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Title: Conducting grain boundaries in the high-dielectric-constant ceramic CaCu{sub 3}Ti{sub 4}O{sub 12}

Abstract

To clarify the electrical property of grain boundaries, the fine-grained ceramics CaCu{sub 3}Ti{sub 4}O{sub 12} have been treated with the hydrofluoric acid to remove the parts of grain boundaries. The dielectric response difference between the etched samples and the pristine ones indicates that the ceramic CaCu{sub 3}Ti{sub 4}O{sub 12} consists of insulating or semiconducting grains with conducting grain boundaries. Therefore, the giant dielectric phenomenon is supposed not to derive from the grain boundary barrier layer capacitance effect. The possible mechanism is discussed.

Authors:
; ; ; ; ;  [1];  [2]
  1. National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093 (China)
  2. (China)
Publication Date:
OSTI Identifier:
20982804
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 101; Journal Issue: 7; Other Information: DOI: 10.1063/1.2713943; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; CALCIUM COMPOUNDS; CAPACITANCE; CERAMICS; COPPER COMPOUNDS; DIELECTRIC MATERIALS; ETCHING; GRAIN BOUNDARIES; HYDROFLUORIC ACID; PERMITTIVITY; TITANATES

Citation Formats

Chen, K., Li, G. L., Gao, F., Liu, J., Liu, J. M., Zhu, J. S., and Department of Physics, Nanjing University, Nanjing 210093. Conducting grain boundaries in the high-dielectric-constant ceramic CaCu{sub 3}Ti{sub 4}O{sub 12}. United States: N. p., 2007. Web. doi:10.1063/1.2713943.
Chen, K., Li, G. L., Gao, F., Liu, J., Liu, J. M., Zhu, J. S., & Department of Physics, Nanjing University, Nanjing 210093. Conducting grain boundaries in the high-dielectric-constant ceramic CaCu{sub 3}Ti{sub 4}O{sub 12}. United States. doi:10.1063/1.2713943.
Chen, K., Li, G. L., Gao, F., Liu, J., Liu, J. M., Zhu, J. S., and Department of Physics, Nanjing University, Nanjing 210093. Sun . "Conducting grain boundaries in the high-dielectric-constant ceramic CaCu{sub 3}Ti{sub 4}O{sub 12}". United States. doi:10.1063/1.2713943.
@article{osti_20982804,
title = {Conducting grain boundaries in the high-dielectric-constant ceramic CaCu{sub 3}Ti{sub 4}O{sub 12}},
author = {Chen, K. and Li, G. L. and Gao, F. and Liu, J. and Liu, J. M. and Zhu, J. S. and Department of Physics, Nanjing University, Nanjing 210093},
abstractNote = {To clarify the electrical property of grain boundaries, the fine-grained ceramics CaCu{sub 3}Ti{sub 4}O{sub 12} have been treated with the hydrofluoric acid to remove the parts of grain boundaries. The dielectric response difference between the etched samples and the pristine ones indicates that the ceramic CaCu{sub 3}Ti{sub 4}O{sub 12} consists of insulating or semiconducting grains with conducting grain boundaries. Therefore, the giant dielectric phenomenon is supposed not to derive from the grain boundary barrier layer capacitance effect. The possible mechanism is discussed.},
doi = {10.1063/1.2713943},
journal = {Journal of Applied Physics},
number = 7,
volume = 101,
place = {United States},
year = {Sun Apr 01 00:00:00 EDT 2007},
month = {Sun Apr 01 00:00:00 EDT 2007}
}
  • In the present work, CaCu{sub 3}Ti{sub 4}O{sub 12} (CCTO) nanoceramics with different grain sizes were prepared by spark plasma sintering (SPS) at different temperatures (SPS-800, SPS-900, SPS-975, and SPS-1050) of the mechanosynthesized nano-powder. Structural and microstructural properties were studied by XRD and field-emission scanning electron microscope measurements. The grain size of CCTO nanoceramics increases from 80 nm to ∼200 nm for the ceramics sintered at 800 °C and 975 °C, respectively. Further increase of SPS temperature to 1050 °C leads to micro-sized ceramics of 2–3 μm. The electrical and dielectric properties of the investigated ceramics were studied by impedance spectroscopy. Giant dielectric constant was observed inmore » CCTO nanoceramics. The dielectric constant increases with increasing the grain size of the nanoceramics with values of 8.3 × 10{sup 3}, 2.4 × 10{sup 4}, and 3.2 × 10{sup 4} for SPS-800, SPS-900, and SPS-975, respectively. For the micro-sized SPS-1050 ceramics, the dielectric constant dropped to 2.14 × 10{sup 4}. The dielectric behavior is interpreted within the internal barrier layer capacitance picture due to the electrical inhomogeneity of the ceramics. Besides the resistive grain boundaries that are usually observed in CCTO ceramics, domain boundaries appear as a second source of internal layers in the current nanoceramics.« less
  • The effect of the addition of glassy phases on the microstructure and dielectric properties of CaCu{sub 3}Ti{sub 4}O{sub 12} (CCTO) ceramics was investigated. Both single-component (B{sub 2}O{sub 3}) and multi-component (30 wt% BaO-60 wt% B{sub 2}O{sub 3}-10 wt% SiO{sub 2} (BBS)) glass systems were chosen to study their effect on the density, microstructure and dielectric properties of CCTO. Addition of an optimum amount of B{sub 2}O{sub 3} glass facilitated grain growth and an increase in dielectric constant. However, further increase in the B{sub 2}O{sub 3} content resulted in its segregation at the grain boundaries associated with a reduction in themore » grain size. In contrast, BBS glass addition resulted in well-faceted grains and increase in the dielectric constant and decrease in the dielectric loss. An internal barrier layer capacitance (IBLC) model was invoked to correlate the dielectric constant with the grain size in these samples. - Graphical abstract: Scanning electron micrograph of 30 wt% BaO-60 wt% B{sub 2}O{sub 3}-10 wt% SiO{sub 2} (BBS) glass-added CaCu{sub 3}Ti{sub 4}O{sub 12} ceramic on sintering.« less
  • Using transmission electron microscopy (TEM) we studied CaCu{sub 3}Ti{sub 4}O{sub 12}, an intriguing material that exhibits a huge dielectric response, up to kilohertz frequencies, over a wide range of temperature. Neither in single crystals, nor in polycrystalline samples, including sintered bulk and thin films, did we observe the twin domains suggested in the literature. Nevertheless, in the single crystals, we saw a very high density of dislocations with a Burger vector of [110], as well as regions with cation disorder and planar defects with a displacement vector (1/4)[110]. In the polycrystalline samples, we observed many grain boundaries with oxygen deficiency,more » in comparison with the grain interior. The defect-related structural disorders and inhomogeneity, serving as an internal barrier layer capacitance in a semiconducting matrix, might explain the very large dielectric response of the material. Our TEM study of the structure defects in CaCu{sub 3}Ti{sub 4}O{sub 12} supports a recently proposed morphological model with percolating conducting regions and blocking regions.« less
  • No abstract prepared.
  • Highlights: • High ϵ′ PVDF/CCTO and La doped CCTO composites prepared by Extrusion. • With addition of ceramic, there is substantial increase in the ϵ′ of matrix PVDF. • Composites exhibit double relaxation behavior. - Abstract: Melt extrusion process has been used to prepare high relative permittivity, ϵ' PVDF–CCTO and PVDF–LaCCTO composites. Phase composition has been studied using powder X-ray diffraction (XRD). Microstructural, dielectric and mechanical properties have also been studied. Young's modulus of PVDF increases with the ceramic reinforcement. Dielectric measurements are made in the frequency range 10{sup −2}–10{sup 6} Hz using two probe Novocontrol impedance analyser (ZG4) frommore » room temp to 120 °C to study the dielectric relaxation. There is a substantial increase in ϵ' of the matrix PVDF on addition of LaCCTO.« less