Low temperature conductivity of cermets

We report on electrical resistivity versus temperature from 50 K down to 1.5 K of PtAl2O3 and AuAl2O3 cermets. When the metal volume fraction q is below the percolation threshold qc, the dc conductivity shows a temperature dependence of the form ln σ ∝ T−n which is usually related to variable range hopping conduction. When T ∗ (T ∗ ≌4.6 K) , the exponent value is n = 1 4 and above T∗ the temperature dependence is modified with n = 1 2 . This behaviour is not clearly understood and is discussed in view of recent theoretical works. For q≌q c a metallic behaviour is observed at high temperature while at liquid helium temperature a two-dimensional electron-electron interaction effect is invoked to describe the anomalous non-metallic behaviour.