Advances in Ceramics for Environmental, Functional, Structural, and Energy Applications II, Ceramic Transactions Volume 266

Abstract

: The stability and reproducibility of dielectric properties displayed by calcium copper titanate (CCTO) ceramics can be of concern when they are used as capacitor dielectrics and energy storage applications. Highly irreproducible dielectric properties were observed for samples tested in ambient conditions suggesting that ambient played an important role on the stability of dielectric properties. Consequently, the effects of various atmospheric conditions such as air, moisture, and inertness of the atmosphere on dielectric properties were studied on dense and phase pure CCTO samples prepared by powder processing and sintering. Stable and reproducible impedance data were successfully achieved by testing the samples in dry N 2 . Especially, low frequency dielectric properties were greatly enhanced in dry ambient than in humid air. This new approach of characterizing dielectric properties of CCTO can be used to eliminate hysteresis due to ambient atmosphere and produce stable and reproducible properties. These results will be presented and discussed. Even when prepared by the same preparation conditions or with small changes in the processing, a wide variations of tan δ and ε′ values were reported for CCTO ceramics. This indicates that this material is still not well characterized to find out the reasons for large variations in its properties. Our preliminary experiments showed that dielectric properties of CCTO are very sensitive to ambient air atmosphere where the samples were kept while measuring the AC impedance irrespective of the sintering temperatures. In order to reliably use the CCTO materials as capacitors, its surrounding atmosphere dependent dielectric properties are necessary to eliminate or decrease. However, to the best of our knowledge, electrical properties of CCTO ceramics has not been systematically investigated in a controlled atmosphere. This may have led to reported data in the published literature that cannot be fully rationalized. effect inconsistent dielectric of of long term on the dielectric properties of CCTO ceramics in both a experiments focused on synthetization of CCTO ceramics and characterization microstctures and its dielectric properties. In the current experiments, the electrical properties such as complex impedance, ε′, tan δ, and DC resistance of the CCTO sample S1070 (sintered for 5 h at 1070°C in air) are measured in both air and dry N 2 atmospheres. Electrical properties are characterized using AC impedance spectroscopy while CCTO samples were kept in controlled ambient air and dry atmospheres as a function of frequency (from 1 Hz to 4 MHz) and temperatures from (23°C to 225°C). We report highly irreproducible impedance spectra when the samples were kept in air at low temperatures. Interestingly, reproducible impedance spectra with a lowered tan δ were seen by switching the atmosphere from air to dry N 2 . Data are analyzed and presented with a consideration for more evidence of temperature and frequency dependency of dielectric properties in both the testing atmospheres. The presence of moisture in air and its influence on dielectric loss is also highlighted for observed changes. This study may provide an understanding of the important roles of surrounding atmosphere and sample preparation conditions on the stability of electrical response of polycrystalline CCTO ceramics. of of ABSTRACT An integrative approach is carried out utilizing piezoelectric and thermoelectric device sciences, computational modeling and engineering design/testing. Numerical FEA simulation is used extensively to guide the frequency dependent transducer design, device fabrication and power electronics conversion. The research is to develop modular hybrid integrated sensing and energy conversion (HISEC) unit with optimized energy density and power efficiency. While electric power converted from roadways by a single unit (occupying an area of less than 0.1 m 2 ) using piezoelectric or thermoelectric mechanism alone, is considered intermittent or inadequate for intended applications, the energy conversion integrations make it possible to have complementary and parallel modes of energy-harvesting from roadways to have a self-sustained power source that supports sensing and data transmission functions. The evaluation and testing results obtained validated the design concept and are the base for further optimizations. The HISEC module developed is independent of the power grid and with on-demand data monitoring and information transmitting capabilities, thus could play an enabling role in applications such as smart-roadways and smart-cities.