Abstract:The rare earth oxide La_ 065Ca_ x MnO_3 with Ca vacancies were prepared, and the magnetic and electric transport behaviors were investigated. The experimental results show that with increasing Ca vacancies, the unit cell volume of La_ 065Ca _x MnO_3 increases, but the Curit temperature decreases and the ferromagnetic interaction is suppressed. The temperature of metal semiconductor transition, T _ tran, decreases, and the peak value of resistance increases with increasing Ca vacancies. The temperature dependence of the resistance above metal-semiconductor transition temperature is simulated based on the polaron-resistance model. The simulated results indicate that the increment of resistance for materials with Ca vacancies is associated with the decrement of decay length of local wave function. Meanwhile, the temperature dependence of resistance from 100 K to 300 K is calculated based on the Dionne model. The calculated data show that the polaron-trapping energy resulted from both the magnetic exchange interaction and the electron-phonon interaction enhance with increasing Ca vacancies, which reduces the active ability of the current carrier. The relationships among Ca content, amount of ions Mn 3+/Mn 4+ and oxygen vacancies in La_ 065Ca _x MnO_3 are also discussed in details.