The structures of the orthorhombic room-temperature phase of Cu
8GeS
6 (phase II) and the monoclinic low-temperature phase of Ag
7TaS
6 (phase II) have been successfully refined based on X-ray diffraction data from 12-fold twinned (Cu
8GeS
6II) and 24-fold twinned (Ag
7TaS
6II) crystals. Respectively among 6 major and 6 minor twin domains of Cu
8GeS
6II, or among 12 major and 12 minor twin domains of Ag
7TaS
6II, the argyrodite-type frameworks, GeS
6or TaS
6, can be superposed to each other in principle, and only Cu-Cu or Ag-Ag network directions differ. At higher temperature, the crystals were considered to be 2-fold twinned crystals of superionic-conductor phase I with a space group
F43m. On cooling, each domain transforms into 6 domains of orthorhombic Cu
8GeS
6II or 12 domains of monoclinic Ag
7TaS
6II. Superposed projections along 6 directions of the structure of Cu
8GeS
6II and along 12 directions of the structure of Ag
7TaS
6II seem to show approximate expressions for Cu-ion and Ag-ion conduction paths in superionic-conductor phases, Cu
8GeS
6I and Ag
7TaS
6I.
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