Microstructural investigations of tin-molybdenum oxides by high-resolution electron microscopy

Tin-molybdenum oxides, formed by the calcination of precipitates in air, have been examined by high-resolution electron microscopy. Low-temperature calcination gives rise to the formation of small tin(IV) oxide-type crystals amidst an amorphous material whereas higher-temperature treatment results in the development of a highly crystalline rutile-related phase composed of larger particles. High concentrations of molybdenum in the initial precipitates inhibits the thermally induced crystal growth. The common occurrence of superficial disorder in the larger particles is associated with surface damage resulting from the volatilization of excess molybdenum as molybdenum(VI) oxide. Planar faults were frequently observed within the particles and, in some cases, these defects were identified as twin boundaries enriched with molybdenum. The formation of these planar faults is discussed in terms of the preparative procedure.