Pb-free ferroelectrics investigated with density functional theory: SnAl1/2Nb1/2O3 perovskites

Interest in Pb-free ferroelectrics has intensified as the search for less toxic Pb replacements continues. Since Sn is isoelectronic with Pb, it has generated great interest. Most of this effort has focused on SnTiO3. Even though it shows impressive ferroelectricity in calculations, synthesis has proved elusive. We therefore use density-functional theory (DFT) to investigate B-site alternatives that involve smaller size to promote perovskite phase stability. In this paper, Sn(Al1/2Nb1/2)O-3 (SAN) is investigated. We demonstrate that SAN is likely to be synthesizable, will be ferroelectric, and perhaps a good piezoelectric material as well. We discuss how cation displacements and their interactions affect the polarization of the solid solution. We also explore the electronic properties of the SAN solid solution and correlate them to the structural findings.