Effect of sintering conditions on the dielectric properties of CaCu3Ti4O12 and La2/3Cu3Ti4O12 ceramics: A comparative study

doi:10.1016/j.physb.2006.03.005

Physica B: Condensed Matter

Volume 382, Issues 1–2, 15 June 2006, Pages 312-319

https://doi.org/10.1016/j.physb.2006.03.005 Get rights and content

Abstract

The microstructural and dielectric properties of La_2/3Cu₃Ti₄O₁₂ (LCTO) ceramics were found to be less sensitive to the sintering conditions. In contrast, these had imprinting effects on the dielectric characteristics of CaCu₃Ti₄O₁₂ (CCTO) ceramics. The dielectric constant of CCTO increased drastically with increase in sintering temperature and duration as a consequence of significant change in the microstructural and compositional heterogeneity, while the increase was nominal in the case of LCTO ceramics. The dielectric behavior of both the ceramics was explained based on the Maxwell–Wagner relaxation arising mostly from the interfaces between grains and the grain boundaries.

Introduction

Electroceramics associated with giant dielectric constants accompanied by low loss have been on increasing demand owing to their potential use in miniaturized devices [1], [2], [3], [4], [5]. Hence, recently synthesized giant dielectric constant material CaCu₃Ti₄O₁₂ (CCTO) has attracted much attention because of its potential technological applications. It shows extremely high dielectric constant (>10⁴) at room temperature [2], [6], [7]. Impedance spectroscopic data obtained on CCTO ceramics demonstrated their electrical heterogeneous character (the existence of electrically semiconductive grains and highly resistive grain boundaries), and large dielectric constant was attributed to grain boundary barrier layer capacitance effects [8], [9], [10]. Apart from this, the dielectric constant of CCTO was reported to be highly dependent on the processing conditions such as milling time, sintering temperature, duration of sintering, etc. [9], [10], [11], [12]. The dielectric constant ranging from 2000 to 80,000 was achieved by varying the sintering temperature and ascribed to giant barrier layer effects at the grain boundary [9].

It is intriguing to note that CCTO is the only member of the ACu₃M₄O₁₂ (A=alkali, alkaline-earth metal, rare-earth metal or vacancy, M=transition metal) family of oxides exhibiting an unusually high dielectric constant (ε_r′>10⁴). All other members of the above series were reported to have dielectric constant less than 3000 [2], [13]. Hence, one is curious to know whether these are also of microstructural dependent. We thought it was worth investigating into the effect of processing conditions on the microstructural and dielectric characteristics of low dielectric constant materials of the series and compare with that of CCTO ceramics. It was noticed that the microstructural features such as grain size and grain boundary layer thickness of CCTO ceramics had strong dependence on the sintering duration at elevated temperatures.

In this paper, we report the details concerning the influence of sintering conditions on the microstructural and dielectric characteristics of La_2/3Cu₃Ti₄O₁₂ (LCTO) and CCTO ceramics belonging to the low and high dielectric constant members of ACu₃M₄O₁₂ family of oxides, respectively. We believe that the present studies would help in providing more insight and rationalizing the dielectric behavior of these ceramics.

Section snippets

Experimental

Polycrystalline ceramic powders of LCTO were prepared via the conventional solid-state reaction route using stoichiometric amounts of La₂O₃, CuO and TiO₂. These were thoroughly mixed in an acetone medium using a ball mill. Subsequently these mixtures were oven dried for about 2 h. This was followed by the calcination of the powder in alumina crucible at 1000–1025 °C with intermittent grinding for 10 h. The formation of the monophasic compound was confirmed via X-ray powder diffraction (XRD) using

Structural and microstructural analyses

The XRD powder pattern obtained for LCTO is shown in Fig. 1. The pattern could be indexed to a cubic cell (space group Im3) associated with the lattice parameter $a = 0.739 nm$ , which is in good agreement with the one reported for LCTO in the literature [13]. Fig. 2(a–c) shows the scanning electron micrographs recorded for LCTO pellets sintered for 10, 20 and 40 h, respectively. It is evident from these micrographs that the grains have smooth faces associated with cubic appearance. There is only a

Conclusions

La_2/3Cu₃Ti₄O₁₂ (LCTO) and CaCu₃Ti₄O₁₂ (CCTO) ceramics were prepared by solid-state reaction route and were sintered for different durations. Systematic studies on the microstructural features and dielectric properties were performed on these samples. Microstructure of the CCTO was found to be strongly dependent on the sintering temperature and duration unlike LCTO. A 10-fold increase in the grain size was observed in CCTO on increasing the sintering duration from 2.5 to 10 h at 1100 °C. The

References (17)

M.A. Subramanian et al.
J. Solid-State Chem.
(2000)
A.P. Ramirez et al.
Solid-State Commun.
(2000)
B.A. Bender et al.
Mater. Sci. Eng. B
(2005)
M.A. Subramanian et al.
Solid-State Sci.
(2002)
R. Gerhardt
J. Phys. Chem. Solids
(1994)
J. Wu et al.
Phys. Rev. Lett.
(2002)
B.-G. Kim et al.
Phys. Rev. Lett.
(2001)
S. Garcia-Martin et al.
Appl. Phys. Lett.
(2005)

There are more references available in the full text version of this article.

Cited by (88)

Tuning dielectric performance in novel Na<inf>1/2</inf>Er<inf>1/2</inf>Cu<inf>3</inf>Ti<inf>4</inf>O<inf>12</inf> ceramics: The interplay of sintering temperature, grain size, and grain boundary resistance
2024, Materials Chemistry and Physics
The synthesis of novel Na_1/2Er_1/2Cu₃Ti₄O₁₂ (NECTO) ceramics using conventional solid-state methods and their characterization as well as their dielectric properties were investigated at various temperatures of sintering. SEM results revealed an increase in average grain size with sintering temperature. The sintered NECTO sample at 1080 °C exhibited good frequency stability and a higher dielectric constant (ε′) of about 6 × 10³ at 1 kHz. It is found that the sintering temperature correlates with the dielectric constant, and it agrees with the IBLC model. Additionally, the sample displayed a dielectric loss (tanδ) of less than 0.08 throughout a wide range of frequencies. Particularly, the sintered sample at 1060 °C for 10 h had a significantly low tanδ of 0.06 and exhibited a ε′ of roughly 3.19 × 10³ at 1 kHz. A significant decrease in tanδ with increased R_gb was observed, suggesting that reduced grain boundary resistance could minimize the dielectric loss. Moreover, optimizing the sintering temperature enhanced the temperature stability of NECTO ceramics.
Investigation of dielectric relaxor-like anomaly behaviour of non-ferroelectric BaZrO<inf>3</inf> polycrystalline ceramic
2023, Materials Science and Engineering: B
The dielectric responses and ac conductivity of non-ferroelectric BaZrO₃ polycrystalline ceramic were examined in the wide ranges of frequency and temperature. The colossal dielectric behaviour was detected in the dielectric spectra, accompanied by two relaxor-like anomalies. The activation energy associated with the relaxor behaviour at low temperature regions was estimated to be 0.85 eV. The bulk relaxation and Maxwell-Wagner relaxation effect are responsible for the oxygen-vacancy induced pseudo-relaxor behaviour at low-temperature dielectric anomalies. The dielectric anomaly at 585 °C was confirmed to be a paraelectric to ferroelectric phase transition induced by the process of disordered to ordered state of oxygen vacancies. A modified empirical Cole-Cole model was proposed to explain the frequency-dependent permittivity and dielectric loss spectra. The two humps at low and high-temperature regions associated with oxygen-vacancy induced pseudo-relaxor and paraelectric to the ferroelectric phase transition, respectively, were observed in the temperature-dependent ac conductivity study.
Low-cost flame synthesized La<inf>2/3</inf>Cu<inf>3</inf>Ti<inf>4</inf>O<inf>12</inf> electro-ceramic and extensive investigation on electrical, impedance, modulus, and optical properties
2023, Ceramics International
An environmentally-friendly synthesis route and low-cost starting materials are more appropriate for the production of ceramic materials at the industry level. With this concern we prepared the La_2/3Cu₃Ti₄O₁₂(LCTO), which is isostructural of CaCu₃Ti₄O₁₂ (CCTO), using the low-cost TiO₂ instead of a high-cost of titanium source (titanium isopropoxide or titanium chloride) using a low-cost wet-chemical route. Although, there are lots of synthetic methods reported for LCTO fabrication in terms of duration, cheap reagents, energy consumption, feasibility, etc. The present method is far better than the others. The prepared ceramic samples were sintered at 1050 ^°C/12 h and studied their structural, morphology and impedance, and modulus studies for further confirmation. The prepared LCTO ceramic shows the pure phase with the cubic type of morphology. The homogenous distribution of all the elements was observed through dispersive X-ray analysis. X-ray photoelectron spectroscopy studies revels that La is in +3 oxidation state, Cu is in a +2 oxidation state, and Ti is multiple (+3 and + 4) oxidation state. The LCTO ceramic displayed the very high dielectric constant (∼3852) and dielectric loss (0.322), at 1 kHz and at room temperature. Calculated the activation energy using the impedance and modulus data and it shows the superior to that of CCTO ceramic synthesized by the same method. The prepared samples exhibited Debye-type relaxation, which is evoked from the impedance and modulus studies. The calculated optical energy bandgap of LCTO (2.06 eV) is found to be lesser than that of the well-known structure of perovskites (BaTiO₃ (3.28 eV), PbTiO₃ (3.18 eV), LiNbO₃ (3.78 eV) and BiFeO₃ (2.67 eV) as well as structure of spinel CoCr₂O₄ (3.10 eV) and LuFe₂O₄ (2.18 eV)) materials.
Effect of Mn-doping on microstructure and electrical properties of La<inf>2/3</inf>Cu<inf>3</inf>Ti<inf>4</inf>O<inf>12</inf> ceramics
2020, Journal of Alloys and Compounds
Citation Excerpt :
Obviously, it can be seen from Fig. 2 (d) that CuO phase exists at the grain boundary of ceramics. In the process of ceramic sintering, the segregation of the Cu-rich phase at the grain boundary is a common phenomenon [15,16]. It is noteworthy that the segregation content of the Cu-rich phase reduces with decreasing thermal etching temperature.
Mn-substituted La_2/3Cu₃Ti₄O₁₂ negative temperature coefficient (NTC) ceramics were successfully prepared by the traditional solid-state method, and their microstructures and electrical properties were also investigated. XRD patterns showed that the ceramics before polishing were covered by a layer of Cu-rich phase. As the Mn content increased, the segregation of Cu-rich phase at the grain boundary decreased, which leads to the gradual increase of the grain boundary resistance. The linear electrical behaviors were slightly enhanced with increasing Mn content. The B_25/300-value and activation energy (E_a) increased gradually with increasing Mn content. The values of ρ₂₅, B_25/300 and E_a of the sintered ceramics were in the range of 7.8 × 10⁵–6.2 × 10⁶ Ω cm, 5751–6235 K and 0.496–0.538 eV, respectively.
Influence of spark plasma sintering temperature on the microstructures, dielectric and I–V properties of CaCu<inf>3</inf>Ti<inf>4</inf>O<inf>12</inf> ceramics
2020, Journal of Alloys and Compounds
CaCu₃Ti₄O₁₂ (CCTO) ceramics were prepared by the sol–gel process and sintered by the spark plasma sintering (SPS) process at different temperatures. The SPS process temperature has an important effect on the microtopography of CCTO ceramics. The results of EDS and positron annihilation spectroscopy indicate that Cu²⁺ diffuses from the inside to the surface of grains during the sintering process at high temperature. The permittivity (ε_r) of CCTO ceramics at the corresponding frequencies increases with increasing SPS temperature. However, the frequency stability of ε_r over the frequency range 40–10⁶ Hz wanes gradually. The CCTO ceramics sintered at 900°Cand 950 °C present very low dielectric loss values(about 0.02) near 10 kHz. The change in ε_r and tanδ for CCTO ceramics can be explained by the internal barrier layer capacitance (IBLC) model and AC (alternating current) impedance spectra. The results of I–V nonlinear characteristics for CCTO ceramics make clear that the potential barrier height has a positive effect on the value of nonlinear coefficient.
An engineering design based on nano/micro-sized composite for CaTiO<inf>3</inf>/CaCu<inf>3</inf>Ti<inf>4</inf>O<inf>12</inf> materials and its dielectric and non-Ohmic properties
2019, Ceramics International
In this research, the dielectric and non-Ohmic properties of nano/micro-sized CaTiO₃/CaCu₃Ti₄O₁₂ composites (NCTO/MCCTO) with different weight percent of CTO (0, 7, 15, and 30 wt%) were examined as a new engineering design. NCTO was prepared after high energy ball milling of calcined CaCO₃ and TiO₂ mixture. Micro-sized CCTO was synthesized after calcination of CaCO₃, CuO, and TiO₂ mixture at 1000 °C. According to the TEM, BET, and SEM analyses; the mean particle size of NCTO and MCCTO was 80 nm and 2.5 μm, respectively. The NCTO/MCCTO powder composites were prepared from direct mixing of pre-synthesized NCTO and MCCTO. After the sintering of green body composites at 1100 °C for 5 h, both relative density and grain size of NCTO/MCCTO composites decreased with the increase in NCTO content. It was found that the abnormal grain growth in the sintered MCCTO changed to the normal grain growth in NCTO/MCCTO composites. The best dielectric properties (ϵ_r: 7050, tanδ: 0.02) was observed for NCTO/MCCTO with 15 wt% CTO. This unique dielectric constant was ascribed to the large grain size of CCTO, and the reduced dead zone of CTO with a low dielectric constant. Due to uniform distribution of CTO with the small size of 0.3–1.5 μm at grain boundaries of CCTO with a large grain size of 5 μm, the number of active interfaces were increased sharply and consequently the maximum breakdown electric field of 7 kV/cm and the nonlinear coefficient of 15 were obtained for NCTO/MCCTO with 15 wt% of NCTO. Therefore, the MCCTO-NCTO composite with 15 wt% of NCTO is a promising candidate for the capacitor and energy storage applications.

View all citing articles on Scopus

View full text

Effect of sintering conditions on the dielectric properties of CaCu3Ti4O12 and La2/3Cu3Ti4O12 ceramics: A comparative study

Abstract

Introduction

Section snippets

Experimental

Structural and microstructural analyses

Conclusions

J. Solid-State Chem.

Solid-State Commun.

Mater. Sci. Eng. B

Solid-State Sci.

J. Phys. Chem. Solids

Phys. Rev. Lett.

Phys. Rev. Lett.

Appl. Phys. Lett.

Effect of sintering conditions on the dielectric properties of CaCu₃Ti₄O₁₂ and La_2/3Cu₃Ti₄O₁₂ ceramics: A comparative study