Impact of A-site rare earth substitution on structural, magnetic, optical and transport properties of double perovskites

Abstract In the current research work R2CoMnO6 (R = La, Sm, Gd and Dy) double perovskites (DPOs) have been synthesized using auto combustion sol-gel method. Structural characterizations were carried out by X-ray diffraction technique and the analysis confirms the correct crystal structure by Rietveld refinement with a monoclinic symmetry (space group P21/n) in all DPOs. Crystallite size has been calculated by using Scherrer and Williamson-Hall (W-H) methods and found that the crystallite size with the decrease in ionic radius (RLn) decreases from 61.37–49.03 nm on average. The IR reflectivity spectrums fitted by the Lorentz oscillator model reveal that the given DPOs have a monoclinic structure and change of R-site also has ability to impact on the crystal structure. The optical band gap has been estimated in the range of 1.30–1.60 eV reflecting that the considered DPOs have potential to be used as light harvesting materials. The resistivity data of all DPOs depict semiconductor like behavior above room temperature and this behavior has been best described by small polaron hopping (SPH) conduction mechanism. Dielectric measurements exhibit usual dielectric dispersion, which is due to the Maxwell-Wagner-type interfacial polarization in all DPOs. AC conductivity measurement also suggests the conduction is due to SPH.