Morphological change of SnO2 crystals formed through the thermal evaporation of a mixture of Sn and graphite powders in air

SnO2 crystals with different morphologies were fabricated via simple thermal evaporation of a mixture of Sn and graphite powders at 1000 °C in air at atmospheric pressure without any catalysts. When a mixture with a high weight ratio of graphite to Sn was used as source material, SnO2 crystals with belt morphology were formed. The crystals had widths in the range of 2-5 μm, and lengths up to several hundred micrometers. As the weight ratio of graphite to Sn in source material decreased, SnO2 nanoparticles with spherical morphology were synthesized. The nanoparticles had typical diameters of 100-300 nm. With further decreasing the weight ratio of graphite to Sn, the morphology of the SnO2 crystals changed from particle to wire and rod. The diameters of the wire- and the rod-shaped crystals were in the range of 50-150 nm and 0.5-1.0 µm, respectively. The morphology of the SnO2 crystals could be easily changed by adjusting the ratio of Sn and graphite in source material. This reveals that the ratio of graphite and Sn in source material is a critical factor to influence the morphology of SnO2 crystals.