Colossal dielectric response in Ba 1.5 Sr 1.5 Co 2 Fe 24 O 41 ceramics at high-temperature
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Colossal dielectric response in Ba1.5Sr1.5Co2Fe24O41 ceramics at hightemperature C. L. Li1 · T. Y. Yan1 · G. O. Barasa1 · Y. H. Li1 · R. Zhang1 · S. Huang2 · S. L. Yuan1 Received: 16 March 2018 / Accepted: 3 April 2018 © Springer Science+Business Media, LLC, part of Springer Nature 2018
Abstract Polycrystalline Ba1.5Sr1.5Co2Fe24O41 ceramics were prepared by the sol–gel method with clear grains and grain boundaries having been identified by the scanning electron microscopy. High-temperature colossal dielectric response has been observed and studied through a series of dielectric and impedance measurements. The electrode effect was also studied and the measurement findings reveal that the colossal dielectric permittivity at low frequency is ascribed to the extrinsic effect of Maxwell Wagner polarization. Dielectric relaxation was identified and investigated by the impedance spectra, which is attributed to the thermally activated model. The complex impedance data is simulated with an equivalent electric circuit and the result suggests that the electric response originates from both the grains and grain boundaries. The activation energies of the grains and grain boundaries are calculated which are 0.62 and 0.67 eV, respectively. The comparable activation energies obtained from the complex impedance spectra and DC conductivity indicates that the relaxation may result from the conduction process. Besides, scaling behaviors are observed below 550 K suggesting that the relaxation time is temperature independent.
1 Introduction Materials with colossal dielectric response (CDR) have attracted remarkable attention for their valuable application in resonators and capacitors [1]. The size of microelectronic devices could be reduced if the materials with high dielectric permittivity as well as the low dielectric loss are developed [2]. CaCu3Ti4O12 as an example of high permittivity material has been extensively studied because it shows extraordinary dielectric permittivity of ~ 105 at ambient temperature [3]. It also shows weak temperature correlation in a large temperature range. The extrinsic effect of Maxwell Wagner type polarization at grain boundaries is considered to be the reason of the CDR in this material [4]. Additionally, the colossal dielectric behavior has also been studied in RFeO3 and R3Fe5O12 [5, 6]. The electrically heterogeneous structure is attributed as the cause for the dielectric properties, which contains semiconducting grains and insulating grain * S. L. Yuan [email protected] 1
School of Physics, Huazhong University of Science and Technology, Wuhan 430074, People’s Republic of China
College of Materials and Environmental Engineering, Hangzhou Dianzi University, Hangzhou 310018, People’s Republic of China
2
boundaries. The search for the giant dielectric materials and studying their underlying CDR mechanism is significant from fundamental and applied point of view. Recently, the CDR has been found in Co2Z-type hexaferrites and the high-temperature relaxation behavior was observed which
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