K 93 Kurlov, A. S. Atomic-vacancy ordering in the lowest tungsten carbide W2C [Текст] / A. S. Kurlov, A. I. Gusev // Journal of Experimental and Theoretical Physics. - 2007. - Vol. 105, № 4. - С. 710-721. - Библиогр. : с. 721 (22 назв.) Рубрики: ХИМИЧЕСКИЕ НАУКИ Кл.слова (ненормированные): АТОМНО-ВАКАНСИОННОЕ УПОРЯДОЧЕНИЕ -- КАРБИД ВОЛЬФРАМА Аннотация: Atomic–vacancy ordering in the lowest tungsten carbide W2C with an L'3-type basic hexagonal structure has been studied by neutron diffraction and X-ray diffraction. In the temperature range 2700–1370 K, the only ordered phase of the lowest tungsten carbide is shown to be the trigonal ε-W2C phase (space group P1m). This trigonal ε-W2 C phase is found to form via a disorder–order phase transition channel, which includes three superstructure vectors (k15(1), k15(2), k17(1) ) of two Lifshitz stars ({k15}, {k17}, and to be described by two long-range order parameters (η15,η17). The distribution function of carbon atoms in the trigonal ε-W2C superstructure is calculated, and the orresponding region of the allowable values of the long-range order parameters η15 and η17 is found. Symmetry analysis of other possible superstructures of the lowest tungsten carbide W2C is performed, and the physically acceptable sequence of phase transformations in W2 C is determined Полный текст |