The dehydration of SrTeO3(H2O) - a topotactic reaction for preparation of the new metastable strontium oxotellurate(IV) phase ε-SrTeO3

Abstract

Microcrystalline single-phase strontium oxotellurate(IV) monohydrate, SrTeO3(H2O), was obtained by microwave-assisted hydrothermal synthesis under alkaline conditions at 180 ◦C for 30 min. A temperature of 220 ◦C and longer reaction times led to single crystal growth of this material. The crystal structure of SrTeO3(H2O) was determined from single crystal X-ray diffraction data: P21/c, Z = 4, a = 7.7669(5), b = 7.1739(4), c = 8.3311(5) A˚ , b = 107.210(1)◦, V = 443.42(5) A˚ 3 , 1403 structure factors, 63 parameters, R[F2 >2s(F2 )] = 0.0208, wR(F2 all) = 0.0516, S = 1.031. SrTeO3(H2O) is isotypic with the homologous BaTeO3(H2O) and is characterised by a layered assembly parallel to (100) of edge-sharing [SrO6(H2O)] polyhedra capped on each side of the layer by trigonal-prismatic [TeO3] units. The cohesion of the structure is accomplished by moderate O–H ◊◊◊ O hydrogen bonding interactions between donor water molecules and acceptor O atoms of adjacent layers. In a topochemical reaction, SrTeO3(H2O) condensates above 150 ◦C to the metastable phase e-SrTeO3 and transforms upon further heating to d-SrTeO3. The crystal structure of e-SrTeO3, the fifth known polymorph of this composition, was determined from combined electron microscopy and laboratory X-ray powder diffraction studies: P21/c, Z = 4, a = 6.7759(1), b = 7.2188(1), c = 8.6773(2) A˚ , b = 126.4980(7)◦, V = 341.20(18) A˚ 3 , RFobs = 0.0166, RBobs = 0.0318, Rwp = 0.0733, Goof = 1.38. The structure of e-SrTeO3 shows the same basic set-up as SrTeO3(H2O), but the layered arrangement of the hydrous phase transforms into a framework structure after elimination of water. The structural studies of SrTeO3(H2O) and e-SrTeO3 are complemented by thermal analysis and vibrational spectroscopic measurements.