Stress effects on the impedance and ferroelectricity of PVDF-BiFeO3-MWCNT films using xanthan gum as dispersant

Composite films based on dispersions of bismuth ferrite (BiFeO3) in polyvinylidene fluoride (PVDF) matrixes were prepared in the presence of multiwalled-carbon-nanotubes (MWCNT), using xanthan gum (XG) as dispersant. Films were prepared by spin coating and characterized by infrared spectroscopy (FTIR) and electronic microscopy (SEM). SEM images showed that samples containing MWCNT and XG presented a uniform morphology with homogeneously dispersed fillers. Impedance spectroscopy analysis (ISA) up to 1 MHz and dielectric polarization curves (P-E loops) were recorded in the presence of applied unidirectional mechanical stresses (up to 10 MPa). The effect of stress on the dielectric permittivity and the relative remnant polarization was successfully described by a constitutive model, which assumes a linear dependence of the piezoelectric coefficient, d33, on the applied stress and the dielectric displacement.