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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 Reißel21IFF-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)

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