INFLUENCE OF Ti~(4+) ON THE ENERGETICS AND MICRO STRUCTURE OF SnO_2 NANOPARTICLES

摘要

Nanocrystalline Sn_(1-x)Ti_xO_2 rutile-structured solid solutions have shown promise as gas sensors and photocatalysts. A fuller understanding of their microstructure and thermodynamics is necessary to improve the performance of the device. In this work, Sn_(1-x)Ti_xO_2 (0.00≤ x ≤0.50) rutile-structured nanoparticles were synthesized by Pechini method at 500°C for 15 h. Upon increasing the Ti~(4+) content, both crystallite size determined by XRD and particle size determined by N_2 adsorption decrease. Surface energies and solid-solid interface energies were calculated by combining water adsorption calorimetry and high temperature oxide melt solution calorimetry. Both surface energy and solid-solid interface energy decreases with the addition of Ti~(4+). It is proposed that the stabilization of the particle and the crystallite size are a consequence of the decrease in the surface and interface energies caused by the Ti~(4+) surface segregation, which is supported by EELS. Given that the surface energy of pure TiO_2 rutile reported in the literature is higher than the surface energy of pure SnO_2, one may expect that the segregation of Ti~(4+) in the surface would increase the surface energy contradicting the results. However, it is suggested that the surface of the nanocrystalline Sn_(1-x)Ti_xO_2 has a similar structure to TiO_2 anatase, which has a lower surface energy compared to both SnO_2 and TiO_2 rutile.