Study of Some Physicochemical Properties of Microwave-Sintered Al3+-Doped Ni-Zn Ferrites for Gas Sensor Applications

A series of Ni0.5Zn0.5AlxFe2–xO4 (0.0 ≤ x ≤ 0.25) nanoferrites have been prepared by sol-gel auto combustion and followed by sintering in a microwave oven at 1100 °C for 30 min. Pure cubic spinel phase was confirmed from the indexed planes in XRD patterns. The experimental lattice parameter (a) was found to be in the range of 8.3908–8.3509 Å in the decreasing order with the doping level of Al3+ ions. The sharp diffraction peaks indicate the crystalline nature of the samples. The microwave sintering is promoting the crystallinity with the substitution of Al3+ ions (42.8–54.4 nm). The saturation magnetization (Ms) gradually decreased with the substitution of Al3+ ions, and highest value of 61.2 emu/g was reported. The dilution of A–B superexchange interaction can be expected from the variation of bond angles. The coercivity is predominantly dependent on the magnetocrystalline anisotropy. Normal dielectric dispersion was observed in the present series of ferrite samples, and the dielectric constant is found to be composition dependent. The low value of dielectric constant was observed for the compositions x = 0.15 and x = 0.25. The present ferrite systems are showing good sensor response to NH3 and least response to H2. In the tested ferrite systems, the composition x = 0.25 is an appropriate selective for sensor fabrication to test NH3 gas.