TEMPERATURE DEPENDENT ELASTIC, PIEZOELECTRIC AND PYROELECTRIC PROPERTIES OF BETA-POLY(VINYLIDENE FLUORIDE) FROM MOLECULAR SIMULATION

摘要

Detailed calculations of the elastic, piezoelectric and pyroelectric properties of the beta phase of poly(vinylidene fluoride) are reported. The calculations are based on an empirical atomistic force field that uses the shell model of electronic polarization. Quasi-harmonic lattice dynamics is used to include the vibrational entropy in the calculation of the crystal free energy. The equilibrium crystal structure and polarization are determined as functions of temperature by minimization of the crystal free energy. The piezoelectric and pyroelectric responses are calculated by taking derivatives of the polarization with respect to strain and temperature, respectively. Changes in the unit cell volume dominate the piezoelectric and pyroelectric responses. Dipole oscillations make negligible contributions to the piezoelectric response. The primary pyroelectric response accounts for approximately 9% of the total pyroelectricity at 300 K. The temperature dependence of the piezoelectric stress coefficients is small. The temperature dependence of the piezoelectric strain coefficients is significant and correlates with the temperature dependence of the elastic compliance constants. Likewise, the temperature dependence of the pyroelectric response reflects that of the thermal expansion coefficients. Copyright (C) 1996 Elsevier Science Ltd. [References: 23]