The effect of partial substitution of Pd in LaMnO3 polycrystalline materials synthesized by sol–gel technique on the electrical performance

This work reports the change in the structural and electrical behavior of partial substitution of manganese by palladium in LaMnO3 perovskite materials synthesized through sol–gel method. X-ray diffraction analysis reveals that all the obtained materials crystallize in the orthorhombic perovskite structure (Pnma space group). Morphological investigations show the presence of fine nanometric particles of similar shape and high tendency to agglomerate, and the elemental analysis highlights the presence of palladium. Detailed study of complex impedance measurements in the frequency range 20 Hz–2 MHz and different temperatures between (30 and 120) °C indicate the presence of electrical relaxation in materials; the activation energy of relaxation decreases from 0.207 eV (0.05% Pd–LMO–Pd1) to 0.102 eV (0.15% Pd–LMO–Pd3) when the x concentration of Pd increases from 0.05 to 0.15. The electrical conductivity analyses indicate that the conduction mechanisms in the low-frequency range (f < 100 kHz) are activated thermally and were explained using the Mott’s variable-range-hopping (VRH) model. In the high-frequency range (f > 100 kHz), the conduction mechanism is due to the charge carriers hopping between the nearest neighboring states, in agreement with the CBH model (correlated barrier hopping). Based on this model, the bandgap energy, Wm was determined. The results show that by increasing the Pd concentration, the value of Wm of the sample increases, from 0.229 eV (LMO–Pd1) to 0.298 eV (LMO–Pd3), in agreement with the decreasing of electrical conductivity of samples.