First-principles investigation of auxetic piezoelectric effect in nitride perovskites

The recently reported auxetic piezoelectric effect, which acts as the electrical counterpart of the negative Poisson's ratio, is of significant technical importance for applications in acoustic wave devices. However, this electric auxetic effect has not yet been reported in perovskite systems. In this work, we employ first-principles calculations to investigate the piezoelectric properties of six polar nitride perovskites with the chemical formula ABN₃ (A = La, Sc, Y; B = W, Mo). Among these, all compounds except ScMoN₃ exhibit the auxetic piezoelectric effect, which is characterized by an unusually positive transverse piezoelectric coefficient, along with a positive longitudinal piezoelectric coefficient. This behavior is in sharp contrast to previously reported results in HfO₂, where both the longitudinal and transverse piezoelectric coefficients are negative. These unusual positive transverse piezoelectric coefficients originate from the domination of the positive internal-strain contribution. We further confirm the auxetic piezoelectric effect with finite electric field calculations. Our research enriches the understanding of the piezoelectric properties of nitride perovskites and provides a new compositional space for the design of novel auxetic piezoelectric materials.