Electromechanics of organic Schottky like contacts, in between piezoelectricity and electrostriction

Piezoelectricity and electrostriction are electromechanical effects at the heart of a variety of applications in transducers. In organic semiconductors an unusual voltage dependences of the electromechanical strain is observed: The converse electromechanical response follows a power law dependence S∝V^α of the mechanical strain S versus the applied voltage V, with an exponent α= 1.5. The power law exponent is in between traditional linear piezoelectricity and quadratic electrostriction. The experimental finding is a direct consequence of the strongly non-uniform electric field distribution within the Schottky contact arrangement. Electromechanical responses of organic Schottky devices appear to be of fundamental interest for the investigation of non-uniform electric field distributions. The experiments also suggest an unusual electrostrictive behavior in all materials with spatially nonuniform electric field distributions, a situation usually encountered in most space charge electrets.