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首页> 外文期刊>Journal of Materials Science. Materials in Electronics >Effect of segregative additives on the positive temperature coefficient in resistance characteristics of n-BaTiO_(3) ceramics
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Effect of segregative additives on the positive temperature coefficient in resistance characteristics of n-BaTiO_(3) ceramics

机译：偏析添加剂对n-BaTiO_（3）陶瓷电阻特性正温度系数的影响

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摘要

The influence of B_(2)O_(3), and Al_(2)O_(3) as segregative additives in modifying the rho-T characteristics has been studied in BaTiO_(3) ceramics with positive temperature coefficient of resistance (PTCR). Reaction of Al_(2)O_(3) at the grain boundary regions of BaTiO_(3) ceramics leads to the segregation of the secondary phase, BaAl_(6)TiO_(12) resulting in broad PTCR jump, whereas B_(2)O_(3) addition gives rise to steeper resistivity jump. Microstructure studies by SEM reveal the formation of coherent second phase layer of barium aluminotitanate surrounding the BaTiO_(3) grains. The EDX results show varying Al to Ti ratio in the early stage of phase formation in BaAl_(6)TiO_(12) resulting in electrically active layer around the BaTiO_(3) grains. The TiO_(2)-excess melt formation results in lower resistivity for 2-4percent Al_(2)O_(3) containing n-BaTiO_(3) ceramics whereas at higher alumina contents, BaAl_(6-)TiO_(12) phase becomes dominant leading to higher resistivity in the sample. Complex impedance analyses support the three-layer regions, corresponding to the contributions from grain interior resistance (R_(g)), grain boundary resistance (R_(gb)), and that from secondary phase (R_(sec)). Electron paramagnetic resonance spectroscopy (EPR) indicated barium vacancies, V_(Ba)~(/) as the major electron trap centers which are activated across the tetragonal-to-cubic phase transition. A charge trapping mechanism is proposed wherein the segregation of secondary phases bring carrier redistribution among the various acceptor states thereby affecting the electrical conductivity of n-BaTiO_(3) ceramics. The presence of Al~(3+)-O~(-)-Al~(3+) or Ti~(4+)-O~(-)-Al~(3+) type hole centers at the grain boundary layer (GBL) regions results in charge redistribution across the modified phase transition temperature due to symmetry-related vibronic interactions resulting in broad PTCR characteristics extending to higher temperatures.
机译：在具有正电阻温度系数（PTCR）的BaTiO_（3）陶瓷中，研究了B_（2）O_（3）和Al_（2）O_（3）作为分离添加剂对改进rh-T特性的影响。 Al_（2）O_（3）在BaTiO_（3）陶瓷晶界区域的反应导致第二相BaAl_（6）TiO_（12）的偏析导致PTCR跃变较大，而B_（2）O_ （3）加法引起陡峭的电阻率跳跃。 SEM的微观结构研究表明，围绕BaTiO_（3）晶粒形成了铝钛酸钡相干的第二相层。 EDX结果表明，在BaAl_（6）TiO_（12）相形成的早期阶段，Al与Ti的比率发生了变化，从而在BaTiO_（3）晶粒周围形成了电活性层。 TiO_（2）过多的熔体形成导致含n-BaTiO_（3）陶瓷的2-4％Al_（2）O_（3）的电阻率降低，而氧化铝含量较高时，BaAl_（6-）TiO_（12）相变为主导导致样品中更高的电阻率。复阻抗分析支持三层区域，分别对应于晶粒内部电阻（R_（g）），晶界电阻（R_（gb））和次级相（R_（sec））的贡献。电子顺磁共振波谱（EPR）表明钡空位V_（Ba）〜（/）是主要的电子陷阱中心，其在四方相到立方相变中被激活。提出了一种电荷俘获机制，其中次级相的分离使载流子在各种受体状态之间重新分布，从而影响n-BaTiO_（3）陶瓷的电导率。 Al〜（3 +）-O〜（-）-Al〜（3+）或Ti〜（4 +）-O〜（-）-Al〜（3+）型孔的存在以晶界层为中心（GBL）区域由于对称相关的电子相互作用而导致电荷在整个相变温度范围内重新分布，从而导致PTCR特性扩展到更高的温度。

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