The synthesis and crystal structure of a magnesium-lithium-scandium protopyroxene

Crystals of protopyroxene solid solution, Li_xSc_xMg_2-xSi₂O₆, 0.1 d x d 0.35, were grown, in solvents of the system Li₂O–V₂O₅–MoO₃, by cooling from 1350 to 650° at 1,5°C per hour. The crystals are transparent, euhedral, and prismatic, elongate parallel to с and up to 15 × 4 × 3 mm in size, with well-developed {010}, {110}, and {121} faces. The cell edges used for structure analysis are: a = 9.251, b = 8.773, and с = 5.377A. Long-exposure X-ray precession photographs showed no diffraction maxima inconsistent with space group Pbcn and no evidence of stack disorder. The crystal structure was refined from 1507 measured X-ray intensities, of which 826 were greater than 3σ of the background intensity. Refinements of the structure in space groups P2₁cn, Pb2n, Pbc2₁ and P2/c yielded structures which did not differ significantly from that in space group Pbcn. The structure is ordered with all of the Sc³⁺ in Ml and all of the Li⁺ in М2.