Synthesis, characterization and thermal behaviour of new copper and rare-earth metal tungstates

Abstract

Three series of new copper and rare-earth metal tungstates with the formulas: CuRE2W2O10 (RE = Nd, Sm, Eu) and Cu3RE2W4O18 (RE = Sm, Eu or RE = Dy, Ho, Er) were synthesized by the solid-state reaction method. The CuRE2W2O10 and Cu3RE2W4O18 (RE = Dy, Ho, Er) compounds crystallize in the monoclinic system. The Cu3RE2W4O18 phases with the large rare-earth ions crystallize in the triclinic system. All obtained compounds melt incongruently below 1273 K. The anion lattice of the Cu3RE2W4O18 phases is built from isolated groups of octahedra (W4O16)8−, while CuRE2W2O10 from WO6 octahedra forming structural elements [(W2O9)6−]∞. The EPR spectra of analyzed compounds consisted of an intense line originating generally from the rare-earth ions and a weak, narrow line from Cu2+ separate centers appearing only on the surface of the grains. The absence of bulk copper in the EPR spectrum is probably due to a very short relaxation time of the Cu2+ subsystem.