Sintering Temperature Dependent Optical and Vibrational Properties of Sm2NiMnO6 Nanoparticle

Double perovskite oxides (DPOs) are interesting materials due to their various important technological properties. Rare earth DPO Sm2NiMnO6 (SNMO) nanoparticle is prepared by sol gel method. Varying the sintering temperature from 650-950 °C, four types of materials are synthesized. Room temperature X-ray diffraction (XRD) patterns show that all the samples have the highest intensity peak at Bragg angle 2θ = 33.05° approximately. Rietveld refinement of the XRD pattern of the materials shows that all the materials are crystallized in P21/n space group. Despite the monoclinic symmetry with the same space group for the samples, there are variations in lattice parameters, crystal volume, bond lengths and bond angles with the change in sintering temperature. The band gap of the materials is obtained using Tauc relation to UV-visible spectra and found to vary from 1.2 to 1.41 eV. The photoluminescence (PL) emission spectra of the sample are measured at various excitation wavelengths. The PL spectra and the emission feature depend on the wavelength of the excitation. Fourier transform infrared (FTIR) spectra of the materials carry the signature of the double perovskite structure. Strong absorption peak at 575 cm – 1 in the FTIR spectra is due to the combined effect of Ni-O and Mn-O stretching vibration. The Raman spectra of the samples taken at 488 nm wavelength are analyzed to obtain the vibrational modes of the samples. Lorentzian lines are used to fit the Raman spectra. Group theoretical study is performed to assign the different vibrational modes of the samples in accordance with the structural symmetry. Phonon modes appeared at 641 cm − 1 are due to stretching (breathing) vibration and at 500 cm − 1 are due to the combination of anti-stretching and bending motion of the (Ni/Mn)O6 octahedra. Variation of the frequency and width of the Raman spectra is correlated with the structural changes of the samples.