Role of Ca2+ doping on the enhancement of dielectric properties of Sr2-xCaxNiWO6 for energy storage device application

In this paper, Sr2-xCaxNiWO6 (x = 0.00, 0.02, 0.04, 0.06) were synthesized using a solid-state reaction method. The crystal structure, optical and dielectric properties of the compounds were examined using X-ray diffraction (XRD), scanning electron microscope (SEM) with energy dispersive (EDX) analysis, Ultraviolet-visible (UV-vis) diffuse reflectance spectroscopy and electrochemical impedance spectroscopy respectively. The Rietveld refinement of XRD confirmed that the compounds crystallized in a tetragonal structure with a space group I4/m. According to the SEM images, the grain sizes of the compounds decreased as the dopant increased. The UV-vis analysis revealed that the band gap energy of the compounds decreased from 3.17 eV to 3.13 eV as the amount of doping increased from x = 0.00 to x = 0.06. A dielectric characterization showed that the dielectric constant (ε') and dielectric loss (tan δ) for all compounds possessed a similar trend where it was higher in low-frequency area (~ 1 Hz) and dropped instantaneously with the enhancement of frequency up to 1 MHz until it reached constant values.