Phase composition, conductivity, and sensor properties of cerium-doped indium oxide

Abstract

The hydrothermal synthesis of In2O3 and CeO2–In2O3 is investigated as well as the properties of sensor layers based on these compounds. During the synthesis of In2O3, intermediate products In(OH)3 and InOOH are formed, which are the precursors of stable cubic (c-In2O3) and metastable rhombohedral (rh-In2O3) phases, respectively. A transition from c-In2O3 to rh-In2O3 is observed with the addition of CeO2. The introduction of cerium into rh-In2O3 results in a decrease in the sensor response to hydrogen, while it increases in composites based on c-In2O3. The data on the sensor activity of the composites correlate with XPS results in which CeO2 causes a decrease in the concentrations of chemisorbed oxygen and oxygen vacancies in rh-In2O3. The reverse situation is observed in composites based on c-In2O3. Compared to In2O3 and CeO2–In2O3 obtained by other methods, the synthesized composites demonstrate maximum response to H2 at low temperatures by 70–100 ​°C, and have short response time (0.2–0.5 ​s), short recovery time (6–7 ​s), and long-term stability. A model is proposed for the dependence of sensitivity on the direction of electron transfer between In2O3 and CeO2.