(Nb,Al)共掺BaTiO_3陶瓷的巨介电及介电弛豫现象（英文）

Colossal Permittivity and Dielectric Relaxations of(Nb, Al) Co-doped BaTiO_3 Ceramics

(Nb,Al)共掺的BaTiO_3陶瓷(BaTi_(0.98)(Nb_(0.5)Al_(0.5))_(0.02)O_3)表现出巨介电现象,介电常数可以达到3×105,介电损耗为0.2。在10^(-1)~10~7 Hz范围内,观察到三种介电弛豫现象,并分别对其进行了分析。低频段(10^(-1)~10 Hz)和中频段(10~3~10~5 Hz)属于非德拜弛豫,分别是由于Maxwell-Wagner电极界面极化和晶界层电容器效应引起的;相反,高频段(10~5~10~7 Hz)属于德拜弛豫,通过阿伦尼乌斯公式的拟合,得到其激活能E=15 meV和频率因子f_0=7×10~6Hz。较小的激活能和频率因子表明其弛豫过程可能来源于复杂缺陷团簇中的电子的局域运动,被称为钉扎电子–缺陷偶极子效应。本研究显示钉扎电子–缺陷偶极子效应可以作为设计新型巨介电钙钛矿材料的依据。

Nb and Al co-doped BaTiO3 ceramics, BaTi0.98（Nb0.5Al0.5）0.02O3, have a colossal permittivity （εГ≈3 × 105, tanδ≈0.2） at room-temperature. Three distinct relaxation processes are observed in the frequency range from l01 to 107 Hz. The low-frequency relaxation between 101 and 10 Hz and the intermediate-frequency relaxation between 10^3 and 105 Hz are non-Debye relaxations, which are attributed to Maxwell-Wagner interfacial polarization, electrode interracial polarization, and barrier layer capacitor. While the high-frequency process between 105 and 107 Hz is a typical Debye-type relaxation with an activation energy of E≈ 15 meV and a frequency factor of f0≈7× 106 Hz. The small activation energy and relatively small frequency factor in the BaTi0.98（Nb0.5Al0.5）0.02O3 ceramics indicate that this relaxation process may derive from local motion of electrons in the complex defect clusters, which results from co-doping and can be named as electron-pinned defect-dipoles. This study suggests that the electron-pinned defect-dipoles mechanism can be used to design colossal permittivity in perovskites, like BaTiO3.