Manufacturing process for a spinel-alon ceramic with high nitrogen content, materials produced therewith, and doped materials

Abstract

A process for producing aluminum oxide nitride, comprising the step of reacting an Al-ON precursor material at a temperature of 1700°C or higher and a pressure of 4 GPa or higher, wherein the Al-ON precursor material is produced by (i) providing an aluminoxane and a nitrogen-containing reagent as starting material; (ii) reacting the starting materials from step (i) to form an inorganic polymer; (iii) thermally treating the inorganic polymer obtained in step (ii) to form the Al-ON precursor material.

Description

FIELD OF THE INVENTIONThe invention relates to the preparation of alumina nitride having spinel structure ("ALON"). By the method of the present invention, ALON having a reduced number of vacancies in the spinel structure as compared with the prior art can be obtained. In some cases, an ALON having a spinel structure can be obtained in a nearly ideal stoichiometry (stoichiometric Al 3 O 3 N).PRIOR ARTAluminum oxide nitride is a transparent ceramic material consisting of aluminum, oxygen and nitrogen atoms. Alumina nitride of spinel (ALON) structure has a cubic (spinel) crystal structure, is optically transparent in the visible and IR range, and can be fabricated into fully dense polycrystalline components with high optical transparency.In addition to its optical properties, ALON has high hardness and strength, good resistance to acids and caustic, and good temperature resistance. It is used above all as transparent ceramic for highly stressed window applications, in particular bulletproof panes, but it is also studied as a special abrasive, more recently also with regard to photocatalytic applications and as a guest material for ions of rare earths for the production of phosphors which can be used, for example, in white LEDs.The production of ALON is known, for example, from U.S. Pat. No. 4,520,116. In a multistage sintering and pressing process, ALON bodies having a density of up to 99% of the theoretical density were obtained. The method was also suitable for doping the ALON with foreign ions such as yttrium or boron.ALON has a defective spinel structure in which not all regular cation lattice sites of the spinel are occupied for reasons of electrical charge neutrality.It is at the same time a mixed crystal with variable nitrogen content. Its chemical composition is described, for example, by formula (1). Al (8+x) / 3 ≅ (1-x) / 3 O (4-x) N x(1)The symbol ≅represents a void in the crystal lattice, on the octahedral cation lattice sites of the spinel. The hypothetical reaction for forming ALON of spinel structure with ideal stoichiometry (i.e., no vacancies; x=1) is normally represented by Al 2 O 3+ AlN→Al 3 O 3 N (2).The hypothetical reaction for forming ALON with vacancies (0<x<1) can be represented as (4-x) / 3Al 2 O 3+ xAlN→Al (8+x) / 3 ≅ (1-x) / 3 O (4-x) N x(3).In the hypothetical reaction (3), x=1 in the case of ALON having a spinel structure in ideal stoichiometry. In case x=0.8, the stoichiometric description of the reaction is 1.067 Al 2 O 3+ 0,8 AlN→Al 2,933 ≅ 0,067 O 3,2 N 0,8.Alternatively, the reaction can be shown in simplified form, where v is the hypothetical molar fraction of AIN in the starting materials. In the hypothetical reaction (4), v in the case of ALON having a spinel structure in ideal stoichiometry is v=50 mol%. Conventionally produced ALON usually starts from a value of 27 mol %≤v≤40 mol %.The charge-balancing Al vacancies in the ALON crystal lattice lead to a lower number of chemical bonds per volume compared to the ideal state of full population, which in turn leads to a reduction in the hardness and other property characteristics such as, for example, strength, crystal-elastic constants or intrinsic fracture toughness. In addition, the optical refractive index is lower due to the Al vacancies and the lower nitrogen content of conventional ALON than would be expected for an ALON with spinel structure in an ideal composition Al 3 O 3 N.The spinel structure of ALON is generally described by cubic space group Fd-3m. Typical lattice constants a 0 of ALON are given in the prior art as 7.938 Å for oxygen-rich and 7.951 Å for nitrogen-rich compositions (Corbin, N. "Aluminum oxynitride spinel: A review", Journal of the European Ceramic Society, 1989, 5, pp. 143-154). According to common theory, lattice parameters in the vicinity of 8.0 Å for the ideal composition Al 3 O 3 N are predicted by extrapolation of lattice parameters in the spinel-SiAlON mixed crystal series (Si 3-x Al x O x N 4-x) for x=3 (Schwarz, M., et al., "Spinel-Sialon", Angew. Chem., 2002, 114, pp. 804 to 808). From the data from the ALON system, lattice constants of 7.973 Å can be obtained (McCauley, J. "Phase relations and reaction sintering of transparent cubic aluminum oxynitride spinel (ALON)", J. Amer. Cerame. Soc., 1979, 62, pp. 476-479) and 7.976 Å (Willems, H. X. "Preparation and Properties of translucent gamma-aluminum oxynitride", 1992, Ph.D. thesis, Technical University Indhoven) for Al 3 O 3 N.Charge-balancing Al vacancies in conventionally produced ALON, which are distributed more or less randomly over the crystal, lead to a higher variance of the local environment in the crystal lattice. Luminescent foreign ions, which are introduced into such an ALON as guest material in a targeted manner, are thus exposed to different ligand fields. Viewed over the entire solid, this leads to a greater line broadening of its emission line, which is frequently undesirable for many applications. Conventional ALON is therefore less suitable as a host material for optical energy conversion, for example for the provision of white light sources based on LEDs, than a host material with a low variance of the local environment, as would be expected for a spinel crystal lattice without vacancies.U.S. Pat. No. 7,163,656 B1 discloses compositions having the empirical formula Al (64+x) / 3 O 32 xN x, where x is in the range from 2 to 7. Such compositions do not have ideal stoichiometry. Further preparation processes are disclosed in O. Zgalate-Lozynskyy et al.: Journal of materials engineering and performance, 31, 2022, 3, pages 2575 to 2582, A. Gromov et al. in Nitride ceramics. Weinheim: Wiley, 2015, pp. 125 to 163 and A. Gromov et al. in Journal of the European ceramic society, 25, 2005, pp. 1575 to 1579.There is therefore a need to provide ALON with as low a number of charge-balancing Al vacancies as possible in the crystal lattice.BRIEF DESCRIPTION OF THE INVENTIONThe above mentioned disadvantages are overcome according to the invention as defined in the appended claims.In one embodiment, the invention provides a method of manufacturing aluminum oxide nitride comprising the step of reacting an Al-O-N precursor material at a temperature of at least 1700°C or higher and a pressure of 4 GPa or higher. Meanwhile, the Al-O-N precursor material is prepared by (i) providing an aluminoxane and a nitrogen-containing reagent as a starting material, (ii) reacting the starting materials to form an inorganic polymer, and (iii) thermally treating the obtained inorganic polymer to form the Al-O-N precursor material. According to the invention, ALON can be obtained by this process with an increased nitrogen content compared with the prior art. In some embodiments, spinel structure ALON may be obtained in ideal stoichiometry without vacancies.In one embodiment, the process of the invention uses an aluminoxane selected from the group consisting of methyloctylaluminoxane (methylaluminoxane modified with octyl groups), methylaluminoxane and triisobutylaluminoxane. In a preferred embodiment, methyloctylaluminoxane is used. It has been found that particularly good results can be achieved when using methyloctylaluminoxane.In one embodiment, ammonia or hydrazine is used as the nitrogen-containing reagent in the process according to the invention. Depending on the process conditions, it may be advantageous to use gaseous ammonia or liquid hydrazine.In particular, according to one embodiment, step (ii) of the method according to the invention can be carried out in a liquid medium, for example in an anhydrous organic solvent. Alternatively, according to a further embodiment, step (ii) of the process according to the invention can be carried out in the solid phase with finely ground pulverulent aluminoxane or aluminoxane as a thin layer on a support, on the one hand, and gaseous nitrogen-containing reagent (ammonia at room temperature or hydrazine at elevated temperature), on the other hand.In a further embodiment of the present invention, in process step (iii), the thermal treatment of the inorganic polymer obtained in the preceding step can be carried out under vacuum or protective gas. In one embodiment, process step (iii) can be carried out under ammonia. The thermal treatment converts the polymers formed into suitable Al-O-N precursor materials by pyrolysis, expulsion of volatile solvent radicals and elimination of -OH radicals formed. By using ammonia as the ambient gas, an increased nitrogen content in the end product can additionally be achieved.If a mixture of pulverulent aluminum oxide and pulverulent aluminum nitride is used as Al-O-N precursor material, then in one embodiment γ-Al 2 O 3 and / or α-Al 2 O 3 can be used as pulverulent aluminum oxide and / or w-AlN can be used as the pulverulent aluminum nitride. γ-Al 2 O 3( alumina) or α-Al 2 O 3( corundum) and w-AlN (AIN having a wurtzite structure) are each readily available and are well-suited for the method according to the invention. Typically, the starting powdered materials (alumina and aluminum nitride) have a particle size in the range of 1 μm to 10 μm.In a further embodiment according to the invention, the starting materials can be introduced in such a ratio for the preparation of the Al-O-N precursor materials that the stoichiometry of Al 3 O 3 N with spinel structure corresponds in ideal stoichiometry. In a further embodiment according to the invention, a proportionally stoichiometric excess of nitrogen can be used in the starting materials, so that there is an atomic ratio of aluminum to oxygen of greater than or equal to 1:1 in the starting materials and an atomic ratio of aluminum to nitrogen is less than 3:1. This selection can be made according to the desired properties of the product obtained, and according to the invention, aluminium oxynitrides having a spinel structure with ideal stoichiometry or, if appropriate, with an excess of nitrogen are possible. In both embodiments, an oxygen content of the AIN powder used, which is dependent on production or storage, may be included in the batch calculation.According to further embodiments, the step of reacting the Al-O-N precursor material can use a temperature in the range from 1700° C. to 2500° C. According to further embodiments, the step of reacting the Al-O-N precursor material can use a pressure in the range from 4 GPa to 15 GPa. In principle, no upper limit of temperature or pressure needs to be set in the embodiment of the present invention, provided that the practical implementation of the method according to the invention remains practical with the desired extreme parameters. A temperature of not more than 2800° C. is usually expedient for this purpose. Thus, the reaction of the precursor materials can be carried out at temperatures higher than 1700° C., or higher than 1750° C., or 1800° C. or higher. For example, the reaction can take place in a range between 1700° C. and 2500° C., or in a range between 1800° C. and 2500° C., preferably in a range from 1900 ° C. and 2500 ° C., even more preferably in a range from 1950° C. to 2500 ° C.Likewise, the reaction of the precursor materials can be carried out at a pressure higher than 4 GPa, or higher than 5 GPa, or higher than 6 GPa, or higher than 7 GPa, or 8 GPa or higher. For example, the reaction can be carried out in a range between 4 GPa and 12 GPa, or in a range between 5 GPa and 10 GPa, or between 5 GPa and 8 GPa.It has been found that it is particularly preferred in the process according to the invention to match the temperature used and the pressure used to one another. Thus, it has proven to be particularly advantageous, when using higher pressures, such as 8 GPa or higher, for example, to also use temperatures which are at the upper limit of the range according to the invention.Part of the present invention is also an aluminum oxide nitride produced by a process according to the invention. The aluminum oxide nitride according to the invention preferably has an increased nitrogen content compared to the prior art and a reduced number of charge-balancing vacancies in the spinel structure.In a further embodiment, the aluminum oxide nitride according to the invention has a spinel structure with ideal stoichiometry without charge-balancing vacancies.In another embodiment, the aluminum oxide nitride of the present invention has a spinel structure having a lattice constant a 0 in the range of 7.960 Å or higher.The present invention also relates to the use of the aluminium oxide nitrides according to the invention. The aluminum oxide nitrides according to the invention can be used in lenses and windows according to the invention. Aluminum oxide nitrides doped with magnetically or optically active ions can be used according to the invention in luminescent materials or (quantum) magnetic materials.In further embodiments, the aluminum oxide nitrides according to the invention can be used as continuous bonding matrix in hard ceramic-ceramic composite materials, for example for use as cutting material for machining material, in particular of ferrous metals, and as components which are subjected to abrasive or load-bearing loads. In this application, further additives can also be used in the composite, such as TiN, TiC, TiCN, TiC / TiN core-shell nanoparticles, ZrN, ZrC, ZrCN, and tantalum and niobium nitrides.In further embodiments, the aluminum oxide nitrides according to the invention can be used in ceramic-metal composite materials and in ceramic-ceramic-metal composite materials.DETAILED DESCRIPTION OF THE INVENTIONThe invention will now be described in detail with reference to exemplary embodiments.By the methods of the present invention, alumina nitride compounds having improved properties can be produced. The methods make it possible to provide aluminum oxide nitride compounds whose elemental compositions approach a stoichiometric "Al 3 O 3 N" compound than compounds known from the prior art.The method according to the invention is based on two findings which are independent of one another. On the one hand, according to the invention, the final step for converting the precursors into the end product is to take place at high pressure and high temperature during a relatively short period of time. On the other hand, the precursors used are either Al-O-N compounds prepared from aluminoxane and nitrogen-containing compounds, or a mixture of pulverulent aluminum oxide and pulverulent aluminum nitride. These precursor routes make it possible for as few foreign elements as possible, such as carbon, sulfur, phosphorus, silicon or others, which are undesirable in the end product, to be contained in the final production step.To achieve the result of the present invention, for the preparation of the Al-O-N compounds in a first step, the starting materials, namely an aluminoxane and a nitrogen-containing reagent, are provided. These starting materials contain all elements which are to be present in the final product, namely aluminium, oxygen and nitrogen. Since it is an object of the present invention to provide an aluminum oxide nitride whose elemental composition comes as close as possible to the ideal state "Al 3 O 3 N", it is advantageous to select the starting materials and their relative amounts in such a way that these elemental ratios are mapped as accurately as possible.Aluminoxanes are alumino-organic polymers of the general formula [RAlO] m[ R 2 AlO 0.5]n[ R 2 AlOH] o, which can be obtained by the partial hydrolysis of trialkylaluminum compounds. Examples of aluminoxanes are triisobutylaluminum (formed by the hydrolysis of triisobutylaluminum) and methylaluminoxane (formed by the hydrolysis of trimethylaluminum) and methyloctylaluminoxane (methylaluminoxane modified with octyl groups). According to the invention, preference is given to using methyloctylaluminoxane.The nitrogen-containing reagent used is preferably N-H-containing bases, such as, for example, ammonia or hydrazine. The following ideal reaction equations represent the reaction of the starting materials in simplified form: 3 [Al(CH 3)- O] n+ n NH 3 → 3 [Al 3 O 3 N] n / 3+ 3 n CH 4; [ Al(CH 3)- O] n+ n NH 3 → [Al(NH2)O]n+n CH4; [Al(CH 3)- O] n+ n N 2 H 4 → [Al(NH-NH 2) O] n+ n CH 4.It should be noted here that the aluminoxanes are very reactive and the reactions are generally strongly exothermic and have to be carried out with cooling, either in anhydrous organic solvents or, in the case of gaseous nitrogen-containing reagents (ammonia at room temperature or hydrazine at elevated temperature), in suitable apparatuses with solid aluminoxane--whether in powder form or as a thin-layer coating on a support material.In addition to the X-ray amorphous Al-O-N-H polymers of interest for further processing, these reactions produce volatile methane or isobutane, so that carbon-containing by-products can easily be removed from the reaction mixture. The polymers obtained are pyrolytically decomposed by thermal treatment in a further process step and remaining methane, ammonia and hydrazine residues are driven off. The thermal treatment may be carried out under vacuum or inert gas, or alternatively in an ammonia atmosphere. This pyrolysis step produces an Al-O-N precursor material which is largely free of impurities.It is particularly advantageous in the case of the use of an ammonia atmosphere that a subsequent (re)increases in the nitrogen content easily takes place on account of the high surface area of the polymer and the organic radicals uniformly distributed therein. In this way, undesired oxygen inputs, which are produced, for example, by residual water contents in the solvent or in the nitrogen-containing reagent during the synthesis of the hydrolysis-sensitive Al-O-N-H polymer or during its handling or storage, can be compensated or overcompensated.Alternatively, as described above, a powdered mixture of aluminum oxide and aluminum nitride may be used as the Al-O-N precursor material. The ready availability of these substances, even with a very high degree of purity, is advantageous. As aluminum oxide, for example, y-Al 2 O 3( alumina) can be used-other aluminum oxide species such as, for example, α-Al 2 O 3 are also conceivable. As aluminum nitride, w-AlN can be used, but other species of aluminum nitride are conceivable. Here too, it is advantageous if the starting materials have the highest possible degree of purity in order to achieve a pure product free from lattice defects.Finally, these precursor materials are converted into the ALON according to the invention by reaction under high pressure and high temperature for relatively short reaction times. It is advantageous here that during this final conversion step, practically no impurities besides aluminum, oxygen and nitrogen are present in the precursor materials.According to the method of the present invention, the ideal stoichiometric element ratios can be obtained according to the general formula Al 3 O 3 N. Depending on the starting materials and process parameters, it may be appropriate to use a slight excess of nitrogen, for example by the thermal treatment in step (iii) taking place under an atmosphere of ammonia. According to the invention, "superstoichiometric" ALON can also be prepared which has more than 50 mol % of AlN content in relation to equation (4).According to the invention, the conversion of the precursor materials to ALON takes place when the sufficient conditions of pressure and temperature are reached. A limitation of the reaction time is not provided according to the invention. Thus, the exposure of the precursor materials to the reaction conditions can take place for a duration of up to 60 minutes or up to 45 minutes or up to 30 minutes. Alternatively, the conditions in a reactor cell can also be returned to ambient conditions immediately after the pressure and temperature conditions according to the invention have been reached.The ALON materials produced according to the invention are distinguished by a high purity and high lattice constants, close to the ALON spinel structure with ideal stoichiometry.The ALON materials obtained can be characterized by X-ray diffraction analysis. By Rietveld refinement, the phase composition of the product and the lattice constant of the cubic ALON can be determined. The ALON materials prepared according to the invention can consist to an extent of almost 100% of spinel ALON, or of a mixture of spinel ALON, aluminum oxide and aluminum nitride. On account of the reaction conditions, the aluminum oxide obtained is normally present as α-Al 2 O 3( corundum).The lattice constant a 0 of the obtained spinel ALON may be 7.960 Å or higher. More specifically, the lattice constant a 0 of the obtained spinel ALON may be in the range of 7.960 Å to 8.010 Å, such as 7.970 Å or higher, or 7.980 Å or higher, or 7.985 Å or higher, or 7.990 Å or higher, or even 7.995 Å or higher. Since for ALON with spinel structure, lattice parameters in the vicinity of 8.0 Å are predicted in ideal stoichiometry, lattice constants above 8.0 Å are also conceivable for an ALON which has a higher nitrogen content than Al 3 O 3 N.As described above, an increased nitrogen content in the end product can be achieved by using ammonia as the ambient gas in the production of Al-O-N precursor materials. It is likewise conceivable that an increased nitrogen content in the end product can be achieved by using an excess of aluminum nitride.The ALON compounds of the present invention can be used in applications requiring high degree of hardness and good transparency in the visible and IR ranges. This includes, for example, optical lenses or ballistic-proof transparent panes. On account of its cubic spinel structure, high-strength ALON according to the invention can also be used in high-pressure sintered composite materials.In its pure form, ALON according to the invention can be used in transparent protective windows which can be subjected to high load, for example for light-sensitive sensors under high-pressure or vacuum conditions, or in aerospace.Rare earth-doped ALON materials, for example doped with yttrium, lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, erbium, thulium, ytterbium and / or lutetium, can additionally be used in luminescence applications such as phosphor-containing labels or the like. The production of doped ALON materials on the basis of the process according to the invention is also part of the present invention.Also part of the present invention are any combinations of features and / or boundaries described herein, insofar as they are not mutually exclusive. The description of the invention relates to certain embodiments of the invention with the aim of illustrating the same. Those skilled in the art will recognize that further modifications and equivalents to the embodiments described herein are possible. Such modifications and equivalents also form part of the overall scope of the invention described.The invention is explained in more detail below with reference to a series of examples. All examples and figures support the scope of the claims. However, the invention is not limited to the specific embodiments shown in the examples and figures.EXAMPLESExample 1 - Preparation of ALON from alumina and aluminum nitrideTwo mixtures were prepared from an alumina powder (γ-Al 2 O 3, baked for 4 hours at 700° C. in a nitrogen stream) and an aluminum nitride powder (w-AlN) in a molar ratio Al 2 O 3: AlN of 1:1 and 1:1.5 by wet milling in methanol for 4 hours by means of a planetary ball mill. The mixing ratio was checked with X-ray diffraction analysis (Cu-Kα radiation) on the basis of the intensity ratios of the reflections of the respective phases.In each case, 84 mg of the powders were pre-compressed in a bore by an octahedral high-pressure cell made of porous ceramic with an edge length of 18 mm to a diameter of 5.4 mm and a height of 2.8 mm. The cell with the sample was compressed to 8 GPa at room temperature and then heated by means of a cylindrical resistance heater made of graphite for 60 seconds at a temperature of 2100° C. After decompressing, the cylindrical samples were removed from the high pressure cell, polished flat with diamond tools and polished at the end face, and then analyzed by X-ray diffraction and other methods.The Rietveld refinements of X-ray diffraction (Co-Kα radiation) recordings gave a phase fraction of 50% spinel ION for the 1:1 mixture and 63% spinel ALON for the 1:1.5 mixture. Lattice constants a 0 of 7.980±0.001 Å and 7.983±0.001 Å were determined, respectively. Aluminum nitride and corundum (α-Al 2 O 3) were identified as further phases.Example 2 - Preparation of ALON from alumina and aluminum nitrideA high-pressure cell was filled with the powder mixtures as described in Example 1. The powders are compressed to a pressure of 8 GPa and then heated at a temperature of 2100°C for 30 minutes.Radiographic examination showed a phase fraction of 89% spinel AION (lattice constant a 0= 7,979 ± 0.001 Å) for the 1:1 mixture. Only corundum (α-Al 2 O 3) was found as secondary phase. The 1:1.5 mixture contained 76% spinel AION (lattice constant a 0= 7,986 ± 0.001 Å), and aluminum nitride and corundum as secondary phases.Example 3 - Preparation of ALON from alumina and aluminum nitrideA high-pressure cell was filled with a 1:1.5 powder mixture as described in Example 1. The powder was compressed to a pressure of 8 GPa. The cell was heated to a temperature of 2500° C. and the heating current was switched off when the maximum temperature was reached.Radiographically, no other phase was detected besides spinel AION. It was evident from the split of the reflections at higher diffraction angles, for example (440) at 2Θ=78.6° or (731) at 2Θ=118.8°, that these were two spinel ALON species. Lattice constants a 0 for the two spinel ALON species of 7.999±0.001 Å and 7.978±0.001 Å were determined.Example 4 - Preparation of ALON from alumina and aluminum nitrideA high-pressure cell is filled with the powder mixtures as described in Example 1. The powders were compressed to a pressure of 5 GPa and then heated at a temperature of 2100°C for 60 seconds.Radiographic examination showed a phase ratio of 76% spinel ALON (lattice constant a 0= 7,973 ± 0.001 Å) for the 1:1 mixture and 70% spinel ALON (lattice constant a 0= 7,976 ± 0.001 Å) for the 1:1.5 mixture. Aluminum nitride and corundum were identified as secondary phases.Example 5 - Preparation of ALON from alumina and aluminum nitrideA high-pressure cell with tubular electrical resistance heater made of rhenium foil was filled with the powder mixtures as described otherwise in Example 1. The powder compact was compressed to a pressure of 7 GPa and heated to 2200° C. The sample was taken after decompressing. The reflections recorded by X-ray diffraction (Co-Kα radiation) could be assigned to a spinel phase having a lattice constant a 0 of 7.987±0.001 Å. No further reflections were measurable, which indicate a further phase.Example 6 - Preparation of ALON from aluminoxane and hydrazineAbout 130 ml of anhydrous toluene were placed under protective gas in a 250 ml single-necked round-bottomed flask equipped with a tap, and, with vigorous stirring (10,000-16,000 U / min), first 0.75 g (23.4 mmol) of anhydrous hydrazine and then 7.236 g (18.8 mmol) of a methyl octyl aluminoxane solution containing 7% by weight of Al in toluene (MMAO, Sigma-Aldrich) were added dropwise using a dispersing apparatus (SilentCrer M, Heidolph).The solvent in the resulting suspension was removed by vacuum distillation first at room temperature and then with heating to about 100° C. The solid remaining was passed through a 32 μm analytical screen under inert gas for deagglomeration. After sieving, 1.36 g of material ("A") was recovered. This was 107.6% by weight based on the idealised reaction: [Al(CH 3)- O] 0,95n[ Al(C 8 H 17)- O] 0,05n+ n N 2 H 4 → [Al(N 2 H 3) O] 0,95n[ Al(C8H17)-O]0,05n+n CH4In a next step, 92 mg of "A" were subjected to the following temperature profile on a quartz glass boat in an electrically heatable vacuum receiver under dynamic vacuum:RT-750°C in 3 h,750° C. for 2 h,Natural cooling by stopping the electrical heating power.57 mg of a light gray solid ("B") were recovered (about, 60% by weight, based on the amount "A") used.Separately, 729 mg of "A" were introduced under protective gas into a rotational tube device made of quartz glass through which flow can pass and, with continuous rotation of the inner tube, a gas stream of anhydrous ammonia was fed at a flow rate of 35 cm / min and a temperature profile as follows:RT-600°C in 2 h,600-750 °C in 1 h,750° C. to 1090° C. in 1:20 h,Natural cooling by stopping the electrical heating power.390 mg of a pure white powder ("C") could be recovered from the spinner.Elemental analysis of sample "B" gave about 31% O and about 10% N. Elemental analysis of sample "C" gave about 31% O and about 12% N. Thus, both samples are close to the stoichiometric composition of an ideal composition spinel ALON (33.6% O, 9.8% N).Example 7 - Preparation of ALON from aluminoxane and hydrazineAs described in Example 6, 1.995 g of anhydrous hydrazine and then 22.08 g of a 7% by weight methyl octyl aluminoxane solution (MMAO, Sigma Aldrich) are added under protective gas to 130 ml of toluene first and dispersed therein. The solution is filtered off through a frit and the filter cake is vacuum-dried. 9.86 g of material were removed and transferred to a quartz glass tube. In a heatable apparatus, the material is discharged with constant rotation in an ammonia stream (20 l / h) having the following heating profile:RT-600°C in 2 h,600-750 °C in 1 h,750° C. to 1090° C. in 1:20 h,This is naturally cooled by stopping the electrical heating power.Elemental analysis by hot gas extraction yields the following contents: oxygen 27.0%, nitrogen 14.3% and hydrogen 0.05%.A portion of the sample was loaded into a pressure cell analogously to Example 5. After compressing to 7 GPa and heating under pressure to 2200°C, the sample was taken after decompressing.Example 8 - Preparation of Eu-doped ALON from aluminoxane and hydrazineAccording to an Eu doping of 0.84 at % based on aluminum, 900 mg of sample "C" prepared in Example 6 and 27.5 mg of pulverulent europium(III) nitride (EuN) were weighed out and homogenized in a spherical ceramic grinding vessel having an inner diameter of 30 mm and comprising 12 grinding balls having a diameter of 4 mm and comprising Al 2 O 3- ceramic and 1.8 ml of anhydrous n-hexane as dispersant for 8 h in a vibrating ball mill at a movement amplitude of about 10 mm and a frequency of 50 Hz. The dispersant was then removed in vacuo.A high-pressure cell was filled with 80 mg of the powder mixture thus produced as described in Example 1.The cell with the sample was heated to 300° C. at room temperature after pre-compression and compressed to 8 GPa at this temperature and then heated at 2150±50° C. at this pressure for 35 minutes.The analysis of the X-ray powder diffractogram recorded from the sample revealed the following phase composition: 84% by mass of spinel AION having a lattice constant a 0 of 7.986±0.001 Å, 16% by mass of w-AlN.The sample thus prepared was subjected to photoluminescence measurement at room temperature. Excitation source: He-Cd laser with an excitation wavelength λ ex= 325 nm, 28.5 μW beam power, 1000 μs exposure time.In the emission spectrum of the sample, an intensive emission band with wavelengths in the visible range was measured with a slightly flattened intensity maximum between 454 and 466 nm, and two significantly weaker maxima at 616 nm and 769 nm. The high intensity band was significantly red-shifted compared with that of an oxygen-rich spinel ALON known from the prior art, with a comparable doping of 1 atomic % Eu and a lattice constant a 0 of 7.9375 Å and a maximum at 392 nm.

Claims

A method for producing alumina nitride, comprising the step of reacting an Al-O-N precursor material at a temperature of 1700°C or higher and a pressure of 4 GPa or higher, wherein the Al-O-N precursor material is produced by (i) providing an aluminoxane and a nitrogen-containing reagent as a starting material; (ii) reacting the starting materials of step (i) to form an inorganic polymer; (iii) thermally treating the inorganic polymer obtained in step (ii) to form the Al-O-N precursor material.The process according to claim 1, wherein the aluminoxane is selected from the group consisting of methyloctylaluminoxane, methylaluminoxane and triisobutylaluminumoxane.The method according to any one of claims 1 or 2, wherein the nitrogen-containing reagent is selected from ammonia and hydrazine.The process according to any one of claims 1 to 3, wherein step (ii) is carried out in an anhydrous organic solvent.The process according to any one of claims 1 to 3, wherein the aluminoxane is in powder or thin layer form and the nitrogen-containing reagent is gaseous and wherein step (ii) is carried out without solvent.The process according to any one of claims 1 to 5, wherein step (iii) is carried out under vacuum or under inert gas or ammonia.Method according to any of the preceding claims, wherein the starting materials for the production of the Al-O-N precursor material are introduced in a ratio corresponding to the stoichiometry of Al 3 O 3 N with an ideal spinel structure.Method according to any one of claims 1 to 6, wherein starting materials are introduced in a ratio such that an atomic ratio of aluminium to oxygen is greater than or equal to 1:1 and an atomic ratio of aluminium to nitrogen is less than 3:1 for the production of the Al-O-N precursor material.Method according to any of the preceding claims, wherein in the step of reacting the Al-O-N precursor material, a temperature of 2000°C to 2700°C and / or a pressure of 4 Gpa to 15 GPa is present.Method according to any one of the preceding claims, wherein prior to the step of reacting the Al-O-N precursor material, the Al-O-N precursor material is provided with a doping element.An alumina nitride prepared by a process of any one of the preceding claims.The alumina nitride of claim 11, wherein the alumina nitride has a spinel structure with ideal stoichiometry.The alumina nitride according to any one of claims 11 to 12, wherein the spinel structure has a lattice constant a 0 of 7.960 Å or higher.Use of an aluminium oxide nitride according to any one of claims 11 to 13 or an aluminium oxide nitride produced according to any one of claims 1 to 10 in optical lenses, windows, luminescent materials, magnetic or quantum magnetic materials, in ceramic-ceramic composites, in ceramic-metal composites or in ceramic-ceramic-metal composites.