Li Yong, Fang Xiaoyong, Cao Maosheng
School of Material Science and Engineering, Beijing Institute of Technology, Beijing 100081, China.
School of Science, Yanshan University, Qinhuangdao 066004, China.
Sci Rep. 2016 Apr 20;6:24837. doi: 10.1038/srep24837.
Tunable frequency is highly sought-after task of researcher, because of the potential for applications in selecting frequency, absorber, imaging and biomedical diagnosis. Here, we report the original observation of thermal frequency shift of dielectric relaxation in La/Nd doped BiFeO3 (BFO) in X-band from 300 to 673 K. It exhibits an unexpected result: the relaxation shifts to lower frequency with increasing temperature. The relaxation maximally shifts about a quarter of X-band. The nonlinear term of lattice vibration plays an important role in the frequency shift. The frequency shift leads to tuning microwave absorption, which almost covers the whole X-band by changing temperature. Meanwhile, the great increase of dielectric loss of La/Nd doped BFO due to thermal excited electron hopping enhances microwave absorption above ~460 and ~480 K, respectively. The microwave absorption of La/Nd doped BFO surpasses -20 dB at 673 K, and the minimum reflection loss of La doped BFO reaches -39 dB. These results open a new pathway to develop BFO-based materials in electromagnetic functional materials and devices for tunable frequency, stealth and thermal imaging at long wavelength.
可调谐频率是研究人员高度追求的任务，因为它在频率选择、吸收器、成像和生物医学诊断等方面具有应用潜力。在此，我们报告了在300至673 K的X波段中，对La/Nd掺杂的BiFeO3（BFO）中介质弛豫热频移的首次观测。它呈现出一个意想不到的结果：弛豫随着温度升高向低频移动。弛豫最大移动约X波段的四分之一。晶格振动的非线性项在频移中起重要作用。频移导致微波吸收可调谐，通过改变温度几乎可以覆盖整个X波段。同时，由于热激发电子跳跃，La/Nd掺杂BFO的介电损耗大幅增加，分别在460 K和480 K以上增强了微波吸收。La/Nd掺杂BFO在673 K时的微波吸收超过-20 dB，La掺杂BFO的最小反射损耗达到-39 dB。这些结果为在电磁功能材料和器件中开发基于BFO的材料开辟了一条新途径，用于可调谐频率、隐身和长波长热成像。
