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During growth of La 0.67 Ca 0.33 MnO 3 in an usual solid state reaction process, the diffusion of La-site metal ions is a rate-limiting factor. In the initial stage of the growth process, La-deficient manganite with rhombohedral structure was easily formed. With the repetition of the grinding±pressing± sintering process, the metal content on the La-site was gradually increased, and the phase was changed from rhombohedral to cubic structure. For slightly La-deficient (La,Ca) 1Àx MnO 3 manganites, the ferromagnetic±paramagnetic (F±P) transition temperature T M is less sensitive to the Lasite deficiency, but their electric transport properties are greatly affected. The slightly La-site deficient compound was characterized by double bumps on its resistivity versus temperature (R±T) curve, one of which was located at higher temperature very near to its temperature T M . For the La 0.67 Ca 0.33 MnO 3 single phase, only one resistance peak was observed at T R on its R±T curve. For the sample sintered at lower temperatures (< 1100 C) in air T R is much less than T M , and no magnetoresistance (MR) peak was observed within the temperature range of 80 K < T < 300 K. But for the sample sintered at 1200 C in air T R is well in agreement with T M and its MR is strongly peaked very close to T M . All the bulk samples showed substantial MR in a magnetic field of 0.6 T at low temperatures that increased almost linearly with decreasing temperature.

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