Crystal structure analysis of tungsten bronzes 尾-SrTa₂O₆ and 尾鈥?SrTa₂O₆ by synchrotron X-ray and neutron powder diffraction

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• 作者：Eunhye Lee^a ; Cheol-Hee Park^b ; Daniel P. Shoemaker^c ; Maxim Avdeev^d ; Young-Il Kim^a ; ^{yikim@ynu.ac.kr}
• 关键词：Tetragonal tungsten bronze ; Neutron diffraction ; Bond valence sum ; Atomic disorder
• 刊名：Journal of Solid State Chemistry
• 出版年：2012
• 期刊代码：130_00224596
• 类别：ch
• 出版时间：July, 2012
• 卷：191
• 期：Complete
• 页码：232-238
• 文件大小：1286 K

摘要

Strontium ditantalum oxide SrTa₂O₆ exists in 伪-, 尾-, and 尾鈥?polymorphs. Herein the crystal structures of the latter two were studied using synchrotron X-ray and constant-wavelength neutron powder diffraction. While 尾鈥?SrTa₂O₆ [space group P4/mbm, a=12.47099(1) 脜, c=3.898210(5) 脜, V=606.271(2) 脜³, Z=5] belongs to the regular tetragonal tungsten bronze (TTB) family, it contains locally disordered strontium atoms within the pentagonal channel. 尾-SrTa₂O₆ [space group Pnam, a=12.36603(2) 脜, b=12.43467(2) 脜, c=7.72403(1) 脜, V=1187.705(4) 脜³, Z=10] can be described as an orthorhombic modification of the TTB, where the octahedral tilting distortion effectively alleviates the bonding strains around TaO₆ and SrO₁₃ polyhedra. For comparison, rynersonite type 伪-SrTa₂O₆ [space group Pnma, a=11.00610(6) 脜, b=7.63397(3) 脜, c=5.62634(3) 脜, V=472.727(5) 脜³, and Z=4] is built from edge-shared dimer units of TaO₆ octahedra. As measured by diffuse-reflection absorption spectroscopy, 伪-, 尾-, and 尾鈥?SrTa₂O₆ have indirect band gap energies of 4.4, 4.0, and 3.8 eV, respectively.