Investigations of the tin-antimony-oxygen system by high-resolution electron microscopy

A range of tin-antimony oxides, prepared by the calcination of precipitates, were examined by high-resolution electron microscopy. Products formed at 600°C contain small crystals of a rutile-type material and, depending on antimony concentration, varying amounts of disordered and/or amorphous phases. The observations are consistent with a resistivity to bulk phase equilibrium under conditions of low temperature and high antimony concentrations. Heating of the tin-antimony oxides to 1000°C for prolonged periods is accompanied by an increase in the crystallinity and particle size of the rutile-type material as a result of the thermally induced aggregation of tin(IV) oxide units. The observations are consistent with limited antimony incorporation in the bulk tin(IV) oxide lattice and a migration of antimony to surface sites. There was no evidence for any discrete, readily identifiable, antimony oxide phases, although a nonrutile-type material was observed at higher antimony concentration. The rutile-type phases often contained planar faults which were identified in some instances as twin boundaries; the possibility that these might provide a means of accommodating antimony within the tin oxide lattice is briefly considered. The relationship between our observations and the information available from other techniques is discussed.