Exploring the tunability of lead free Ba0.5Sn0.5TiO3 to mimic PbTiO3

Abstract

Can a material be designed and engineered to use as a replacement for an environmentally unfriendly material? In the specific context of lead titanates, the quest for finding such material replacements is ongoing, beginning from lead free alternatives with simple perovskite compositions, extending to hybrid and double perovskite compositions. In this work, we have demonstrated through ab initio density functional theory investigations the tunability of multiple properties of a simple perovskite Ba0.5Sn0.5TiO3 to mimic that of PbTiO3. Our results show that A-site Sn enhances the polarization of Ba0.5Sn0.5TiO3 closer to that of PbTiO3 and tunes its pressure dependent polarization behavior to become similar to that of PbTiO3 and dissimilar to that of BaTiO3 by reorienting the displacements profiles of A, B site and O atoms to become like that of their counterparts in PbTiO3. Compressive pressures facilitate transition from indirect to direct bandgap, increase the mobility of charge carriers and lead to stronger exciton binding in Ba0.5Sn0.5TiO3 opening up its use for optoelectronics. Ba0.5Sn0.5TiO3 has an early onset of absorption and its absorption spectra in UV range is qualitatively similar to PbTiO3 albeit with reduced absorption peak heights and broadening. The absorption spectra of Ba0.5Sn0.5TiO3 can be modified via application of strains and peak absorption heights can be changed to become similar to that of PbTiO3. We also demonstrate that the dielectric constant as well as refractive index of Ba0.5Sn0.5TiO3 can be modulated to increase (decrease) by applying compressive (tensile) strains. The study of mechanical properties demonstrates that Ba0.5Sn0.5TiO3 is more ductile and is mechanically stable even under higher compressive strains making it excitingly attractive for device applications over other lead-free alternatives that are known to display poor stabilities. These comprehensive investigations demonstrate for the first time that all the physical properties of Ba0.5Sn0.5TiO3 can be tuned as desired for a chosen device application making it a competitive and green replacement to lead titanates.