Structural, electronic, elastic, and piezoelectric properties of α -quartz and M X O 4 ( M = Al , Ga, Fe; X = P , As) isomorph compounds: A DFT study

Abstract : We report the structural, electronic, elastic, and piezoelectric properties of some ␣-quartz SiO 2 isotypes, namely, AlPO 4 , GaPO 4 , GaAsO 4 , and FePO 4. This family of crystals is well known for its elastic and piezoelectric properties related to their MO 4 and XO 4 tetrahedral units, especially the M-OX bridging angle and the tilt angle ␦, the most distorted structures being expected to exhibit the highest piezoelectric coupling constant. We have then computed the optimized structure of each MXO 4 isomorph compound in order to study the variation in the elastic and piezoelectric tensors with respect to and ␦. A comparison between our results at the density-functional theory level and the available data ͑theoretical and experimental ones͒ has been made. The differences observed for the whole class of systems has been discussed and a comparison with the SiO 2 ␣-quartz behavior is made.