Self-Healing Behavior of Piezoelectric Crystals Studied Using Polarized Light

It is challenging to quantify the self-healing efficiency in crystalline materials with atomic precision. Organic crystals with self-healing capabilities are of particular interest due to their wide-ranging potential applications. In this study, we present a comprehensive polarization Mueller matrix analysis of a self-healing crystal. Our results not only probe and quantify the crystal’s various optical properties but also offer new insights into its self-healing mechanism. We observe that the mechanical stress-induced changes of the microscopic polarization properties of the crystal are manifested as the reduction of anisotropic parameters, e.g., diattenuation and retardance, in the imperfectly healed and fractured crystal. This reduction in amplitude and phase anisotropy parameters is interpreted as the manifestation of the photoelastic effect, where some remnant strain within the broken crystal leads to the alteration of the dielectric tensor of the anisotropic crystal. These alterations, in turn, explain changes in the macroscopic piezoelectric polarization through the orientation of the permanent dipoles and the generation of stress-induced surface charges, which leads to the autonomous self-healing of the crystal. Beyond its remarkable self-healing properties, the crystal also exhibits rich optical properties, e.g., strong polarization anisotropy effects, nonlinear properties, etc.