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Structural variants in the low-temperature beta phase of stoichiometric cuprous selenide

Symmetry lowering from Td2(f43m) to C3s (Cm) at alfa -> beta first-order phase transition of the superionic conductor Cu2Se is described by two nonequivalent wave vectors: kR=[2pi/ac](111/222) and km=[2pi/ac]((11/33) 0 Four orientation variants of the rhombohedrally deformed cage sublattice are equally probable equilibrium structures which correspond to four rays in the star of kR. Such twinning was observed using a microfurnace built for the Weissenberg goniometer. Three monoclinic beta-phase structure variants displaying together pseudorhombohedral symmetry can couple to each body cube diagonal as a cage distortion direction, giving a total of 12— the number of rays in the star of km.

copper selenide; structural variants

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