Two Types of Negative Thermal Expansion Observed in PbCr<sub>1–<i>x</i></sub>Ti<sub><i>x</i></sub>O<sub>3</sub>
Yuki Sakai, Kana Matsuno, Takumi Nishikubo, Masayuki Fukuda, Shogo Wakazaki, Masahito Ikeda, Kazuki Takahashi, Zhao Pan, Lei Hu, Masaki Azuma
Abstract
Two negative thermal expansions (NTEs) with different mechanisms were observed in solid solutions of perovskite-type oxides PbCrO 3 and PbTiO 3 . PbCr 1– x Ti x O 3 was found to adopt a cubic structure the same as that of PbCrO 3 for x ≤ 0.6 and a PbTiO 3 -type tetragonal structure for x ≥ 0.7. The NTE observed at x ≤ 0.6 was accompanied by a cubic-to-cubic phase transition originating from the rearrangement of Pb 2+ /Pb 4+ in a complex local structure called a charge glass. The volume shrinkage of −2.5% observed in PbCrO 3 is sufficiently large despite the absence of intermetallic charge transfer, which is the origin of pressure-induced cubic-to-cubic phase transition and 9.8% volume collapse. The NTE in the tetragonal phase was caused by the ferroelectric-to-paraelectric phase transition, the same as in PbTiO 3 . We succeeded in significantly lowering the working temperature of PbTiO 3 as an NTE material by Cr substitution while retaining a large volume shrinkage of 0.6%.