Structural, electronic, elastic, and piezoelectric properties of α-quartz and MXO_4 (M=Al, Ga, Fe; X=P, As) isomorph compounds: A DFT study

摘要

We report the structural, electronic, elastic, and piezoelectric properties of some α-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-O-X bridging angle θ and the tilt angle δ, 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 θ and δ. A comparison between our results at the density-functional theory level and the available data (theoretical and experimental ones) has been made. The differences observed for the whole class of systems has been discussed and a comparison with the SiO_2 α-quartz behavior is made.