Molten salt synthesis of oxygen-deficient SnO2 crystals with enhanced electrical conductivity

Spiky polycrystalline SnO 2 balls assembled from pyramid-shaped SnO 2 nanocrystals with surface oxygen vacancies were synthesized by a simple and facile in-situ molten salt oxidation method using SnCl 2 as the tin source and graphite as the surface reductant. In this method, perfect SnO 2 nanocrystals are first formed on the surface of graphite particles at 500 °C. By increasing the processing temperature to 700 °C, the formation of surface oxygen vacancy defects was confirmed, supported by various characterisation methods including Raman and XPS spectroscopy. A sharp increase in the bulk electrical conductivity of the samples was detected by exceeding the onset temperature corresponding to the formation of oxygen deficient SnO 2 crystals, at which the conductivity of the sample significantly outperformed that of commercial SnO 2 nanoparticles. The formation of oxygen vacancies on SnO 2 crystals is thermodynamically studied, and suggested to occur by surface carbon reduction of the crystals at sufficiently high temperatures. The enhanced electrical conductivity of oxygen deficient SnO 2 crystals can lead to a wider application of tin oxides in advanced electrical applications.