Of Cr <sub>. Nano 2 </ Sub> O <sub> 3 </ Sub>-based Gas Sensing Materials

The oxide semiconductor gas sensors with simple structure, low cost and high sensitivity have been widely applied. It is still necessary for the sensors to improve their stability and selectivity. It is urgent to develop new gas-sensing materials. Therefore, the development of Cr₂O₃ nano-material as a new candidate for the gas-sensing material is of great significance.In this paper, precipitation, hydrothermal synthesis and citrate methods were used to synthesize Cr₂O₃ nanopowders, and co-precipitation method was used to synthesize Cr_2-xM_xO₃(x=0.1-0.5)(M=Fe,Sn,Ni)nanopowders. The structures of materials have been characterized by XRD, SEM, BET and XPS techniques. Their thick film-type gas sensors were fabricated and their gas sensitivities were measured to acetone, 1-propanol, ethanol, methanol, benzene and toluene. The results show that Cr₂O₃ prepared by precipitation method with nano-powders has better gas sensitivities. The sensitivity of the powders sintered at 450 oC is better than that of the material sintered at 350 oC. The thick-film sensor has high gas sensitivities to 1-propanol, acetone, ethanol and methanol gases at the best heating voltage of 4 V. It could detect 1-propanol, acetone and ethanol as low as 10μL·L^-1 and exhibits good humidity-resistivity. After Fe, Sn and Ni elements were doped, the electrical conductivity and gas sensitivities of the materials were improved to some extent and the working temperature was also decreased a little. Among Cr_2-xM_xO₃(x=0.1-0.5) (M=Fe,Sn,Ni) materials, Cr_1.5Ni_0.5O₃ has the highest gas sensitivity to 1-propanol, and decrease in the order of acetone, ethanol and methanol. It could detect 5μL·L-1 of 1-propanol, acetone and ethanol. The response and recovery times of Cr_1.5Ni_0.5O₃ were significantly shortened than that of pure Cr₂O₃. The Cr_1.5Ni_0.5O₃ nanomaterial still shows better humidity-resistivity.Cr_1.5Ni_0.5O₃ thin film was prepared by the RF sputtering method and heated at 700oC for 5 h. The XPS analysis indicated that the composition and surface state of Cr_1.5Ni_0.5O₃ thin film are basically similar to those of the powder. Comparing with the Cr_1.5Ni_0.5O₃ thick film, the response and recovery capabilities of Cr_1.5Ni_0.5O₃ thin film was increased, but the gas sensitivity was a little decreased.