Bronzoid phases in the pseudo-binary system AxNb xW 1− xO 3 with A = K and Cs

Abstract

The systems A x Nb x W 1− x O 3, A = K, Cs, have been studied at 1200°C for compositions x < 0.5. Phases with intergrowth tungsten bronze (ITB) structure form for x ∼ 0.08 – 0.12 and with hexagonal tungsten bronze (HTB) structure for x ∼ 0.20 (with a small homogeneity range). The potassium system contains a tetragonal tungsten bronze (TTB)-type phase at x ∼ 0.45 – 0.60 and cesium forms a pyrochlore phase at x∼0.35 – 0.40. The alkali contents of the HTB and pyrochlore phases are considerably lower than those of phases prepared at 900°C. The tunnel occupancy is approximately the same, ∼ 60 %, in the ITB, HTB and pyrochlore phases prepared at 1200°C. Two types of superstructures have been observed in the HTB-type crystals.