Effect of equal amounts of Mn and Co dopant addition on the structural, electrical and magnetic properties of PVDF films

Pure and doped poly(vinylidene fluoride) (PVDF) films were prepared by casting. Films with various concentrations of equal amounts of two fillers (MnCl2 and CoCl2) were prepared. The microstructure and physical properties of these films were studied by X-ray diffraction (XRD), infrared (IR), optical absorption, direct current (DC) electric conduction, DC magnetic susceptibility and electron spin resonance (ESR). The XRD scans evidenced a semicrystalline structure containing α- and/or β-PVDF phases. IR spectra confirmed these findings and revealed some structural defects such as mono-fluorinated alkenes and head-to-head segments. The optical absorption spectra suggested the presence of: (a) an optical gap (Eg) which depends on filler concentration (W) and (b) tetrahedral Co2+ coordination for all the filling levels (FLs). The electric conduction data were interpreted on the basis of an intrachain one-dimensional interpolaron hopping model and the calculated charge hopping distance was in the range of 3.0-4.4 nm. The temperature dependence of the DC magnetic susceptibility exhibited Curie-Wiess behaviour with positive values of the paramagnetic Curie temperature (θP) for W≤6 wt% and negative θP for W>6. The ESR analysis revealed the existence of: (a) both isolated and aggregated Mn2+ and/or Co2+ ions within the PVDF matrix and (b) octahedral Co2+ and/or divalent state of Mn2+, which confirmed the optical absorption implications. The present films could be used for optical and magnetic sensors