Polar–Nonpolar Transition-Type Negative Thermal Expansion with 11.1% Volume Shrinkage by Design
Takumi Nishikubo, Takashi Imai, Yuki Sakai, Masaichiro Mizumaki, Shogo Kawaguchi, Norihiro Oshime, Ayumu Shimada, K. Sugawara, Kenji Ohwada, Akihiko Machida, Tetsu Watanuki, Kosuke Kurushima, Shigeo Mori, T. Mizokawa, Masaki Azuma
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 non-polar 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 high-angle 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.