This article reports a study of electrical properties of new Zinc Phosphate glass/Cobalt composites (45 mol.%
ZnO–55 mol.%P2O5) (ZP/Co). The measurements of electrical conductivity at room temperature as a function
of cobalt's concentration showed a non-conducting to conducting phase transition at percolation threshold of
27 vol.%. The Seebeck coefficient obtained under the same conditions, accompanies a sign, with high positive
and negative values below and above the percolation threshold respectively, depicting a p- to n-type conducting
phase transition, confirming the conductivity measurements. Then, the measurements of electrical conductivity
and Seebeck coefficient above the percolation threshold as a function of temperature showed an original
conducting to insulating phase transition, called Positive Temperature Coefficient (PTC) at T = 420 K, associated
to a high negative value of S ≤ −8000 μV/K, with the highest power factor PF = σS2 ≈ 8 × 10−3 W m−1 K−2
.
The thermal measurements of volume expansion confirm this transition, indicating matrix dilation around this
temperature. However, the thermal behavior of the electrical conductivity and Seebeck coefficient data obtained
below the percolation threshold showed different mechanisms i.e.; Small Polaron Hopping (SPH) mechanism at
high temperatures and Mott's Variable Range Hopping (VRH) at low temperatures