Sensing properties of rare earth oxide doped In2O3 by a sol–gel method

The powders of pure In2O3 and Eu3+, Gd3+, Ho3+-doped In2O3 with the structure of bixbyite-type were synthesized by a sol–gel method in the citric acid system. The structure and crystal phase of the powders were characterized by using an X-ray diffractometer. The gas sensing characteristics were obtained by measuring the response magnitude as a function of various controlling factors like dopant, operating temperature, concentrations of the test gases and the response time. The results showed that pure In2O3 had poor selectivity, while the In2O3 sensors doped with 5 wt.% Eu2O3, 5 wt.% Gd2O3, and 5 wt.% Ho2O3 increased the gas-sensing performance towards H2S as a reducing gas, but decreased gas towards Cl2 as an oxidizing gas at 195 °C. Namely, doping of the rare earth oxides remarkably improved the selectivity for H2S. In addition, it was found that among the dopants, 5 wt.% Ho2O3 gave the highest the response value, selectivity, stability and the most excellent response and recovery characteristics to H2S at 195 °C. Thus, the Ho2O3-doped In2O3 is a promising candidate for detection of H2S in environments.