Enhanced piezoresistivity in Ni--silicone rubber composites

This paper reports that the nickel--silicone rubber composites with enhanced piezoresistivity were synthesized with much reduced nickel concentration. A large piezosensitivity of 0.716/kPa and a gauge factor of 600 have been obtained for a composite sample with filler-polymer ratio of 2.7:1 by weight. Measurements of resistance as a function of uniaxial force reveal that the piezoresistance arises predominantly from the internal heterogeneity of the material and the effect of geometrical changes of samples under pressure is neglectably small. The nonlinear current--voltage characteristic of the composite depends strongly on the filler content, the initial compression and the electrical current flowing in the sample. Ohmic behaviour has been observed only in the highly compressed samples. The breakdown strength decreases with increasing filler content of the composite. Both I-V and R-f characteristics indicates that the resistivity of the composites decreases with electrical field, suggesting that the composite may also be used to make voltage sensitive resistors for protecting circuits. All the experimental results favour a quantum tunnelling mechanism of conductivity. It finds that the concept `negative resistance', often used to describe the phenomena that current decreases with increasing voltage, is not appropriate and should be avoided.