The relaxor-like behavior in CaCu3Ti4O12 was investigated in details. The dielectric anomaly was found to be an extrinsic phenomenon related to oxygen vacancy. Annealing treatments in N2 and O2 atmospheres revealed that the relaxor-like behavior is composed of two types of relaxations with close relaxation parameters. Impedance analysis showed that the relaxations appearing in the low- and high-temperature wings of the anomaly are related to the dipolar and Maxwell-Wagner (MW) relaxation, respectively. Both relaxations are induced by the hopping motions of confined carriers related to single-ionized oxygen vacancies, and they are intimately linked with each other. The relaxor-like anomaly is attributed to the combining effect of these two relaxations, i.e., the dipolar relaxation first creates a steplike increase followed by a rapid decrease in dielectric constant caused by the MW relaxation, thereby, giving rise to the relaxor-like behavior.

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We reported the dielectric properties of CaCu 3 Ti 4 O 12 in the temperature range from room temperature to 800°C and the frequency range from 20 Hz to 10 MHz. Apart from the widely reported dielectric anomaly occurring around 200°C, three additional dielectric anomalies were found. The new anomalies are very sensitive to electrode sintering conditions and annealing atmospheres, indicating that they are dependent not only on the electrode-sample contact but also on oxygen vacancies. Since the perovskite-related CaCu 3 Ti 4 O 12 (CCTO) has been reported to have colossal and flat dielectric constants in the order of 10 3 -10 5 in a wide temperature range around room temperature, which presents promising potential applications for kinds of devices, researchers have carried out a great deal of investigations on this material [1][2][3]. In addition to the stunning colossal dielectric behavior with its main features appearing in the temperature range below room temperature, a relaxor-like dielectric anomaly occurring in the temperature range from 400 to 600 K was considered as another surprising feature in CCTO [4][5][6]. Although this feature is still an open question and ascribed to various causes, such as ferroelectric relaxor [4], electronic ferroelectrics [5], artificial phenomenon due to negative capacitance, and pseudo-relaxor caused by Maxwell-Wagner (MW) relaxation [6], it reveals the rich dielectric phenomena in CCTO at high temperatures. These phenomena have not been illustrated thoroughly until now. In this work, we measured samples of CCTO in the high temperature range from room temperature to 800°C. The results showed that apart from the above-mentioned dielectric anomaly, three additional anomalies related to oxygen vacancy and electrode-sample contact were found. ceramics, dielectrics, grain boundaries ExperimentalCCTO pellets used for dielectric measurements were prepared by solid-state reaction method. High-purity (99.99%) powders of CaCO 3 , TiO 2 and CuO were mixed according to molar ratios and well ground in a mortar. The mixture were fired in air at 1000°C for 12 h and then reground, followed by a sintering process at 1100°C for 29 h. Finally, the mixture was pressed into pellets and sintered in air at 1100°C for 10 h. The purity of the resultant compound was examined by powder X-ray diffraction (XRD) on an XD3 diffractometer with Cu K radiation. After polishing both sides of the samples, platinum or silver paint were coated on them and fired at high temperature for different time to remove the polymeric components. Details about the sintering temperature and time were listed in Table 1. A Wayne Kerr 6500B precise impendence analyzer with a heating ramp of 3 K/min controlled by a Stanford temperature controller was used to collect data for temperature dependent dielectric properties. The dielectric measurements were performed in ambient air. Annealing treatments were performed in flowing (200 mL/min) O 2 and N 2 (both with purity >99.999%) at 1000°C for 2 h. The heating and cooling rates in samp...

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