Ab initio study of structure in boron nitride, aluminum nitride and mixed aluminum boron nitride amorphous alloys

Car-Parrinello molecular dynamics is applied to the liquid quench simulatio n of the amorphous networks of BN, AlN and AlBN2. Structural and elastic pr operties were determined. It is found that AlN has a stronger tendency to c hemical order than BN, driven by the greater energy penalty for "wrong bond s." AlN, however, has a stronger tendency to form an amorphous structure as judged by the energy difference between the crystalline and amorphous stat es. There is some experimental evidence for an amorphous form of AlN. BN wa s simulated at two densities, 2.0 and 3.0 g/cm(3). Even at the higher densi ty, the fraction of tetrahedral coordination remained low, in contrast to A lN, enabling us to predict that the tetrahedral amorphous form of BN does n ot form under liquid quench conditions. The amorphous network with the form ula AlBN2 has an intermediate tendency to form a tetrahedral structure and has a relatively high elastic modulus. This material is predicted to be of value for application as a wear resistant coating. (C) 2000 American Instit ute of Physics. [S0021-8979(00)06422-7].