Effect of La3+ and Ba2+ Substitution on Structural and Electrical Properties of Charge Ordered Divalent-Doped Sm0.5Ca0.5MnO3 Manganite

Abstract

The fascinating characteristics of mixed valence perovskite manganite, such as its colossal magnetoresistance and charge ordering, have drawn a lot of attention. Despite the continuous study, it is still difficult to modify the charge ordering and its structure by A-site substitution. Thus, this study addresses the problem of understanding the effect of A-site substitution with different cations on structural and electrical properties of manganite. Through this study, the solid-state reaction approach was used to synthesize the charge ordered Sm_0.5Ca_0.5MnO₃, Sm_0.2La_0.3Ca_0.5MnO₃ and Sm_0.5Ca_0.2Ba_0.3MnO₃ manganite. The structural and electrical properties of these materials were investigated. The single-phase, well-crystallized samples were all in an orthorhombic structure with a Pnma space group, according to the X-ray diffraction patterns. La³⁺ and Ba²⁺ substituted samples through Rietveld refinement show higher values of unit cell volume, indicating that the substitution at manganite's A-site was successful. According to Fourier transform infrared spectroscopy, the metal-oxygen and Mn-O bonds are visible at the 550 cm⁻¹ and 650 cm⁻¹ bands, respectively. While the four-point probe method was used to examine the impact of La³⁺ and Ba²⁺ electrical resistivity. Sm_0.5Ca_0.5MnO₃ and Sm_0.5Ca_0.2Ba_0.3MnO₃ manganite exhibit insulating properties in a temperature range of 30 K to 300 K, according to electrical resistivity measurements, while Sm_0.2La_0.3Ca_0.5MnO₃ exhibits a metal-insulator transition. The magnetoresistance effect is demonstrated by the fact that all samples' resistivity was reduced by adding an external magnetic field of 0.8 T. The suppression of charge-ordered phase in Sm_0.2La_0.3Ca_0.5MnO₃, which is linked to increase in tolerance factor shows significant role and improved the double exchange mechanism. In Sm_0.5Ca_0.2Ba_0.3MnO₃, on the other hand, the weakening of charge-ordered phase is related to the A-site mismatch cation, which has bigger impact than high value of bandwidth and tolerance factor.