New Method of Preparation of Superionic BaSnF 4
- PDF / 110,950 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 110 Downloads / 189 Views
DD6.23.1
NEW METHOD OF PREPARATION OF SUPERIONIC BaSnF4 Georges DÉNÈS*, Abdualhafed. MUNTASAR and Tony Retrif Laboratory of Solid State Chemistry and Mössbauer spectroscopy, Laboratories for Inorganic Materials, Department of Chemistry and Biochemistry, Concordia University, Montreal, Quebec, H3G 1M8, Canada ABSTRACT The first preparation of superionic BaSnF4, BaSnF4(ssr), was carried out in 1975 by direct reaction at high temperature between appropriate amounts of BaF2 and SnF2 under inert conditions in sealed copper tubes. In the present work, BaSnF4(aq2) was synthesized for the first time by the wet method. X-ray powder diffraction and Mössbauer spectroscopy were used to characterize the products, and show that BaSnF4(aq2) and BaSnF4(ssr) are the same material. INTRODUCTION BaSnF4 has been shown to be a fast fluoride-ion conductor (superionic) [1], and it is isostructural with α-PbSnF4, the latter being the highest performance fluoride-ion conductor known to date [2]. The high mobility of the fluoride ions in the α-PbSnF4 structure has been attributed to the local disturbance created by the replacement of half of the Pb2+ ions in the fluorite-type structure of β-PbF2 by covalently bonded Sn(II), and to the presence of a vacant fluoride-ion layer between two adjacent tin layers. MSnF4 (M = Sr and Ba) were prepared first by Dénès et al. in 1975 [3] by direct reaction of appropriate amounts of SnF2 and MF2 at 500oC, under dry conditions, in inert atmosphere. For the synthesis of α-PbSnF4 in dry conditions, 250oC must be used since phase transitions take place at higher temperatures. In addition, α-PbSnF4 can also be prepared by the wet method: α-PbSnF4(aq1) precipitates when a solution of Pb(NO3)2 is added to a solution of SnF2, however, BaSnF4 could not be prepared by the same method, using Ba(NO3)2 [3]. Recently, a new method of preparation of BaSnF4 was discovered in our laboratory, by leaching in water appropriate amounts of barium tin(II) chloride fluorides, also newly discovered in our laboratory. Pure BaSnF4 is obtained on stirring the precipitate in water for 24 hours, only for 0.735 < X > 0.870, and if Ba → Sn, where X is the molar fraction of BaCl2 in the reaction mixture, and Ba → Sn means that the BaCl2 solution was added to the SnF2 solution. Some of the properties of BaSnF4 prepared by the two methods have been investigated. *
To whom all correspondence should be addressed: [email protected]
DD6.23.2
EXPERIMENTAL PROCEDURES The following reactants were used in the synthesis: SnF2 (99%) from Ozark Mahoning, BaCl2⋅2H2O (analytical grade) from American Chemical, BaF2 (99%) from Allied chemical and Dye Corporations, and doubly distilled water. Sample preparation and leaching procedures are described below. Characterization of the samples was carried out by X-ray powder diffraction and Mössbauer using methods described elsewhere [4&5]. RESULTS AND DISCUSSION First preparation of BaSnF4 from aqueous solution The reaction between aqueous solutions of SnF2 and BaCl2 results in the precipitation of
Data Loading...
