La_(0.67)Sr_(0.33)Mn_(1-x)Fe_xO_3体系的正电子湮没研究

Positron Annihilation Study on the La_(0.67)Sr_(0.33)Mn_(1-x)Fe_xO_3 System

采用固相反应方法制备了名义成分为La0.67Sr0.33Mn1-xFexO3(0x0.2)的系列样品.利用X射线衍射、激光拉曼、正电子湮灭等实验手段并结合输运测量,对该系列样品进行了研究.结果表明,各样品均为正交钙钛矿结构;随着掺杂量的增加,样品的电阻率ρ急剧变大,绝缘体-金属转变峰随着掺杂浓度x的增加,峰值对应温度向低温区移动,这是由于样品内部晶体结构的变化所导致的.掺杂样品中缺陷及电子结构的变化与掺杂浓度密切相关,这主要是由于样品中的Mn3+被Fe3+所替代,部分Mn3+-O2-Mn4+铁磁双交换作用键被打断,样品中的铁磁与反铁磁作用的相互竞争以及样品内部电子局域化所形成的极化行为等因素的影响所导致的.

This paper investigate the La0.67Sr0.33Mn1-xFexO3（0≤x≤0.2）system.The ceramic samples are prepared by the solid state reaction method.The influence of Fe doping on electric properties of La0.67Sr0.33MnO3 is studied by X-ray diffraction method,Laser Raman spectra,ρ-T measurement.The results show that all the samples have orthorhombic pervoskite structure,and with the increase of Fe doping concentration x,the peak value of resistivity ρ increases quickly,and the peak of corresponding insulator-metal transition temperature moves to low temperature region resulting from the change of crystal structure.The doping sample deficiency and change of electronic structure depend on the doping density because of the substitution of Mn3＋ by Fe3＋ hereby the ferromagnetic Mn3＋-O2--Mn3＋ double exchange interactions are partially destroyed and the competition between ferromagnetic and anti-ferromagnetic effect as well as the polarization are caused by the electrons localization.