Atomistic configurational effects on piezoelectric properties of La3Ta0.5Ga5.5O14 and a new piezoelectric crystal design

Abstract

Single crystalline langatate (LTG, La3Ta0.5Ga5.5O14) has been widely used as a sensor material in high temperature applications because of its thermally stable piezoelectric properties. In this research, to elucidate the relationship between piezoelectric tensors and local ionic configurations, first-principles calculations based on density functional perturbation theory (DFPT) were performed on various local ionic structures. The results indicate that two independent relaxed-ion piezoelectric coefficients, e11 and e14, increased with increases in La(3e)–O and Ta(1a)–O distances or decreases in Ga(3f,2d)–O distances. Thus, to obtain high piezoelectric constants in this crystal, ions larger than La3+ should be incorporated at 3e sites to open the distance between 3e ions and oxygen ions, and ions smaller than Ga3+ should be introduced at 2d and 3f sites to reduce the distance between Ga and O ions. Finally, from this design rule, a new crystal, BTAS (Ba3TaAl3Si2O14), which belongs to the same P321 group, is proposed. The calculated relaxed-ion piezoelectric coefficient e11 of BTAS was 17.7% higher than the coefficient of a LTG crystal. This significant increase confirms BTAS as a useful new piezo-material, especially in applications where there is also a need to reduce the use of more expensive elements.