Ni-Zn ferrite thick film gas sensors

Nanocrystalline ferrite samples with composition NixZn1-xFe2O4 (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) were prepared by oxalate co-precipitation method. Thick film of ferrites was prepared by screen printing techniques on glass substrates. The ferrite samples were characterized by X-ray diffraction (XRD), thermo gravimetric and differential thermal analysis (TG-DTA), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy and field emission scanning electron microscopy techniques. The TG-DTA and XRD confirms the formation of ferrite phase and cubic spinel structure. FT-IR spectra show two major absorption bands near 400 and 600 cm(-1) corresponding to tetrahedral and octahedral sites respectively. The structural parameters like lattice constant, crystallite size, ionic radii, ionic bond lengths and force constants of ferrite powders were calculated. The grain size of the ferrite thick films was lies in the range 30-65 nm. Gas sensing properties of ZnFe2O4, NiFe2O4 and Ni0.6Zn0.4Fe2O4 thick films was studied for liquid petroleum gas (LPG), ethanol (C2H5OH) and chlorine (Cl-2). Zinc ferrite thick film shows high sensitivity (82 %), good response (30 s) and recovery time (90 s) for ethanol as compared to LPG and Cl-2. Nickel ferrite thick film shows good sensitivity (63 %), better response (30 s) and recovery time (70 s) for LPG. Ni0.6Zn0.4Fe2O4 is more sensitive for Cl-2 followed by ethanol as compare to LPG. Among nickel, zinc and Ni0.6Zn0.4Fe2O4 thick films, zinc ferrite thick film is more sensitive for LPG, C2H5OH and Cl-2.