Investigation on phase formation of Sr₂SnO₄ and effect of La-doping on its structural and optical properties

The reaction mechanism for the formation of Sr₂SnO₄ by solid-state reaction between SrCO₃ and SnO₂ has been investigated using thermal analysis (TG and DSC) combined with X-ray diffraction (XRD) techniques. It is observed that the formation of single-phase Sr₂SnO₄ takes place by reaction between SrO and SrSnO₃ at temperatures ≥ 900 °C. Based on these studies, a few compositions of the system Sr_2−xLa_xSnO₄ (x = 0.01, 0.02, 0.04, 0.06 and 0.10) have been synthesized by calcination at 1000 °C for 8 h. Rietveld refinement of the XRD data confirmed that all the synthesized samples have tetragonal structure, space group (I4/mmm) and symmetry group D_4h¹⁷. The crystallite size and induced lattice strain has been calculated using size strain plot (SSP), varies from 30 to 50 nm and from (3.00 to 6.27) × 10⁻³, respectively. Raman and Fourier transformed infrared (FTIR) spectroscopy techniques have been utilized to ponder local changes in the structure of Sr₂SnO₄ with La incorporation. The optical properties of the samples have been studied using UV–Vis spectroscopy. The systematic shift in the position of the absorption edge (toward the higher wavelength) indicates the incorporation of La in the lattice of Sr₂SnO₄. The direct and indirect band gap of the samples calculated through Tauc's plot. The variation in the value of direct band gap is attributed to changes in the charge compensation mechanism or/reduction in particle size.