Defect Structure, Phase Separation, and Electrical Properties of Nonstoichiometric Tetragonal Tungsten Bronze Ba0.5鈥?i>xTaO3鈥?i>x

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• 作者：Xiaojun Kuang ; Fengjuan Pan ; Jiang Cao ; Chaolun Liang ; Matthew R. Suchomel ; Florence Porcher ; Mathieu Allix
• 刊名：Inorganic Chemistry
• 出版年：2013
• 出版时间：November 18, 2013
• 年：2013
• 卷：52
• 期：22
• 页码：13244-13252
• 全文大小：482K
• 年卷期：v.52,no.22(November 18, 2013)
• ISSN：1520-510X

文摘

New insight into the defect chemistry of the tetragonal tungsten bronze (TTB) Ba_0.5鈥?i>xTaO_3鈥?i>x is established here, which is shown to adapt to a continuous and extensive range of both cationic and anionic defect stoichiometries. The highly nonstoichiometric TTB Ba_0.5鈥?i>xTaO_3鈥?i>x (x = 0.25鈥?.325) compositions are stabilized via the interpolation of Ba²⁺ cations and (TaO)³⁺ groups into pentagonal tunnels, forming distinct Ba chains and alternate Ta-O rows in the pentagonal tunnels along the c axis. The slightly nonstoichiometric Ba_0.5鈥?i>xTaO_3鈥?i>x (x = 0鈥?.1) compositions incorporate framework oxygen and tunnel cation deficiencies in the TTB structure. These two mechanisms result in phase separation within the 0.1< x < 0.25 nonstoichiometric range, resulting in two closely related (TaO)³⁺-containing and (TaO)³⁺-free TTB phases. The highly nonstoichiometric (TaO)³⁺-containing phase exhibits Ba²⁺ cationic migration. The incorporation of (TaO)³⁺ units into the pentagonal tunnel and the local relaxation of the octahedral framework around the (TaO)³⁺ units are revealed by diffraction data analysis and are shown to affect the transport and polarization properties of these compositions.