C is a cation that prefers square-coordinated lattice sites

busy, and
B a medium-sized cation that coordinated the octahedral

Grid places occupied,
mean, characterized in that

on the one hand, the square coordinated lattice sites (the

2+ cations C) are occupied by copper cations (more precisely with Cu cations), which have unpaired electrons, and on the other hand the octahedrally coordinated lattice sites (of the cations B) are at least partly occupied by ions of transition elements such as Ni ³⁺ , Co ³⁺ , Mn ³⁺ , Fe ³⁺ , Cr ³⁺ , Rh ³⁺ , Ru ³⁺ , In ³⁺ , Cr ⁴⁺ , Mn ⁴⁺ , Ru ⁴⁺ , Pt ⁴⁺ , Ir ⁴⁺ , Pd ⁴⁺ , Rh ⁴⁺ and / or U ⁵⁺ , which have unpaired electrons, are occupied.

The invention also relates to a process for the preparation of these crystalline compounds, which is characterized in that that the constituents of these compounds can be heated under pressure in a closed container, as is used for the hydro-

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thermal synthesis is used.

According to the invention and in particular according to the specified embodiments as well as the preferred embodiments are possible if, for example, crystalline compounds with a perovskite structure, wants to produce the magnetic or conductive properties as follows or in an analogous manner.

One of the processes described below is used to prepare one of the compounds given above with a deformed perovskite structure of the general formula ACoB ₄ O ₁ ^, in which A is a cation with a large ionic radius that can occupy a dodecahedrally coordinated lattice site (and 12 neighboring oxygen ions is surrounded),

2+ C is the copper cation, in particular the Cu cation, which is accessible to the Jahn-Teller effect and has a preference for square-coordinated lattice sites (and which is surrounded by 4 neighboring or nearby oxygen ions that are arranged in a square around this cation C. , while the other neighboring oxygen ions are significantly further away) and
B a cation of medium size, which can easily occupy lattice sites with octahedral coordination,

mean, where these cations B are at least partly, i.e. exclusively or partly, provided by ions of transition elements that have unpaired electrons, such as ions of the following formulas: Ni ³⁺ , Co ³⁺ , Mn ³⁺ , Fe ^{3 +} , Cr ³⁺ , Rh ³⁺ , Ru ³⁺ , In ³⁺ , Cr ⁴⁺ , Mn ⁴⁺ , Ru ⁴⁺ , Pt ⁴⁺ , Ir ⁴⁺ , Pd ⁴⁺ , Rh ⁴⁺ and / or U ^{5 +} .

The structure of the compounds of the general formula AC ₃ B ₄ O ₁₂ is similar to the perovskite structure, with all cations A, B and C occupying similar positions as the cations of perovskite. It should be remembered that the perovskite _{corresponds to the general formula ABO 3 (CaTiO 3} and BaTiO ₃ can be mentioned as examples at temperatures above 120 ° C.). The perovskite is part of the simple cubic system, with your

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the ions A, B and 0 occupy the following positions in the unit cell:

A VKi ~ Ki "O ^- )

it £ λ l *

B (0, 0, O) 0 (1/2 0 0

(0 1/2 0

(0 0 1/2

In the compounds according to the invention of the general formula AC ₃ B ₄ O _12, the ions B occupy the lattice sites of the perovskite with octahedral coordination, i.e. the lattice sites of the Ti, while the ions A and C of the compounds according to the invention occupy the lattice sites of the Ca or Ba ions occupy. While in the perovskite the Ca or Ba ions are surrounded by 12 equally spaced oxygen ions, in the compounds according to the invention only the ions A show a coordination of 12 (and are therefore located on a dodecahedrally coordinated lattice site). In contrast to this, the cations C have a very special coordination due to the distortion of the oxygen ion lattice, which is given by 4 closely spaced oxygen ions that form a square around cation C and 4 less closely spaced oxygen ions that are arranged in the form of a rectangle, which is perpendicular to the said square. Finally, the last 4 mentioned neighboring oxygen ions are further away. This arrangement results in a sequence between the different cations A and C, which are located at the lattice sites of calcium or barium. It also follows that the unit cell is doubled in the three spatial directions and, assuming that the volume of the unit cell of the perovskite can be represented by a χ a χ a, has a volume of 2a χ 2a χ 2a. Despite the distortion, the

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the latter elementary cell has the cubic symmetry, so that it is a cubic centered grid. There are 24 oxygen ions per unit cell, that is, eight times more than in the underlying perovskite structure, the contains only 3 oxygen ions per unit cell.

The centered cubic unit cell of the compounds according to the invention thus comprises 2 cations A, 6 cations C (copper), 8 cations B (ions of transition elements of the type specified above) and 24 oxygen ions.

This structure is analogous to the structure discussed in the article by Marezio, Dernier, Chenavas and Joubert, the one describes such structure and see them on page 19 for the case

1+ 3+ 3+ 4+ of the compound NaMn ₇ O ₁₂ or more precisely Na Mn ₃ ( ^Mn 2 ^Mn 2 ^ ° 12 '

explained.

However, this compound has neither ferromagnetic properties nor conductive properties and does not contain a copper cation.

In contrast, the compounds according to the invention have either ferromagnetic properties or conduction properties for the reasons specified below and are included in

2+ their structure is copper cations, especially Cu cations.

Compounds with a cubic perovskite structure that contain copper cations have already been described. Reference is made in particular to the publication by Deschanvres, Raveau and Tollemer in the "Bulletin de la Societe Chimique de France" (1967) page 4077. These are compounds of the formula Ca _{Q 5} Cu _{1 5} Ti ₂ Og and Cd _{Q 5} Cu _{1 5} Ti ₃ O ₆ .

These latter compounds do contain copper cations however, not the strongly magnetic or conductive properties of the compounds according to the invention due to the Absence of transition metal ions of the type: Ni, Co, Mn #

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Fe ³⁺ , Cr ³⁺ , Rh ³⁺ , Ru ³⁺ , - In ³⁺ , Cr ⁴⁺ , Mn ⁴⁺ , Ru ⁴⁺ , Pt ⁴⁺ , Ir ⁴⁺ , Pd, Rh and / or U to the octahedrally coordinated lattice sites (cations B).

Indeed, the extremely useful properties of the compounds of the invention are a consequence of their simultaneous Presence of copper cations at the square coordinated lattice sites and of the transition metal ions mentioned at the octahedrally coordinated lattice sites.

When the unpaired electrons of the the octahedral lattice sites occupying transition metal ions are localized, the spins of these localized unpaired electrons occur with the

2+

Spins of the unpaired electrons of the Cu cations in interaction, which results in magnetic properties which are analogous to those of ferrites of the garnet type and of the spinel type. In this case, the compounds according to the invention form a third class of "ferrites" (i.e. not containing iron Ferrites, which could also be called copper ferrite perovskites).

On the other hand, if the unpaired electrons of the octahedral Transition metal ions occupying lattice sites are not localized, these electrons enter the conduction band and result an electronic conductivity, so that the invention Compounds that are oxides are given metallic properties.

When the concentration of the unpaired electrons is high, the magnetic properties predominate even at room temperature. On the other hand, when this concentration is relatively low, these magnetic properties exist only at low temperatures. It should be noted that the ions of the transition elements with unpaired electrons, i.e. the following ions Ni ³⁺ , Co ³⁺ , Mn ³⁺ , Fe ³⁺ , Cr ³⁺ , Rh ³⁺ , Ru ³⁺ , In ³⁺ , Cr ⁴⁺ , Mn ⁴⁺ , Ru ⁴⁺ , Pt ⁴⁺ , Ir ⁴⁺ , Pd ⁴⁺ , Rh ⁴⁺ and / or U ⁵⁺ , in part (and with the loss of the useful properties described above) by the

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3+ 3+ ions of the following transition elements: Al, Ga /

Ge ⁴⁺ , Ti ⁴⁺ , Sn ⁴⁺ , Ta ⁵⁺ , Sb ⁵⁺ , Nb ⁵⁺ , As ⁵⁺ , V ⁵⁺ , Mo ⁶⁺ , W ⁶⁺ , Te ⁶⁺ and / or U. It should be noted that this partial replacement can also be made for connections with electronic conduction properties without departing from the scope of the invention.

The dodecahedrally coordinated lattice site (of the cation A) can be represented by one of the following cations: Na, Ca, Cd, Sr, Ln

(Cations of the rare earth elements such as Y ³⁺ ), Th ⁴⁺ , U ⁴⁺ , Ce,

4+ 4+

Pr, cations of tetravalent actinic elements such as Am,

4+
Po, be occupied or vacant.

The compounds according to the invention can, for example, and can be used without restricting the invention for the following purposes:

1. The compounds with magnetic properties, that is, the Compounds containing cations with unpaired localized electrons on the octahedrally coordinated lattice sites can be applied in the field of the already known ferrites (ferrites of the garnet type and of the spinel type) It should be noted that the ferrites according to the invention come closer to the ferrites of the garnet type than the spinel-type ferrites. The compounds according to the invention are particularly suitable for the conventional Replace ferrites in:

a) Devices for exploiting the Faraday effect (devices to rotate the plane of oscillation of light, facilities for circular polarization of light, isolators, magneto-optical devices, if the connections applied in layers thin enough to be transparent);

b) in resonance arrangements (devices for rotating the plane of oscillation of light, isolators and resonance circulators).

2. The electronically conductive connections, i.e. the connections those at the octahedral coordinated lattice sites

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Have cations with unpaired non-localized electrons, can be used in fuel cells. It is known that those commonly used in fuel cells Metal electrodes can be attacked by acids or other electrolytes in the fuel cell. In the inventive Compounds with conductive properties are oxides that are not attacked by the electrolytes. They can therefore be used with advantage in fuel cells, in particular around the electrodes (for example the platinum electrodes) with one of a compound according to the invention to cover existing metal oxide layer.

The following examples serve to further illustrate the invention and deal with the preparation of the invention Links.

The manufacturing processes can be divided into two categories, depending on whether the compounds according to the invention are attached to the octahedral koori
are or not.

4+ octahedrally coordinated lattice sites occupied by Mn cations

A) Creation of compounds which are based on the octahedral coordi-

4+
merten lattice sites have Mn cations.

Since the manganese in the valence state 4 is generally unstable at temperatures above 600 ° C (with a reduction

4+ 3+

from Mn to Mn), the reactions must take place in a closed Container can be carried out under pressure. The simplest method is that for the hydrothermal Synthesis applied container to use. The manganese oxide (MnO ^) or a higher quality manganese salt (for example from reaction mixture containing tetravalent manganese) is placed in a noble metal shell (Au, Ag, Pt) in order to ensure contact with to prevent the wall of the autoclave. The reaction takes place in a closed system. The pressure applied can go through Water vapor can be formed in the form of a supercritical fluid, a noble gas (argon) or, preferably, oxygen. It's from

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It is important to have a sufficiently high oxygen partial pressure in order to keep the manganese in the oxidation state 4 at temperatures which are high enough for the reaction to take place. When added to the reaction medium one with the connection does not react oxidizing agent (for example, HClO.,) Is added, it constitutes oxidant by it decomposes (HClO -.-> HCl + O ö- _0), a sufficiently high oxygen partial

4+
pressure safe to keep all Mn cations in a tetravalent state. If such an oxidizing agent is not added, some of the Mn ions are reduced to Mn ions until the oxygen released during this reduction is such

4+ 3+ has high partial pressure that the reaction Mn <-> Mn

becomes reversible.
example 1

2+ 2+ 4+ Creation of the connection Ca Cu ₃ Mn. O ₁₃ For example, an intimate mixture of the following composition Ca (OH) ₂ , 10 H ₃ O, 3 Cu (OH) ₂ and 4 MnO ₂ (preferably amorphous) is prepared. The reaction mixture is introduced into a closed tube made of gold and treated inside an autoclave for 48 hours at a pressure of 2 kbar and a temperature of 700.degree. The sample obtained under these conditions contains 80% CaCu ₃ Mn ₄ O ₁₂ in the form of a well-crystalline and strongly magnetic powder, a small amount of a

2+ 3+
Spinels of the formula Ca Mn ₂ O ₄ , which indicates that under these conditions a reduction in manganese has occurred to a certain extent, and a small amount of unconverted CuO.

Example 2

Creation of the compound NaCu ₃ ⁺ (Mn ₃ ⁺ V ⁵⁺ ) O ₁₂

It starts with 3 Cu (OH) ₂ , 3 MnO ₂ and NaVO ₃ , encloses the mixture in a tight platinum capsule and treats it for one hour at 40 kbar and 1000 ^° C. The pressure causes:

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a) that the Na cation has a dodecahedral coordinated lattice site occupied, although it tends to occupy a smaller lattice space;

b) that the reduction of the Mn ⁺ and V ⁺ cations is prevented, which leads to a very dense medium.

Example 3

Production of the compound SrCu ^ Mn ₄ O ₁₉

A mixture of the composition Sr (OH) ₂ , 10 H ₂ O, 3 Cu (OH) ₂ and 4 MnO _{2 is} used as the starting material - the intimately mixed mixture is introduced into a tight capsule and treated for one hour at 40 kbar and 1000 ° C.

Example 4

3+ 2+ 4+ 3+ Establishing the connection Ln Cu ₃ ( ^Mn 3 Mn) ° io

(Ln stands for cations of the rare earth elements and for Y ³⁺ ).

A mixture of the following components is used: ^ Ln ₂ O ₃ + 3 Cu (OH) ₂ + 3 MnO ₂ + - ^ Mn ₃ O ₃ .

The intimate mixture is placed in a tight capsule and heated to 1000 ^° C. for one hour at a pressure of 20 to 80 kbar. The pressure applied must be higher, the lower the ionic radius of the rare earth element that coordinates the dodecahedral Should occupy the grid place. The pressure also guarantees a good tightness of the capsule, which is necessary to maintain the correct ratio between the cations Mn ⁺ and Mn. The compounds in this series, which contain rare earth elements with a large ionic radius (La ⁺ , Pr ⁺ , Nd ⁺ , Ce ^+, etc.) can be prepared using the same starting materials by hydrothermal synthesis at 650 ° C. and 2 kbar.

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Example 5

Establishing the connection Ln ³⁺ (Cu ²⁺ Mn ₃ ⁺ M ³⁺ ) O ₁₂

a) Mn ³⁺ - Al ³⁺ , Ga ³⁺ , Fe ³⁺ , Cr ³⁺

The method of preparation described above is used. For rare earth elements with a large ionic radius, one can also use hydrothermal synthesis at 650 ° C and 2 kbar.

b) M ³⁺ = CO ³⁺ , Ni ³⁺

An oxidizing agent such as KClO ₃ or HClO _{3 is} added to the sample and Co ²⁺ (OH) ₂ or Ni ²⁺ (OH) _{2 are used} , which are oxidized at high temperature and at high pressure by the oxygen that is generated by the following Reactions released:

HClOo ? HCl + - ^ O ₉ or

KCiO ₃ > KCi + | o ₂

Example 6

Preparation of the compounds of the general formula Th ⁴⁺ Cu ₃ (Mn ₂ ⁺ M ³⁺ ) O ₁₂ , in which M ³⁺ = Mn ³⁺ , Cr ³⁺ , Al ³⁺ , Ga ³⁺ .

A mixture of the following composition is used: Th (OH) ₄ + 3 Cu (OH) ₂ + M ₃ O ₃ + 2 MnO ₂ , where M stands for the abovementioned cations (Mn, Cr, Al, Ga).

The intimate mixture is brought in a sealed tube made of gold and treated them for 48 hours at a pressure of 2 kbar and a temperature of 700 ⁰ C. The product obtained is readily crystallized and contains traces of ThO _2, CuO or M ₀ Oo that have not been fully implemented-

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B) Making the connections on the octahedral

4+ coordinated lattice sites do not have any Mn cations.

Example 7

3+ Preparation of the compound ThCu ₃ (Ti ₃ Fe ₂ ) ° - | 2 A mixture of the following composition Th (OH) is used as the starting material . + 3 Cu (OH) ₂ + Fe ₃ O ₃ + 2 TiO ₃ . The intimate mixture is ^{calcined in air at 1050 °} C. for several days, the material being ground several times during the calcining. This method only gives the cubic phase with a yield of 60% to 70%. By double decomposition of a mixture of nitrates (or other salts such as the citrate), followed by calcination at 600 ⁰ C or 700 ° C, the yield can be significantly increased.

Example 8

Preparation of the compound Sr ²⁺ Cu ₃ ⁺ (Ta ₃ ⁺ Fe ₃ ⁺ ) O ₁₂ A mixture of the composition Sr (OH) ~ + 10 H ₂ O + 3 Cu (OH) ₂ + Ta ₂ O ₅ + Fe _{2 is calcined} O ₃ for 3 days at 1050 ° C. Under these conditions, the desired product is obtained with a yield of about 70%.

Example 9

Production of the compound Nd ³⁺ Cu ₃ ⁺ (Ru ₃ ⁺ Fe ³⁺ ) O ₁₃

The starting material used is a mixture of the following composition: - ^ Nd ₃ O ₃ + 3 Cu (OH) ₂ + 3 Ru ³⁺ O ₂ + ■ j Fe ₃ O ₃ .

The mixture calcined for 24 hours at 100 ° C. gives the expected cubic phase, that of trace impurities (CuO) is accompanied.

The connection can also be held with other rare earth elements can be made from Nd.

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Claims (4)

Claims Crystalline compounds with a deformed perovskite structure, which has lattice sites with dodecahedral, square and octahedral coordination, of the general formula AC ₃ B ₄ O ₁₂ , in which A is a cation with a large ionic radius that can occupy a dodecahedrally coordinated lattice site that is also unoccupied can be (gap connection), C is a cation that prefers square-coordinated lattice sites busy, and B is a medium-sized cation that occupies the octahedrally coordinated lattice sites, mean, characterized in that on the one hand, the square coordinated lattice sites (the 2+ cations C) with copper cations (more precisely with Cu cations), which have unpaired electrons, are occupied, and on the other hand the octahedrally coordinated lattice sites (of the cations B) at least partially with ions of transition elements such as Ni ³⁺ , Co ³⁺ , Mn ³⁺ , Fe ³⁺ , Cr ³⁺ , Rh ³⁺ , Ru ³⁺ , In ³⁺ , Cr ⁴⁺ , Mn ⁴⁺ , Ru ⁴⁺ , Pt ⁴⁺ , Ir ⁴⁺ , Pd ⁴⁺ , Rh ⁴⁺ and / or U ⁵⁺ , which have unpaired electrons, are occupied. 2. Crystalline compounds according to claim 1, characterized characterized in that said transition metal ions having unpaired electrons are partly through 3+ 3+ the following transition metal ions are replaced: Al, Ga, Ge ⁴⁺ , Ti ⁴⁺ , Sn ⁴⁺ , Ta ⁵⁺ , Sb ⁵⁺ , Nb ⁵⁺ , As ⁵⁺ , V ⁵⁺ , Mo ⁶⁺ , W ⁶⁺ and / or U 3. Crystalline compounds according to claim 1 or 2, characterized in that the cation A is Na, Ca, Cd, Sr, Ln (cations of the rare earth elements, Y ³⁺ ), Th ⁴⁺ , U ⁴⁺ , Ce ⁴⁺ , Pr ⁴⁺ , cations of tetravalent 4+ 4+ actinide elements, such as Am or Po, are present. 509843/0706 4. Process for the preparation of the crystalline compounds according to one of the preceding claims, characterized characterized in that the constituents are heated under pressure in a closed container of the type as used for hydrothermal synthesis. 509843/0706