An X-ray structural analysis of cesium substitution in the barium hollandite phase of synroc

Abstract

The X-ray structures of polycrystalline barium hollandite with cesium partially substituting for barium (viz [ Ba x Cs y ] [ Al 2 x+ y Ti 8 − 2 x − y ] O 16) have been determined using the Rietveld refinement technique. Electron microprobe results indicate that the level of cesium substitution is constrained by the condition that the total volume occupied per unit cell by the cesium and barium ions remains substantially constant. X-ray refinement revealed that the structural parameters defining the positions of the titanium, aluminium and oxygen ions are not affected greatly by cesium substitution. The only significant change occurs in the parameter z which defines the average Cs/Ba position. This increases with the level of cesium indicating that these ions tend to occupy a more central location with respect to their coordinating oxygen ions. An analysis of the (Cs/Ba)-O bond lengths suggests a limit of structural stability corresponding to 0.25 cesium ions per unit cell.