Average and local structure of the Pb-free ferroelectric perovskites (Sr, Sn)TiO3 and (Ba,Ca,Sn)TiO3

The characteristic structural off-centering of Pb2+ in oxides, associated with its 6s(2) lone pair, allows it to play a dominant role in polar materials, and makes it a somewhat ubiquitous component of ferroelectrics. In this work, we examine the compounds Sr0.9Sn0.1TiO3 and Ba0.79Ca0.16Sn0.05TiO3 using neutron total scattering techniques with data acquired at different temperatures. In these compounds, previously reported as ferroelectrics, Sn2+ appears to display some of the characteristics of Pb2+. We compare the local and long-range structures of the Sn2+-substituted compositions to the unsubstituted parent compounds SrTiO3 and BaTiO3. We find that even at these small substitution levels, the Sn2+ lone pairs drive the local ordering behavior, with the local structure of both compounds more similar to the structure of PbTiO3 rather than the parent compounds.