Nonlinear flexoelectricity in noncentrosymmetric crystals

Abstract

We explore the elastic, dielectric, piezoelectric, and flexoelectric phenomenological coefficients as functions of microscopic model parameters such as ionic positions and spring constants in the two-dimensional square-lattice model with rocksalt-type ionic arrangement. Monte Carlo simulation reveals that a difference in the given elastic constants of the diagonal springs, each of which connects the same cations or anions, is responsible for the linear flexoelectric effect in the model. We show the quadratic flexoelectric effect is present only in noncentrosymmetric systems, and it can overwhelm the linear effect in feasibly large strain gradients. It can also be seen that the linear flexoelectric effect is suppressed by increasing the degree of inversion symmetry breaking due to a rigid dipolar feature.