A CAS research group, headed by Dr. XIAO Wansheng from the Institute of Geochemistry, announced a scientific discovery at the in-situ high pressure X-ray diffraction facilities of the Beijing Synchrotron Radiation Facility (BSRF) that a pressure would induce isostructural phase transition in a perovskite material PbCrO3.

This cubic-cubic phase transition involved a large volume collapse of 9.8%; which was found in the cubic perovskite for the first time and would make a significant impact on the studies of physics, chemistry, material sciences and earth sciences. The results have been published in PNAS (PNAS, 2010, 107, 14026-14029)

Perovskite structure is a sort of materials of scientific importance in physics, material science and earth science. With a dense structure, when the outside environment (temperature and pressure) changes, it adjusts its structure by the distortion, rotation and tilt of the coordinated octahedrons in their co-corner locations, and furthermore, even changes its symmetry leading to a phase transition.

Normally, such a phase transition does not show an obvious non-continuous change in their bonding length, therefore, without a marvelous change on the volume. However, the abnormal large volume collapse found in the PbCrO3 perovskite in this study might be produced by a special physical mechanism. It will be a challenge for the traditional theory of the phase transition in perovskites, and will possibly open a new way to study the high pressure behavior of these materials.

The key X-ray diffraction data in characterization in this isostructural phase transition were obtained at the high-pressure beam line of BSRF (Figure below). The research group was made up of the scientific staff from the Institute of Geochemistry, the Institute of High Energy Physics and the Institute of Fluid Physics.

The X-ray patterns of the in-situ X-ray diffraction

　　　　

The P-V relationships of the cubic PbCrO3 (low- and high-pressure) perovskite phases. A 9.8% volume collapse is shown at a quite low pressure.