Regensburg 2010 – wissenschaftliches Programm
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DF: Fachverband Dielektrische Festkörper
DF 17: Nano- and microstructured dielectrics
DF 17.5: Vortrag
Donnerstag, 25. März 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 cp of the percolation threshold[4]. Therefore it can be
the aim to get very close to cp.
BaTiO3 is an insulator, and if finite size effects
can be neglected, the d.c. conductivity remains zero below cp.
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 cp 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 ccrit. The concentration ccrit
depends sensitively
on the size of the nanoparticles and is about 10% smaller than cp 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)