Growth of NiWO₄ crystals from a Na₂W₂O₇ flux

Abstract

Well-formed rod crystals of NiWO₄ were grown from a Na₂W₂O₇ flux by a slow cooling method. The solubility of NiWO₄ in Na₂W₂O₇ increased with increasing temperature. At 1100 °C, NiWO₄ was dissolved in Na₂W₂O₇ at a concentration of about 45 mol %. The eutectic temperature was 615± 5 °C. Flux growth was conducted by heating mixtures at 1100 °C for 10 h, followed by cooling to 500 °C at a rate of 5 °C h⁻¹. The brownish and transparent crystals up to 15 mm in length were grown from the mixtures of about 40 g. The most suitable solute content was 30 mol %. The grown crystals were bounded by the {100}, {010}, {110}, {102}, and {111} faces. In certain instances, the {111} faces disappeared. The EPMA data showed that sodium from the flux used was not contained within the grown crystals. The crystals of NiWO₄ had a d.c. electrical resistivity of about 1 × 10¹¹ Ω cm.