中文摘要：

掺杂量、A位阳离子平均半径及失配因子是影响掺杂锰基钙钛矿氧化物从顺磁绝缘体到铁磁金属转变的主要因素，为了突出研究失配因子的影响，本文固定掺杂量和A位阳离子平均半径制备了一系列样品。0和5T磁场下电阻率与温度关系测量表明，随着失配因子的增加，绝缘体-金属转变温度向低温区移动且与σ^2岩保持线性关系；通过调节失配因子，样品La0.53Sm0.17Sr0.3MnO3的磁电阻在室温附近达到了极大值。结合样品的电输运行为，对实验结果进行了讨论。

英文摘要：

Three factors control the transition from paramagnetic insulator to ferromagnetic metal. The first is the hole doping. The second factor is the average ionic radius of the A site cation rA. The last one concerns the ionic size mismatch σ^2 at the A site. In order to study the effect of σ^2, a series of samples were prepared with constant value of x and rA. The measurement of resistivity versus temperature dependence under magnetic field （0 and 5 T） indicates that the insulator-metal transition temperature moves towards the low temperature region with increasing σ^2. The magnetoresistance of La0.53Sm0.17Sr0.3MnO3 obtains its maximum at room temperature. The experimental observation was discussed based on the measurement of the transport properties