The Effect Of The Second Phase To La_2/3Ca_1/3MnO₃ Grains System

In our work, we prepared nominal La_2/3Ca_1/3MnO₃ grains with sol-gel method, then we introduced the Cu dependent material and the Sb₂O₅ material respectively to the La_2/3Ca_1/3MnO₃ grains system with physical and chemical method. We discuss the effect of the second phase in these compounds, experimental results indicated that:1. When the second phase is the Cu dependent material, the study of temperature dependence of resistivity at zero field shows that, the resistivity of the composites decreases prodigiously with small addition level. With the addition level decreases, the composites becomes sensitively to the magnetic field, the measurement for temperature dependence of magnetoresistance (MR) indicates that MR effect can be largely enhanced in the composites with the second phase addition.2. When the second phase is the Sb₂O₅ material, the study of temperature dependence of resistivity at zero field shows that, the metal-insulator transition temperature (Tp) and the resistivity of the composites are dependent on Sb₂O₅ addition level x. When x<3%, Tp shifts towards low temperature and resistivity increases with the increase of x. But Tp shifts towards high temperature and resistivity decreases with further increasing of x. The measurement for temperature dependence of magnetoresistance (MR) indicates that MR effect can be largely enhanced in the composites with small Sb₂O₅ addition.Based on the structure that the La_2/3Ca_1/3MnO₃ grains are surrounded by the the second phase, just like the sandwich structure, we give a possible interpretation to the enhanced magnetoresistance (MR) effect observed in these composites.