Fabrication of NH3 gas sensors using lithium-substituted ZnFe2O4 nano-ferrite

In this study, metal nitrates were used as precursors and citric acid as a chelating and combustion agent to synthesize lithium-substituted zinc ferrite Li_xZn_1−xFe₂O₄ (0.00 ≤ x ≤ 0.12) for gas sensing applications that aim to detect small traces of NH₃ molecules. The effects of Li-doping on the structural and morphological properties of Li_xZn_1−xFe₂O₄ nano-ferrite were investigated using X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). XRD findings indicated that the synthesized samples formed a pure phase with crystallite sizes ranging from ∼17–28 nm. The preparation process produced spherical particles with high porosity, as confirmed by FESEM images. The grain size of the samples was calculated using the Image J software. The gas response of ZnFe₂O₄ nano-ferrite with different Li doping at different operating temperatures and a constant NH₃ gas concentration was studied. Sensing measurements revealed that Li doping increases the ZnFe₂O₄-based sensor’s response to NH₃ gas. At 200°C, the 0.12 Li–ZnFe₂O₄ nano-ferrite showed the highest sensitivity. Li_xZn_1−xFe₂O₄ is a promising candidate to fabricate an ammonia sensor with high performance.