Anomalous broad dielectric relaxation in Bi1.5Zn1.0Nb1.5O7 pyrochlore -: art. no. 054106
Anomalous broad dielectric relaxation in Bi1.5Zn1.0Nb1.5O7 pyrochlore -: art. no. 054106
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DOI：
10.1103/physrevb.66.054106
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发表时间：
2002-08-01
影响因子：
3.7
通讯作者：
Randall, CA
中科院分区：
文献类型：
--
作者：
Kamba, S;Porokhonskyy, V;Randall, CA
采用低频电容电桥、高频同轴技术、时域透射太赫兹光谱和红外光谱相结合的方法研究了Bi1.5Zn1.0Nb1.5O7立方烧绿石陶瓷在100 Hz ~ 100 THz范围内的复介电响应。在10 K和400 K之间获得的数据揭示了玻璃状的介电行为：在很宽的频率和温度范围内观察到介电弛豫，并且介电常数和损耗最大值随着测量频率的增加而向更高的温度值移动近200 K。弛豫频率的分布在冷却时变宽，可以用均匀分布来描述。在10（11）Hz附近的高频端几乎与温度无关，低频端服从阿克里乌斯定律，激活能约为0.2eV。弛豫被分配到烧绿石结构中的A和O'位置的原子在几个局部势能极小值之间的局部跳跃。跳跃的势垒高度分布在0和0.2 eV之间。这种异常宽的分布可能是由于Zn ~（2+）原子和空位在Bi ~（3+）位上的不均匀分布引起的无规场和非周期性原子间势。在低温下观察到与频率无关的介电损耗（1/f噪声），这似乎是无序系统在低温下的普遍行为。
The complex dielectric response of Bi1.5Zn1.0Nb1.5O7 cubic pyrochlore ceramics was investigated between 100 Hz and 100 THz by a combination of low-frequency capacitance bridges, a high-frequency coaxial technique, time domain transmission THz spectroscopy, and infrared spectroscopy. The data obtained between 10 K and 400 K revealed glasslike dielectric behavior: dielectric relaxation is observed over a wide frequency and temperature range, and the dielectric permittivity and loss maxima shift to higher temperature values by almost 200 K with increasing measuring frequency. The distribution of relaxation frequencies broadens on cooling and can be described by a uniform distribution. The high-frequency end of the distribution at similar to10(11) Hz is almost temperature independent and its low-frequency end obeys the Arrhenius Law with an activation energy of similar to0.2 eV. The relaxation is assigned to the local hopping of atoms in the A and O' positions of the pyrochlore structure among several local potential minima. The barrier height for hopping is distributed between 0 and 0.2 eV. Such an anomalously broad distribution may have its origin in the inhomogeneous distribution of Zn2+ atoms and vacancies on Bi3+ sites, which gives rise to random fields and nonperiodic interatomic potential. Frequency independent dielectric losses (1/f noise) are observed at low temperatures, which seems to be a universal behavior of disordered systems at low temperatures.