Disorder in BaThF6 - refinement of anharmonic displacement parameters from high-pressure single-crystal X-ray diffraction data

作者：Friese Karen^*; Morgenroth Wolfgang; Maria Posse Jose; Grzechnik Andrzej

来源：Dalton Transactions, 2011, 40(9): 1902-1910.

DOI：10.1039/c0dt00924e

The structure of BaThF6 has been investigated as a function of temperature and pressure with single-crystal X-ray diffraction using synchrotron radiation. The compound crystallizes in the tysonite structure, space group P6(3)/mmc (a = 4.296(1) angstrom and c = 7.571(1) angstrom at ambient conditions). It is stable at least down to 150 K and up to 4 GPa. In the entire range of pressures and temperatures studied here, the compound is characterized by a high degree of disorder, both on the cationic and anionic positions. Despite the different valence states and sizes, both cations occupy the same crystallographic site in the ideal tysonite structure. The cationic disorder is described by two alternative approaches. The first model corresponds to a split-atom position model in which Ba2+ is maintained on a special position with site symmetry (6) over bar m2, while Th4+ is slightly displaced from the respective position. In the second model, both cations are maintained on the ideal position and anharmonic displacement parameters using a tensor of third order are introduced. Anharmonic displacement parameters have been refined from high-pressure single-crystal X-ray data measured in situ in a diamond anvil cell for the first time. The feasibility and general problems of anharmonic refinements of high-pressure X-ray data are further commented.

• 出版日期2011