Studies of phases structurally related to hexagonal tungsten bronze in the system ATO₃ - WO₃ (A = K, Rb, Cs; T = V, Nb, Ta)

Detta är en avhandling från Stockholm : Stockholm University

Sammanfattning: The oxidized analogues (bronzoids) of tungsten bronzes in the systems dTO^-WO^ with A = K, Rb, Cs; T = Ti, V, Nb, Ta and A/W < 1 are reviewed with emphasis on the K-Nb and Cs-Nb systems. The different phases observed in these systems are isostructural with intergrowth tungsten bronze (ITB), hexagonal tungsten bronze (HTB), tetragonal tungsten bronze (TTB) and pyrochlore. Their composition and temperature ranges of formation are described and discussed. Two different superstructures of HTB have been observed and may be associated with ordering of alkali atoms. The occasional occurrence of ITB-type phases with long-period superstructures may be explained by a screw dislocation mechanism. Defects of several kinds in a WO^-type matrix, some related to HTB, have been observed in HREM images, and these have been interpreted.

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