Synthesis and Study of the Effect of Ba²⁺ Cations Substitution with Sr²⁺ Cations on Structural and Optical Properties of Ba_2-xSr_xZnWO₆ Double Perovskite Oxides (x = 0.00, 0.25, 0.50, 0.75, 1.00)

The effect of Sr²⁺ substitution on the morphology, crystal structure, and optical properties of double perovskite oxide Ba_2-xSr_xZnWO₆ (x = 0.00, 0.25, 0.50, 0.75, 1.00) were investigated. Scanning electronic microscopy demonstrated that all samples have similar microstructure morphology but differ in the range of grain sizes. X-ray diffraction measurements indicated that these materials crystallize in a (Fm-3m) cubic crystal structure, and also confirmed the tolerance factor. Rietveld analysis revealed that the lattice parameter decreased from 8.11834 to 8.039361 Å when the substitution of Ba²⁺ with Sr²⁺ cations increased from zero to 100%. Fourier transform infrared (FTIR) and Raman spectroscopies displayed a symmetric stretching vibration of WO₆ octahedra at 825 cm^-1, and an anti-symmetric stretching mode of WO₆ was observed by FTIR at 620 cm^-1. A strong peak at 420 cm^-1 was also observed in the Raman spectra and is due to the W-O-W bending vibration modes. UV-Vis diffuse reflectance spectroscopy was carried out for the series, and the band gap energy decreased from 3.27 eV for Ba₂ZnWO₆ to 3.02 and 3.06 eV for Ba_1.75Sr_0.25ZnWO₆ and Ba_1.5Sr_0.5ZnWO₆, respectively. The excitation and emission photoluminescence properties were investigated at room temperature.