Carnotite analogues: synthesis, structure and properties of the Na1–xKxUO2VO4 solid solution (0 ⩽x⩽1)

Abstract

Crystal structures of synthetic K₂(UO₂)₂V₂O₈(carnotite) and Na₂(UO₂)₂V₂O₈ have been refined using single-crystal X-ray diffraction. The alkali-metal ions were shown to lie between [(UO₂)₂V₂O₈]_∞, layers. A continuous solid solution was obtained between these two compounds. Both compounds and the solid solution have high ionic conductivity. For example, K and Na compounds have conductivities at 500 °C of 9.2 × 10^–5 and 1.7 × 10^–4 S cm^–1, respectively, and activation energies of 0.57 and 0.52 eV.