The Influence Of Doping Of B Sites On The Structure And Property Of ACu₃Ti₄O₁₂

In this paper,(Fe_1/2Nb_1/2)⁴⁺ doped ACu₃Ti₄O₁₂ materials were prepared by the solid state reaction method and the influences of(Fe_1/2Nb_1/2)⁴⁺ doping with high concentration on the microstructure,dielectric and electrical properties of ACu₃Ti₄O₁₂ materials were studied.CaCu₃[Ti_1-x(Fe_1/2Nb_1/2)_x]₄O₁₂?x=0.0,0.1,0.2,0.5?samples were prepared by the one-step solid state reaction method.As the concentration of(Fe_1/2Nb_1/2)⁴⁺ doping reach up to 50mol%,the samples kept single phase and no secondary phase was observed.The lattice constants of samples increased with(Fe_1/2Nb_1/2)⁴⁺ doping.For pure CaCu₃Ti₄O₁₂?CCTO?,two Debye relaxations were observed in the frequency range and the plateau in the intermediate frequency range was attributed to the interfacial polarization at grain boundaries,while for(Fe_1/2Nb_1/2)⁴⁺ doped CCTO,a Debye relaxation was also observed in the measurement frequency range.Besides,the dielectric constant of CCTO increased with(Fe_1/2Nb_1/2)⁴⁺ doping.And this result may be attributed to a slow polarization,which was introduced by(Fe_1/2Nb_1/2)⁴⁺ doping.In the impedance spectroscopy,it was revealed that the grain resistivity of samples increased with(Fe_1/2Nb_1/2)⁴⁺ doping,while the grain boundary resistivity of samples decreased.This indicated that the electrical heterogeneity between grains and grain boundaries reduced with(Fe_1/2Nb_1/2)⁴⁺ doping,resulting in the decrease of the height of Schottky potential barrier at grain boundaries.The one-step solid state reaction method was still used to prepare the samples with higher doping concentration.The existence of secondary phase was found and could not eliminated readily.Thus new two-step solid reaction method was used to prepared samples with higher doping concentration.For this new method,FeNbO₄ precursor was prepared firstly,and then other reagents reacted with FeNbO4 to prepare samples.The(Fe_1/2Nb_1/2)⁴⁺ doping concentration reached to 60mol% successfully and the sample still kept single phase.By measuring the impedance spectroscopy,the response of surface layer was found in addition to the responses of grain and grain boundary.Bi_2/3Cu₃(Fe_1/2Nb_1/2)₄O_12-x Bi₂O₃?x=-0.02?0.00?0.02?0.05?samples were prepared by two-step solid state reaction method.It was found that the main crystallization phase was still body-centered cubic perovskite-related structure,while secondary phases also existed in the samples.By measuring the relationship between temperature and dielectric constant,it was found that the temperature dependence of dielectric constant of samples was strong.Besides,in the impedance spectroscopy measured at different temperatures,the conduction activation energies of grain and grain boundary could be calculated,revealing the more obvious conduction response of grain boundary with(Fe_1/2Nb_1/2)⁴⁺ doping.