Ensi Cao

Microstructure, dielectric properties and impedance spectroscopy of Ni doped CaCu3Ti4O12 ceramics

Ni doped CaCu3Ti4O12 ceramics (CaCu3−xNixTi4O12, x = 0, 0.05, 0.1, 0.2) were prepared by a sol–gel method and the influence on the microstructure, dielectric properties and impedance spectroscopy has been investigated. CaCu3−xNixTi4O12 ceramics can cause a remarkable increase in the grain size and exhibit a very high dielectric constant (e′) over a wide frequency range at room temperature. The e′ value of the CaCu2.9Ni0.1Ti4O12 ceramic sintered at 1060 °C for 8 h was between 7.1 × 104 and 9.6 × 104 over the frequency range of 20 Hz to 100 kHz. Besides, a very low dielectric loss (tan δ) of 0.025 was observed for the CaCu2.95Ni0.05Ti4O12 ceramic sintered at 1060 °C for 8 h with e′ ∼ 4.2 × 104 at about 1 kHz. These results indicate that Ni doping at the Cu site may improve the dielectric properties of CaCu3Ti4O12. The giant dielectric response behavior can be attributed to the internal barrier layer capacitance (IBLC) effect.

The Oxygen Vacancies Correlated Ferromagnetism in Transition Metal-Doped ZnO Nanowires

The magnetic properties of 3d transition metal (TM = V, Cr, and Mn)-doped ZnO nanowires (NWs) with and without oxygen vacancy are investigated by ab initio calculations. The magnetic moments can be induced by TM impurities in ZnO NWs, localized on the 3d TM atoms and their neighboring O atoms. Furthermore, the ferromagnetism in V-, Cr-, and Mn-doped ZnO NWs is strongly correlated with oxygen vacancies.

Influence of MgTiO 3 -Doping on Microstructure and Dielectric Properties of CaCu 3 Ti 4 O 12 Ceramics

The application of CaCu3Ti4O12 (CCTO) is limited due to its high low-frequency dielectric loss. An internal barrier layer capacitance effect seems to be the most widely accepted explanation for the giant-ε′ phenomenon of CCTO ceramics. According to the effect, wrapping the semiconducting grains of CCTO ceramics in insulating materials is an effective way to reduce the low-frequency dielectric loss. CCTO/MgTiO3 composite ceramics were prepared, and their crystalline structures, microstructures, dielectrical properties and complex impedance were systematically investigated. The results show that MgTiO3 has been wrapped around the CCTO grains in our CCTO-based ceramics. Compared with pure CCTO ceramics, the low-frequency dielectric loss was not reduced by MgTiO3-doping, because the resistance of MgTiO3 phase boundaries in the CCTO/MgTiO3 composite ceramics as prepared is lower than the grain boundaries resistance of pure CCTO ceramics. After annealing in oxygen, the low-frequency permittivity and dielectric loss of CCTO/MgTiO3 composite ceramics significantly decreased, which should be attributed to the increase of the resistance of insulating MgTiO3 phase boundaries and CCTO grains.

Dielectric Property of High Density CaCu3Ti4O12 Ceramics: Dielectric Property of High Density CaCu3Ti4O12 Ceramics

利用热压方法制备了高密度的CaCu 3 Ti 4 O 12 陶瓷, 研究了其微观结构、晶格结构和介电性质。实验发现, 短时间热压方法制备的陶瓷的相对密度就能达到98.3%, 并且微观结构呈现晶粒尺寸双峰分布的特点。XRD显示热压方法制备的陶瓷中含有少量的Cu 2 O第二相, 而经过退火处理的热压陶瓷则只含有CuO第二相。热压方法制备的陶瓷和经过退火处理的热压陶瓷的室温介电频谱上有两个介电弛豫, 而常规方法制备的陶瓷只有一个。并且热压方法制备的陶瓷的低频介电常数高达2×10 5 , 经过退火处理的热压陶瓷的低频介电常数更是达到1×10 6 。本研究进一步讨论了其微观结构和介电性质之间的关系。利用热压方法制备了高密度的CaCu 3 Ti 4 O 12 陶瓷, 研究了其微观结构、晶格结构和介电性质。实验发现, 短时间热压方法制备的陶瓷的相对密度就能达到98.3%, 并且微观结构呈现晶粒尺寸双峰分布的特点。XRD显示热压方法制备的陶瓷中含有少量的Cu 2 O第二相, 而经过退火处理的热压陶瓷则只含有CuO第二相。热压方法制备的陶瓷和经过退火处理的热压陶瓷的室温介电频谱上有两个介电弛豫, 而常规方法制备的陶瓷只有一个。并且热压方法制备的陶瓷的低频介电常数高达2×10 5 , 经过退火处理的热压陶瓷的低频介电常数更是达到1×10 6 。本研究进一步讨论了其微观结构和介电性质之间的关系。

Giant Dielectric-permittivity Property of NaCu3Ti3NbO12 and NaCu3Ti3SbO12 Ceramics and Low Dielectric Loss in NaCu3Ti3SbO12 Ceramics: Giant Dielectric-permittivity Property of NaCu3Ti3NbO12 and NaCu3Ti3SbO12 Ceramics and Low Dielectric Loss in NaCu3Ti3SbO12 Ceramics

利用传统的固相反应工艺制备了NaCu 3 Ti 3 NbO 12 和NaCu 3 Ti 3 SbO 12 陶瓷, 对它们的介电性质和晶格结构进行了研究。结果显示, 两种陶瓷都存在低频介电常数高于7×10 3 的巨介电行为; 在室温或者更低温度下, 两种陶瓷的介电频谱(40 Hz~110 MHz)的实部只出现一个介电弛豫, 而更高温度下的介电频谱的实部则会有两个介电弛豫; XRD结果显示两种陶瓷中都含有少量的CuO第二相。这些实验结果能用CCTO陶瓷中的内阻挡层电容效应解释。NaCu 3 Ti 3 SbO 12 陶瓷的室温介电损耗在40 Hz到7 kHz的宽频率范围内低于0.05, 并且其1 kHz的介电损耗在-50~ 80℃的宽温度范围内低于0.05, 这对于实际应用有重要意义。利用传统的固相反应工艺制备了NaCu 3 Ti 3 NbO 12 和NaCu 3 Ti 3 SbO 12 陶瓷, 对它们的介电性质和晶格结构进行了研究。结果显示, 两种陶瓷都存在低频介电常数高于7×10 3 的巨介电行为; 在室温或者更低温度下, 两种陶瓷的介电频谱(40 Hz~110 MHz)的实部只出现一个介电弛豫, 而更高温度下的介电频谱的实部则会有两个介电弛豫; XRD结果显示两种陶瓷中都含有少量的CuO第二相。这些实验结果能用CCTO陶瓷中的内阻挡层电容效应解释。NaCu 3 Ti 3 SbO 12 陶瓷的室温介电损耗在40 Hz到7 kHz的宽频率范围内低于0.05, 并且其1 kHz的介电损耗在-50~ 80℃的宽温度范围内低于0.05, 这对于实际应用有重要意义。