Enhanced bulk photovoltaic response in Sn doped BaTiO<inf>3</inf> through composition dependent structural transformation

Polycrystalline BaTi1-xSnxO3 samples (x = 0.06, 0.07, 0.08, 0.09, 0.10, and 0.11) were synthesized by the solid state technique. The samples exhibit the tetragonal phase at 300 K. In addition, the samples x = 0.06, 0.07, 0.08, and 0.09 also show the orthorhombic phase with enhanced phase fractions upon poling. However, the % orthorhombic phase fractions show an increase up to x = 0.07 and a decrease with an increase in x. The dielectric studies indicate that TC (cubic to tetragonal phase transition) shifts toward lower temperature where the samples x = 0.10 and 0.11 show the tetragonal phase at 300 K. The samples exhibit the maximum remnant polarization and piezoelectric coefficient for x = 0.08. But the bandgap for the x = 0.07 sample shows the value of 2.61 eV before poling and 2.95 eV after poling. A giant photovoltaic (PV) response is seen in the samples with the open-circuit voltage (VOC) as large as 16 V (for x = 0.07). VOC shows a decreasing trend with an increase in the Sn content after x = 0.07, and it did not follow the trend in polarization and the bandgap. The observed results are correlated with the structural symmetry of the compound, and they are validated by the band-structure calculations. The experimental and theoretical studies indicate that the sample with the orthorhombic phase is preferable for the enhanced photovoltaic response in comparison to the tetragonal phase. These studies show a new way to achieve a large photovoltaic response so as to design the system for several device applications such as UV detectors and microactuators.