The CaCu3Ti4O12(CCTO) ceramic was prepared through conventional solid-state method. The effects of synthesis process(synthesis temperature and synthesis time) of powder on ceramic microstructures, CuO segregation and ...The CaCu3Ti4O12(CCTO) ceramic was prepared through conventional solid-state method. The effects of synthesis process(synthesis temperature and synthesis time) of powder on ceramic microstructures, CuO segregation and electrical properties were investigated. The phase composition was determined by X-ray diffraction and the microstructure was examined by SEM. The dielectric constant, dielectric loss, and resistance of the ceramic were also determined by a precision impedance tester. The results show that, as the synthesis temperature increases, the CCTO ceramic grain size decreases and the stoichiometric ratio of Cu/Ca at the grain boundary increases, the dielectric constant increases and the dielectric loss decreases(40 < f < 10 kHz). In addition, when the synthesis time is shorter than 12 h, the Cu/Ca ratio of CCTO decreases and the dielectric constant increases with time increase. However, when the synthesis time exceeds 12 h, this trend is just the opposite. It is further proved that Cu at the grain boundary is not conducive to the dielectric constant of CCTO.展开更多
We investigate the dopant site selectivity of CaCu_(3)Ti_(4)O_(12)(CCTO)using the first principles calculations.Our results show that,for four cases of possible occupancy by La atom,lattice expansions and formation en...We investigate the dopant site selectivity of CaCu_(3)Ti_(4)O_(12)(CCTO)using the first principles calculations.Our results show that,for four cases of possible occupancy by La atom,lattice expansions and formation enthalpies with different dopant quantities indicate that doped La cations are preferentially substituted for Ca sites in CaCu_(3)Ti_(4)O_(12),which is excellent in agreement with the experimental observation(Choi et al.Adv.Mater.21(2009)885).Furthermore,more interesting information of doping is also explored by the analysis of density of states and it is found that La substituting for Cu may advance the electron conduction in CCTO.It supplies a potential solution for limitations of CCTO devices by exploring the effect when La substitutes for Cu sites in the CCTO crystal.展开更多
在电场为3.5 k V/cm的条件下,对Ca Cu3Ti4O12陶瓷进行了60 h的直流老化,研究了老化过程对Ca Cu3Ti4O12陶瓷介电性能和电气特性的影响.J-E特性测试结果表明,直流老化导致Ca Cu3Ti4O12陶瓷击穿场强、非线性系数和势垒高度明显降低.介电性...在电场为3.5 k V/cm的条件下,对Ca Cu3Ti4O12陶瓷进行了60 h的直流老化,研究了老化过程对Ca Cu3Ti4O12陶瓷介电性能和电气特性的影响.J-E特性测试结果表明,直流老化导致Ca Cu3Ti4O12陶瓷击穿场强、非线性系数和势垒高度明显降低.介电性能测试结果表明,低频介电常数和介电损耗明显增大,并且介电损耗随频率的变化遵从Debye弛豫理论,可分解为直流电导损耗和弛豫损耗,直流老化主要导致了电导损耗的增加.在低温233 K,介电损耗谱中出现两个弛豫峰,其活化能分别为0.10,0.50 e V,认为对应着晶粒和畴界的弛豫过程,且不随直流老化而变化.通过电模量谱对Ca Cu3Ti4O12陶瓷的弛豫过程进行了表征,发现直流老化导致的界面空间电荷在外施交变电场的作用下符合Maxwell-Wagner极化效应,并在低频区形成新的弛豫峰.在高温323—473 K的阻抗谱中,晶界弛豫峰在直流老化后明显向高频移动,其对应的活化能从1.23 e V下降到0.72 e V,晶界阻抗值下降了约两个数量级.最后,建立了Ca Cu3Ti4O12陶瓷的阻容电路模型,分析了介电弛豫过程与电性能之间的关联.展开更多
文摘The CaCu3Ti4O12(CCTO) ceramic was prepared through conventional solid-state method. The effects of synthesis process(synthesis temperature and synthesis time) of powder on ceramic microstructures, CuO segregation and electrical properties were investigated. The phase composition was determined by X-ray diffraction and the microstructure was examined by SEM. The dielectric constant, dielectric loss, and resistance of the ceramic were also determined by a precision impedance tester. The results show that, as the synthesis temperature increases, the CCTO ceramic grain size decreases and the stoichiometric ratio of Cu/Ca at the grain boundary increases, the dielectric constant increases and the dielectric loss decreases(40 < f < 10 kHz). In addition, when the synthesis time is shorter than 12 h, the Cu/Ca ratio of CCTO decreases and the dielectric constant increases with time increase. However, when the synthesis time exceeds 12 h, this trend is just the opposite. It is further proved that Cu at the grain boundary is not conducive to the dielectric constant of CCTO.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11074017 and 51032002the IHLB(No PHR201007101),the Beijing Nova Program(No 2008B10)+1 种基金the Beijing Natural Science Foundation(No 1102006)the Scientific Research Foundation for the Returned Overseas Chinese Scholars of the Ministry of Education.
文摘We investigate the dopant site selectivity of CaCu_(3)Ti_(4)O_(12)(CCTO)using the first principles calculations.Our results show that,for four cases of possible occupancy by La atom,lattice expansions and formation enthalpies with different dopant quantities indicate that doped La cations are preferentially substituted for Ca sites in CaCu_(3)Ti_(4)O_(12),which is excellent in agreement with the experimental observation(Choi et al.Adv.Mater.21(2009)885).Furthermore,more interesting information of doping is also explored by the analysis of density of states and it is found that La substituting for Cu may advance the electron conduction in CCTO.It supplies a potential solution for limitations of CCTO devices by exploring the effect when La substitutes for Cu sites in the CCTO crystal.
文摘在电场为3.5 k V/cm的条件下,对Ca Cu3Ti4O12陶瓷进行了60 h的直流老化,研究了老化过程对Ca Cu3Ti4O12陶瓷介电性能和电气特性的影响.J-E特性测试结果表明,直流老化导致Ca Cu3Ti4O12陶瓷击穿场强、非线性系数和势垒高度明显降低.介电性能测试结果表明,低频介电常数和介电损耗明显增大,并且介电损耗随频率的变化遵从Debye弛豫理论,可分解为直流电导损耗和弛豫损耗,直流老化主要导致了电导损耗的增加.在低温233 K,介电损耗谱中出现两个弛豫峰,其活化能分别为0.10,0.50 e V,认为对应着晶粒和畴界的弛豫过程,且不随直流老化而变化.通过电模量谱对Ca Cu3Ti4O12陶瓷的弛豫过程进行了表征,发现直流老化导致的界面空间电荷在外施交变电场的作用下符合Maxwell-Wagner极化效应,并在低频区形成新的弛豫峰.在高温323—473 K的阻抗谱中,晶界弛豫峰在直流老化后明显向高频移动,其对应的活化能从1.23 e V下降到0.72 e V,晶界阻抗值下降了约两个数量级.最后,建立了Ca Cu3Ti4O12陶瓷的阻容电路模型,分析了介电弛豫过程与电性能之间的关联.
