American Chemical Society
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Pressure-Induced Crystallization and Characterization of the Tin Borate β-SnB4O7

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posted on 2007-01-23, 00:00 authored by Johanna S. Knyrim, Falko M. Schappacher, Rainer Pöttgen, Jörn Schmedt auf der Günne, Dirk Johrendt, Hubert Huppertz
In the last years, several investigations were performed in the ternary system Sn−B−O as a simplified variant of the tin-based amorphous composite oxide (TCO), a material in use as negative electrode of lithium-ion rechargeable batteries. All compounds in this system are glasses, so the synthesis of crystalline approximands for a more detailed structural investigation would be favorable. The use of high-pressure/high-temperature conditions (7.5 GPa and 1100 °C; Walker-type multianvil apparatus) led to the synthesis of the first crystalline tin borate β-SnB4O7. The single-crystal structure determination of β-SnB4O7 showed Pmn21, a = 1086.4(2) pm, b = 444.80(9) pm, c = 423.96(8) pm, Z = 2, R1 = 0.0155, and wR2 = 0.0324 (all data). In contrast to the isotypic phases MB4O7 (M = Sr, Pb, Eu, β-Ca, and β-Hg), the position of the tin atom in β-SnB4O7 is influenced by the existence of a stereochemically active lone pair. Furthermore, we report on thermoanalytical aspects (DTA-TG and temperature-resolved in situ powder diffraction), DFT calculations, IR spectroscopy, Mössbauer spectroscopic results, and solid-state NMR investigations on β-SnB4O7. The latter method allows us to make a general differentiation of Sn2+ and Sn4+ in Sn−O systems on the basis of well-separated 117/119Sn chemical shifts.