Promoted room temperature NH₃ gas sensitivity using interstitial Na dopant and structure distortion in Fe_0.2Ni_0.8WO₄

The demand for gas-sensing operations with lower electrical power and guaranteed sensitivity has increased over the decades due to worsening indoor air pollution. In this report, we develop room-temperature operational NH₃ gas-sensing materials, which are activated through electron doping and crystal structure distortion effect in Fe_0.2Ni_0.8WO₄. The base material, synthesized through solid-state synthesis, involves Fe cations substitutionally located at the Ni sites of the NiWO₄ crystal structure and shows no gas-sensing response at room temperature. However, doping Na into the interstitial sites of Fe_0.2Ni_0.8WO₄ activates gas adsorption on the surface via electron donation to the cations. Additionally, the hydrothermal method used to achieve a more than 70-fold increase in the surface area of structure-distorted Na-doped Fe_0.2Ni_0.8WO₄ powder significantly enhances gas sensitivity, resulting in a 4-times increase in NH₃ gas response (R_g/R_a). Photoluminescence and XPS results indicate negligible oxygen vacancies, demonstrating that cation contributions are crucial for gas-sensing activities in Na-doped Fe_0.2Ni_0.8WO₄. This suggests the potential for modulating gas sensitivity through carrier concentration and crystal structure distortion. These findings can be applied to the development of room-temperature operational gas-sensing materials based on the cations.