Impact of strontium doping on the structural and NTCR properties of ZnO ceramics

The work illustrates a solid-state reaction technique to synthesize the strontium-doped zinc oxide ceramics (Zn_1-xSr_xO) at varying dopant concentrations (x = 0–0.03). The phase of the synthesized sample was investigated using X-ray diffraction (XRD) and its structural parameters were analyzed using Rietveld refinement. The elemental composition and morphology of the synthesized samples were evaluated using Energy-Dispersive X-ray Spectroscopy (EDX) and Field Emission Scanning electron microscopy (FESEM). The optical behavior was evaluated using UV–Vis diffuse reflectance spectra (UV–Vis DRS). The negative temperature coefficient of resistance (NTCR) behavior was examined through impedance spectroscopy. The synthesized samples showed a single-phase hexagonal wurtzite structure up to x = 0.03, which indicates that the Sr²⁺ ion is substituted in the ZnO lattice. Significant changes in the morphology were observed in the FESEM micrograph of Sr-doped ZnO ceramic samples. EDX analysis confirms the presence of Sr dopant in the ZnO lattice. The band gap (E_g) of ZnO was found to be decreased with Sr doping. The synthesized sample shows that resistance decreases as temperature rises, as obtained from impedance measurement, confirming the NTCR nature. A temperature-dependent electrical relaxation phenomenon at high temperature was observed. A parallel RC circuit has been observed for both ZnO and Sr-doped samples.