Abstract
Accurate X-ray diffraction study of langasite (La3Ga5SiO14) single crystal has been performed using the data obtained on a diffractometer equipped with a CCD area detector at 295 and 90.5 K. Within the known La3Ga5SiO14 model, Ga and Si cations jointly occupy the 2d site. A new model of a “multicell” consisting of two different unit cells is proposed. Gallium atoms occupy the 2d site in one of these cells, and silicon atoms occupy this site in the other cell; all other atoms correspondingly coordinate these cations. This structure implements various physical properties exhibited by langasite family crystals. The conclusions are based on processing four data sets obtained with a high resolution (sin θ/λ ≤ 1.35 A–1), the results reproduced in repeated experiments, and the high relative precision of the study (sp. gr. P321, Z = 1; at 295 K, a = 8.1652(6) A, c = 5.0958(5) A, R/wR = 0.68/0.68%, 3927 independent reflections; at 90.5 K, a = 8.1559(4) A, c = 5.0913(6) A, R/wR = 0.92/0.93%, 3928 reflections).
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