Abstract--The crystal structure of cronstedtite-1T was refined in space group P3 l m, using two crystals: a triangular tabular crystal from Herja, Romania and a conical crystal from Lostwithiel, Cornwall, England. The Herja sample has the composition of (Fe2+2.20Fe3+080)(Sil.20Fe3+0.78A10.02)Os(OH) 4 and the Lostwithiel sample has the composition, of (FeZ+232Fe3+0~68)(Si132Fe3+0.66A1002)O5(OH) 4. The results of refinements are as follows: a = 5.512(1) A, c = 7.106(1) A, R = 3.07%, and 342 independent reflections; and a = 5.503(1), c = 7.104(1) A, R = 2.24%, and 335 independent reflections for the Herja and Lostwithiel samples, respectively. The structure consists of one tetrahedral and one octahedral sheet. There is one octahedral site, M1, occupied by Fe only, and one tetrahedral site, T1, occupied by Si and Fe in the ratio of 0.617(8):0.383 (Herja) and 0.699(6):0.301 (Lostwithiel). Positions of two hydrogen atoms were determined from a difference map for the Lostwithiel data. The ditrigonalization angle of the tetrahedral sheet is ct = -11.5 ~ (Herja) and a = -11.1 ~ (Lostwithiel), and the structures have a Franzini-layer type of B. The crystals studied are affected by +-b/3 stacking faults which produced slight streaking of h -k r 3n reflections.
Sr(14/11)CoO(3) (i.e. Sr(14)Co(11)O(33), tetradecastrontium undecacobalt tritriacontaoxide), a new phase in the hexagonal perovskite Sr(x)CoO(3) system, has been prepared and its structure solved from single-crystal X-ray data within the (3 + 1)-dimensional formalism. Sr(14/11)CoO(3) crystallizes in the trigonal symmetry, R3;m(00gamma)0s superspace group with the following lattice parameters: a(s) = 9.508 (2), c(s) = 2.5343 (7) Å, q = 0.63646 (11)c(*) and V(s) = 198.40 (13) Å(3). With the commensurate versus incommensurate test not being conclusive, the structure was considered as commensurate (P32 three-dimensional space group), but refined within the (3 + 1)-dimensional formalism to a residual factor R = 0.0351 for 47 parameters and 1169 independent reflections. Crenel functions were used for the oxygen and cobalt description and a Gram-Charlier expansion up to the third order of the atomic displacement parameter was employed for one Co atom. The structure is similar to that of Sr(6/5)CoO(3), but with a different sequence of the octahedra and trigonal prism polyhedra along the [CoO(3)] chains. An interesting feature evidenced by the non-harmonic expansion is the displacement of the prismatic Co atoms from the site center, towards the prism rectangular faces.
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