Ab initio approach to photostriction in classical ferroelectric materials

The change of shape under illumination by visible light, called photostriction, is investigated in the classical ferroelectrics barium titanate and lead titanate. By means of the $\mathrm{\ensuremath{\Delta}}\mathrm{SCF}$ method, the use of first-principle calculations confirms that the converse piezoelectric effect is the main driving force of the photostriction of the polar axis in those materials. As a result, when compared to barium titanate and bismuth ferrite, lead titanate is a better photostrictive material in the direction of the polar axis, due to its larger longitudinal piezoelectric constant. On the other hand, in directions transverse to the polar axis, photoinduced electronic pressure can also become a sizable contribution that can either compete or cooperate with the piezoelectric effect, depending on the transitions involved. A simple Landau model is further developed and shows reasonable qualitative agreement with results from $\mathrm{\ensuremath{\Delta}}\mathrm{SCF}$ calculations, which is promising for a fast screening of materials with high photostrictive effects.