Sintering,Optical And Electrical Properties Of ITO Nanopowder

Tin-doped indium oxides (ITO) have two phases:cubic bixbyite structure ITO (c-ITO) and hexagonal corundum structure ITO (h-ITO), which has been widely used in optical and electrical devices due to its high transmittance and excellent electrical properties. In this study, the h-ITO nanopowders were prepared by solvothermal method, the c-ITO nanopowders were synthesized by coprecipitation method with CTAB and the ITO targets were obtained by normal pressure sintering method at oxygen atmosphere. The effect of crystal structures on sintering, optical and electrical properties of ITO nanopowder was discussed. Then, the influence of content of sintering aids (Nb2O5-Bi2O3, ZnO-Bi2O3) and sintering temperature on sintering behaviors, mircostructures and electrical properties was studied.The results indicate that the transmittance and optical band gap of c-ITO nanopowers is higher than that of h-ITO nanopowders, and the photoluminescence intensity of c-ITO is lower than that of h-ITO at room temperature with an excitation of 370nm.. The sintering properties of c-ITO are better than that of h-ITO, but the electrical resistivity of c-ITO targets is lower than that of h-ITO targets. When sintering temperature increased, the relative density of c-ITO gradually increased, but the relative density of h-ITO decreased firstly, and then increased. It can be explained by that the movement of atoms may be promoted as the phase transformation process of h-ITO to c-ITO, and then the dramatic coarsening appears during the h-ITO sintering process which may result in the anti-densification process. When the content of Nb2O5-Bi2O3 (2wt.% to 8wt.%) and sintering temperature (1350??1550?) increased, the relative density of c-ITO targets increased firstly, and then decreased, the electrical resistivity decreased firstly, then increased. When sintering temperature reached 1450?, the maximum relative density of c-ITO was 99.6%, and the lowest electrical resistivity was 1.7×10-4 ?·cm. As the sintering temperature and content of Nb2O5-Bi2O3 increased continuously, the growth of grains is easier for the existence of liquid phase (Bi3NbO7), and there are more large grains, and structures of bridged and staggered between grains, which deteriorates densification and electrical performance. When the content of ZnO-Bi2O3 was range from 2 wt.% to 8 wt.%, the relative density of c-ITO gradually increased, carrier concentration decreased, carrier mobility increased and electrical resistivity decreased. When sintering temperature was 1400? and content of ZnO-Bi2O3 was 8 wt%, the max relative density was 99.3% and the lowest electrical resistivity was 7.32×10-4 ?·cm, which because liquid phase (Bi38Zn058) and oxygen vacancies created in the process of ZnO doped ITO can promote the mass transfer. However, the sublimation of ZnO becomes more intensive at higher temperature due to the rapid growth of vapor pressure of ZnO. As results, numerous pores are created, the grain scattering aggravates, which leads to the deterioration of densification and electrical conductivity.