One-step solvothermal synthesis of cubic-shaped ITO nanoparticles precisely controlled in size and shape and their electrical resistivity

Highly crystalline cubic-shaped ITO nanoparticles with narrow size distribution were successfully prepared through a one-step process from a mixed ethylene glycol solution of indium and tin salts. The present paper is focused on the detailed study on their solvothermal synthesis, in particular, the effect of process variables on the size and shape. In the present system with using glycol as a solvent, it was observed that the direct formation of ITO nanoparticles occurred from the dissolution-recrystallisation of the amorphous-like indium hydroxides initially formed as precursors. The mean size of the ITO nanoparticles was controlled from 15.1 to 43.5 nm by changing the initial NaOH concentration. The high resolution transmission electron microscopic and the Fourier transform (FT) analyses showed that the as-prepared nanoparticles have single-crystalline structure and were bound by a {200} plane. In addition, judging from the FT image, Sn ions in the cubic crystal structure of In₂O₃ were substituted homogeneously to form stable oxygen defects. The effect of particle size and morphology on the resistivity of the resultant powder was found to be distinct. Namely, the lower resistivity of well-crystallized cubic-shaped nanoparticles with the larger size, compared with the finer particles with random shape, was due to the lower interparticle resistivity because of the face-to-face contact for the former, but point-to-point contact for the latter.