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 14.06.2011   Карта сайта     Language По-русски По-английски
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14.06.2011

rnal of Alloys and Compounds
Volume 509, Issue 29, 21 July 2011, Pages 7697-7701



Dielectric relaxation behaviors of pure and Pr6O11-doped CaCu3Ti4O12 ceramics in high temperature range


L.F. Xua, P.B. Qia, X.P. Songa, X.J. Luoa and C.P. YangCorresponding Author Contact Information, a, E-mail The Corresponding Author





a Faculty of Physics and Electronic Technology, Hubei University, Wuhan 430062, People's Republic of China




Received 15 November 2010;


revised 16 February 2011;


accepted 19 February 2011.


Available online 5 March 2011.












Abstract



Pure and Pr6O11-doped CaCu3Ti4O12 (CCTO) ceramics were prepared by conventional solid-state reaction method. The compositions and structures were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The influences of Pr-ion concentration on dielectric properties of CCTO were measured in the ranges of 60 Hz–3 MHz and 290–490 K. The third phase of Ca2CuO3 was observed from the XRD of CCTO ceramics. From SEM, the grain size was decreased obviously with high valence Pr-ion (mixing valence of Pr3+ and Pr4+) substituting Ca2+. The room temperature dielectric constant of Pr-doped CCTO ceramics, sintered at 1323 K, was an order of magnitude lower than the pure CCTO ceramics due to the grain size decreasing and Schottky potential increasing. The dielectric spectra of Pr-doped CCTO were flatter than that of pure CCTO. The loss tangent of Pr-doped CCTO ceramics was less than 0.20 in 2 × 102–105 Hz region below 440 K. The complex impedance spectra of pure and Pr-doped CCTOs were fitted by ZView. From low to high frequency, three semicircles were observed corresponding to three different conducting regions: electrode interface, grain boundary and grain. By fitting the resistors R and capacitors C, the activation energies of grain boundary and electrode contact were calculated. All doped CCTOs showed higher activation energies of grain boundary and electrode than those of pure CCTO ceramics, which were concordant with the decreasing of dielectric constant after Pr6O11 doping





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