CONICET | Buscador de Institutos y Recursos Humanos

The dielectric properties of composites formed by dispersions of two types of ceramic particles, BiFeO3 (multiferroic) and CoFe2O4 (ferromagnetic), in PVDF (poly-vinyliden-di-fluoride, a ferroelectric elastomer) were studied at room temperature as function of particle concentration. The studies include determination of dielectric polarization curves in the presence of external magnetic fields, H (that is, P-E plots in the presence of H, where P is the dielectric polarization and E the external applied electric field). Characterization includes also impedance spectroscopy (10-1-106 Hz) and IR analysis, determination of DC-leakage currents, and the frequency response when composites are incorporated into an AC-circuit.The inclusion of ceramics increases the ferroelectric order. Impedance spectroscopy shows the presence of several distributions of dipole relaxation processes, some of which are assigned to charge rearrangements at the different interfaces of the system, for example at the ceramic-polymer interfaces. The addition of ceramic particles induces negative magneto-electric coupling, that is, decrease of P when applying H, . This behaviour is opposite to previously observed for BiFeO3 dispersed in a non-ferroelectric matrix (SBR), where . The negative magneto-electric coupling in the ceramic/PVDF systems is not observed in the absence of particles and its absolute magnitude increases with the proportion of ceramics in the composite. All studies suggest a strong polymer-particle interaction, where the interfaces between the two components play a central role. The observation of negative magneto-electric coupling using two different types of ceramic is an evidence of the presence of a matrix-mediated coupling type, possibly through a magnetostriction mechanism at the ceramic-polymer interfaces.