The effect of a cation radii on structural, magnetic and electrical properties of doped manganites La0.6-xPrxSr0.4MnO3

摘要

Structural, magnetic and transport properties of La0.6-xPrxSr0.4MnO3 with x = 0.0, 0.03, 0.06, 0.18, 0.3, 0.42, 0.54 and 0.6 are studied. The system exhibits a rhombohedrally distorted (R3c) perovskite structure for xless than or equal to0.3. A rhombohedral-orthorhombic (Pnma) structure transition is detected in the doping range from x = 0.42 to 0.6. The structure refinement by Rietveld analysis of the X-ray powder diffraction data shows that the average distance Mn-O increases in the rhombohedral phases and decreases in the orthorhombic phases. Results show that the Curie temperature decreases from 374 to 3 10 K when < r(A) > varies from 1.254 to 1.231 Angstrom. Electrical measurements show that all samples exhibit a metallic to semiconducting transition with increasing temperature. Meanwhile, the size of the resistivity p increases near T-C. This phenomenon is interpreted as a gradual bending of the Mn-O-Mn bond angle, with decreasing < r(A) >, which causes the narrowing of the electronic bandwidth and the effect of the A-site variance sigma(2). (C) 2004 Elsevier Inc. All rights reserved.