Controlling the Ratio of Rhombohedral to Cubic Phases of In2O3 by Cobalt Doping and Its Effect on Sensor Response to Hydrogen.

The effect of cobalt doping in the concentration range 0.01 to 0.25 at.% on the structural and sensory properties of nanocomposites based on two-phase indium oxide synthesized by the hydrothermal method is investigated. The phase ratio is shown to change depending on the concentration of added cobalt. Co concentration of up to 0.1 at.% promotes rhombohedral-to-cubic phase transition, while concentrations exceeding 0.1 at.% stabilize the metastable phase of indium oxide. Doping leads to a reduction in particle size and an increase in the specific surface area and porosity of the composites. The sample with cobalt concentration of 0.025 at.% exhibits the maximum sensor response, which is attributed to phase transformation induced by vacancy formation. Increasing the Co concentration produces a sharp decrease in the sensor signal and a reduction in the optimal operating temperature.