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 patterns refined by Rietveld confirm that these compounds exhibited 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 was about 220% at TIM = 268K and La-vacancy content x = 0.04. For V-LYCMO compounds, there exists metal-insulator transition at about 50K, and a very large magnetoresistance (over 106%) was observed at the temperature ranging from 40 to 50K.

Structure and Transport Properties of (La1-x-yY)2/3Ca1/3MnO3 with La-Site Vacancies. G.Luo, G.Liu, X.Li, W.Xiong, X.Wu: Transactions of Nonferrous Metals Society of China, 2007, 17[5], 992-5