Multicell Model of La3Ga5GeO14 Crystal: A New Approach to the Description of the Short-Range Order of Atoms

摘要

The multicell model alternative to the model of mixed atomic sites used now is proposed for a single crystal of La3Ga5GeO14 belonging to the langasite family. The multicell consists of four unit cells. In three identical cells of the structure, atoms adapt to the Ge atom occupying one of the two 2d positions on the threefold symmetry axis. In the fourth cell, atoms surround the Ge atom located at the 1a position. The multicell model allows one to study the short-range order of atoms by the methods of classical structure analysis based on Bragg scattering. Four high-resolution data sets measured at 295 and 111.5 K are used in the study. The results are obtained with high relative precision (space group P321, Z = 1; at 295 K a = 8.2020(6) angstrom and c = 5.1065(6) angstrom, R/wR = 0.81/0.73% for 3829 unique reflections; at 111.5 K a = 8.1939(1) angstrom and c = 5.1022(4) angstrom, R/wR = 0.85/0.76% for 3880 reflections).