Non-stoichiometric CaCu <sub> 3 </ Sub> Ti <sub> 4 </ Sub> O <sub> 12 </ Sub> Ceramics And Doping Characteristics

CCTO ceramic has broad application prospects in the large-capacity capacitors, dynamic random access memory and other fields, because of its high dielectric constant and temperature stability. But CCTO ceramic has mainly problems in two aspects: on the one hand, its dielectric constant varys greatly owing to different compositions and processes, even up to one magnitude differences, poor reproducibility; on the other hand, its dielectric loss is large. Therefore, it is necessary to improve its dielectric constant and reproducible, while reduce its dielectric loss.To improve its dielectric constant and repeatability, this paper was proposed to change Ca, Cu, Ti elements in different proportions by the solid state technique, and to find the regular pattern that the non-stoichiometry single element impacts on its dielectric properties, and then to find the regular pattern that the non-stoichiometry Ca and Ti, Ca and Cu, Cu and Ti impact on its dielectric properties. The results showed that the non-stoichiometry Ca, Cu, or Ti element impacted differently on its dielectric properties, and that the abnormal dielectric constant existed owing to the deficiency of Cu and Ti. The results also showed that when Ca, Cu, Ti atomic molar ratio was 1.08:3.00:4.44, its relative dielectric constant reached 4×105 at 1KHz , and its dielectric constant improved one magnitude than the standard stoichiometry CCTO ceramics. Its high dielectric constant derived from the larger particle size and the thinner boundary layer, and supported IBLC model.On the basis of ultra-high dielectric constant components in the formula and the firing process, the paper was proposed to doping the high insulation LTCC glass and nano-SiO2 powder at grain boundary of the non-stoichiometry CCTO ceramic in order to reduce its dielectric loss especially the leakage loss. The results showed that CCTO ceramics doped with the high insulation glass would not only speed up the reaction and lower sintering temperature, but also increase significantly the grain boundary resistance and reduce its leakage loss. The results also showed that the negative capacitance effect was firstly observed when the non-stoichiometry CCTO material excessed with a slight CuO and doped with nano-SiO2 powder. It was essentially different with the negative capacitance observed in the P-N junction in the light-emitting diode. The negative capacitance effect was not from the phase of the current - voltage change, but from the capacitor resonant. In particular, this found that the negative capacitance effect at some frequency provides us with the possibility to use capacitor instead of inductance in some frequency band.