Institute for Solid State Physics, University of Tokyo, Kashiwanoha 5-1-5, Kashiwa, Chiba, 277-8581, Japan.
Department of Physics, Tohoku University, 6-3 Aramaki, Aoba, Sendai, 980-8578, Japan.
Sci Rep. 2016 Nov 30;6:37896. doi: 10.1038/srep37896.
The discovery of the post-perovskite transition, which is the structural transition from the perovskite to post-perovskite structure in MgSiO under pressure, has aroused great interests in geosciences. Despite of previous extensive studies, key factors of the post-perovsktie transition are still under hot debate primarily due to the big difficulty in performing systematic experiments under extreme conditions. Hence, search for new materials showing the post-perovskite transition under ambient pressure has been highly expected. We here report a new-type of materials CrAX (A = Ga, Ge; X = C, N), which exhibits the post-perovskite transition as a function of "chemical pressure" at ambient physical pressure. The detailed structural analysis indicates that the tolerance factor, which is the measure of the ionic radius mismatch, plays the key role in the post-perovskite transition. Moreover, we found a tetragonal perovskite structure with loss of inversion symmetry between the cubic perovskite and orthorhombic post-perovskite structures. This finding stimulates a search for a ferroelectric state in MgSiO.
在压力下，镁橄榄石中从钙钛矿到后钙钛矿结构的相变——后钙钛矿相变的发现，引起了地球科学领域的极大兴趣。尽管之前已经进行了广泛的研究，但由于在极端条件下进行系统实验的难度很大，后钙钛矿相变的关键因素仍在激烈争论中。因此，人们非常期望能在常压下找到具有后钙钛矿相变的新材料。我们在这里报告了一种新型的材料 CrAX（A=Ga、Ge；X=C、N），它在常压下作为“化学压力”的函数表现出后钙钛矿相变。详细的结构分析表明，容忍因子（衡量离子半径不匹配的指标）在后钙钛矿相变中起着关键作用。此外，我们发现了一种四方钙钛矿结构，它在立方钙钛矿和正交后钙钛矿结构之间失去了反演对称性。这一发现促使人们在 MgSiO 中寻找铁电态。
