Effect of Li doping on the magnetotransport properties of La0.7Ca0.3-yLiyMnO3 system:: Decrease of metal-insulator transition temperature

With increasing the Li doping level in La0.7Ca0.3-yLiyMnO3 (0less than or equal toyless than or equal to0.3), the system is driven from a higher-conductivity regime to a lower-conductivity regime, which is in sharp contrast with the behavior of Na or K doping. Compared to those of K or Na, the ionic radius of Li is much smaller than that of Ca. Therefore, substitution of Ca by Li results in a smaller average A-site radius, narrowing the bandwidth and hence enhancing the band gap and resistivity. The effect of random disorder of La3+ and A(2+) also plays an important role leading to charge localization. (C) 2003 American Institute of Physics.