Phase Relations and Crystal Structures of Zn and Cd Tungstates

The systems ZnO-WO3 and CdO-WO3 show similar phase relations, each having a 1:1 phase. Invariant points established are 1182°C and 56 mol% ZnO, 1090° and 34 mol% ZnO, and 1105° and 31.5 mol% CdO. The crystal structure of CdWO4, determined by the single-crystal method, was isostructural with ZnWO4, a wolframite type. Cell dimensions are a=0.5013, b= 0.5090, and c= 0.5866 nm and γ= 91.46° with a space group P2/b and Z = 2. The measured and calculated densities are 7.83 and 7.79 g/cm3, respectively. ZnWO4 and CdWO4 formed a complete series of solid solutions at 900° to 1160°C, above which melting occurred.