LaFeO_3纳米材料电四极超精细相互作用TDPAC测量  

Study of Quadrupole Interactions in Nano-LaFeO_3 Perovskites by Time Differential Perturbed Angular Correlation

作　　者：杜恩鹏[1] 葛智刚[1] 郑永男[1] 周冬梅[1] 左翼[1] 袁大庆[1] 王平生[1] 段晓[1] 石海松[1] 王建波[2] 李发伸[2] 朱升云[1] 

机构地区：[1]中国原子能科学研究院,北京102413 [2]兰州大学磁学和磁性材料教育部重点实验室,甘肃兰州730000

出　　处：《原子核物理评论》2005年第1期54-57,共4页Nuclear Physics Review

基　　金：国家自然科学基金资助项目(10275097)~~

摘　　要：采用时间微分扰动角关联方法测量了LaFeO3 纳米中的电四极超精细相互作用. 扰动角关联探针核14057 La 14058 Ce由139La(n,γ)140La反应产生, 实验只观察到一个La晶位的四极相互作用. 在室温下, 20和 40nm以及晶体LaFeO3 的四极相互作用频率ω0 分别为 687. 4 , 698. 3和 742. 9Mrad/s, 频率分布宽度系数σ分别为 0. 014, 0. 009和 0. 001, 电场梯度不对称系数η=0. 实验数据表明, 电场梯度主轴与晶轴方向一致; 样品具有菱方结构, 晶体到纳米发生菱方向正交结构转变, 纳米尺度越小, 越趋于正交结构; 由于邻近核的扰动, 随纳米颗粒增大, 四极相互作用频率分布宽度系数σ变小, 晶体时最小.The quadrupole interactions in the nano-and crystalline LaFeO_3 perovskites have been investigated by TDPAC. The TDPAC probing nuclei ^(140)_(57)La-^(140)_(58)Ce were produced through the nuclear reaction ^(139)La(n.γ)^(140)La at the CIAE heavy water experimental reactor. One electric quadrupole interaction was detected for each material, which is assigned to the La site. The quadrupole interaction frequencies of 687.4, 698.3 and 742.9 Mrad/s with a distribution coefficient of 0.014, 0.009 and 0.001 were observed at room temperature for the 20 and 40 nm nano-LaFeO_3 and crystalline LaFeO_3, respectively. The fitting yielded the EFG asymmetry parameter η=0, which indicates that the principal axes of the EFG is aligned with the crystallographic axes. The experimental results show that the structure of crystalline LaFeO_3 is rhombohedral, the changing of the structure towards the orthorhombic structure takes place from the crystalline LaFeO_3 to the nano-LaFeO_3, and the smaller the nano-grain size, the larger the change. The frequency distribution is caused by the perturbation of the neighboring atoms, and thus, the distribution coefficient increases with decreasing the nano-grain size and the crystalline LaFeO_3 arrives at its maximum.

关 键 词：四极相互作用 超精细相互作用 LAFEO3 晶体 电四极 系数 扰动 观察 频率分布 实验 

分 类 号：O571.21[理学—粒子物理与原子核物理] O643.36[理学—物理]