SYSTEMATIC SEARCH OF MATERIALS WITH HIGH-TEMPERATURE STRUCTURAL PHASE-TRANSITIONS - APPLICATION TO SPACE GROUP P2(1)2(1)2(1)

The existence of a pseudosymmetry in a crystal structure is indicative of a slightly distorted structure of higher symmetry. If the distorti on is small enough, it can be expected that the crystal acquires this more symmetric configuration at a higher temperature after a phase tra nsition. The aim of the present study is the development of a general procedure for the Systematic search of pseudosymmetric structures in t he available structural databases. The first step is the determination of all relevant supergroups of the space group associated to the know n structure. This problem is reduced to the generation of minimal supe rgroups of space groups using the existing data on their maximal subgr oups and normalizers. The determined pseudosymmetry elements are then applied to the crystal structure and a quantitative comparison of the transformed structure acid the original one is performed. Pseudosymmet ry is detected when the difference is under a certain threshold. As an example we present the results obtained for inorganic structures with space group P2(1)2(1)2(1) retrieved from the Inorganic Crystal-Struct ure Database. A significant number of compounds with known phase trans itions at high temperatures have been clearly detected as pseudosymmet ric with differences between the transformed and the original structur es lower than 1.0 Angstrom. About 20 additional structures were detect ed with pseudosymmetric features under the same threshold. These compo unds are considered as having a high probability of exhibiting a phase transition at higher temperatures.