Structural Changes in Poly (Vinylidene Fluoride) by Electric Fields

Uniaxially stretched poly (vinylidene fluoride) (PVDF) films, containing 6 phase only or both ¿ and B phases, as well as 12 pm biaxially oriented commercial PVDF films were investigated by means of modified x-ray and infrared techniques. The structural changes were examined in response to the applied poling field ( 450 MV/m) and the poling tem perature at various levels. The changes in the orientation state determined by pole-figure measurements, the various crystal phase transitions, the conformational conversion from TGTG to TT, and the increase of crystallinity in the S phase are discussed in comparison with the piezoelectric strain and stress coefficients d31 and e31.