One Site, Two Cations, Three Environments: s2 and s0 Electronic Configurations Generate Pb-Free Relaxor Behavior in a Perovskite Oxide

T Wesley Surta; Thomas A Whittle; Matthew A Wright; Hongjun Niu; Jacinthe Gamon; Quinn D Gibson; Luke M Daniels; William J Thomas; Marco Zanella; Philippa M Shepley; Yang Li; Anton Goetzee-Barral; Andrew J Bell; Jonathan Alaria; John B Claridge; Matthew J Rosseinsky

doi:10.1021/jacs.0c10572

One Site, Two Cations, Three Environments: s² and s⁰ Electronic Configurations Generate Pb-Free Relaxor Behavior in a Perovskite Oxide

J Am Chem Soc. 2021 Jan 27;143(3):1386-1398. doi: 10.1021/jacs.0c10572. Epub 2021 Jan 14.

Authors

T Wesley Surta¹, Thomas A Whittle¹, Matthew A Wright¹, Hongjun Niu¹, Jacinthe Gamon¹, Quinn D Gibson¹, Luke M Daniels¹, William J Thomas¹, Marco Zanella¹, Philippa M Shepley², Yang Li³, Anton Goetzee-Barral³, Andrew J Bell³, Jonathan Alaria⁴, John B Claridge¹, Matthew J Rosseinsky¹

Affiliations

¹ Department of Chemistry, University of Liverpool, Liverpool L69 7ZD, U.K.
² School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, U.K.
³ School of Chemical and Process Engineering, University of Leeds, Leeds LS2 9JT, U.K.
⁴ Department of Physics, University of Liverpool, Liverpool L69 7ZE, U.K.

Abstract

The piezoelectric devices widespread in society use noncentrosymmetric Pb-based oxides because of their outstanding functional properties. The highest figures of merit reported are for perovskites based on the parent Pb(Mg_1/3Nb_2/3)O₃ (PMN), which is a relaxor: a centrosymmetric material with local symmetry breaking that enables functional properties, which resemble those of a noncentrosymmetric material. We present the Pb-free relaxor (K_1/2Bi_1/2)(Mg_1/3Nb_2/3)O₃ (KBMN), where the thermal and (di)electric behavior emerges from the discrete structural roles of the s⁰ K⁺ and s² Bi³⁺ cations occupying the same A site in the perovskite structure, as revealed by diffraction methods. This opens a distinctive route to Pb-free piezoelectrics based on relaxor parents, which we demonstrate in a solid solution of KBMN with the Pb-free ferroelectric (K_1/2Bi_1/2)TiO₃, where the structure and function evolve together, revealing a morphotropic phase boundary, as seen in PMN-derived systems. The detailed multiple-length-scale understanding of the functional behavior of KBMN suggests that precise chemical manipulation of the more diverse local displacements in the Pb-free relaxor will enhance performance.