Effect of annealing temperature on optical, dielectric and NH3 gas sensing properties of ZnxFe3−xO4 (x = 0 and 0.5) nanoparticles synthesized by sol-gel auto-combustion method

Abstract

The effect of annealing temperature and Zn doping on structural, magnetic, optical, dielectric, and gas sensing properties of iron oxide nanoparticles have been investigated. For this purpose, ZnxFe3−xO4 (x = 0 and 0.5) nanoparticles have been synthesized using sol-gel auto-combustion method. The samples are annealed at 200, 400, and 500 °C temperatures for 6 h. With the increase in annealing temperature, for x = 0, the transition from Fe3O4 (magnetite, cubic) to α-Fe2O3 (hematite, rhombohedral) phase is confirmed from the XRD analysis. With Zn doping, independent of annealing temperatures, for ZnxFe3−xO4 nanoparticles, the cubic spinel structure is evidently observed. The lattice constant of iron oxide nanoparticles increases with Zn2+ doping. With increase in annealing temperature and with Zn doping in iron oxide nanoparticles, the particle size decreases from 63.89 nm to 29.25 nm. With the increase in annealing temperature and doping with Zn in iron oxide, the reduction in the band gap is observed. Dielectric properties of synthesized ZnxFe3−xO4 (x = 0 and 0.5) nanoparticles have been investigated as a function of frequency. At room temperature, the sensitivity (%) as a function of flow rate have been investigated and observed that ZnxFe3−xO4 (x = 0 and 0.5) nanoparticles annealed at 500 °C achieved the highest sensitivity towards NH3 gas. For Zn doped iron oxide nanoparticles, the enhanced sensitivity is attributed to smaller particle size and increased specific surface area as compared to that of host nanoparticles.