Virtual crystal approximation study of nitridosilicates and oxonitridoaluminosilicates

We present a density functional theory study of a variety of nitridosilicate and oxonitridoaluminosilicate systems. For the nitridosilicates, we have shown that the DFT-calculated equilibrium structures of BaYb-Si4N7, SrYb-Si4N7 and EuYb-Si4N7 are in good agreement with experiment. We then used the virtual crystal approximation (VCA) to study the effects of oxygen-doping on the nitrogen sites. We then added Si/Al disorder into our system, in order to model the properties of BaYb-SiAlON for pressures up to 50 GPa, in order to investigate recent experimental findings. We have found that this system is stable over the whole pressure range, and that the compression mechanism is pure bond length shortening. (C) 2008 Elsevier Ltd. All rights reserved.