Hydrothermal synthesis and characterization of a new potassium phosphatoantimonate
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A new potassium phosphatoantimonate with a composition of 4K2O • 4Sb2Os • P2O5 • 8H2O, which crystallizes in a monoclinic system with a = 23.952 A, b = 9.515 A, c = 8.193 A, and /3 = 124.77, was hydrothermally synthesized and characterized by powder x-ray diffraction, chemical composition analysis, x-ray photoelectron spectroscopy, and 31P MAS-NMR techniques. The potassium ion can be exchanged by other monovalent ions.
Since 1985, several phases of potassium phosphatoantimonate have been synthesized and characterized.1"6 These compounds exhibit interesting structural variations with Sb/P ratio in composition from three-dimensional frameworks to layered structures, and some of them show considerable ion-exchange properties and fast ion mobilities.7'8 These interesting compounds were exclusively synthesized by solid state reaction hitherto. With an aim to develop a new synthesis route and microporous ionic conductors of the above-mentioned type compounds, we begin the systematic investigation of hydrothermal synthesis in K2O-Sb2O5-P2O5-H2O systems. A new potassium phosphatoantimonate was syn-
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FIG. 2. XRD pattern of the potassium phosphatoantimonate.
FIG. 1. SEM micrograph of crystallites of the potassium phosphatoantimonate. J. Mater. Res., Vol. 9, No. 11, Nov 1994
thesized by a hydrothermal route, and characterized by many modern techniques. A typical procedure of the synthesis is as follows: SbCl3 is mixed with H3PO4 (85 wt. %), H2O2 (30 wt. %) was added dropwise to the mixture, and then a solution was obtained. Deionized water and KOH were added to the resulting solution in turn. The final mixture with molar composition 5K2O: Sb2O5:0.5P2O5:200H2O, in which the pH is 7-8, was sealed with 80% fill in a Teflon-lined T316 stainless-steel autoclave, of which the volume was 17 ml, for crystallization under autogenous pressure, and hydrothermal crystallization was carried out at 250 °C 1994 Materials Research Society
2745
Communications
morphology of thin sheets (Fig. 1), and this implies that the product is a pure and single phase. The XRD study indicates that the potassium phosphatoantimonate has a unique powder x-ray diffraction pattern, which can be indexed with the monoclinic system a = 23.952 A, b = 9.515 A, c = 8.193 A, and f3 = 124.78 (Fig. 2). This new compound was also characterized by 31 P MASNMR techniques. The 31 P MAS-NMR result shows that there is one situation of P atom in the compound (Fig. 3). According to Ref. 9, the chemical shift of —6.77 ppm implied that the compound has a layered structure. The preliminary study on ion-exchange of this compound shows the potassium ion is exchangeable. The studies on ion-conductive behaviors of this compound and ionexchange products are in progress.
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FIG. 3. 31P MAS-NMR spectrum of the potassium phosphatoantimonate.
for 8 days. After naturally cooling at room temperature, the product was filtered and washed with de-ionized water, and dried at ambient temp
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