Heterovalent Pb-substitution in ferroelectric bismuth silicate Bi2SiO5

Abstract

Systematic tuning of the ferroelectric phase transition in Bi₂SiO₅ was demonstrated using element substitution, where nominally heterovalent Pb was successfully substituted for Bi up to 20%. Comprehensive studies using powder X-ray diffraction analysis, dielectric measurements, X-ray absorption spectroscopy, and first-principles calculations revealed that charge compensation for heterovalent substitution was achieved via introduction of a considerable number of oxygen vacancies in Bi₂O₂ layers, resulting in the nominal composition (Bi_1−x³⁺Pb_x²⁺)₂SiO_5−x. The oxygen vacancies were found to induce local disordering of SiO₄ tetrahedral chains, sandwiched between the Bi₂O₂ layers, leading to a decrease in the ferroelectric phase transition temperature and broadening of the phase transition in Bi₂SiO₅.