# Flexoelectricity

${\displaystyle P_{i}=d_{ijk}\sigma _{jk}+\mu _{ijkl}{\frac {\partial \epsilon _{jk}}{\partial x_{l}}}}$
Here, the flexoelectric coefficient, ${\displaystyle \mu _{ijkl}}$, is a fourth-rank polar tensor and ${\displaystyle d_{ijk}}$ is the coefficient corresponding to the direct piezoelectric effect.