New Colossal-Dielectric-Constant materials

In recent times there are strong efforts to find new high-ε' materials with better properties. Indeed there are some promising candidates, the most prominent of them being CaCu3Ti4O12. Compared to ferroelectrics-based dielectrics, CCTO exhibits a nearly temperature-independent colossal dielectric constant (CDC) around room temperature, which is highly advantageous for possible technical application (yellow and red areas in Fig. 1). Only at low temperatures and/or high frequencies it shows a marked and strongly frequency-dependent decrease of the dielectric constant from values up to 105 to magnitudes of the order of 100.


Fig. 1. Temperature- and frequency-dependent dielectric constant of single-crystalline CCTO. [Taken from P. Lunkenheimer et al., Colossal dielectric constants in transition-metal oxides, Eur. Phys. J. ST 180, 61 (2010). Copyright by EDP Sciences, Springer-Verlag, 2010. With kind permission of The European Physical Journal (EPJ)]

From the beginning there have been many speculations about the microscopic origin of the CDCs in CCTO. Nowadays it is quite commonly accepted that a nonintrinsic Maxwell-Wagner mechanism is the correct explanation. However, there is still some discussion about the type of interfaces giving rise to the Maxwell-Wagner effect in CCTO - external, e.g. Schottky diodes at the contact-sample interface, or internal, e.g., grain boundaries (for further details, see, e.g., P. Lunkenheimer et al., Eur. Phys. J. Special Topics 180, 61 (2010)).

The properties of CCTO seem to be far from ideal for straightforward application if considering, e.g., its relatively high dielectric loss or its applicability in the technologically important high frequency range around GHz. Thus, there is an ongoing search for new, better CDC materials. Some of the materials investigated in our group are:

As an example, Fig. 2 demonstrates the occurrence of colossal dielectric constants in La15/8Sr1/8NiO4. Most remarkable is the fact that, in contrast to many others, this material retains its colossal magnitude of ε' well into the GHz range.

Fig. 2. Broadband dielectric spectra of La15/8Sr1/8NiO4 for various temperatures. The inset shows a comparison of ε' of La15/8Sr1/8NiO4 and CaCu3Ti4O12 at room temperature. [from S. Krohns et al., Appl. Phys. Lett. 94, 122903 (2009). Copyright (2009) American Institute of Physics]


Interestingly the system La2-xSrxNiO4 is known to exhibit electronic phase separation, namely a stripe-like ordering of holes, in large portions of its phase diagram. Thus one may speculate that spontaneously arising internal interfaces may cause the CDCs in this system, which would be of high interest for technical application.

Overall it is clear that, aside of the famous CCTO, there are many other materials with CDCs. Further investigation of those and the search for new ones are necessary to achieve the final goal of the application of new CDC materials in capacitive circuit elements. In this search, material parameters should not be the sole guidance. It is equally important to also take into account the economic merits and resource availability of the new materials (click here to learn more).

Here are some publications of our group on new colossal-dielectric-constant materials:
  1. Origin of apparent colossal dielectric constants
    P. Lunkenheimer, V. Bobnar, A.V. Pronin, A.I. Ritus, A.A. Volkov, and A. Loidl, Phys. Rev. B 66, 052105 (2002).
  2. Non-intrinsic origin of the colossal dielectric constants in CaCu3Ti4O12
    P. Lunkenheimer, R. Fichtl, S.G. Ebbinghaus, and A. Loidl, Phys. Rev. B 70, 172102 (2004).
  3. Dielectric behavior of copper tantalum oxide
    B. Renner, P. Lunkenheimer, M. Schetter, A. Loidl, A. Reller, and S.G. Ebbinghaus, J. Appl. Phys. 96, 4400 (2004).
  4. Apparent giant dielectric constants, dielectric relaxation, and ac-conductivity of hexagonal perovskites La1.2Sr2.7BO7.33 (B = Ru, Ir)
    P. Lunkenheimer, T. Götzfried, R. Fichtl, S. Weber, T. Rudolf, A. Loidl, A. Reller, and S.G. Ebbinghaus, J. Solid State Chem. 179, 3965 (2006).
  5. Broadband dielectric spectroscopy on single-crystalline and ceramic CaCu3Ti4O12
    S. Krohns, P. Lunkenheimer, S.G. Ebbinghaus, and A. Loidl, Appl. Phys. Lett. 91, 022910 (2007).
  6. Colossal dielectric constants in single-crystalline and ceramic CaCu3Ti4O12 investigated by broadband dielectric spectroscopy
    S. Krohns, P. Lunkenheimer, S.G. Ebbinghaus, and A. Loidl, J. Appl. Phys. 103, 084107 (2008).
  7. Colossal dielectric constant up to GHz at room temperature
    S. Krohns, P. Lunkenheimer, Ch. Kant, A.V. Pronin, H.B. Brom, A.A. Nugroho, M. Diantoro, and A. Loidl, Appl. Phys. Lett. 94, 122903 (2009).
  8. Colossal dielectric constants: A common phenomenon in CaCu3Ti4O12 related materials
    J. Sebald, S. Krohns, P. Lunkenheimer, S.G. Ebbinghaus, S. Riegg, A. Reller, and A. Loidl, Solid State Commun. 150, 857 (2010).
  9. Correlations of structural, magnetic, and dielectric properties of undoped and doped CaCu3Ti4O12
    S. Krohns, J. Lu, P. Lunkenheimer, V. Brizé, C. Autret-Lambert, M. Gervais, F. Gervais, F. Bourée, F. Porcher, and A. Loidl, Eur. Phys. J. B 72, 173 (2009).
  10. Colossal dielectric constants in transition-metal oxides
    P. Lunkenheimer, S. Krohns, S. Riegg, S. G. Ebbinghaus, A. Reller, and A. Loidl, Eur. Phys. J. Special Topics 180, 61 (2010).
  11. Route to resource-efficient novel materials
    S. Krohns, P. Lunkenheimer, S. Meissner, A. Reller, B. Gleich, A. Rathgeber, T. Gaugler, H. U. Buhl, D. C. Sinclair, and A. Loidl, Nature Mater. 10, 899 (2010).

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