Complex impedance analyses of n-BaTiO3 ceramics showing positive temperature coefficient of resistance
Complex impedance analyses of n-BaTiO3 ceramics showing positive temperature coefficient of resistance
复制标题
DOI：
10.1023/a:1018592618321
复制
发表时间：
1997-02-01
影响因子：
2.8
通讯作者：
Kutty, TRN
中科院分区：
文献类型：
--
作者：
Hari, NS;Padmini, P;Kutty, TRN
研究了晶界改性剂对不同气氛下制备的半导体BaTiO3陶瓷阻抗谱的影响。在N-2 + H-2气氛中退火的未掺杂BaTiO3陶瓷样品在欧姆Ni电极的Cole-Cole图中显示出一个单一的半圆。在空气中烧结的供体掺杂样品的阻抗谱显示重叠的半圆，这可能表明颗粒内部的弛豫过程，例如在深阱处的电子捕获和脱陷。居里点（T-c）附近的晶粒电阻（R(g)）所显示的最小值有力地支持了这一点，而晶界电阻（R(gb)）随温度的行为与直流电阻相似，即正的电阻温度系数（PTCR）。电子顺磁共振（EPR）结果表明，电荷捕获是由相变过程中电子在原生和外来受体态的重新分配引起的。因此，存在于正方相和正交相中的中性钡空位（V-Ba(X)）转变为立方相和菱形相中的单电离钡空位（V-Ba’）。从电阻率变化与阱态电荷再分配的相关性来看，可以设想PTCR效应与晶界区域中浓度较高的受体态电荷捕获有关。阻抗谱数据支持这一结论。
The influence was studied of grain boundary layer modifiers on the impedance spectra of semiconducting BaTiO3 ceramics processed in various atmospheres. Ceramic samples of undoped BaTiO3 annealed in an N-2 + H-2 atmosphere showed a single semicircle in the Cole-Cole plot when ohmic Ni electrodes were used. Impedance spectra of donor-doped specimens sintered in air showed overlapping semicircles which may indicate relaxational processes within the grains, e.g. electron trapping and detrapping at the deep traps. This is strongly supported by the minima shown by the grain resistance (R(g)) around the Curie point (T-c), whereas the behaviour of the grain boundary resistance (R(gb)) with temperature is similar to the d.c. resistance, i.e. a positive temperature coefficient of resistance (PTCR). Electron paramagnetic resonance (EPR) results indicate that the charge trapping is caused by the redistribution of electrons at native and extrinsic acceptor states during phase transitions. Thus, the neutral barium vacancies (V-Ba(X)) present in the tetragonal and orthorhombic phases change into singly ionized barium vacancies (V-Ba') in the cubic and rhombohedral phases. From the correlation between the resistivity changes and the charge redistribution at the trap states, it is envisaged that the PTCR effect is related to charge trapping at the acceptor states having higher concentration in the regions of the grain boundary layer. The impedance spectral data support this conclusion.