Carbon nanofibre (CNF)/Al2O3 composites with concentrations between 1 and 9 vol.% of CNF were prepared by the traditional ceramic processing route followed by spark plasma sintering. The dielectric properties of these composites have been studied in a broad frequency range from mHz to the infrared range. Unlike conventional composites, the percolation threshold in this system is more complex depending on the particles topology. Positive and negative variations by several orders of magnitude in the low frequency AC conductivity have been detected for concentrations near the threshold at ∼2 vol.% of CNF. To explain these results, a modified percolation model has been proposed which takes into consideration the effect of the concentration of the filler on the microstructure of the composite. © 2013 Elsevier Ltd. All rights reserved.

The authors acknowledge funding through Projects No. 2010CZ0004, MAT2009-14534, MAT2011-29174-C02-01, the Czech Science Foundation Project P204/12/0232 and Czech Ministry of Education (Project MP0902). L. Fernandez-Garcia acknowledges JAE Predoctoral program for PhD grant.

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