Stannous tungstate, ${\mathrm{SnWO}}_4,$ crystallizes in the low-temperature α and high-temperature β phases. $\alpha -{\mathrm{SnWO}}_4$ powders were prepared by heating an equimolar mixture of SnO and ${\mathrm{WO}}_3$ either in vacuum or in argon atmosphere at 600 °C for 15 h. The high-temperature β phase was obtained as metastable at room temperature after heating the mixture at 800 °C and rapid quenching. In addition to x-ray-diffraction studies, ${}^{119}\mathrm{Sn}$ Mössbauer and Raman spectroscopies were used as “local” probes for the characterization of the phase structures in the semiconducting and gas-sensitive powders. The composition of the powders was measured by the energy-dispersive spectroscopy of x rays. Mössbauer spectroscopy, especially, as a very local probe for tin atoms gave valuable information of small extra phase(s) in the α- and $\beta -{\mathrm{SnWO}}_4$ powders originating in the oxidation of ${\mathrm{Sn}}^{2+}$ ions in the ${\mathrm{SnWO}}_4$ structures into the ${\mathrm{Sn}}^{4+}$ form. The ${\mathrm{Sn}}^{2+}$ Mössbauer doublet from both α and β phases showed some asymmetry not published before. The asymmetry was possible to relate to the Goldanskii-Karyagin effect with calculations based on published results for the atomic positions and thermal displacement parameters in the x-ray temperature factor of the α- and $\beta -{\mathrm{SnWO}}_4$ structures. Raman spectra are given together with peak frequencies from a curve fit for both α- and β-phase powders. The symmetries and selection rules of the normal modes at the center of the Brillouin zone are also given for both α and β phases.

• Received 20 January 1998

DOI:https://doi.org/10.1103/PhysRevB.57.13491