Influence of Annealing Temperature on Berthelot-Type Hopping Conduction Mechanism in Carbon-Nickel Composite Films

Electrical conductivity of carbon-nickel composite films annealed at temperatures 300, 500 and 800 degrees C is studied over a temperature range of 50-300 K. While the conductivity data above room temperature show extended state conduction, lowering the temperature from 150 to 50K leads to the Berthelot-type conduction mechanism. It can be seen that the films annealed at 500 degrees C have the maximum conductivity. The extent of the carrier wave function at 500 degrees C has the minima 2.87x10(-7) cm and 2.45x10(-7) cm in octahedral-metal stretching vibrations and intrinsic stretching vibrations of the metal at the tetrahedral site, respectively. The average distances between two vibration octahedral and tetrahedral sites at 500 degrees C also have the minima 1.13x10(-7) cm and 0.97x10(-7) cm, respectively. The Berthelot temperature for films annealed at 800 degrees C has the minimum of 94.3 K.