X-ray diffraction, magnetic and electrical properties in the manganites (La1-xNdx)0.7Sr0.3MnO3

In several series of samples (La1-xNdx)(0.7)Sr0.3MnO3 (0less than or equal toxless than or equal to1), we studied the evolution of structure, magnetic and electrical properties with x and the average ionic radius of the A site [r(A)], which systematically varied while keeping the ratio Mn3+/Mn4+ fixed. Based on the classical ceramic preparation method, the samples have perovskite-like structure with different degrees of distortion (rhombohedral and orthorhombic). With increasing Nd concentration, a systematic decrease in the ferromagnetic transition temperature (T-C), the metal semi-conducting transition temperature (T-p) and the cell volume is observed. 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) 2002 Elsevier Science B.V. All rights reserved.