Structure of Aluminum Nitride

Aluminum nitride crystallizes in the hexagonal wurtzite-type structure with a space group Pb mc (186) and the lattice parameters a = 311pm and c = 498 pm. 

It forms two interpenetrating hexagonal close-packed (h.c.p.) arrangements of aluminum and nitrogen atoms in tetrahedral coordination. Viewed along the [00.1] direction, the layers are stacked ABAB... 

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Aluminum nitride (AIN) differs from other A B compounds in its hexagonal wurtzite structure. The lattice parameters of this compound are a = 3.111 k, c = 4.978 A, and c/a = 1.600 [1]. Thus, the structure of aluminum nitride differs from the perfect wurtzite structure, which consists of regular tetrahedra and is characterized by the axial ratios c/a = 1.633. Moreover, aluminum nitride has distinctive physical and physicochemical properties. 

The structure of aluminum nitride is normally hexagonal close-packed (hep) of the wurtzite (2H) type (hP4) and is shown in Fig. 12.4. The difference between this structure and the zincblende structure of cubic boron nitride shown in Fig. 12.3 should be noted (the so-called chair form vs the boat form). 

Figure 12.4 Schematic representation of the crystal structure of aluminum nitride.

The measures of solid state reactivity to be described include experiments on solid-gas, solid-liquid, and solid-solid chemical reaction, solid-solid structural transitions, and hot pressing-sintering in the solid state. These conditions are achieved in catalytic activity measurements of rutile and zinc oxide, in studies of the dissolution of silicon nitride and rutile, the reaction of lead oxide and zirconia to form lead zirconate, the monoclinic to tetragonal transformation in zirconia, the theta-to-alpha transformation in alumina, and the hot pressing of aluminum nitride and aluminum oxide. 

Fibers of aluminum nitride have been produced by the melt-spinning of ethyl-alazanes derived from the reactions of triethylaluminum and ammonia.72 The spinnable products have compositions such as (I l AIN11 )c(Et2A INH2 )v(Et3 A1 ),] which probably consist of linked alazane rings and chain structures. Pyrolysis in ammonia gives aluminum nitride fibers. 

TABLE 1. Reduced Values of the Squares of the Structure Amplitudes of Aluminum Nitride... 

Fig. 6. Dependences of the reduced values of the square of the structure amplitude F of aluminum nitride at 0 K on H = 2(slni>)A for various values of Z 1) 0 2) 3 3) 2 4) 1 5) 4, a) Experimental values b) theoretical values.

The atomic and crystalline structure of the three covalent nitrides, aluminum, boron, and silicon nitrides, is less complex than that of the interstitial nitrides. Their bonding is essentially covalent. 

CVD plays an increasingly important part in the design and processing of advanced electronic conductors and insulators as well as related structures, such as diffusion barriers and high thermal-conductivity substrates (heat-sinks). In these areas, materials such as titanium nitride, silicon nitride, silicon oxide, diamond, and aluminum nitride are of particular importance. These compounds are all produced by CVD. 1 1 PI... 

F.S. Ohuchi and M. Kohyama, Electronic Structure and Chemical Reactions at Metal/ Alumina and Metal/Aluminum Nitride Interfaces, Journal of Amercian Ceramic Society, Vol.74(No.6), 1991, p.1163. 

Numerous ceramics are deposited via chemical vapor deposition. Oxide, carbide, nitride, and boride films can all be produced from gas phase precursors. This section gives details on the production-scale reactions for materials that are widely produced. In addition, a survey of the latest research including novel precursors and chemical reactions is provided. The discussion begins with the mature technologies of silicon dioxide, aluminum oxide, and silicon nitride CVD. Then the focus turns to the deposition of thin films having characteristics that are attractive for future applications in microelectronics, micromachinery, and hard coatings for tools and parts. These materials include aluminum nitride, boron nitride, titanium nitride, titanium dioxide, silicon carbide, and mixed-metal oxides such as those of the perovskite structure and those used as high To superconductors. 

Whenever silicon nitride is synthesized in the presence of aluminum-containing compounds (frequently used as a flux material in process of growing whiskers), there is a high probability of the formation of /3 -SiA10Ns. Up to two-thirds of the silicon in /3-Si3N4 can be substituted by Al without a change of structure. The /3 -SiAl()N has mechanical and physical properties similar to y3-Si3N4. It is, however, thermodynamically more stable than silicon nitride. 

As shown Fig. 1, high-emissivity aluminum nitride materials use aluminum nitride as the matrix for transmittance and metallic tungsten particles as emissivity particles and have a structure in which the dispersion of the tungsten particles is changed in stages. 

By using a technique to form aluminum nitride and metallic tungsten into a graded structure, we were able to broaden the knowledge of high-radiant flux aluminum nitride materials. 

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