Bond Relaxation Mechanisms of Piezoelectricity and Pyroelectricity for AlScN and GaScN: Composition and Temperature Dependencies

Employing the bond-order-length-strength theory, an analytical correlation for electromechanical properties of AlScN and GaScN systems (including the elastic constant, dielectric constant, piezoelectric stress constant, and pyroelectric coefficient) in response to the composition and temperature is proposed. Our results suggest that (i) when using Sc atoms to replace Al or Ga atoms, the elongation in the equilibrium atomic distance, the increase in the lattice tensile strain, and the weakening of interatomic interaction energy along the a direction dominate the composition effects of the elastic constant and dielectric constant, while the contraction in the equilibrium atomic distance, the increase in the lattice compressive strain, and the strengthening of interatomic interaction energy along the c direction govern the composition-dependent piezoelectric stress constant and pyroelectric coefficient and (ii) the influences of the temperature on the elastic constant, dielectric constant, piezoelectric stress constant, and pyroelectric coefficient all originate from a thermally driven lattice expansion and softening of interatomic interaction energy. The current analytical equation goes beyond the range of existing approaches, which not only uncovers quantitative information but also offers a penetrative understanding of the dynamical mechanisms behind the doping- and temperature-induced changes in electromechanical properties.