Study On Doping Modification Of CaCu₃Ti₄O₁₂ Ceramics With Colossal Dielectric Constant

CaCu₃Ti₄O₁₂（hereinafter referred to as CCTO）ceramic is a material with perovskite structure,and its dielectric constant is almost constant in the frequency range of10²-10⁵Hz.In addition to the typical TiO₆ octahedron,CCTO has a rigid CuO₄ square structure that can effectively inhibit the ferroelectric phase transition of the perovskite structure,making the dielectric constant of CCTO almost constant in the temperature range of 100-600K.The excellent dielectric properties make CCTO promising to replace ferroelectric materials that are currently widely used.However,the giant dielectric constant is often accompanied by high dielectric losses,which limits the practical application of CCTO ceramic.The CCTO ceramics herein are all prepared by the conventional solid phase reaction method.And analyzed at room temperature by X-ray diffraction（XRD）to observe the crystallographic phase.The field emission scanning electron microscopy（SEM）was used to observe the surface morphology of ceramics by backscattered electron imaging.The energy dispersive spectrometer（EDS）was used to analysis the cations distribution in the grain and at grain boundary.And X-ray photoelectron spectroscopy（XPS）was used to study the valence state of metal cations in CCTO ceramics.Dielectric frequency spectra of CCTO samples were measured at different temperatures by a broadband dielectric spectrosmeter.In this paper,the effects of donor and acceptor doping at the Ca or Ti sites on the dielectric properties and point defect structure of CCTO ceramics were investigated.It is revealed experimentally that dielectric loss at the intermediate frequency region is restrained effectively by donor doping.While,Schottky barrier height at the grain boundary decreases obviously,which leads to the increase of dielectric loss at low frequency region.As for acceptor doping,Schottky barrier at grain boundary is increased and dielectric loss at low frequency is reduced.At the same time,grain conductance is restrained and dielectric loss at high frequency region is decreased.Antisite point defects were formed by Cu²⁺doping on Ca²⁺site or Ca²⁺doping on Cu²⁺site.It is found that antisite point defects has little effect on the dielectric properties CCTO ceramics.For the condition that Cu²⁺doping on Ca²⁺site,the change of dielectric properties is similar to that of acceptor doping.Dielectric loss at the intermediate frequency is reduced.Although Cu-rich phase segregation at grain boundary is promoted by the increase of Cu content,it has little effect on the overall dielectric properties of CCTO ceramics.