Bonding in the Doubly Disordered Ba_1−xSn_xCl_1+yF_1−y Solid Solution

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• 作者：Dé ; nè ; s ; Georges ; Muntasar ; Abdualhafed
• 关键词：barium tin chloride fluoride ; solid solution ; tin(II) bonding type ; Mö ; ssbauer spectroscopy ; X ; ray diffraction
• 刊名：Hyperfine Interactions
• 出版年：2004
• 出版时间：2004
• 年：2004
• 卷：153
• 期：1/4
• 页码：91-119
• 全文大小：682 KB

文摘

New materials were prepared in the SnF₂/BaCl₂ system by precipitation, and in the SnF₂/BaCl₂/BaF₂ system by direct reactions at high temperature in dry conditions. Stoichiometric BaSn₂Cl₂F₄ and BaSnClF₃⋅0.8H₂O, and a wide Ba_1−xSn_xCl_1+yF_1−y solid solution were prepared for the first time. Elemental analysis, X-ray diffraction and ¹¹⁹Sn Mössbauer spectroscopy were used for the characterization and study of bonding in the new materials. Mössbauer spectroscopy was shown to be an excellent method for probing both the type of bonding at tin(II) (ionic or covalent) and the bond strength at the tin sublattice. Tin(II) is covalently bonded in the stoichiometric phases and ionic (Sn²⁺ stannous ion) in the precipitated Ba_1−xSn_xCl_1+yF_1−y solid solution. The case of Ba_1−xSn_xCl_1+yF_1−y prepared in dry conditions is more complex. At negative y values (Cl : F <1) and more particularly at high x (solid solution rich in tin), a mixture of Sn²⁺ and covalent Sn(II) is observed, with a normal sublattice strength for Sn(II). At positive y values (Cl : F >1) and more particularly at low x (poor in tin), all the tin(II) is in the ionic form. Furthermore, at high x and high y, the tin(II) sublattice strength decreases so drastically that the tin recoil free fraction at ambient temperature is nearly zero. The bonding type and tin sublattice strength can be explained in terms of preference of covalent bonding with F and when tin clustering occurs, whereas an excess Cl around Sn(II) forms ionic bonding and tin rattling due to ionic size mismatch.