Crystal structure and electrical properties of new tungsten bronzes: BxWO3 (0.01 ≤ x ≤ 0.08)

Boron tungsten bronzes BxWO3 (0.01 ≤ x ≤ 0.08) were synthesized by hybrid microwave method from mixtures of WO3 and amorphous boron powder. With the increase of boron content, the crystal structure of BxWO3 transforms from orthorhombic (x = 0.01) to tetragonal α (x = 0.048) and then to tetragonal β (0.07 ≤ x ≤ 0.08). The average size of crystallites is in the range of 1–10 μm. All samples show semiconducting behaviour in their temperature dependence of resistivity. The conduction behaviour above 80 K for samples with x = 0.01 and 0.08 can be explained using the variable-range hopping and thermally activated mechanism, respectively. Comparative experiments showed that boron bronze phases cannot be obtained by the microwave heating of pure WO3 powder or a mixture of B2O3 and WO3 under the same conditions.