Poling‐time dependence of the field‐induced phase transition and piezoelectric response of poly(vinylidene fluoride) films

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Abstract
We have examined the poling time dependence of the field‐induced phase transition (from phase II to polar phase II) of biaxially oriented poly(vinylidene fluoride) films by x‐ray methods. These results were compared with the poling‐time dependence of the piezoelectric response (d31 and e31) determined using a piezotron Model U (Toyo Seiki, Tokyo). The piezoelectric response shows an initial rapid increase with poling time followed by a slow increase as the poling time increases. The x‐ray results show that the field‐induced phase transition is time dependent, and occurs first for those crystallites with their a axes perpendicular to the film surface. Crystallites with a in the plane of the film transform at a much slower rate. The data indicate that the poling time dependence of d31 and e31 (and, presumably, film polarization) are dependent on the transition rates.