Discovery of photoinduced bidirectional shape deformation in inorganic solid

Under photoirradiation, inorganic photostrictive materials undergo a unidirectional deformation (mainly expansion), resulting in tiny strains one to two orders of magnitude smaller than the electric field-driven strains. Here, we report an unprecedented bidirectional deformation under photoirradiation in inorganic solid Pb3V2O8, showing expansion (up to 0.01%) at low photoexcitation and, at high photoexcitation, becoming contracted with compressive strain over 0.4%, comparable to electric field-induced strains. We find that the expansion at low photoexcitation is prompted by photoinduced thermal and nonthermal expansion owing to the elongation of Pb–O bonds driven by photoexcitation-generated interatomic force, whereas the contraction at high photoexcitation with a much larger strain is driven by the V dimerization via an electron-lattice self-amplification process when the photoexcitation-generated V–O interatomic force overwhelms the Pb–O interatomic force. These findings provide a promising candidate with more degrees of freedom for photoactuation and also open a new avenue to design photostrictive materials.