Phase Formation, Polymorphism, Optical Properties, and Conductivity of Nd2WO6-Based Compounds and Solid Solutions

The phase formation of neodymium tungstate Nd2WO6 from mechanically activated oxides was studied in a wide temperature range: 25–1600°C. Conditions for the formation of various polymorphic modifications were determined: low-temperature orthorhombic β-Nd2WO6 and δ-Nd2WO6 (P212121 (no. 19)); high-temperature monoclinic Nd2WO6 (C12/c1 (no. 15)). Optical absorption spectra were studied for polymorphic ceramics with a nominal composition of Nd2WO6. Differences in the spectra of δ-Nd2WO6 and monoclinic Nd2WO6 were detected. Both modifications (δ-Nd2WO6 and monoclinic Nd2WO6) showed proton conductivity with activation energies of 1.05 and 1.06 eV, respectively. For the Ca-containing solid solution with a monoclinic structure (Nd $$_{{1 - x}}$$ Cax)2WO $$_{{6-\delta }}$$ (x = 0.01), whose overall conductivity increases compared to that of pure monoclinic Nd2WO6, hole conductivity predominates in air.