Full strain tensor measurement upon photostriction in a ferroelectric crystal

Photostriction refers to the direct conversion of light into a mechanical strain, which provides great potential in optoelectronic applications such as photostrictive actuators and optomechanical sensors. Since the discovery of the effect, numerous materials have constantly been explored. The mechanisms behind photostriction depend on the material under study. For instance, photostriction in non-polar semiconductors is caused by the change in atomic bond lengths induced by photo-excited carriers in the conduction band,¹ whereas in polar semiconductors, it is understood as a combination of photovoltaic and converse piezoelectric effect.²

The photostriction in ferroic materials is of great interest due to the interplay of strain and ferroic degrees of freedom. Several techniques such as capacitance dilatometer,² time-resolved x-ray diffractometer,³ and Raman spectrometer,⁴ have been implemented to measure photostriction in BiFeO₃, PbTiO₃, and SrRuO₃, respectively, but in all cases, an elongation along a single direction only is measured, which limits our understanding of the mechanisms. Here, we report measurements of the full strain tensor upon photostriction using rainbow-filtered x-ray Laue micro-diffraction on a PbTiO₃ single crystal, chosen as a model system. The measurements are carried out for several excitation wavelengths, laser power, and laser polarization. A preliminary analysis of the results suggests that the behavior of deviatoric strain components is consistent with the theoretical report, validating the approach.⁵ Further, a detailed analysis of full-strain tensor components will be discussed.

1. J. Buschert et al., Solid State Commun. 80, 419–422 (1991).

2. B. Kundys et al., Nat. Mater. 9, 803-805 (2010).

3. Y. Li et al., Sci. Rep. 5, 16650 (2015).

4. T.-C Wei et al., Nat. Commun. 8, 15108 (2017).

5. C. Paillard et al., Phys. Rev. B 96, 045205 (2017).