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Updated: Mar 6, 2026
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Published on: July 26, 2016
High-Pressure Synthesis and Structural Instability of A-Site-Ordered Quadruple Perovskite LaHg3Ti4O12+δ
Bowen Zhang1, Jun Deng1, Ning Sun1,2
1Center for High-Pressure Science and Technology Advanced Research, Beijing 100093, China.
Abstract:
PbHg3Ti4O12 (PHTO) represents the first example of ferroelectricity in quadruple A-site-ordered perovskites AA'3B4O12, which features Hg2+ ions in an unusual 8-fold coordination at the A'-site, forming a structural bridge between simple perovskites and conventional A-site-ordered perovskites. Here, we engineer the A-site charge and lone-pair activity by substituting La3+ for Pb2+, and synthesize a new A-site-ordered perovskite LaHg3Ti4O12+δ (LHTO) under high-pressure and high-temperature conditions. LHTO crystallizes in the centrosymmetric Im3̅ structure at room temperature and is isostructural with PHTO, retaining the 8-fold coordination of the Hg2+ ions. Structural and dielectric characterizations, and first-principles calculations, show a structural instability around 90 K driven by phonon soft modes dominated by Ti-O vibration and the weakening of lone pair, which prevents the development of long-range ferroelectric order. Our results establish a dual A-site design strategy─tuning both lone-pair activity and electron doping─for controlling ferroelectricity in A-site-ordered quadruple perovskites and uncover a competing instability characteristic of this intermediate-coordination regime.
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