Structure of BaCuSi4O10

Barium copper tetrasilicate, BaCuSi4O10, Mr = 473.2, tetragonal, P4/ncc, a = 7.440 (2) c = 16.097 (6) A, V = 891.2 (4) A3, Z = 4, Dx = 3.527 g cm-3, Mo Kα, λ = 0.71073 A, μ = 73.59 cm-1, F(000) = 884, T = 296 K, R = 0.0202, wR = 0.0167 for 290 reflectioons with I > 3 σ(I). This royal- blue plate-like crystal, a by-product of the Tl-bearing superconductors, was identified by both electron microprobe and single-crystal diffraction to be the barium copper silicate BaCuSi4O10. The structure consists of rings of four-linked SiO4 tetrahedra. Each ring is connected to four others to form a silicate layer in the ab plane. The compound is a synthetic isotype of the rare mineral gillespite (BaFeSi4O10) [Pabst (1943, 1958). Am. Mineral. 28, 372-390; 43, 970-980]. Two silicate phases with new structure types as by-products of the Tl-bearing oxide superconductors were recently reported by Finger, Hazen and Hemley [Am. Mineral. (1989), 74, 952-959]. In this work we report the microanalysis results and the crystal structure of the said blue plate crystal. (orig.)