Influence of annealing temperature on the existence of polar domain in uniaxially stretched polyvinylidene-co-hexafluoropropylene for energy harvesting applications

Abstract

The structural and electroactive properties of the as-prepared random copolymer polyvinylidene-co-hexafluoropropylene thin film are explored as a function of thermal treatment at various temperature regions. The thermal treatment of the polymer thin film not only changes the structural conformations that is very natural but establishes a polar domain in the non-polar α-phase. Here, we discover an anomalous temperature-dependent crossover behavior from the non-polar α-phase to an appreciable enhancement in ferroelectric and piezoelectric responses. The maximum unipolar strain (Smax=−5.01%), an ultrahigh value of normalized piezoelectric coefficient (d33∗=−556pm/V), high electromechanical coupling factor (Kp=0.78) factor including the high dielectric constant (ϵ′=23at100Hz) at a relatively low electric field of 900 kV/cm may, therefore, be an effect of the established polar domain for the sample annealed at 105 °C. The direct piezoelectric charge coefficient (d33), a key factor for the performance of a prepared polymer thin film system as an energy harvester, lies in the range of −10±2pC/N. Also, the annealed sample exhibited a persistent polarization after several cumulative cycles of applied stress.

Asymmetric Electrode Influence upon Ferroelectric Switching Dynamics in Ag/PVDF‐HFP/ITO Capacitor Structures

“…The variation in the peak positions of polar γ phase for 80 and 160 nm thick PVDF–HFP films is attributed to the different crystallization process during film preparation, which causes the slight change in the C–H and C–F bond angles due to resultant strain. [ 15,28,29 ]…”

The Mystery of Dimensional Effects in Ferroelectricity

“…A maximum polarization of 12 μC/cm 2 at 4 V has been observed for 100 nm thick P(VDF-TrFE) film which is attributed to the presence of crystalline β-phase (a type of crystal orientation) [54]. Similarly, Xu et al [55] suggested the preferential crystal orientation for the maximum polarization of 10 μC/cm 2 and apparent coercive field $6 MV/m in 500 nm thick PVDF film at a very low switching voltage of 3 V. The study of ferroelectric polymer in their ultra-low dimensions were not possible until the discovery of Langmuir-Blodgett (LB) [56] technique of monolayer formation as the thin films constructed by the conventional route of synthesis such as uniaxial or biaxial drawing [57], solvent casting [58], uniaxial stretching [59] or spin coating limited the thickness as thin as $ 60 nm only [50]. Langmuir-Blodgett (LB) monolayer transfer technique produces high-quality ferroelectric polymer ultrathin films which are few monolayers thick and can be switched at 1 V, permitting precise control of the film nanostructures [5].…”

Structural, microstructural, and ferroelectric studies of polyvinylidene fluoride‐hexafluoropropylene (PVDF‐HFP) thin films in Ag/Cu/PVDF‐HFP/Cu capacitor structures

“…The incorporation of HFP [CF 2 CF(CF 3 )] affects the asymmetry in [CH 2 -CF 2 ] chain conformations and as well as the crystallinity percentage. Literature reports that the dimethyl sulfoxide (DMSO), 19 dimethylformamide (DMF), [20][21][22] Ethyl Acetate 23 and acetone [23][24][25] solvents are utilized for the formation of polar PVDF-HFP thin films. In addition, mixing with magnesium nitrate [Mg(NO 3 ) 2 ], 21,26 metal nanoparticles, 19,20 quenching, 26 electrical poling, 27 mechanical stretching 22,26 have been utilized to enhance the ferroelectric polarization.…”

“…Literature reports that the dimethyl sulfoxide (DMSO), 19 dimethylformamide (DMF), [20][21][22] Ethyl Acetate 23 and acetone [23][24][25] solvents are utilized for the formation of polar PVDF-HFP thin films. In addition, mixing with magnesium nitrate [Mg(NO 3 ) 2 ], 21,26 metal nanoparticles, 19,20 quenching, 26 electrical poling, 27 mechanical stretching 22,26 have been utilized to enhance the ferroelectric polarization. Many works in the literature focused upon characterizing the structural, dielectric, and ferroelectric characteristics of PVDF-HFP films with thickness ranging from 0.9 to 120 μm and it is observed that preparation method, annealing temperature, and solvent influences the crystal structure and electrical properties.…”