Advances in Materials Science and Engineering

Advances in Materials Science and Engineering / 2014 / Article

Research Article | Open Access

Volume 2014 |Article ID 187420 | 6 pages |

Microstructural and Dielectric Properties of Zr Doped Microwave Sintered Synthesized by Sol-Gel Route

Academic Editor: Pavel Lejcek
Received25 Dec 2013
Accepted20 Mar 2014
Published13 Apr 2014


Polycrystalline samples with the chemical formula CaCu3O12 (, 0.02, 0.1, 0.2, 0.5, and 0.1) CCTZO were synthesized from metal nitrate solutions by the sol-gel method, followed by conventional and microwave heat treatments. The X-ray diffraction pattern of powder calcined at 800°C in conventional furnace for 3 h showed formation of a single phase. The crystal structure did not change on doping with zirconium and it remained cubic in the five studied compositions. The surface morphology of samples sintered at 1000°C in microwave furnace for 10 min was observed using a high resolution scanning electron microscope (HR-SEM). The grain sizes were in the range of 250 nm–5 μm for these samples. HRSEM results show that doping with Zr enhanced grain growth or densification. Energy dispersive X-ray spectroscopy (EDX) confirmed the presence of Zr. The dielectric characteristics of Zr doped CCTO were studied with an LCR meter in the frequency range of 50 Hz–1 MHz. A very high dielectric constant 21,500 was observed for the sample doped with Zr (0.02 mol%) at 50 Hz.

1. Introduction

It has been a long-term effort in the electronic industry and scientific community to seek novel dielectric materials. High dielectric constant leads to miniaturization of capacitive components, thus offering the opportunity to decrease the size of electronic devices. For high dielectric constant, materials based on ferroelectric BaTiO3 are commonly used. BaTiO3 is a ferroelectric material exhibiting high dielectric constant. In 1967, a new class of materials having the general formula ACu3Ti4O12 (, Ba, Sr) was discovered [1]. Among them, CaCu3Ti4O12 has an edge over BaTiO3 in practical applications in terms of temperature stability [2]. Due to their unique dielectric properties, both the CaCu3Ti4O12 (CCTO) ceramics [3, 4] and the doped CCTO [57] have attracted ever-increasing attention for their practical microelectronic applications including capacitors and memory devices [810].

Extensive investigation has been made to identify the origin of the colossal dielectric property of CCTO [1113]. The dielectric property of CCTO has been related to its microstructure [14]. The studies, concerning the different processing and preparation conditions such as sol-gel derivation [15, 16], sintering method, temperature and time [17, 18], doping [6, 19], electrode material, pellet thickness [5, 20], and the dielectric characteristics of CCTO, demonstrated their strong influence on the dielectric properties of CCTO ceramics.

Developing high dielectric materials synthesized with lower calcination/sintering temperature has become the subject of study for many researchers. While some recently published reports concentrate on different synthesis techniques to reduce the processing temperature, other reports focus on substitutions to change the material properties. However, very limited work on the effects of substituting impurity along with lower processing temperature CCTO has been reported [21, 22]. The purpose of the present work is to dope Zr (0, 0.02, 0.1, 0.2, and 0.5 mol%) into CCTO ceramics and to investigate the effects of doping on the surface morphology and dielectric properties of Zr-substituted CCTO ceramics. Microwave sintering is adopted in this work due to its advantages over conventional heating techniques which include reduced processing time, energy saving, fine microstructures, and improved material properties [2326]. The understanding of the electric and dielectric behavior of these ceramics would facilitate the processing of CCTO to achieve certain electrical properties under desired sintering temperature. To our best knowledge, the dielectric response to the substitution of Zr for Ti in CaCu3Ti4O12 microwave sintered ceramics has not been studied.

2. Experimental Procedure

CCTZO powders were synthesized by the sol-gel method. The starting materials were Ca(NO3)2·4H2O, Cu(NO3)2·3H2O, C12H28O4Ti, and zirconium oxychloride. Glacial acetic acid and citric acid were used as chelating reagents. Calcium nitrate and copper nitrate were dissolved in ethanol (solution 1). Titanium tetraisopropoxide stabilized by acetylacetone was dissolved in isopropyl alcohol. With this solution, zirconium nitrate dissolved in ethanol was mixed (solution 2). After stirring for 40 min, solution 1 was added slowly to solution 2. These two solutions were mixed in a beaker and stirred continuously using a magnetic stirrer at room temperature. Thereafter, acetic acid and citric acid were added to this mixture. The temperature of the magnetic stirrer was increased to 90°C. The ratio of titanium tetraisopropoxide : acetylacetone : citric acid was kept at 3 : 2 : 0.25, respectively. A transparent solution was obtained after a constant stirring for 3 hrs. When the solution was dried, the viscous liquid began to form a transparent viscous gel. The gel was kept in a hot air oven at 110°C for 2 days. This resulted in a loose and brown ash powder. The dried precursor was calcinated in a conventional furnace at 800°C for complete crystallization. The calcinated powder was uniaxially pressed into pellets of 10 mm in diameter and 2 mm in thickness with an applied load of 3.5 tons for 4 minutes, using polyvinyl alcohol (PVA) as the binder. Microwave sintering was completed by using a VBCC 2-magnetron microwave heating furnace in which the compacted samples were sintered at 1,000°C at a ramping rate of 50°C/min and soaked for 10 min followed by fast cooling to room temperature at a rate of 20°C/min. The sintering temperature was measured with a pyrometer and it was standardized with reference to a thermocouple and the emissivity was measured to be between 0.90 and 0.98 for the different samples of CCTZO. The microwave output power level was about 2.2 KW with 2.45 GHz frequency and it was controlled by a Eurotherm PID controller. XRD studies were carried out with an X’PERT-PRO diffractometer (Philips, the Netherlands) using CuKα1 radiation at 45 kV and 40 ma ( nm) in a wide range of 2θ (. The microstructure of sintered pellets was measured by FE-SEM (FEI Quanta 200FEG). Silver paste was coated over the parallel faces of the pellets and the dielectric constant measurements were made using an LCR meter (Hioki 3532-50) in the frequency range of 50 Hz–1 MHz at room temperature.

3. Results and Discussion

3.1. X-Ray Diffraction Pattern of Calcined CaCu3O12 Powder

XRD patterns of CCTZO powder calcinated in a conventional furnace at 800°C for 3 hours are shown in Figure 1. All the XRD diffraction peaks match with the standard powder diffraction pattern (JCPDS card number: 75-2188). The major planes correspond to (211), (220), (013), (222), (400), (422), and (440) of cubic (CaCu3)Ti4O12. From the XRD patterns it is clear that the concentration of zirconium doped with CCTO is within the limit of its solubility up to as an impurity phase is observed in the samples (). For the sample (), extra peaks are present besides the main peaks which indicates that the excess amount of zirconia is not within the limit of its solubility. But the () sample’s major peaks belong to the ZrO2 phase.

3.2. FE-SEM Analysis

The microstructure of CaCu3O12 (, 0.02, 0.1, 0.2, and 0.5) ceramics, sintered at 1000°C for 10 min in a microwave furnace, is shown in Figures 2(a)2(e). The grains are found to be in the size range of 250 nm–5 μm. The morphology of the undoped specimen consists of mostly cubic grains. For the dopants with , the grains attain cubic shape. When the dopant level increases (, 0.2, and 0.5), a polyhedral type of grains occurs. Also with the increase in dopant levels, the size of the grains grows bigger and denser. This is in accordance with the earlier report of Jesurani et al. [27]. The porosity is intergranular in nature and is not observed in the samples of higher concentrations of doping due to the high agglomeration of grains. Thomas et al. reported that the dielectric properties of CCTO ceramics have shown a strong dependence on microstructure [28]. The dense microstructure of the sample can possess good dielectric properties. Energy dispersive X-ray (EDX) analysis of CaCu3Ti3.5Zr0.5O12 ceramic powder shows the evidence for the presence of zirconium in Figure 2(e) (inset).

3.3. Dielectric Studies

Figures 3(a) and 3(b) and Table 1 show the dielectric constant and dielectric loss as a function of frequency of samples sintered at 1,000°C for 10 minutes. The dielectric constants of these samples are 21,500, 1570, 12,300, and 7960 and the corresponding Zr concentrations are 0.02, 0.10, 0.20, and 0.5 for 50 Hz. The dielectric constant does not exhibit a constant variation with frequency for various doping concentrations. However, the dielectric constant () of pure CCTO ceramic is almost a constant through the whole frequency range with a lower value (1462–1730). This behavior may be attributed to the differences in grain size. According to the internal boundary layer capacitance (IBLC) model, the effective dielectric constant is inversely proportional to the ratio of thickness of the insulating layer (i.e., grain boundary) to the grain size. A greater number of crystal defects are able to exist in larger grains than in smaller ones. This allows for more internal barrier layers [29]. The dielectric permittivity in CCTO strongly depends on the grain size, and an increase of the grain size leads to an increase of the dielectric permittivity. For IBLC ceramics [30], (/), where is the grain size and is the thickness of the grain boundary.

Frequency Hz

1 K15720.0652901.9112000.1262004.1150600.81
10 K15270.0611401.5710900.0843000.7336100.33
100 K14910.063011.399610.1333900.3424700.31
1 M14620.1774.21.257240.3712401.0614900.52

Apart from the grain boundary regional defects, the presence of interfacial polarization in these materials also plays an important role for enhancement of the dielectric constant in the low-frequency region. The interfacial space charge polarization arises due to the accumulation of charge carriers at the interface of semiconducting grains and insulating grain boundaries. In the present investigation, CCTZO with zirconium () gives a high dielectric constant 21,500 which is five times larger than that of CCTO [31] and its dielectric loss is 5.

The frequency dependent dielectric loss () is presented in Figure 3(b) as a function of different Zr concentrations (, 0.02, 0.1, 0.2, 0.5, and 1.0). It can be observed that there is no constant variation of tan value with frequency. The dielectric losses are higher at low frequencies up to 100 Hz. Dielectric loss for all the compositions shows a sharp decreasing trend up to 100 kHz and small rising at 1 MHz. Higher concentration may produce more oxygen vacancies and space charges; thus, more obvious dielectric relaxation can be observed which gives rise to more dielectric losses. These results agree with the previous reports of dielectric behavior of the CCTO ceramics [32, 33].

Choudhury et al. [34] have reported that the dielectric constant of Zr doped BaTiO3 samples sintered at 1250°C showed a maximum value of about 1000 for 100 kHz frequency. Gómez-Yáñez et al. [35] reported that the dielectric constant and dielectric loss are 576 and 0.33, respectively. When Zr doped BaTiO3 is synthesized by mechanical alloying [35], its dielectric constant and dielectric loss are 539 and 0.035, respectively. When the sample is sintered in the range of 1200–1400°C, as in the present investigation, a higher dielectric constant (6020) is obtained accompanied by low dielectric loss (0.52). The sintering temperature is also low (1000°C) compared to that in the earlier reports.

4. Conclusion

CaCu3O12 (, 0.02, 0.1, 0.2, and 0.5) ceramics were successfully synthesized by the sol-gel method. Structural and dielectric characterization of CCTZO ceramics doped with small amounts of Zr was carried out. The use of microwave sintering resulted in the formation of a dense sintered CCTZO in just 10 minutes. When the Zr concentration increased, the grain sizes also increased. The observed dielectric behavior of all the five samples agrees well with the internal barrier layer capacitor (IBLC) model. A high dielectric constant of 21500 was achieved for a moderate Zr doping (), that is, for CaCu3Ti3.98Zr0.02O12 ceramics, and the sintering temperature is also brought down to 1000°C.

Conflict of Interests

The authors declare that there is no conflict of interests regarding the publication of this paper.


We would like to thank SRM University for providing the Nanotechnology Center Facilities and ITMA and Universiti Putra Malaysia for the presubmission final editing of this paper.


  1. A. Deschanvres, B. Raveau, and F. Tollemer, “Substitution of copper for a divalent metal in perovskite-type titanates,” Bulletin de la Société Chimique de France, vol. 11, pp. 4077–4078, 1967. View at: Google Scholar
  2. W. Li, S. Qiu, N. Chen, and G. Du, “Enhanced dielectric response in Mg-doped CaCu3Ti4O12 ceramics,” Journal of Materials Science & Technology, vol. 26, no. 8, pp. 682–686, 2010. View at: Publisher Site | Google Scholar
  3. C. Masingboon, P. Thongbai, and S. Maensiri, “Giant dielectric response in perovskite-delivative CaCu3Ti4O12 prepared by polymerized complex method,” Advances in Science and Technology, vol. 45, pp. 2345–2350, 2006. View at: Google Scholar
  4. T. B. Adams, D. C. Sinclair, and A. R. West, “Decomposition reactions in CaCu3Ti4O12 ceramics,” Journal of the American Ceramic Society, vol. 89, no. 9, pp. 2833–2838, 2006. View at: Publisher Site | Google Scholar
  5. B. K. Kim, H. S. Lee, J. W. Lee, S. E. Lee, and Y. S. Cho, “Dielectric and grain-boundary characteristics of hot pressed CaCu3Ti4O12,” Journal of the American Ceramic Society, vol. 93, no. 9, pp. 2419–2422, 2010. View at: Publisher Site | Google Scholar
  6. F. Luo, J. He, J. Hu, and Y.-H. Lin, “Electric and dielectric behaviors of Y-doped calcium copper titanate,” Journal of the American Ceramic Society, vol. 93, no. 10, pp. 3043–3045, 2010. View at: Publisher Site | Google Scholar
  7. W.-X. Yuan, “Effect of the addition of polyvinyl alcohol on electric and dielectric properties of giant dielectric constant material CaCu3Ti4O12,” Journal of the American Ceramic Society, vol. 93, no. 10, pp. 3020–3022, 2010. View at: Publisher Site | Google Scholar
  8. A. P. Ramirez, M. A. Subramanian, M. Gardel et al., “Giant dielectric constant response in a copper-titanate,” Solid State Communications, vol. 115, no. 5, pp. 217–220, 2000. View at: Publisher Site | Google Scholar
  9. M. A. Subramanian, D. Li, N. Duan, B. A. Reisner, and A. W. Sleight, “High dielectric constant in ACu3Ti4O12 and ACu3Ti3FeO12 phases,” Journal of Solid State Chemistry, vol. 151, no. 2, pp. 323–325, 2000. View at: Publisher Site | Google Scholar
  10. C. C. Homes, T. Vogt, S. M. Shapiro, S. Wakimoto, and A. P. Ramirez, “Optical response of high-dielectric-constant perovskite-related oxide,” Science, vol. 293, no. 5530, pp. 673–676, 2001. View at: Google Scholar
  11. C. Homes, T. Vogt, S. M. Shapiro, S. Wakimoto, M. A. Subramanian, and A. P. Ramirez, “Charge transfert in the dielectric constant materials CaCu3Ti4O12 and CdCu3Ti4O12,” Physical Review B, vol. 67, no. 9, Article ID 092106, 4 pages, 2003. View at: Publisher Site | Google Scholar
  12. V. P. B. Marques, P. R. Bueno, A. Z. Simões et al., “Nature of potential barrier in (Ca1/4,Cu3/4)TiO3 polycrystalline perovskite,” Solid State Communications, vol. 138, no. 1, pp. 1–4, 2006. View at: Publisher Site | Google Scholar
  13. P. Thongbai, C. Masingboon, S. Maensiri, T. Yamwong, S. Wongsaenmai, and R. Yimnirun, “Giant dielectric behaviour of CaCu3Ti4O12 subjected to post-sintering annealing and uniaxial stress,” Journal of Physics: Condensed Matter, vol. 19, no. 23, Article ID 236208, 2007. View at: Publisher Site | Google Scholar
  14. Y. Lin, Y. B. Chen, T. Garret et al., “Epitaxial growth of dielectric CaCu3Ti4O12 thin films on (001) LaAlO3 by pulsed laser deposition,” Applied Physics Letters, vol. 81, no. 4, pp. 631–633, 2002. View at: Publisher Site | Google Scholar
  15. L. Liu, H. Fan, P. Fang, and X. Chen, “Sol-gel derived CaCu3Ti4O12 ceramics: synthesis, characterization and electrical properties,” Materials Research Bulletin, vol. 43, no. 7, pp. 1800–1807, 2008. View at: Publisher Site | Google Scholar
  16. D.-L. Sun, A.-Y. Wu, and S.-T. Yin, “Structure, properties, and impedance spectroscopy of CaCu3Ti4O12 ceramics prepared by sol-gel process,” Journal of the American Ceramic Society, vol. 91, no. 1, pp. 169–173, 2008. View at: Publisher Site | Google Scholar
  17. S. Kwon, N. Triamnak, and D. P. Cann, “Decomposition kinetics of CaCu3Ti4O12,” in Proceedings of the 17th IEEE International Symposium on the Applications of Ferroelectrics (ISAF '08), pp. 1–4, Santa Re, NM, USA, February 2008. View at: Publisher Site | Google Scholar
  18. W. Q. Ni, X. H. Zheng, and J. C. Yu, “Sintering effects on structure and dielectric properties of dielectrics CaCu3Ti4O12,” Journal of Materials Science, vol. 42, no. 3, pp. 1037–1041, 2007. View at: Publisher Site | Google Scholar
  19. S.-H. Hong, D.-Y. Kim, H.-M. Park, and Y.-M. Kim, “Electric and dielectric properties of Nb-doped CaCu3Ti4O12 ceramics,” Journal of the American Ceramic Society, vol. 90, no. 7, pp. 2118–2121, 2007. View at: Publisher Site | Google Scholar
  20. B. S. Prakash and K. B. R. Varma, “Effect of sintering conditions on the microstructural, dielectric, ferroelectric and varistor properties of CaCu3Ti4O12 and La2/3Cu3Ti4O12 ceramics belonging to the high and low dielectric constant members of ACu3M4O12 (A=alkali, alkaline-earth metal, rare-earth metal or vacancy, M=transition metal) family of oxides,” Physica B: Condensed Matter, vol. 403, no. 13–16, pp. 2246–2254, 2008. View at: Publisher Site | Google Scholar
  21. A. K. Rai, N. K. Singh, S. K. Acharya, L. Singh, and K. D. Mandal, “Effect of tantalum substitutions on microstructures and dielectric properties of calcium copper titanate (CaCu3Ti4O12) ceramic,” Materials Science and Engineering B, vol. 177, no. 14, pp. 1213–1218, 2012. View at: Publisher Site | Google Scholar
  22. A. K. Rai, N. K. Singh, S.-K. Lee, K. D. Mandal, D. Kumar, and O. Parkash, “Dielectric properties of iron doped calcium copper titanate, CaCu2.9Fe0.1Ti4O12,” Journal of Alloys and Compounds, vol. 509, no. 36, pp. 8901–8906, 2011. View at: Publisher Site | Google Scholar
  23. S. Kanagesan, S. Jesurani, R. Velmurugan, S. Prabu, and T. Kalaivani, “Study of morphological and magnetic properties of microwave sintered barium strontium hexaferrite,” Journal of Materials Science: Materials in Electronics, vol. 23, no. 8, pp. 1511–1514, 2012. View at: Publisher Site | Google Scholar
  24. D. K. Agrawal, “Microwave processing of ceramics,” Current Opinion in Solid State and Materials Science, vol. 3, no. 5, pp. 480–485, 1998. View at: Google Scholar
  25. Y. Fang, D. K. Agrawal, D. M. Roy, and R. Roy, “Transparent mullite ceramics from diphasic aerogels by microwave and conventional processings,” Materials Letters, vol. 28, no. 1–3, pp. 11–15, 1996. View at: Google Scholar
  26. P. Piluso, L. Gaillard, N. Lequeux, and P. Boch, “Mullitization and densification of (3Al2O3 + 2SiO2) powder compacts by microwave sintering,” Journal of the European Ceramic Society, vol. 16, no. 2, pp. 121–125, 1996. View at: Publisher Site | Google Scholar
  27. S. Jesurani, S. Kanagesan, and K. Ashok, “Microstructure and dielectrical responses of pure and cobalt-doped CaCu3Ti4O12 ceramics by sol–gel synthesis route,” Journal of Materials Science: Materials in Electronics, vol. 64, no. 2, pp. 335–341, 2012. View at: Publisher Site | Google Scholar
  28. P. Thomas, K. Dwarakanath, and K. B. R. Varma, “Effect of calcium stoichiometry on the dielectric response of CaCu3Ti4O12 ceramics,” Journal of the European Ceramic Society, vol. 32, no. 8, pp. 1681–1690, 2012. View at: Publisher Site | Google Scholar
  29. L. F. Xu, P. B. Qi, S. S. Chen, R. L. Wang, and C. P. Yang, “Dielectric properties of bismuth doped CaCu3Ti4O12 ceramics,” Materials Science and Engineering B, vol. 177, no. 6, pp. 494–498, 2012. View at: Publisher Site | Google Scholar
  30. A. R. West, T. B. Adams, F. D. Morrison, and D. C. Sinclair, “Novel high capacitance materials:- BaTiO3:La and CaCu3Ti4O12,” Journal of the European Ceramic Society, vol. 24, no. 6, pp. 1439–1448, 2004. View at: Publisher Site | Google Scholar
  31. S. Jesurani, S. Kanagesan, T. Kalaivani, and K. Ashok, “Dielectric properties of Erbium doped CaCu3Ti4O12 prepared by sol-gel self combustion method,” Journal of Materials Science: Materials in Electronics, vol. 23, no. 3, pp. 692–696, 2012. View at: Publisher Site | Google Scholar
  32. C. Mu, H. Zhang, Y. Liu, Y. Song, and P. Liu, “Rare earth doped CaCu3Ti4O12 electronic ceramics for high frequency applications,” Journal of Rare Earths, vol. 28, no. 1, pp. 43–47, 2010. View at: Publisher Site | Google Scholar
  33. C. Mu, H. Zhang, Y. He, J. Shen, and P. Liu, “Influence of dc bias on the dielectric relaxation in Fe-substituted CaCu3Ti4O12 ceramics: grain boundary and surface effects,” Journal of Physics D: Applied Physics, vol. 42, no. 17, Article ID 175410, 2009. View at: Publisher Site | Google Scholar
  34. S. Choudhury, S. Akter, M. J. Rahman et al., “Structural, dielectric and electrical properties of zirconium doped barium titanate perovskite,” Journal of Bangladesh Academy of Sciences, vol. 32, no. 2, pp. 221–229, 2008. View at: Google Scholar
  35. C. Gómez-Yáñez, E. Cruz-Aquino, J. J. Cruz-Rivera, and R. Linares-Miranda, “BaTiO3 devices doped with Zr using mechanical alloying,” Journal of Alloys and Compounds, vol. 434-435, pp. 806–808, 2007. View at: Publisher Site | Google Scholar

Copyright © 2014 S. Jesurani et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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