在La_(5/8)Ca_(3/8)MnO_3体系中Co替代效应的正电子实验研究  

Positron annihilation study on the effect of Co-doping in La_(5/8)Ca_(3/8)MnO_3 system

作　　者：姚恺[1] 张金仓[1] 李领伟[1] 曹桂新[1] 敬超[1] 曹世勋[1] 

机构地区：[1]上海大学物理系

出　　处：《核技术》2006年第1期37-41,共5页Nuclear Techniques

基　　金：国家自然科学基金(No.10574087);上海市科委重点基础研究项目(No.04JC14039);上海市重点学科建设项目资助课题(No.T0104)

摘　　要：利用正电子湮没技术和X射线衍射等实验手段结合输运测量,对La5/8Ca3/8Mn1-xCoxO3(0≤x≤0.3)系统进行了研究。结果表明,各样品均为正交钙钛矿结构;随Co掺杂浓度x的增加,电阻率峰值ρp迅速增大,对应的绝缘—金属转变温度Tp降低。正电子寿命实验表明,各寿命参数τ1、τ2和I2存在很强的Co替代依赖关系。其中,短寿命分量τ1和长寿命分量τ2在整体上表现出随Co掺杂量的增大而降低的趋势,而I2随Co掺杂量x增大而增大。相应的局域电子密度ne随x的增大而逐渐增大。结合对样品输运特性研究的实验结果,可以证明,随着Co掺杂量的增大,样品内部电子局域化程度逐渐增强,这主要是由于Co离子对Mn离子的替代部分破坏了Mn3+—O2-—Mn4+导电网络,并使体系内电子–声子耦合效应增强,造成巡游电子数量减少,处于局域态的电子数增多。The La5/8Ca3/8Mn1-xCoxO3 （0≤x≤0.3） has been systematically studied by means of positron annihilation technique and X-ray diffraction method together with the transport properties measurement. The results show that all the samples have orthorhombic pervoskite structure, and with the increase of Co doping concentration x, the peak value of resistivity ρp increases quickly, and the corresponding metal-insulator transition temperature Tp decreases. The positron annihilation parameters τ1, τ2 and I2 show strong x dependence. The shorter lifetime τ1 and longer lifetime rE show a decreasing trend with the increase of x in totally, while the longer lifetime intensity/2 shows an increasing trend. The local electron density ne calculated from positron lifetime parameters has an increasing trend with the increase of x, Together with the transport properties, it could be confirmed that with the increase of Co doping concentration the electron localization effect is strengthened gradually. The Co doping at Mn site causes the conduction network of Mn^3＋ - O - Mn^4＋ partly destroyed. It also enhances the electron - phonon coupling effect, then causes the number of itinerant electrons to decrease and the number of electrons in localized state to increase.

关 键 词：正电子湮没 电子局域效应 输运特性 

分 类 号：O484[理学—固体物理]