SBR/BiFeO₃ Elastomer Capacitor Films Prepared under Magnetic and Electric Fields Displaying Magnetoelectric Coupling

Abstract

The dielectric properties of elastomer composites formed by dispersions of bismuth ferrite (BiFeO 3) multiferroic filler particles in styrene− butadiene rubber (SBR) were studied. The SBR/BiFeO 3 films (10−100 μm) were prepared in the presence of electric (E) or magnetic fields (H), showing remarkable characteristics in comparison with systems obtained in its absence. The dispersed multiferroic fillers form clusters of much smaller size when prepared under E or H. The dielectric constant, ε (measured up to 1 MHz), increases with BiFeO 3 concentration until reaching saturation. The rise of ε was obtained at concentrations much lower for samples prepared in the presence of E or H than in its absence. Saturation is assigned to connectivity between filler clusters at the largest concentrations, increasing leakage currents and limiting the dielectric behavior. The whole dependence of ε with BiFeO 3 concentration was described using a proposed model. The dc resistivities, ρ, increase with BiFeO 3 concentration but remain high (ρ ≈ 10 GΩ•cm), allowing using the films as capacitors with filter action between 100 kHz and 7 MHz. The films prepared in the presence of H present strong dependence of the ferroelectric response with magnetic fields applied af ter preparation; that is, electromagnetic coupling was observed in those samples. 49 (SBR) embedded with Fe 3 O 4 −Ag superparamagnetic particles 50 by evaporating the solvent between two magnets. The particles 51 group forming needle-like structures aligned in the direction of 52 the magnetic field applied during preparation, providing the 53 anisotropic properties. The concentration threshold for 54 obtaining the desired effect is significantly reduced in 55 comparison with random composites. 9 56 Other devices of high relevance are elastomer/multiferroic 57 capacitors, where a multiferroic filler, which presents 58 simultaneously magnetic and electric orders at room temper-59 ature, 10,11 is dispersed in the elastomer polymer. The 60 exploration of these systems has already been started recently 61 using BiFeO 3 nanoparticles, which are the paradigmatic single-62 phase multiferroic compounds. 12−16 For instance, Bhadra et 63 al. 13 used the ferroelectric elastomer poly(vinylidene fluoride) 64 (PVDF), whose dielectric response was enhanced by randomly 65 dispersing BiFeO 3. Tamboli et al. and Ahlawat et al. reported

Dielectric Behavior and Electro-Magnetic Coupling at Room Temperature in BiFeO3/PVDF and CoFe2O4/PVDF Composites

“…It is also interesting to compare the ME coupling of BiFeO 3 in styrene–butadiene–rubber (SBR) and PVDF. In BiFeO 3 /SBR composites, the coupling is always positive, P increases with H , although it was only clearly observed in samples that were electrically or magnetically poled during preparation (and for W ≥ 50) . In those poled BiFeO 3 /SBR composites there is an almost linear increase of P R with H , while for BiFeO 3/ PVDF and CoFe 2 O 4 /PVDF a decrease in P R was observed which is not monotonous with H but it reaches a plateau.…”

“…Some authors report magneto electric effect as voltage induction due to the application of an AC magnetic field. In this work and in our previous one, the magneto electric effect is determined from the change in dielectric polarization curves ( P – E ) under different static magnetic fields ( H ). Therefore, the aims of the present work are to characterize the dielectric response and to explore the electro-magnetic coupling of ceramic/PVDF composite films at room temperature.…”

“…That is the case of styrene–butadiene rubber (SBR) and polydimethylsiloxane (PDMS), previously used in our group to implement different devices based on particle/polymer composites. ,− In these works, magnetite–silver agglomerates (simultaneously magnetic and conductors) were dispersed in PDMS and SBR to implement both magnetic field sensors (based on magnetoresistivity) and mechanical stress sensors (based on piezoresistivity). BiFeO 3 , a well-known multiferroic material which presents magnetic and electric orders at room temperature, was also incorporated into SBR to obtain elastic dielectrics for capacitors . The features of impedance spectra were well accounted by modeling the composite by an R//C equivalent circuit, where the static dielectric constant, ε s , increases with BiFeO 3 proportion.…”

“…BiFeO 3 , a well-known multiferroic material which presents magnetic and electric orders at room temperature, was also incorporated into SBR to obtain elastic dielectrics for capacitors. 8 The features of impedance spectra were well accounted by modeling the composite by an R//C equivalent circuit, where the static dielectric constant, ε s , increases with BiFeO 3 proportion. Dielectric-magnetic coupling was observed in these systems, that is, the possibility of modifying the dielectric polarization per unit volume, P, by applying an external magnetic field, H.…”

Increased Surface Roughness in Polydimethylsiloxane Films by Physical and Chemical Methods

“…An interesting alternative not explored in the literature as a method of inducing roughness, as far as we know, is to prepare structured composites for which nanofillers are preferentially oriented in a direction perpendicular to the surface. Our group has extensive experience with preparing structured composites using magnetic nanofillers, such as cobalt ferrites (CoFe 2 O 4 ), which are oriented by magnetic fields applied during curing or solvent evaporation [29,30,31,32,33,34,35,36,37,38]. These works suggest the possibility of increasing the roughness by preparing composites containing not only MWCNT, but also CoFe 2 O 4 magnetic nanoparticles, and curing the composite in the presence of a magnetic field perpendicular to the surface, generating structured PDMS/MWCNT/CoFe 2 O 4 composites.…”