Piezoresistive and posistor effects in polymer-semiconductor and polymer-ferropiezoceramic composites

In this study, piezoresistive and posistor effects in polymer-semiconductor and polymer-ferropiezoceramic composites have been investigated. The results show that composites based on crystallizable polymers, such as PVDF, HDPE, and PP dispersed by semiconductors and ferropiezoelectric fillers have piezoresistive and posistor properties, respectively. At low pressure, charge carriers tunneling through the located thin polymer among filler particles into the barrier define the conductivity of the composite. When pressure value is increased from 0 to 1 MPa, the thickness of the interlayer decreases and tunnel conductivity descends exponentially depending on barrier height. The piezoresistor sensitivity of a composite based on PVDF-70% vol+Si-30% vol is higher than a composite based on HDPE-70% vol+Ge-30% vol. Furthermore, the posistor properties of polymer composites dispersed by ferropiezoceramic are determined as the maximum resistance that varies significantly with temperature. Posistor effect in composites based on polymer+ferropiezoceramic is associated with the height of the barrier layer, which changes according to properties of filler, polymer, and dielectric permittivity of two-phase composites. The highest specific resistance related to HDPE-70% vol+BaTiO$_{3}$-30% vol composite was observed at $\sim$403 K.