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

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.