Effect of Pr3+ Substitution at the A-Site on the Structural and Electrical Properties of Hole-Doped La-Based Manganites

Abstract

In this study, the effect of praseodymium substitution at La-site on structural and electrical transport properties of La_0.5Ba_0.5MnO₃ was investigated. Polycrystalline La_0.5-xPr_0.5x Ba_0.5MnO₃ (x = 0, 0.50, 1.00) were synthesized using a conventional solid-state method. The powder X-ray diffraction patterns show a single-phase orthorhombic distorted perovskite structure with space group Pnma. The Rietveld refinement analysis showed that the unit cell volume decreased as Pr³⁺ substitution increased which may be attributed to the different ionic radii of ions. Electrical resistivity measurements by using standard four-point probe resistivity measurement in a temperature range of 30 K to 300 K. As the Pr³⁺ concentration increases, metal-insulator transition, TMI decreases from 264K (x=0) to 157K (x=1.00) while resistivity increases from 1.16 Ω.cm (x = 0) to 20.3 Ω.cm (x =1.00).The decreased TMI are attributed to the decrease in tolerance factor which indicates enhancement in MnO₆ octahedral distortion consequently reduce double exchange interaction. The electrical resistivity in the metallic region for all samples was fitted with the combination of domain/grain boundary, electron-electron, electron-magnon and electron-phonon scattering processes. The resistivity behaviour in the insulating region for all samples was attributed to small polaron hopping model which revealed that the activation energies increased as Pr³⁺ content increased due to the enhancement in the distortion of MnO₆ octahedral.