Crystal structure analysis of tungsten bronzes beta-SrTa(2)O(6) and beta '-SrTa(2)O(6) by synchrotron X-ray and neutron powder diffraction
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Date
2012-07-01
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Academic Press Inc Elsevier Science
Abstract
Strontium ditantalum oxide SrTa(2)O(6) exists in alpha-, beta-, and beta'-polymorphs. Herein the crystal structures of the latter two were studied using synchrotron X-ray and constant-wavelength neutron powder diffraction. While beta'-SrTa(2)O(6) [space group P4/mbm, a=12.47099(1) angstrom, c=3.898210(5) angstrom, V=606.271(2) angstrom(3), Z=5] belongs to the regular tetragonal tungsten bronze (TTB) family, it contains locally disordered strontium atoms within the pentagonal channel. beta-SrTa(2)O(6) [space group Pnam, a = 12.36603(2) angstrom, b=12.43467(2) angstrom, c=7.72403(1) angstrom, V=1187.705(4) angstrom(3), Z=10] can be described as an orthorhombic modification of the TTB, where the octahedral tilting distortion effectively alleviates the bonding strains around TaO(6) and SrO(13) polyhedra. For comparison, rynersonite type alpha-SrTa(2)O(6) [space group Prima, a=11.00610(6) angstrom, b=7.63397(3) angstrom, c=5.62634(3) angstrom, V=472.727(5) angstrom(3), and Z=4] is built from edge-shared dimer units of TaO(6) octahedra. As measured by diffuse-reflection absorption spectroscopy, alpha-, beta- and beta'-SrTa(2)O(6) have indirect band gap energies of 4.4, 4.0, and 3.8 eV, respectively. © 2012, Elsevier Ltd.
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Keywords
Tungsten bronze, Strontium, Barium, Dielectric materials, Tantalum, Niobium
Citation
Lee, E., Park, C. H., Shoemaker, D. P., Avdeev, M., & Kim, Y. I. (2012). Crystal structure analysis of tungsten bronzes beta-SrTa(2)O(6) and beta '-SrTa(2)O(6) by synchrotron X-ray and neutron powder diffraction. Journal of Solid State Chemistry, 191, 232-238. doi:10.1016/j.jssc.2012.03.047