Crystal structure and electrical properties of Ca xWO 3 (0.01 ≤ x ≤ 0.15) prepared by hybrid microwave synthesis

Abstract

Calcium tungsten bronzes Ca x WO 3 (0.01 ≤ x ≤ 0.15) were synthesized by hybrid microwave method from mixtures of CaO, WO 3 and tungsten powder. Single-phased samples can be obtained by microwave heating within 40 min. With the increase of calcium content, the crystal structure of Ca x WO 3 transforms from orthorhombic (0.01 ≤ x ≤ 0.02) to tetragonal (0.03 ≤ x ≤ 0.11) and then to cubic (0.12 ≤ x ≤ 0.15). The average size of crystallites is in the range 1–5 μm. All samples show semiconductor behaviour in their temperature dependence of resistivity. The electrical conduction mechanism changes from variable-range hopping to the thermally activated mechanism when x > 0.12.