The Preparation And Modification Of Copper Calcium Titanate With High Dieletric Constant By Coprecipitation Method

Dielectric material is widely used as a kind of electronic materials, which playsan important role in scientific research and practical application. The specific capacityof multilayer ceramic capacitor （MLCC） is proportional to dielectric coefficient K ofdielectric material. Therefore, the desire for the capacitors with both large capacityand small size makes research of high dielectric constant materials popular.Most materials with high dielectric constant are ferroelectric materials, such asBaTiO3. This kind of dielectric materials possess ferroelectricity, relaxation andstructural transformation, making dielectric constant sensitive to the change oftemperature and leading to poor stability. Copper calcium titanate （CCTO） is a kind ofnon-ferroelectric material with high dielectric constant, owning many features asfollows:（1） extremely large dielectric constant ε and small dielectric loss δ （ε is about10⁴and δ is about0.2at room temperature and1KHz）;（2） The dielectric response ofCCTO has good thermal stability （the dielectric constant keeps stationary in a widerange of temperature （100-400K））. The synthesis process of CCTO is not relativelycomplicated, and solid reaction, sol-gel and co-precipitation process were generallyemployed for the fabrication.CCTO ceramic powders were synthesized using oxalate as precipitant viaco-precipitation process in this thesis. Phase composition was analyzed through theX-ray diffraction （XRD）, and morphology and size of particles were observed usingscanning electron microscope （SEM）. The composition and decompositiontemperature of components involved in the temperature-rise period were analyzed bydifferentialthermal-thermogravimetry （DTA-TG）. Dielectric properties were tested onelectrochemical workstation IM6e impedance tester. Studying the dielectric propertiesof a series of CCTO ceramic samples synthesized via oxalate co-precipitation process,the optimum experimental parameters were as follows: the pH value of suspension was about3; presintering temperature was850℃; calcination temperature was1100℃for10h. The dielectric constant and loss of optimal sample were16129and0.233at room temperature for1KHz, respectively.The large dielectric constant of CCTO was often companied with large dielectricloss, limiting its practical application as electronic materials. Sr²⁺ and Cr³⁺ ions wereused as doping ions in this thesis to investigate the composition and microstructure ofCCTO after single/co-doping, owing to the dielectric properties including dielectricloss varied when CCTO was doped with ions. The experimental results indicated thatthe dielectric properties of Ca_1-xSr_xCu₃Ti_4-yCryO_12-y/2 samples precalcinated at850℃and calcinated at1100℃for10h were as follows: x=0.1,y=0, the dielectric constantwas large（ε=18125at room temperature for1KHz） while the dielectric loss was alsolarge（δ=0.25at room temperature for1KHz）; x=0,y=0.15, the dielectric loss becamesmaller（δ=0.138at room temperature for1KHz） while the dielectric constant was alsosmaller（ε=5162at room temperature for1KHz）; x=0.15,y=0.15, the dielectricconstant was large（ε=9187at room temperature for1KHz） while the dielectric loss,on the contrary, was smaller（δ=0.11at room temperature for1KHz）.The dielectric properties of CCTO were also investigated by changing themorphology without introducing foreign elements. The morphology of CCTOchanged by adding polyethyleneglycol （PEG） in the co-precipitation process and PEGdecomposed in the subsequent treatment. The experimental results indicated that thedielectric constant of CCTO precalcinated at850℃, calcinated at1100℃for10h andmodified by7.5g/L PEG maintained large（ε=9775at room temperature for1KHz）,and dielectric loss was smaller than unmodified CCTO, and independent withfrequency in the range of104-105Hz; additive PEG made CCTO resultant temperaturedecrease from720℃to670℃without compositive or structural change.