Enhanced dielectric properties of Ag-doped CCTO ceramics for energy storage devices

Lee, Ji-Won,Koh, Jung-Hyuk Elsevier 2017 Ceramics international Vol.43 No.12

<P><B>Abstract</B></P> <P>Ag-doped CaCu<SUB>3</SUB>Ti<SUB>4</SUB>O<SUB>12</SUB> powders were subjected to high-energy milling to produce nano-sized particles, and the resulting ceramics were analyzed in terms of the dielectric properties and sintering temperature. Ag dopant was added to CaCu<SUB>3</SUB>Ti<SUB>4</SUB>O<SUB>12</SUB> powders to reduce the sintering temperature, and the Ag-doped CaCu<SUB>3</SUB>Ti<SUB>4</SUB>O<SUB>12</SUB> ceramics were sintered at temperatures from 975 to 1125°C to determine the optimum sintering temperature according to the various dopant ratios. The relative dielectric permittivity at a frequency of 1kHz of the 2mol% Ag-doped CaCu<SUB>3</SUB>Ti<SUB>4</SUB>O<SUB>12</SUB> ceramics was higher than that of undoped CaCu<SUB>3</SUB>Ti<SUB>4</SUB>O<SUB>12</SUB> ceramics. The addition of Ag to the CaCu<SUB>3</SUB>Ti<SUB>4</SUB>O<SUB>12</SUB> ceramics was observed to lower the sintering temperature from 1125 to 1075°C. Moreover, the 2mol% Ag-doped CaCu<SUB>3</SUB>Ti<SUB>4</SUB>O<SUB>12</SUB> ceramics prepared from nano-size particles exhibited an improved relative dielectric permittivity. These results suggest that Ag-doping and reducing the particle size of the CaCu<SUB>3</SUB>Ti<SUB>4</SUB>O<SUB>12</SUB> ceramics decreases their sintering temperature and improves their dielectric properties.</P>

Microstructures and Dielectric Properties of Cu-deficient and Excess CaCu3Ti4O(12) Polycrystalline Ceramics

( Sung Yun Lee ),( Duk Keun Yoo ),( Sang Im Yoo ) 대한금속재료학회 ( 구 대한금속학회 ) 2007 ELECTRONIC MATERIALS LETTERS Vol.3 No.1

We report the important roles of Cu composition in CaCu3Ti4O(12) (CCTO) polycrystalline ceramics. These roles include influencing the microstructural change and remarkably high dielectric constant, ε(r) in a relatively low frequency region. For this purpose, CaCu(2.8)Ti4O(12) (Cu2.8) and CaCu(2.9)Ti4O(12) (Cu2.9) powders with a Cu-deficient composition, CaCu(3.1)Ti4O(12)(Cu3.l) and CaCu(3.2)Ti4O(12) (Cu3.2) powders with a Cu-excess composition and CaCu3Ti4O(12) (Cu3.0) (CCTO) powder were prepared. All of these samples were calcined at 950℃ for 24h, and then sintered at 1060℃ for 12h using a conventional solid-state ceramic process. As the Cu composition decreased, the Cu-deficient samples changed from a duplex microstructure including abnormally grown grains and fine grains to a microstructure almost fully covered with fine grains without any abnormally grown grains. However, the Cu-excess samples showed fine-grained microstructures in which no abnormally grown grains were observed with Cu-rich seco1ldary phases segregated at the grain boundaries compared with CCTO. Relative dielectric constants of the, ε(r) values of the samples were strongly affected by the size and population of abnormally grown grains which were varied with the amount of Cu-rich secondary phases.

Structure and electrical properties of Pr6O11-doped CaCu3Ti4O12 NTC ceramics

Zuo Yang,Tian Jian,Tian Yuxin,Miao Guangtan,Fu Peng 한국세라믹학회 2023 한국세라믹학회지 Vol.60 No.3

The xPr6O11–(1 − x)CaCu3Ti4O12 (CCTO) ceramics with perovskite structure were prepared by the solid-state reaction method. The effects of Pr 6O11 addition on the microstructure and electrical properties of the CCTO ceramics were studied. The addition of Pr 6O11 promoted the sintering of CCTO ceramics, and the mean grain sizes increased gradually from 2.13 to 5.08 μm with increasing Pr 6O11 content. All the samples had noticeable negative temperature coefficient (NTC) effect, and both the grain and grain boundary effects contributed to their NTC characteristics. The thermistor characteristic parameter B25/75 decreased from 6883 to 5291 K as Pr 6O11 contents increased from 0.00 to 0.08. The analysis shows that the conductivity of Pr 6O11–CCTO ceramics arises mainly from the electron hopping transport mechanism. The GB resistances are noticeably higher than grain resistances at the same Pr 6O11 content. All the samples showed electrical relaxation behavior. The above observations indicate that the structures and electrical properties of CCTO ceramics can be attuned precisely by adjusting the Pr 6O11 concentration.

Phase evolution and enhanced dielectric properties of BaO.Nd₂O₃.TiO₂.B₂O₃ glass-based dielectrics containing CaCu₃Ti₄O₁₂

Key, S.H.,Lee, D.W.,Jung, J.W.,Kim, B.K.,Cho, Y.S. Elsevier Sequoia 2012 JOURNAL OF ALLOYS AND COMPOUNDS Vol.530 No.-

CaCu<SUB>3</SUB>Ti<SUB>4</SUB>O<SUB>12</SUB> (CCTO) has been studied as a filler for the potential high k LTCC (low temperature co-fired ceramics) materials based on a nonconventional BaO.Nd<SUB>2</SUB>O<SUB>3</SUB>.TiO<SUB>2</SUB>.B<SUB>2</SUB>O<SUB>3</SUB> glass in terms of firing temperature and CCTO content. The material system was proven to be high crystallizable as the resultant crystalline phases of BaTi(BO<SUB>3</SUB>)<SUB>2</SUB>, BaNd<SUB>2</SUB>Ti<SUB>5</SUB>O<SUB>14</SUB> and NdBO<SUB>3</SUB> were observed. The relative content of the crystalline phases were strongly dependant on firing temperature and CCTO content. Interestingly, the 30wt% CCTO sample showed early densification at 610-670<SUP>o</SUP>C and then unexpected expansion after 850<SUP>o</SUP>C. The 40-60wt% CCTO samples showed the unexpected secondary densification behavior over the temperature range of 850-950<SUP>o</SUP>C. As a promising example, a combination consisting of the glass and 40wt% CCTO exhibited k ~55 and tanδ ~0.07, which is very rare at this low sintering temperature of 850<SUP>o</SUP>C. These materials system were found to be chemically very stable especially in the H<SUB>2</SUB>SO<SUB>4</SUB> acid solution.

Improved dielectric properties of the CaCu₃Ti₄O₁₂ composites using BaTiO₃-coated powder as precursor

Kim, H.E.,Choi, S.M.,Hong, Y.W.,Yoo, S.I. Elsevier Sequoia 2014 Journal of alloys and compounds Vol.610 No.-

A high dielectric loss and a large leakage current of CaCu<SUB>3</SUB>Ti<SUB>4</SUB>O<SUB>12</SUB> (CCTO) ceramics could be greatly suppressed by using BaTiO<SUB>3</SUB> (BTO)-coated CCTO powder as precursor. BTO-coated CCTO precursors with 5, 10, and 15mol% BTO relative to CCTO were prepared by a sol-gel process and a subsequent calcination at 850<SUP>o</SUP>C for 3h in pure oxygen gas atmosphere. All samples were sintered at 1060<SUP>o</SUP>C for 12h in air. Compared with pure CCTO sample of ε<SUB>r</SUB>~52,000 and tanδ~0.38 at 100kHz, all CCTO composite samples exhibited significantly reduced dielectric losses and leakage currents. Among all CCTO composite samples, the sample using 5mol% BTO-coated CCTO powder exhibited the most improved properties of the dielectric loss (tanδ~0.04 up to 100kHz) and the leakage current (less than 1% up to DC field of ~1kV/cm) although a large suppression in its dielectric constant (ε<SUB>r</SUB>~6000 up to 100kHz) was unavoidable. This improvement is mainly attributed to a relatively uniform distribution of the second phases such as Ba<SUB>4</SUB>Ti<SUB>12</SUB>O<SUB>27</SUB> and CaTiO<SUB>3</SUB> at the CCTO grain boundary, which were formed by the chemical reaction between CCTO and BTO during the sintering process.

Direct Correlations of Grain Boundary Potentials to Chemical States and Dielectric Properties of Doped CaCu₃Ti₄O₁₂ Thin Films

Cho, Ahra,Han, Chan Su,Kang, Meenjoo,Choi, Wooseok,Lee, Jihwan,Jeon, Jaecheol,Yu, Sujae,Jung, Ye Seul,Cho, Yong Soo American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.18

<P>Colossal dielectric constant CaCu<SUB>3</SUB>Ti<SUB>4</SUB>O<SUB>12</SUB> has been recognized as one of the rare materials having intrinsic interfacial polarization and thus unusual dielectric characteristics, in which the electrical state of the grain boundary is critical. Here, the direct correlation between the grain boundary potential and relative permittivity is proposed for the CaCu<SUB>3</SUB>Ti<SUB>4</SUB>O<SUB>12</SUB> thin films doped with Zn, Ga, Mn, and Ag as characterized by Kelvin probe force microscopy. The dopants are intended to provide the examples of variable grain boundary potentials that are driven by chemical states including Cu<SUP>+</SUP>, Ti<SUP>3+</SUP>, and oxygen vacancy. Grain boundary potential is nearly linearly proportional to the dielectric constant. This effect is attributed to the increased charge accumulation near the grain boundary, depending on the choice of the dopant. As an example, 1 mol % Ag-doped CaCu<SUB>3</SUB>Ti<SUB>4</SUB>O<SUB>12</SUB> thin films demonstrate the best relative permittivity as associated with a higher grain boundary potential of 120.3 mV compared with 82.6 mV for the reference film. The chemical states across grain boundaries were further verified by using spherical aberration-corrected scanning transmission electron microscopy with the simultaneous electron energy loss spectroscopy.</P> [FIG OMISSION]</BR>

Phase Evolution and Grain-Boundary Contributions in CaCu_(3-x)Zn_xTi_4O_(12)

Oh Hyeon Kwon,Byeong Kon Kim,Yeon Hwa Jo,Paul Gouri Sankar,Yul Gyo Jung,Jung Won Lee,Tae Sung Jung,조용수 대한금속·재료학회 2011 ELECTRONIC MATERIALS LETTERS Vol.7 No.4

Extensive substitutions of Zn in Ca(Cu_(1-x)Zn_x)_3Ti_4O_(12) (x = 0, 0.1, 0.5, 1.0 and 2.0) dielectrics are investigated in terms of the phase evolution, dielectric properties and grain boundary resistivity. The composition of CaCu_(2.9)Zn_(0.1)Ti_4O_(12) (x = 0.1) densified at a relatively low sintering temperature of 1000°C showed a k value of approximately 7,000 and a tanδ value of approximately 0.07 at 10 kHz, which is better than the values for pure CaCu_3Ti_4O_(12) (CCTO). The improved dielectric properties are also believed to be related to the lower grain boundary resistivity of ~1676 kΩ.cm, as obtained from a Cole-Cole plot. Beyond this level of Zn,the degradation of the dielectric constant was associated with unexpected crystalline phases, in this case Ca_2Zn_4Ti_(16)O_(38), CaTiO_3, and Zn_2TiO_4, which were observed as the level of Zn increased. Although the degradation does not match that of pure CCTO, an addition of Zn up to x=1.0 can hold the dielectric constant at the level of a few thousands, which is still promising compared to other high-k dielectric materials that must be densified below −1000°C to meet the subsequent microcircuit requirements.

Improved Dielectric Properties of BaTiO3-Added CaCu3Ti4O12 Polycrystalline Ceramics

Hui Eun Kim,Soon-Mi Choi,Sung Yun Lee,Youn-Woo Hong,유상임 대한금속·재료학회 2013 ELECTRONIC MATERIALS LETTERS Vol.9 No.3

The effects of the BaTiO3 (BTO) additive on the electrical properties of CaCu3Ti4O12 (CCTO) polycrystalline ceramics were systematically investigated. Various amounts of BTO powder up to 15 mol. % were added to CCTO powder. Each batch was ball-milled, pressed into pellets, and finally sintered at 1060°C for 12 h in air. Compared with pure CCTO sample (εr ~ 52,000 and tan δ ~ 0.38 at 100 kHz), BTO-added CCTO samples commonly showed significantly reduced dielectric losses although their dielectric constants were decreased approximately by one order of magnitude (for instance, εr ~ 4,075 and tan δ ~ 0.02 at 100 kHz for 5 mol. % BTO-added CCTO sample). In addition, the breakdown voltages of BTO-added CCTO samples were much higher than that of pure CCTO sample, and thus the leakage currents were greatly reduced at the applied voltage above ~ 10 V. A large reduction in the dielectric losses and leakage currents is attributed to the secondary phases segregated at the CCTO grain boundary which are composed of CaTiO3, Ba4Ti12O27,and unreacted BTO.

CaCu3Ti4O12입자로부터 유도된 내부 분극을 이용한 마찰대전발전소자의 성능향상

박지현,김지혜,김상우 한국진공학회 2020 한국진공학회 학술발표회초록집 Vol.2020 No.8

Effect of Mn Doping on the Electronic Structures of CaCu3Ti4O12 Ceramics

Z. H. Sun,김철환,H. B. Moon,Y. H. Jang,C. H. Song,Y. S. Yang,J. H. Cho 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.54 No.2

In order to understand the drastic decrease in the permittivity in Mn-doped CCTO compounds (CCMTO), we report the effect of Mn dopant on the electronic structure of CCTO by using X-ray photoelectron spectroscopy (XPS). The XPS results show that Mn doping has a strong influence on the valence band and core levels of CCTO. The disorder at Ca/Cu sites is observed in polycrystalline CCTO, but not in CCMTO. The drastic decrease in the permittivity in CCMTO can be attributed to two reasons: the suppression of the Ca/Cu disorder and the removal of the grain boundary (internal) barrier layer capacitance mechanism.