Piezoelectric Anisotropy of KNbO3 by Molecular Dynamics Simulations Using a Shell Model

By molecular dynamics simulations using a shell model, we predicted the temperature dependence of the piezoelectric coefficients of KNbO3. The results were similar to those by phenomenological calculations by the Landau-Ginzburg-Devonshire (LGD) theory for KNbO3 and BaTiO3, first-principles effective Hamiltonian for the rhombohedral phase of BaTiO3, and a first-principles calculation for the rhombohedral phase of KNbO3. We also predicted the temperature dependence of the longitudinal piezoelectric surface d(33)* of KNbO3. The results were also similar to the previous calculations, since the temperature dependence of the piezoelectric constants were similar to them. The large shear piezoelectric constants especially near the phase transition temperatures resulted in the maximum of d(33)* along the nonpolar directions except for the tetragonal phase near the tetragonal-cubic phase transition temperatures.