Transactions of Nonferrous Metals Society of China
JOURNAL OF RAILWAY SCIENCE AND ENGINEERING
|Vol. 17 No. 5 October 2007|
（1. School of Materials Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, China; 2. School of Materials Science and Engineering, Nanchang University, Nanchang 330031, China; 3. Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093, China ）
Abstract:Several samples of manganese oxides La(1−x)2/3Ca1/3MnO3 (V-LCMO) and (La0.7−xY0.3)2/3Ca1/3MnO3 (x＜0.15) (V-LYCMO) with vacancies at La-site (La-vacancy) were prepared by solid-state reaction method. The X-ray diffraction(XRD) patterns refined by Rietveld confirm that these compounds exhibit single phase structure with orthorhombic symmetry (Pnma). The lattice parameters, Mn—O bond length and Mn—O—Mn bond angle vary with La-vacancy concentration, as an indication of the occurrence of the local Jahn-Teller effect. The measurement result of V-LCMO compounds shows that the maximum magnetoresistance(MR) is about 220% at TIM=268 K and La-vacancy content x=0.04. For V-LYCMO compounds, there exists metal-insulator transition at about 50 K, and a very large MR (over 106%) is observed at the temperature ranging from 40 K to 50 K.
Key words: La(1−x)2/3Ca1/3MnO3; (La0.7−xY0.3)2/3Ca1/3MnO3; La-vacancy; orthorhombic symmetry; Jahn-Teller effect