Efeitos de ferroeletricidade e condutividade em filmes compósitos de PVDF/(K,Na)NbO3

Abstract

In the present work, polymeric composite films of poly(vinylidene fluoride), PVDF, were synthesized with the addition of ceramic sodium and potassium niobate (KxNa1-xNbO3, KNN, for x=0.48; x=0.50; ex=0 .52, herein called KNN48, KNN50 and KNN52, respectively). Concentrations of 1, 5, 10 and 20% by mass of KNN were used, in order to study the influence of the K/Na ratio of KNN on the ferroelectric properties of PVDF, according to different methodologies of synthesis of composite films and the variation of ceramic concentration. For this, the methods of synthesis were used here called: chemical method (MQ), involving the evaporation of solvent; the physical method (MF), through heat pressing; and the physical-chemical method (MFQ), which consists of the thermal pressing of the films obtained by the chemical method. Thus, it was possible to observe a significant increase in the remaining and maximum polarization in the physical method for higher concentrations of KNN, while they were less significant in the chemical method. In the physical-chemical method, the remaining polarization showed an average increase of 482.05% between the concentrations of 0 and 20% of ceramic, higher than the average increase observed for the samples of the chemical method (235.71%) and lower than the increase average observed in the samples of the physical method (1021.21%), this same intermediate tendency of increasing polarization for the samples of the physicalchemical method is verified in the maximum polarization. The highest values of remaining polarization and maximum polarization in the chemical method were verified for PVDF/KNN50. A similar trend of polarization variation, verified in the ferroelectric characterization, was verified when analyzing the variation of the β phase fraction. Characterization by DC conductivity was also performed, in which a correlation was observed between the variation of the linearity of the experimental data and the ceramic concentration. This aspect can be explained by the forms of interaction between the ceramic grains promoted in different ways according to the composite film synthesis methodology and the stoichiometry analyzed for KNN. These characteristics were evaluated by optical microscopy, through the analysis of the morphology of the composite films.