Effect of A-site Gd3+ substitution on structural, optical and electrical properties of La2-xGdxCrMnO6 double perovskites

Nanocrystalline new double perovskites La2-xGdxCrMnO6 (x = 0.5, 1.0, 1.5 and 2.0) have been prepared by employing auto-combustion sol-gel method. Herein, we investigate the influence of Gd3+ on structural, optical and transport properties of La2CrMnO6. The Rietveld refinement reveals that the said materials crystallize in orthorhombic structure with Pbnm space group symmetry. The vibrational phonon modes have been examined using the infrared reflectance technique and were fitted using the Lorentz oscillator model. The spectra contain various IR active phonon modes. The position and width of these modes were determined and correlated with ionic substitution at the A-site. The optical conductivity shows the semiconducting nature of the series. The Raman spectra with active modes were also studied in connection with substitution. The optical bandgap varies from (1.62-1.67 eV) which has been estimated from diffuse reflectance spectra and found to increase with substitution whereas the Urbach energy decreases with increasing Gd3+ content. A significant change has been observed in resistive response and the resistivity vary from (1.8 * 10(5)Omega - cm) to (3.5 * 10(3)Omega - cm). The crossover behaviour at -400K from variable range hopping to small polaron hopping has been observed.