DTA/TG, IR, EPR and XPS studies of some praseodymium(III) tungstates

The praseodymium(III) tungstates (Pr2W2O9 and Pr2WO6) have been prepared as polycrystalline powders by thermal treatments of Pr6O11/WO3 mixtures in air. It was found the existence of only two polymorphic modification of Pr2W2O9. The low-temperature polymorph of Pr2W2O9 undergoes reversible polymorphic transition at 1390 K. Pr2W2O9 melts incongruently at 1462 K. Low-temperature modification of Pr2WO6 is thermally stable up to 1773 K. EPR spectra had shown weak only interactions between tungstate W5+ ions that were confirmed also by XPS measurements. Hyperfine structure of W4+ ions was also recognized. The spectra characteristics for Pr4+ ions were not observed both in EPR and XPS experiments.