A refinement of the structure of barium tantalum oxide, Ba5Ta4O15

The Crystal Structure of Ba8Ta6NiO24: Cation Ordering in Hexagonal Perovskites

“…The Rietveld method with a modified (2) 1.12 (6) markable distortions of the intensities in the small angle Ba4 6c 0.3087(7) 0 0.880 (2) 1.12 (6) range and to negative thermal parameters for some atoms.…”

“…deduced from the nominal composition of the compound Ba 8 Ta 6 NiO 24 (Z ϭ 3). The electron densities in both posiThe X-ray diffraction pattern revealed a single phase tions were estimated by the refinement (with fixed thermal sample for the nominal composition Ba 8 Ta 6 NiO 24 and it parameters) of its occupancies assuming a filling by only was indexed on a hexagonal lattice with cell parameters Ta atoms.…”

“…when some of the ''cubic'' (c) layers are shifted by (1/3, In the present paper we describe the results of the syn-2/3, 0) introducing ''hexagonal'' (h) layers. As a consethesis and the structural investigation of the new hexagonal quence of such a shift groups of face-shared octahedra perovskite-like oxide Ba 8 Ta 6 NiO 24 with cation vacancies (FSO) appear. The separation between cations in neighin the B positions.…”

On the Luminescence of Ba5M4O15(M=Ta5+, Nb5+)

“…This article describes the luminescence properties of the perovskite-type materials, Ba Ta O and Ba Nb O . Shannon and Katz have determined that Ba (Ta, Nb) O crystallizes with hexagonal symmetry (space group P3m1) (3). The structure consists of five close-packed oxygen and barium layers.…”

Reinvestigation of the crystal structure of pentastrontium tetraniobate, Sr5Nb4O15

“…It is definitively a member η = 5 of the homologous series of complex oxides with cation-deficient perovskite-related structure with trigonal symmetry formulated as A n B n -iC>3n. The РЗс 1 space group chosen instead that of Ba5Ta40i5 [2,3] corresponds to a doubling of the oparameter due to a global reverse rotation of ТЮб octahedra (-15°) around the с axis (see figure). As observed in LasTi^is [4| and BaLa4Ti40i5 [5], this cooperative rotation of all the octahedra is the simplest way to provide Sr 2+ cations with a [6+3] coordination without any distortion of these octahedra.…”