Given the consensus that pressure improves cation order in most of known materials, a discovery of pressure-induced disorder could require reconsideration of order-disorder transition in solid state physics/chemistry and geophysics. Double perovskites Y2CoIrO6 and Y2CoRuO6 synthesized at ambient pressure show B-site order, while the polymorphs synthesized at 6 and 15 GPa are partially-ordered and disordered respectively. With the decrease of ordering degrees, the lattices are shrunken and the crystal structures alter from monoclinic to orthorhombic symmetry. Correspondingly, long-range ferrimagnetic order in the B-site ordered phases are gradually overwhelmed by B-site disorder. Theoretical calculations suggest that unusual unit cell compressions under external pressures unexpectedly stabilize the disordered phases of Y2CoIrO6 and Y2CoRuO6.
@article{arxiv.2003.08025,
title = {Pressure-induced inverse order-disorder transition in double perovskites},
author = {Zheng Deng and Chang-Jong Kang and Mark Croft and Wenmin Li and Xi Shen and Jianfa Zhao and Richeng Yu and Changqing Jin and Gabi Kotliar and Sizhan Liu and T. A. Tyson and Ryan Tappero and Martha Greenblatt},
journal= {arXiv preprint arXiv:2003.08025},
year = {2020}
}