【摘要】 采用传统的固相反应法制备出了高质量的La_0.7Ca_0.3MnO₃（其中x=0.00,0.05,0.10,0.15,0.20）系列样品,并对其进行了XRD,电阻-温度测量.实验结果表明,随着Eu掺杂量的增加,样品的金属-绝缘体转变温度朝低温附近移动,峰值电阻增加.通过对A位平均离子半径和尺寸无序度的计算,我们发现,由Eu掺杂导致A位平均离子半径〈rA〉减小,尺寸无序度σ2增大,使晶格畸变加剧,从而削弱了eg巡游电子在Mn3+和Mn4+之间的跃迁,同时促进了自旋极化子的形成.我们还对样品电阻-温度曲线的高温部分进行了拟合,对于x=0.00的样品,曲线可以用非绝热近似下的小极化子模型拟合;当掺杂量为x=0.05,0.10,样品的导电机理符合变程跳跃模型;进一步加大掺杂量,当x=0.15,0.20时,样品的电输运行为可以用晶格极化子与自旋极化子共存来解释.更多还原

【Abstract】 We have fabricated high-quality polycrystalline samples of La_0.7Ca_0.3MnO₃（x=0.00, 0.05, 0.10, 0.15, 0.20） using the conventional solid-state reaction method. Powder X-ray diffraction and the temperature dependence of resistance measurements are carried out to analyze the samples’ properties. The experimental results indicate that with the increase of Eu dopant, MIT （metal-insulator transition） temperature moves to lower temperature and the peak resistance become higher. We also calculate the average A-site ion radius 〈r A 〉 and size disorder σ2 of all samples, respectively. From the calculated data, we obtain that, with the increase of Eu dopant, the reduced average A-site radius 〈r A 〉 and enlarged size disorder σ2 lead to the suppression of the hopping of itinerant electron between Mn 3+ -O 2- -Mn 4+ and aiding the formation of lattice polarons. We also fit the data with several physical models. As to x=0.00, nonadiabatic polaron is the best fitted model; As to x=0.05,0.10, their R^T curves obey variable range hopping model very well, but with the increase of dopant, when x=0.15,0.20, the transportation mechanism could be explained by the coexistence of lattice and spin polarons.更多还原