Regensburg 2010 – scientific programme

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DF: Fachverband Dielektrische Festkörper

DF 17: Nano- and microstructured dielectrics

DF 17.5: Talk

Thursday, March 25, 2010, 16:50–17:10, H11

Conductivity of BaTiO₃ metallic composites below the percolation threshold due to finite size effects — •Hans Lustfeld¹ and Martin Reißel² — ¹IFF-1, Forschungszentrum Jülich, D52425 Jülich — ²Fachhochschule Aachen, Abteilung Jülich, D52428 Jülich

The high dielectric permittivity є of BaTiO₃ can be enhanced further by adding metallic nanoparticles, e.g. Ni[1,2] or Ag[3](,size of particles ≈ 10· 10⁻⁹m). This enhancement becomes arbitrarily high at the concentration c_p of the percolation threshold[4]. Therefore it can be the aim to get very close to c_p. BaTiO₃ is an insulator, and if finite size effects can be neglected, the d.c. conductivity remains zero below c_p. However, modern Multi Layer Ceramic Capacitors (MLCC’s) have a layer thickness of about 1−5· 10⁻⁶m only[5], finite size effects become important and lead to increasing finite conductivities when approaching c_p from below. Here we present calculations for the conductivity in the brick layer model[6] and for a modification of the brick-layer model. A main result obtained for both these models is an exponentially strong increase of the d.c. conductivity, as soon as the concentration increases beyond c_crit. The concentration c_crit depends sensitively on the size of the nanoparticles and is about 10% smaller than c_p for typical sizes.
[1] C. Pithan et.al., Int. J. Mater. Res. 97, 5 (2006)
[2]Y-C. Huang et.al., J. Am. Ceram. Soc., 90, 1438 (2007)
[3]Y.Cheng et.al., Appl. Phys. Lett. 91, 252903 (2007)
[4]W.T. Doyle, J. Appl. Phys. 85, 2323 (1999)
[5]S. Halder et.al., J. Sol-Gel. Sci. Techn. 42, 203 (2007)
[6]N.J. Kidner et.al., J. Am. Ceram. Soc. 91, 1733 (2008)