Bull C L, Funnell N P, Ridley C J
ISIS Neutron and Muon Facility, STFC, Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX, UK.
School of Chemistry, University of Edinburgh, David Brewster Road, Edinburgh EH9 3FJ, UK.
Philos Trans A Math Phys Eng Sci. 2023 Oct 16;381(2258):20220332. doi: 10.1098/rsta.2022.0332. Epub 2023 Aug 28.
The nuclear and magnetic structure of [Formula: see text] has been investigated using neutron and X-ray powder diffraction as a function of pressure and temperature. The orthorhombic symmetry (space group [Formula: see text]) remains stable up to the highest temperature (1500 K) and pressure (approx. [Formula: see text]) considered. There is a crossover in the magnitude of the and -lattice parameters at approximately 1135 K, caused by competing effects of octahedral tilting and distortion. The material is antiferromagnetic ([Formula: see text] K) with [Formula: see text] symmetry, with a maximum moment of [Formula: see text] on the [Formula: see text] sites aligned along the direction of the [Formula: see text]-axis. The application of pressure shows an abnormal softening in the unit-cell volume, which is suggestive of a continuous approach to a second-order phase transition. Raman spectroscopy measurements at ambient temperature were collected as a function of pressure up to approximately [Formula: see text] GPa, with discontinuous mode behaviour further suggesting the existence of a transition above 7 GPa. The measured structural changes in [Formula: see text] are compared extensively in the wider context of other lanthanide orthochromites, and the comparative effects of - and -site substitution on the polyhedral tilts and distortion are discussed. This article is part of the theme issue 'Exploring the length scales, timescales and chemistry of challenging materials (Part 1)'.
已利用中子和X射线粉末衍射研究了[化学式：见原文]的核结构和磁结构，该研究是作为压力和温度的函数进行的。直至所考虑的最高温度（1500 K）和压力（约[化学式：见原文]），正交对称性（空间群[化学式：见原文]）仍保持稳定。在大约1135 K处，由于八面体倾斜和畸变的竞争效应，a和b晶格参数的大小出现交叉。该材料在[化学式：见原文] K时为反铁磁性，具有[化学式：见原文]对称性，在沿c轴方向排列的[化学式：见原文]位点上最大磁矩为[化学式：见原文]。压力的施加显示出晶胞体积的异常软化，这表明正在持续接近二级相变。在环境温度下收集了拉曼光谱测量数据，该数据是压力高达约[化学式：见原文] GPa的函数，不连续的模式行为进一步表明在7 GPa以上存在转变。在更广泛的其他镧系正铬酸盐背景下，对[化学式：见原文]中测量到的结构变化进行了广泛比较，并讨论了A和B位点取代对多面体倾斜和畸变的比较效应。本文是主题为“探索具有挑战性材料的长度尺度、时间尺度和化学性质（第1部分）”的一部分。
