| AC characterization of electroceramics: Issues and way out |
| Jong-Sook Lee |
| Chonnam National University |
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Keywords: parametric analysis, constant phase elements, Cole-Davidson dielectric function
AC characterization technique is an indispensable tool for electroceramic materials, both conducting and dielectric, and for devices comprising them [1-7]. Although the technique is widely applied and getting ever popular, the information therefrom is so far much limited and often disputable. Full parametric analysis based on physical models can provide an unambiguous set of material and device properties. A choice from conventional models such as a brick-layer (Voigt) model and a Debye (Maxwell) model is not generally straightforward, however. Often, the distinction between the ceramic dielectrics and poor (ionic and/or electronic) ceramic conductors is blurred. The electrical roles of the grain boundaries/interfaces and electrodes are multifaceted: constriction, space-charge effects, selectively blocking. Commonly observed dispersive responses are difficult to describe even by employing constant phase elements (CPEs) as generalized capacitors, which arbitrarily adjustable frequency dependence. Frequency-dependent CPEs cannot provide the physical interpretation of capacitance effects. The mono-frequency capacitance analyses typically used for the temperature- or bias-dependence suffer similarly from the frequency-dependent capacitances. In fact, despite strong frequency dispersion in impedance and admittance response, well-defined capacitance effects are indicated in the AC behaviors of a variety of electroceramics. They can be successfully described by employing Cole-Cole or Cole-Davidson dielectric functions, connected in parallel or in ladder network, with the characteristic relaxation times () thermally activated similarly as the bulk conduction and with temperature-independent, constant exponents (). The AC response of the electroceramics can be thus simulated as a function of frequency and temperature [1]. It is suggested that ¡°R¡±-centered impedance spectroscopy should be shifted to ¡°C¡± spectroscopy with capacitance parameters, which are less affected by the connectivity and inhomogeneity than resistance parameters.
References:
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[7] J.-S. Lee et al., Solid State Ionics 68 (1994) 139; J. Electrochem. Soc. 142 (1995) 1169; Solid State Ionics, 98 (1997) 15; J. Electrochem. Soc., 147, (2000) 2407; J. Mater. Res. 16 (2001) 2739; J. Mater. Res. 19, 864-871 (2004); J. Mater. Res. 20 (2005) 2101; Monat. Chem., 140 (2009) 1113; Appl. Phys. Lett. 96 (2010) 202104. |
| Acknowledgements : Fundamental R&D Program for Core Technology of Materials funded by the Ministry of Knowledge Economy, Energy Efficiency & Resources Core Technology program (20122010100110 of KETEP granted financial resource from the Ministry of Trade, Industry & Energy, World Class University (WCU) program (R32-2009-000-20074-0) & Fusion Research Program for Green Technologies (2011-0019304), Basic Science Research Program (KRF-2007-412-J02002) through NRF funded by the Ministry of Science, ICT & Future Planning, Republic of Korea, and KIMS Internal Program "Development of Advanced Powder Materials Technology for New Growth Engine and Its Transfer to Industry. |
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