An oxygen nonstoichiometry study of barium polytitanates with hollandite structure

A series of barium titanium oxides with various Ba/Ti ratios having a hollandite structure were obtained by firing chemical synthesized oxide precursors under reducing atmosphere conditions (H2/N2 gas mixture flow) at temperatures of 1100°C and above. An oxygen nonstoichiometry was determined by a thermogravimetric analysis through oxidizing in air. It was shown that barium titanium hollandites may adopt both oxygen excess and oxygen-deficient stoichiometries within the structure. As a limiting case the barium titanium hollandites with only tetravalent titanium ions were obtained. The influence of oxygen nonstoichiometry on the hollandite monoclinic–tetragonal phase transition and a barium superstructure ordering was investigated and discussed. Distortion scaling rules are considered to compare this work with earlier investigations on hollandites.