Study On Dielectric Relaxation Mechanism And Doping Modification Of CaCu₃Ti₄O₁₂ Ceramics With Colossal Dielectric Constant

CaCu₃Ti₄O₁₂?hereinafter referred to as CCTO?ceramic is a new type of colossal dielectric constant material.Its dielectric constant is higher than 10⁴ and almost unchanged in the temperature range from 100K to 600K and the frequency range from 10²to 10⁵Hz.However,loss angle tangent,tand?11?is higher than 0.1 in the wide frequency range,which seriously affects its application in capacitor materials,high density information storage materials and so on.Therefore,the study on dielectric relaxation mechanism and the origin of high dielectric loss is very important for the optimization of dielectric properties of CCTO ceramic.In this paper,CCTO ceramics are prepared by conventional solid state reaction process.The crystalline structure of CCTO is measured by X-ray diffraction?XRD?to be cubic perovskitein.The polarization mechanism of CCTO is analyzed by dielectric frequency spectrum at different temperatues with the help of wide band dielectric spectroscopy.At the same time,the relationship between giant dielectric constant and the microstructure was verified by Scanning Electron Microscopy?SEM?and Energy Dispersive Spectroscopy?EDS?.The optimal process for preparing CCTO ceramic was obtained by adjusting sintering time,sintering temperature and pressing pressure.It is found that the samples prepared under 9MPa pressure and sintered at 1100^oC for 20h own quite excellent dielectric properties.The origin of colossal dielectric constant was explored by modulation cooling ways and heat treat atmosphere.It is found that the colossal dielectric constant of CCTO originates from grain conduction.The effect of acceptor doping on dielectric properties of CCTO ceramics was studied in this paper.It was found that point defect structure of CCTO is unchanged after Na doping,impling that dirlectric relaxation of CCTO comes from intrinsic point defect oxygen vacancy.As expected,grain conductivity was decreased after doping,which leads to the increase of high frequency dielectric relaxation.This verifies that giant dielectric constant originates from grain condction.At the same time,DC loss at low frequency of dielectric spectrum is found to be depressed effectively because of the increase of barrier height at grain boundary after acceptor doping.The influence of donor doping on dielectric properties of CCTO ceramics was studied also.It was found that dielectric loss at middle frequency is reduces significantly after Nd doping for the inhibition of donor oxygen vacancy.The loss angle tangent is only 0.05 at1KHz when 0.03mol Nd is doped.At the same time giant dielectric constant of 10⁴ is maintained since donor doping of Nd is benefical for grain conduction.However,DC loss at low frequency increases a little for the decrease of Schottky barrier after Nd doping.