Effect of synthesizing temperatures on the microstructure and electrical property of CaCu3Ti4O12ceramics prepared by sol-gel process

A sol-gel process was used to synthesize gel precursors of CaCu3Ti4O12 (CCTO) ceramics. The XRD patterns show that a considerable amount of CCTO phase has been formed after the gels were calcined at 800 °C and 900 °C and after the sintering process for the samples all the second phases have disappeared. The SEM images display that the microstructure morphology is obviously affected by synthesizing temperatures. The grain size increases with the increasing sintering temperature and some melt Cu-rich phase appears at grain boundaries of the sample sintered at 1100 °C. Positron annihilation lifetime and Doppler broadening spectra results indicate that the concentration of Cu2+ vacancies increases with the increase of sintering temperature and the defect species remains the same. High defect concentration of samples sintered at1070 °C and 1100 °C leads to poor stability of permittivity and large dielectric loss values at low frequencies and poor nonlinear behavior. The results of impedance spectroscopy support well the views.