Structural stability improvement, Williamson Hall analysis and band-gap tailoring through A-site Sr doping in rare earth based double perovskite La2NiMnO6

The structural, morphological and optical properties of single-phase polycrystalline La2-xSrxNiMnO6 (x = 0, 0.3 and 0.5), synthesized by solid state reaction were investigated. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM)/energy dispersive analysis of X-rays (EDAX), Raman spectroscopy and diffuse reflectance spectroscopy (DRS) to elucidate the role of A-site Sr-doping in double perovskite La2NiMnO6. Rietveld analysis of XRD patterns revealed that all the samples have monoclinic structure with space group P2(1)/n. Positive gradient in the Williamson Hall plots revealed the presence of tensile strain in all the samples. The morphological studies revealed that average grain size increases along with appreciable decrease in porosity with Sr doping. The Ni/Mn antisite disorder was introduced in the La2NiMnO6 by Sr-doping confirmed by an increase in the full width at half maximum (FWHM) and decrease in intensity of the Raman modes at around 540 and 665 cm(-1) which correspond to the antisymmetric stretching and symmetric stretching modes, respectively. DRS results reveal that the band gap in La2NiMnO6 can be tuned down by Sr-doping to a value of 1.37 eV (very close to 1.40 eV, considered as optimum value for better efficiency of a solar cell). Thus, Sr-doped La2NiMnO6 may be of prime importance for applications in solar cells.