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1、Giant dielectric properties of CaCu3Ti4O12 ceramicsprepared by citric acid solgel method#QIU YANG, CHEN LIANG*5101520253035(School of Physics,HUAZHONG UNIVERSITY OF SCIENCE AND TECHNOLOGY)Abstract: A series of CaCu3Ti4O12 (CCTO) samples are prepared by a citric acid sol-gel method andsubsequent sint
2、ering and dielectric properties are investigated. Systematical characterizations by bothx-ray diffraction and Raman spectra identify component phases of the sintered products, verifying theformation of single phased CCTO if the suitable sintering temperature and durations are selected. Wellcrystalli
3、zed grains with the size of several microns are attained for the samples sintered at 1020 C for5 h, will make a contribution to giant dielectric behavior, evidenced by the highest value of 2.5104 in the frequency range of 102 to 5105 Hz. Dielectric spectroscopy measurements show thatsimilar dielectr
4、ic dispersions are observed for the sintered samples, which can be well interpreted bythe interface polarization from grain boundaries and the bulk effect.Key words: giant dielectric effect, sintering processing,sol-gel method0 IntroductionStimulated by the integration and miniaturization of electro
5、nic devices, many studies areengaged in exploring high-permittivity dielectric materials due to their applications in capacitorsand memory devices. However, most of the high-permittivity dielectric materials generally containlead and are extremely sensitive to the service temperature, which restrict
6、s their practicalapplications. Recently, a lead-free cubic perovskite material CaCu3Ti4O12 (CCTO) has drawnconsiderable research efforts, because of its unusual dielectric properties.18 The dielectricconstant of CCTO with a magnitude of 104 around radio frequency at room temperature can beachieved,
7、and the dielectric constant is almost temperature independent from 100 to 600 K.13 Sofar, many investigations have been carried out on the origin of the unusual dielectric properties.18Among all the models to explain the intriguing dielectric behavior of CCTO, the internal grainboundary barrier laye
8、r capacitance (IBLC) model is commonly accepted.4 The CCTO ceramicsare generally prepared by a standard solid state reaction method. However, this method suffersfrom the limitations of longer preparation period, impurity phases, inhomogeneity and otherdisadvantages. As a wet chemical method, the sol
9、-gel method has been widely used in preparingdielectric ceramics for its advantages of atomic scaled reactions, lower reaction temperatures,shorter reaction times and uniform microstructures. 9, 10In this paper, a series of CCTO ceramics have been synthesized by a citric acid sol-gelmethod. The effe
10、ct of sintering conditions on the microstructure and dielectric properties areinvestigated.Foundations: Specialized Research Fund for the Doctoral Program of Higher Education(20100142120079)Brief author introduction:QIUYANG,1988,male, doctor, Materials ScienceCorrespondance author: CHENLIANG，1979，ma
11、le, Associate Professor,Materials Science. -1-1 Experimental procedureThe CaCu3Ti4O12 polycrystalline ceramics were prepared by a citric acid solgel method. Thesynthesis procedure was outlined in Fig. 1. The calcium nitrate Ca(NO3)24H2O, copper (II) nitrate40455055Cu(NO3)2.3H2O, tetrabutyl titanate
12、(IV) C16H36O4Ti were used as raw materials. TheCa(NO3)24H2O and Cu(NO3)23H2O were dissolved in distilled water and then citric acid wasadded. C16H36O4Ti was dissolved in citric acid water solution, and then the two solutions weremixed together. The mixture was adjusted to a PH value of 6.57.5 by add
13、ing ammonia. After that,the precursor solution was aged at room temperature for 10 h. Then the solution was dried at 120C for 6 h to form xerogel. The precursory powders were cold-pressed into pellets of 1 mmthickness and 12 mm diameters. The pellets were sintered in air at 1020 C for 2 h (sample A)
14、, at1020 C for 5 h to (sample B), and at 1080 C for 2 h (sample C). Silver electrodes were coated onboth sides of the specimens for electrical measurements. The temperature of possibledecomposition and crystallization was determined by the thermogravimetric-differential thermalanalysis (TG-DTA) (Dia
15、mond, PerkinElmer Instrument, USA). The crystal structure of thesamples was investigated by X-ray diffraction (XPert PRO, PANalytical B.V, NED). The Ramanscattering was examined by a confocal Raman microspectroscopy (RM-1000, Renishaw, UK).The micrographs were investigated by field emission scanning
16、 electron microscopy (VEGA,TESCAN, CZ). Dielectric properties of the ceramics were obtained with a precision impedanceanalyzer (6500B, WK, UK).Fig. 1. Flow diagram for the preparation procedure of CCTO samples.-2-DTA(uv)TG(%)(220)(013)(222)(123)(400) (440)(211)Intensity(a.u.)(422)2 Results and discussion6065Figure 2 represents the TG-DTA curves of precursory powders with the temperature scanfrom 50 to 1150 C in air. Continuous
