Formation of metallic indium-tin phase from indium-tin-oxide nanoparticles under reducing conditions and its influence on the electrical properties

The correlation between defect structure, metal segregation, and electrical resistivity of indium-tin-oxide nanopowder upon treatment in reducing atmosphere was investigated. Morphology and defect structure have been investigated by in situ synchrotron x-ray diffraction and transmission electron microscopy, while traces of metallic indium have been detected by susceptibility measurements utilizing the superconducting properties of indium. With increasing treatment temperature under reforming gas the film resistivity decreases down to rho=1.6x10(-2) Omega cm at 330 degrees C annealing temperature. For even higher treatment temperatures, the resistivity increases further. This is accompanied by extractions of metallic indium. Under forming gas, grain growth could be observed at 350 degrees C, while in air grain growth starts at 650 degrees C. Furthermore forming gas causes a lattice expansion of ITO which persists in oxygen, at least for several hours. The results are discussed with respect to results published in the literature. (C) 2008 American Institute of Physics.