Large Bulk Photovoltaic Response by Symmetry-Breaking Structural Transformation in Ferroelectric [Ba (Zr0.2Ti0.8) O3] <inf>0.5</inf>[(Ba0.7Ca0.3)Ti O3] <inf>0.5</inf>

The photovoltaic effect in noncentrosymmetric ferroelectrics is gaining much research interest due to its remarkable above band-gap photovoltage. Among the available ferroelectric systems, the 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 with its high piezocoefficient is considered as an attractive lead-free multifunctional ferroelectric material. The photovoltaic studies on this compound reveal the discovery of a large photogenerated electric field of 368Vcm-1, one of the highest values reported in polycrystalline ferroelectric systems. It is demonstrated that the large photovoltaic response in this ferroelectric system is due to the symmetry breaking structural transformation from the tetragonal to rhombohedral and orthorhombic phases. Density functional calculations show that this symmetry breaking transformation leads to the reduction of electron and hole effective masses and delocalization and reorientation of the conduction charge cloud along the polarization direction, which, in turn, gives a high photovoltaic response.