Hydrothermal Synthesis of Rutile-Type Complete Solid Solution Nanoparticles in the TiO2-SnO2 System under Acidic Conditions

Rutile-type complete solid solutions between TiO2 and SnO2 were directly formed as nanoparticles via the forced co-hydrolysis of precursor solutions of TiCl4 and SnCl4 under acidic hydrothermal conditions at 240 degrees C. The change in the lattice parameters a(0) and c(0) of rutile (Ti, Sn) O-2 solid solutions followed the Vegard's Law. The crystallite size of rutile-type TiO2 was varied from 118 to 22.5 nm by the formation of rutile-type solid solutions with 10 mol% SnO2. The crystallite size of the rutile-type solid solutions containing more than 20 mol% SnO2 was maintained in the range of 10-14 nm by the control of crystallite growth owing to the presence of SnO2. The specific surface area of the rutile-type solid solutions corresponded well to the change in the crystallite size. The optical band gap was gradually decreased with decreased SnO2 content in the rutile-type solid solutions. The beginning of the phase separation was observed in the sample Ti0.5Sn0.5O2 by heating at 1200 degrees C above 1 h in air, since the rutile-type solid solutions were metastable in the large area of miscibility gap below T-c = 1430 degrees C in the TiO2-SnO2 system.