Dielectric dispersion of CaCu3Ti4O12 ceramics at high temperatures

Zhang, J. L.; Zheng, Peng; Wang, C. L.; Zhao, Minglei; Li, J. C.; Wang, J. F.

doi:10.1063/1.2077864

Cited by 166 publications

(111 citation statements)

References 13 publications

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“…However, if there is any kind of planar defects in SCs generating strong relaxations, should they not contribute to a separate relaxational response in PCs, where grains can reach sizes up to 100 µm, too? Interestingly, it seems clear now that indeed there is a second relaxation in CCTO PCs 9,12,14 and it even was already observed in one of the earliest reports on CCTO 2 .…”

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confidence: 95%

“…Nearly all experimental evidence for a non-intrinsic mechanism so far is based on measurements of ceramic samples (e.g., refs. 4,5,6,7,9,11,12,13). However, extremely high values of ε' of the order of 10 5 were observed particularly in CCTO single crystals (SCs) 3 .…”

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confidence: 99%

“…This demonstrates the tremendous interest in new high-ε' materials, which are prerequisite for further advances in the development of capacitive electronic elements. It soon became clear that the colossal ε' in CCTO must have a non-intrinsic origin 4,5,6,7,8,9,11,12,13 . Nowadays usually the results are interpreted within an "internal barrier layer capacitor" (IBLC) picture: Polarization effects at insulating grain boundaries between semiconducting grains or other internal barriers generate non-intrinsic colossal values of ε', accompanied by a strong Maxwell-Wagner (MW) relaxation mode.…”

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confidence: 99%

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Broadband dielectric spectroscopy on single-crystalline and ceramic CaCu3Ti4O12

Krohns

Lunkenheimer

Ebbinghaus

et al. 2007

Applied Physics Letters

135

117

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We present dielectric measurements of the colossal dielectric constant material CaCu 3 Ti 4 O 12 extending up to 1.3 GHz also covering so far only rarely investigated single crystalline samples. Special emphasis is put on the second relaxation reported in several works on polycrystals, which we detect also in single crystals. For polycrystalline samples we provide a recipe to achieve values of the dielectric constant as high as in single crystals.Among the vast number of papers on the extremely high ("colossal") dielectric constants (ε') found in CaCu 3 Ti 4 O 12 (CCTO) there are at least ten so-called "highly-cited" papers 1,2,3,4,5,6,7,8,9,10 . This demonstrates the tremendous interest in new high-ε' materials, which are prerequisite for further advances in the development of capacitive electronic elements. It soon became clear that the colossal ε' in CCTO must have a non-intrinsic origin 4,5,6,7,8,9,11,12,13 . Nowadays usually the results are interpreted within an "internal barrier layer capacitor" (IBLC) picture: Polarization effects at insulating grain boundaries between semiconducting grains or other internal barriers generate non-intrinsic colossal values of ε', accompanied by a strong Maxwell-Wagner (MW) relaxation mode. As an alternative, a "surface barrier layer capacitor" (SBLC) picture was proposed, assuming, e.g., the formation of Schottky diodes at the contact-bulk interfaces 8,9,14 . Nearly all experimental evidence for a non-intrinsic mechanism so far is based on measurements of ceramic samples (e.g., refs. 4,5,6,7,9,11,12,13). However, extremely high values of ε' of the order of 10 5 were observed particularly in CCTO single crystals (SCs) 3 . With only few exceptions 11 , measurements of polycrystals (PCs) reveal much lower values in the range of 10 3 -10 4 . There are no grain boundaries in SCs and thus there were speculations about other internal boundaries as, e.g., twinboundaries 4,6,15,16 . However, if there is any kind of planar defects in SCs generating strong relaxations, should they not contribute to a separate relaxational response in PCs, where grains can reach sizes up to 100 µm, too? Interestingly, it seems clear now that indeed there is a second relaxation in CCTO PCs 9,12,14 and it even was already observed in one of the earliest reports on CCTO 2 .It leads to even larger ε' values than the well-known main relaxation. Thus one could speculate that one of the two relaxations is due to grain boundaries and the other due to planar defects within the grains. Alternatively, one relaxation could be due to an IBLC and the other to a SBLC mechanism 9 . In the present work we aim to elucidate differences and similarities in SC and PC behavior, address the question of the second relaxation, and try to help solving the IBLC/SBLC controversy. For this purpose, we performed measurements on various samples including single-crystals, which to our knowledge so far only were investigated in two works 3,16 . The spectra cover up to nine frequency decades and extend up to the technically relev...

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Broadband dielectric spectroscopy on single-crystalline and ceramic CaCu3Ti4O12

Krohns

Lunkenheimer

Ebbinghaus

et al. 2007

Applied Physics Letters

135

117

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“…21 Nowadays, it is widely accepted that the high permittivity value of sintered CCTO ceramics is associated with an internal barrier layer capacitance (IBLC) structure. [23][24][25] In this model, the conductivity of a sample is prevented from percolating by the presence of insulating blocking layers at the surfaces or at internal domain boundaries. Thus, the behaviour of CCTO can be explained in terms of semiconducting grains surrounded by insulating grain boundaries, which make it to be considered as a very promising high dielectric constant filler for applications in microelectronic, mainly in capacitive applications.…”

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confidence: 99%

Towards materials with enhanced electro-mechanical response: CaCu3Ti4O12–polydimethylsiloxane composites

et al. 2012

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We describe a straightforward production pathway of polymer matrix composites with increased dielectric constant for dielectric elastomer actuators (DEAs). Up to date, the approach of using composites made of high dielectric constant ceramics and insulating polymers has not evidenced any improvement in the performance of DEA devices, mainly as a consequence of the ferroelectric nature of the employed ceramics. We propose here an unexplored alternative to these traditional fillers, introducing calcium copper titanate (CCTO) CaCu 3 Ti 4 O 12 , which has a giant dielectric constant making it very suitable for capacitive applications. All CCTO-polydimethylsiloxane (PDMS) composites developed display an improved electro-mechanical performance. The largest actuation improvement was achieved for the composite with 5.1 vol% of CCTO, having an increment in the actuation strain of about 100% together with a reduction of 25% in the electric field compared to the raw PDMS matrix.

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“…Correspondingly, broad shoulders in σ' and tan δ show up. Interestingly, if CCTO is investigated in a sufficiently broad temperature and frequency range, also there a second relaxation is detected (8,11,12,19). It should be noted that the loss tangent of LSNO (also termed dissipation factor; Fig.…”

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Colossal dielectric constant up to gigahertz at room temperature

Krohns

Lunkenheimer

Kant

et al. 2009

Applied Physics Letters

192

148

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In recent years, large effort has been put into the development and characterization of new colossal-ε' materials. For example, the recent discovery (1,2) of "colossal" values of the dielectric constant, ε', up to about 10 5 in CaCu 3 Ti 4 O 12 (CCTO) has aroused tremendous interest and a huge number of publications deals with its investigation and optimization. Aside of the extensively investigated CCTO, there are also some reports of other colossal-ε' materials (e.g., refs. (3,4,5,6,7)), mainly transition metal oxides. While there is no clear definition, the term "colossal" typically denotes values of ε' > 10 4 . Such materials are very appealing for the further miniaturization of capacitive components in electronic devices and also in giant capacitors that may replace batteries for energy storage.Of course, colossal dielectric constants are also found in ferroelectrics where close to the phase transition very large values are reached. However, ferroelectrics are characterized by a strong temperature dependence of ε' around their critical temperature, which restricts their applicability. In contrast, CCTO and other materials stand out due to their colossal-ε' values being nearly constant over a broad temperature range around room temperature. But in all these materials a strong frequency dependence is observed, revealing the signature of relaxational contributions, namely a steplike decrease of ε' above a certain, temperaturedependent frequency, accompanied by a peak in the dielectric loss. Intrinsic relaxations are commonly observed, e.g., in materials containing dipolar molecules, which reorient in accord with the ac field at low frequencies, but cannot follow at high frequencies. However, the extensive investigations of CCTO, have quite clearly revealed that the observed relaxation features are due to a nonintrinsic effect, termed Maxwell-Wagner (MW) relaxation (8,9,10). It arises from heterogeneity of the sample, which is composed of a bulk region with relatively high conductivity and one or several relatively insulating thin layers. The equivalent circuit describing such a sample leads to a relaxation-like frequency and temperature dependence (10). The insulating layers can arise, for example, from surface effects (e.g., depletion regions of Schottky diodes at the electrodes) or internal barriers (e.g., grain boundaries). However, this is rather irrelevant from an application point of view (e.g., external surface layers are used to enhance the capacitance in ferroelectrics-based multi-layer ceramic capacitors). Thus, although in CCTO the exact mechanism is not yet finally clarified, the interest in this material is still high. This is, amongst others, demonstrated by the fact that since its discovery in 2000, twelve socalled "highly-cited" papers on this topic have appeared (source: ISI Web of Science, Nov. 2008). Unfortunately, at room temperature the relaxation in CCTO leads to a decrease of ε' in the MHz region and around GHz only values of the order of 100 are observed (8,11,12). In contrast, electron...

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Dielectric dispersion of CaCu3Ti4O12 ceramics at high temperatures

Cited by 166 publications

References 13 publications

Broadband dielectric spectroscopy on single-crystalline and ceramic CaCu3Ti4O12

Broadband dielectric spectroscopy on single-crystalline and ceramic CaCu3Ti4O12

Towards materials with enhanced electro-mechanical response: CaCu3Ti4O12–polydimethylsiloxane composites

Colossal dielectric constant up to gigahertz at room temperature

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