【摘要】 利用溶胶—凝胶法制备了纳米多晶La_0.7Sr_0.3MnO_3-δ（简称LSM）块体样品.详细研究了在不同烧结温度下的LSM样品电阻率随测量温度的变化关系.随着温度从室温降低,电阻率（ρ）在250 K附近存在最大值,低于该温度后,样品表现为金属导电特性,随后在50 K左右存在一极小值.通过对输运性质的研究表明在低温下（<50 K）,ρ随温度降低而升高的现象与隧穿效应的理论模型(lnραT^-1/2)符合得很好,表明这种现象是由于传导电子在通过邻近LSM晶粒间表面/界面层时的隧道效应所导致的.利用自旋回波法测量了样品中⁵⁵Mn的核磁共振谱图,结果表明样品中存在这种绝缘性的势垒.更多还原

【Abstract】 The resistivity of bulk polycrystalline La_0.7Sr_0.3MnO_3-δ（LSM）,deliberately fabricated to produce nanoscale grains sintered at different temperatures,was investigated as a function of temperature.With temperature decreasing below room temperature the resistivity （ρ） exhibited a maximum near 250 K below which it displayed"metallic"behaviour,i.e.ρ∝T² at 50～170 K.However,ρsubsequently exhibited a minimum near 50 K,below which it well fit the predictions for the tunneling of conduction electrons through insulating interfacial layers viz.inρ∝T^-1/2,a result interpreted as conduction-electron tunneling between adjacent LSM granules.The ⁵⁵Mn zero field spin-echo nuclear magnetic resonance spectra indicated that the insulating barrier existed in LSM.The minimum ofρoccuring in these samples may have resulted from the competition of the tunneling effect and the intrinsic metallic transport mechanism of LSM.更多还原