Preparation And Dielectric Properties Of CaCu₃Ti₄O₁₂ And NaCu₃Ti₃NbO₁₂ Ceramics

With the development of electronic devices to high performance,smart and size miniaturization,materials with high dielectric constant have attracted more and more attention.CaCu₃Ti₄O₁₂（CCTO）ceramic have a wide application prospect due to its high dielectric constant,good temperature stability.While the dielectric loss of CCTO ceramics is very high,which may lead to fever and instability in the practical application or even cause damage to the devices.Under these circumstances,it will be an important issue to looking for an effective method that can not only maintain the high dielectric constant of CCTO ceramic,but also significantly reduce its dielectric loss.The CCTO ceramics were prepared by traditional solid state method.In this paper,the phase structure,microstructure and dielectric properties of CCTO ceramics were studied through different process conditions as well as non-stoichiometric of Cu and Ti.It was found the value of dielectric constant is only about 110 at 1 kHz,which is much smaller than the reported.Even by changing the Cu/Ti stoichiometric cannot improve the dielectric properties of samples.In addition,NaCu₃Ti₃NbO₁₂ ceramics were also obtained and studied on its phase structure,microstructure and dielectric properties.Non-stoichiometric of Ti/Nb and MnO₂ doping were designed to lower the dielectric loss of NaCu₃Ti₃NbO₁₂ceramics.NaCu₃Ti₃NbO₁₂ ceramics prepared by solid-state reaction exhibit a giant dielectric constant.Dielectric spectrum shows that the polarization effect of electrode is very significant at room temperature.The sintering temperature has great influence on the grain boundary resistance and dielectric loss of NCTNO ceramic dielectric properties than calcining temperature.With the increase of the sintering temperature,the dielectric loss decreased.No change in crystal structure was observed in different Ti/Nb stoichiometric of NaCu₃Ti_3-xNb_1+xO₁₂ ceramics.Increasing Nb content can inhibit the growth of grains,while the increase of Ti content can promote the grain size.Two dielectric relaxations were observed at room temperature within the measuring frequency range of 20 Hz–1MHz.It is found that the value of tanδdecrease and dielectric loss peaks shift to higher frequency with increasing content of Nb.When Ti and Nb ratio was 2.9:1.1,the relative dielectric constant can reach 3×10⁴ at 1 kHz,the dielectric loss also decreased from 1.7 to 0.9.The dielectric constant is not necessarily related to grain size,but depends on the resistance of grain and grain boundary.Changing the doping content of MnO₂ has little influence on the dielectric constant of NCTNO ceramic.While the dielectric loss increased with the raising of MnO₂ contents.Due to the grain boundary relaxation time increasing,the dielectric loss peak shifts to low frequency.