Structural Model of Planar Defects in CaCu3Ti4O12 Exhibiting a Giant Dielectric Constant

Whangbo, M.‐H.; Subramanian, M. A.

doi:10.1021/cm060323f

Cited by 110 publications

(72 citation statements)

References 8 publications

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“…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?…”

mentioning

confidence: 99%

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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mentioning

confidence: 99%

Broadband dielectric spectroscopy on single-crystalline and ceramic CaCu3Ti4O12

Krohns

Lunkenheimer

Ebbinghaus

et al. 2007

Applied Physics Letters

135

117

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“…Thus, the distortion between these complex clusters causes a polarization and/or difference in charge density in the structure [47,48], which is able to promote a charge transfer from the ½TiO 6 x d / ½TiO 6 x o These complex clusters can also creates the (h ) holes 4 electron (e 0 ) pair or ½TiO 6 d 4½TiO 6 0 o clusters in the CTO, CCTO1 and CCTO2 systems. The charge transference in (Ca 1Àx Cu x ) TiO 3 crystals is also represented by KrögereVink notation [49] by means of clusters notations in Equation (2):…”

Section: X-ray Absorption Near Edge Structure Spectroscopy Analysesmentioning

confidence: 99%

Structural refinement and photoluminescence properties of irregular cube-like (Ca1−xCux)TiO3 microcrystals synthesized by the microwave–hydrothermal method

Oliveira¹,

Moura²,

Mazzo³

et al. 2012

Materials Chemistry and Physics

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“…Whangbo and Subramanian explained the high dielectric constant in terms of its crystal structure, where the high dielectric property may arise from local dipole moments associated with off-center displacement of Ti ions, but the transition to a ferroelectric state is frustrated by the TiO 6 octahedral tilt which is required to accommodate the CuO 2 square planar coordination. [32] It may be probable that the present work is associated with such structural behavior at high temperatures. …”

Section: Introductionmentioning

confidence: 84%

Effect of Cd Dopant on Dielectric Properties of CaCu3Ti4O12

Onodera

Takeuchi

Hiramatsu

2010

Trans. Mat. Res. Soc. Japan

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, 0.01, 0.03, 0.05 and 0.1 was studied in the frequency range of 10 kHz-1 MHz over the temperature range of 300-850 K. It is found that the chemical substitution of Cd ions at the Ca sites results in decrease in dielectric constant by 9% -55% for Cd-doped CaCu 3 Ti 4 O 12 , at room temperature. Although the decrease in the dielectric constant was observed by Cd doping, no drastic suppression of dielectric response could be observed by Cd-doping. The dielectric anomaly was found at T 1 (727 K for x=0.05), which suggests a phase transition. This T 1 decreases linearly with increasing x. CdCu 3 Ti 4 O 12 is still a member of high-dielectric materials.

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Structural Model of Planar Defects in CaCu₃Ti₄O₁₂ Exhibiting a Giant Dielectric Constant

Cited by 110 publications

References 8 publications

Broadband dielectric spectroscopy on single-crystalline and ceramic CaCu3Ti4O12

Broadband dielectric spectroscopy on single-crystalline and ceramic CaCu3Ti4O12

Structural refinement and photoluminescence properties of irregular cube-like (Ca1−xCux)TiO3 microcrystals synthesized by the microwave–hydrothermal method

Effect of Cd Dopant on Dielectric Properties of CaCu<sub>3</sub>Ti<sub>4</sub>O<sub>12</sub>

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