Gd,Co共掺杂对BiFeO3陶瓷电输运和铁磁特性的影响

采用快速液相烧结法制备BiFeO₃和Bi_0.95Gd_0.05Fe_1-xCo_xO₃ (x= 0, 0.05, 0.1, 0.15, 0.2)陶瓷样品,研究Gd, Co共掺杂对BiFeO₃微观结构, 介电性能和铁磁性的影响. X射线衍射谱表明:所有样品的主衍射峰与纯相BiFeO₃相符合且 具有良好的晶体结构,随着Co³⁺掺杂量x的增大, Bi_0.95Gd_0.05Fe_1-xCo_xO₃样品的主衍射峰(104)与(110)逐渐相互重叠, 当x大于0.1时, 样品呈现正方晶系结构; J-V特性显示Gd³⁺, Co³⁺共掺杂有效地降低BiFeO₃陶瓷的漏导电流,其降低幅度为1-2个数量级; 当f=10³ Hz时, Bi_0.95Gd_0.05Fe_0.8Co_0.2O₃的介电常数是BiFeO₃的6倍, 而Bi_0.95Gd_0.05Fe_0.95Co_0.05O₃和 Bi_0.95Gd_0.05Fe_0.85Co_0.15O₃样品的介电损耗最小,均为0.01.室温下, Bi_0.95Gd_0.05Fe_1-xCo_xO₃样品磁性与BiFeO₃相比显著增强. 在磁场为30 kOe的作用下,Bi_0.95Gd_0.05Fe_1-xCo_xO₃ (x= 0, 0.05, 0.1, 0.15, 0.2)的剩余磁化强度M_r分别是BiFeO₃的34, 60, 105, 103, 180倍.样品磁性增强的主要原因是Gd, Co掺杂使BiFeO₃的晶格结构发生变化导致BiFeO₃自身储存的磁性能被释放, Gd³⁺的4f电子与Fe³⁺或Co³⁺的3d电子自旋相互作用及样品中存在局域的 Fe-O-Co磁耦合三者共同作用的结果.

Effects of Gd and Co doping on the electrical and ferromagnetism properties of BiFeO3 ceramics

Multiferroic Bi_0.95Gd_0.05Fe_1-xCo_xO₃ (x= 0, 0.05, 0.1, 0.15, 0.2) ceramics were prepared by rapid liquid phase sintering method. We studied effect of Gd and Co doping on the structure, electrical and ferromagnetism properties of BiFeO₃ ceramics. The structure and morphology of BiFeO₃ ceramics are characterized by X-ray diffraction (XRD). The results show that all the peaks for Bi_0.95Gd_0.05Fe_1-xCo_xO₃ (x= 0, 0.05, 0.1, 0.15, 0.2) samples can be indexed according to the crystal structure of pure BiFeO₃. And X-ray diffraction analysis reveals a phase transition in Gd-Co codoped BiFeO₃ ceramics when x is larger than 0.1.
The current densities of all samples measured at room temperature are approximately three orders of magnitude lower than that of BFO ceramic, and the leakage current of the ceramics at room temperature exhibits two distinctive conduction behaviors: Ohmic conduction and space charge limited (SCL) conduction mechanism.
For all the samples studied here, the dielectric constant and dielectric loss decrease with the increase of frequency in a range from 1 kHz to 1 MHz. The dielectric constants of Bi_0.95Gd_0.05Fe_1-xCo_xO₃ (x= 0, 0.05, 0.1, 0.15,0.2) samples are nearly 1.9, 2.68, 3.85, 5.3, and 6 times larger than that of pure BiFeO₃ (ε_r= 61.2) ceramic at 1 kHz, respectively. And the dielectric losses of Bi_0.95Gd_0.05Fe_1-xCo_xO₃ samples become smaller than that of BFO ceramic.
The magnetic measurements show that all the samples possess strong ferromagnetism at room temperature expect BiFeO₃ and Bi_0.95Gd_0.05FeO₃ which are weakly ferromagnetic. Under an external magnetic field of 30 kOe, the values of M_r of Bi_0.95Gd_0.05Fe_1-xCo_xO₃ are 34, 60, 105, 103 and 180 times that of BiFeO₃, respectively.