PYROELECTRIC COEFFICIENT AND HEAT-CAPACITY OF A FERROELECTRIC COPOLYMER OF VINYLIDENE FLUORIDE AND TRIFLUOROETHYLENE AT LOW-TEMPERATURES

The temperature dependence of the static pyroelectric coefficient p and dynamic pyroelectric response voltage V(s) of a highly crystallized ferroelectric copolymer of vinylidene fluoride (75 mol%) and trifluoroethylene (25 mol%) is measured in the temperature range of 10-300 K. The observed p and the heat capacity C(p) derived from p/V(s) both decrease with decreasing temperature, tending toward zero in the vicinity of 0 K. The temperature dependence of C(p) is fitted to the capacity contributed from three- and one-dimensional acoustical modes of vibrations with Debye temperatures of 52 K and 460 K, respectively, and contributed from main optical vibrations. It is found that the one-dimensional acoustical vibrations and optical vibrations with an average frequency of about 290 cm-1 dominantly contribute to the primary pyroelectric coefficient p(i).