New composites of ZnO–P 2 O 5 /Ni having PTC transition and high Seebeck coefficient
Journal of Non-Crystalline Solids(2012)
摘要
In this article, we report the electrical conductivity (σ) and Seebeck coefficient (S) of ZnO–P2O5 matrix filled with conductive powder of nickel (Ni). The variation of σ versus volume fraction of Ni showed a non-conducting to conducting phase transition at percolation threshold (28vol. %). The change of S from high positive to negative values exhibits that this transition is accompanied by the passing of carrier charge from p to n type. On the other hand, the measurements of σ and S as function of temperature, above the percolation threshold, showed a positive temperature coefficient (PTC) phase transition at Tc≥400K, linked with a high S=−5000μV/K, giving highest power factor PF=σ.S2≈2.10−4Wm−1K−2. The temperature dependence of the volume expansion enabled to confirm that this transition is associated to the thermal volume variation in matrix. However, the temperature dependence of σ below the percolation threshold showed two different mechanisms: thermally activated hopping behavior at high temperatures and Mott's variable range hopping (VRH) at low temperatures.
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关键词
Composites,Electrical properties,Glass ceramics,PTC devices,Percolation
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