Switching Lead for Tin in PbHfO3: Noncubic Structure of SnHfO3

The removal of lead from commercialized perovskite-oxide-based piezoceramics has been a recent major topic in materials research owing to legislation in many countries. In this regard, Sn(II)-perovskite oxides have garnered keen interest due to their predicted large spontaneous electric polarizations and isoelectronic nature for substitution of Pb(II) cations. However, they have not been considered synthesizable owing to their high metastability. Herein, the perovskite lead hafnate, i.e., PbHfO3 in space group Pbam, is shown to react with SnClF at a low temperature of 300 degrees C, and resulting in the first complete Sn(II)-for-Pb(II) substitution, i.e. SnHfO3. During this topotactic transformation, a high purity and crystallinity is conserved with Pbam symmetry, as confirmed by X-ray and electron diffraction, elemental analysis, and 119Sn Mossbauer spectroscopy. In situ diffraction shows SnHfO3 also possesses reversible phase transformations and is potentially polar between. 130-200 degrees C. This so-called 'de-leadification' is thus shown to represent a highly useful strategy to fully remove lead from perovskite-oxide-based piezoceramics and opening the door to new explorations of polar and antipolar Sn(II)-oxide materials.

Automated summary

The removal of lead from commercialized perovskite-oxide-based piezoceramics has become an important topic in materials research due to legislation in many countries. Sn(II)-perovskite oxides, which have large spontaneous electric polarizations and can substitute for Pb(II) cations, have attracted interest. However, they have not been considered synthesizable due to their high metastability. In this study, a low temperature reaction at 300 degrees C between perovskite lead hafnate and SnClF resulted in the first complete Sn(II)-for-Pb(II) substitution, SnHfO3. The resulting compound exhibited high purity, crystallinity, and potentially reversible phase transformations and polarization between 130-200 degrees C.