Methane sensors based on ZnGa2O4 ceramics with addition of Er for combustion monitoring systems

Ceramic pellets of pure ZnGa₂O₄ and ZnGa₂O₄ with Er-addition are synthesized and their structural and gas-sensitive properties are investigated. The addition of Er leads to the formation of a second Er₃Ga₅O₁₂ phase in the ZnGa₂O₄ matrix and a larger active surface which allows an 11.1-fold increase in the response of ZnGa₂O₄ to 10⁴ ppm of CH₄. At the maximum response temperature corresponding to 650 °C, the responses to 100 and 10⁴ ppm of CH₄ for ZnGa₂O₄ with Er addition were 2.91 a.u. and 20.74 a.u., respectively. ZnGa₂O₄ with Er addition is characterized by a wide dynamic range of CH₄ concentrations, from 100 ppm to 20000 ppm, weak dependence of gas-sensitive characteristics on humidity in the relative humidity range of 30–70 %, weak changes of gas-sensitive characteristics under cyclic gas exposure. The samples also demonstrate high responses to NO₂ and H₂, which at a gas concentration of 100 ppm and a temperature of 650 °C are 3.37 a.u. and 4.77 a.u., respectively. A plausible mechanism of the sensing effect of ZnGa₂O₄ with Er addition is proposed and prospects for the development of high-temperature CH₄ sensors based on the studied samples for combustion monitoring systems and determination of the ideal fuel/air mixture are discussed.