Investigation of Structural and Electrical properties of La_(0.7)(Ba_(1-x)Ca_x)_(0.3)MnO_3 compounds by sol-gel method

摘要

In this paper, we explored structural and electrical properties of La_(0.7)(Ba_(1-x)Ca_x)_(0.3)MnO_3 (x = 0; 0.03; and 0.05) compounds. The general structure of perovskite manganites is AMnO_3 (A= trivalent rare earth with divalent ion-doped). Average A-site cation size, external pressure, and the variance of the cation size σ~2 are one of many factors that affected to magneto-transport properties of manganites as reported by others. In this work we focus only on the electrical properties in La_(0.7)Ba_(0.3)MnO_3 Ca-doped compound which may influence crystal structure resulting resistivity phenomena under magnetic field influence. All samples were synthesized by sol-gel method from which fine powders were obtained. The X-ray powder diffraction pattern of powder materials shows that all samples are fully crystalline with a rhombohedral structure. Rietveld refinement shows that the presence of calcium has changed some crystal structural parameters such lattice parameter, Mn-O bond length, and Mn-O-Mn angles. The electrical resistivity of all synthesized materials investigated by four point probe method using Cryogenic Magnet in the temperature range of 50-300 K under influence a magnetic field shows resistivity temperature dependent. In fact presence of calcium has reduced the resistivity. It might occure because it has made an enhancement in the mobility of hopping electrons. The magnetic external field causes the resistivity decreased for all samples because host spin align by delocalizing the charge carries so electron itinerant through the lattice suggested by other authors. Both calcium dopant concentration and the applied external magnetic field shows strong correlation in reduction of resistivity.