Heterostructure Fe₂O₃–In₂O₃ Nanoparticles as Hydrogen Gas Sensor

Fe₂O₃–In₂O₃ (9:1 mol.%) heterostructure nanoparticles were prepared by the thermal decomposition of stoichiometric amounts of Fe₂C₂O₄ 2H₂O and In(OH)₃ at 400°C for 20 h. The sample was characterized by x-ray diffraction (XRD), Fourier-transform infrared spectrometry, thermogravimetry–differential thermal analyzer, scanning electron microscopy/transmission electron microscopy, and a superconducting quantum interference device magnetometer. The XRD pattern could be indexed to both the rhombohedral α–Fe₂O₃ and cubic bixbyite In₂O₃ phases. This heterostructure system showed ferromagnetic properties (due to the presence of γ–Fe₂O₃ phase) from 5 to 300 K and a spin-glass-like behavior of magnetization versus temperature under zero-field-cooled and field-cooled conditions. H₂ gas-sensing property was observed from 100 ppm to 2 ppm at 200 °C and 250 °C. Response and recovery times were about 275 s and 500 s, respectively, and the sensitivity varied from 2% to 21% as the H₂ increased from 2 to 100 ppm. The R_a/R_g varied from 1 to 1.3 and the plot of R_a/R_g versus H₂ could be fitted to the sigmoidal logistic function, y = A₂ + (A₁ − A₂) / (1 + (x/x₀)^p.