Polar–Nonpolar Transition-Type Negative Thermal Expansion with 11.1% Volume Shrinkage by Design

Abstract

Chemical substitution for the tuning of the working temperature of phase-transition-type negative thermal expansion (NTE) materials generally reduces the volume shrinkage during the transition. We have investigated the effects of electron doping and reduction of 6s 2 lone-pair activity in PbVO 3 with a large polar distortion (c/a = 1.23) and found that the combination of Bi and Sr substitutions for Pb enables a temperature-induced polar to nonpolar transition with 11% volume shrinkage, even larger than the pressure-induced volume collapse of PbVO 3 (∼10.6%), and is the largest value among the NTE materials reported so far. The domain structure of the coexisting cubic and tetragonal phases with such a huge volume difference was successfully observed by highangle annular dark-field scanning transmission electron microscopy and the spatial distribution of domains by Bragg coherent X-ray diffraction imaging. The temperature hysteresis is reduced by repeated heating/cooling cycles, suggesting that the changes in the domain structure dominate the NTE properties.

Pressure Induced Amorphization of Pb2+ and Pb4+ in Perovskite PbFeO3

“…Similar to PbCoO 3 and PbCrO 3 mentioned above, , a pressure-induced charge transfer between Pb and Fe is expected to occur, resulting in a Pb 2+ Fe 4+ O 3 high-pressure (HP) phase. Such a transition is expected to be accompanied by a huge volume reduction which leads to the development of technologically important new negative thermal expansion materials as seen in the cases of BiNiO 3 and PbVO 3 . ,− …”