Perovskite-oxide Bi1-xPbxNiO3 for 0.60 ≤ x ≤ 0.80 was found to show a polar orthorhombic-to-nonpolar orthorhombic phase transition accompanied by negative thermal expansion. Bi1-xPbxNiO3 showed successive crystal structure changes depending on the amount of Pb. As the amount of Pb increased, the crystal structure changed from a triclinic one with Bi3+/Bi5+ long-range ordering to an orthorhombic one with Bi3+/Bi5+ short-range ordering; then, it changed into a polar orthorhombic structure without Bi3+/Bi5+ ordering and finally to a polar LiNbO3-type one. The key to the inversion symmetry breaking in PbNiO3, where both 6s2 lone-pair and Jahn-Teller active cations are absent, is the high-valency state of Pb4+. Our results suggest that the polar orthorhombic phase can be realized by using high-valence A-site cations in addition to controlling the tolerance factor.
ASJC Scopus subject areas
- 化学 (全般)