Structural, dielectric, ferroelectric and piezoresponse force microscopy characterizations of bilayered Bi _0.9Dy _0.1FeO ₃/K _0.5Na _0.5NbO ₃ lead-free multiferroic films

The structure, dielectric and ferroelectric properties of the bilayered Bi _0.9Dy _0.1FeO ₃/K _0.5Na _0.5NbO ₃ (BDF/KNN) lead-free thin films deposited on the Pt/TiO ₂/SiO ₂/Si substrates by pulsed laser deposition with different thickness ratios have been characterized. It is found that the introduction of the bottom KNN layer can effectively reduce the leakage current of the composite film, allowing the high polarization of the BDF layer to be displayed. The bilayered film with KNN to BDF thickness ratio of 1.2 exhibits the best dielectric and ferroelectric properties, with a remanent polarization 2P _r 16.3 μC/cm ². The polar domain structure of that film has been imaged by means of piezoresponse force microscopy (PFM) and the switching of the polarization has been realized under an applied electric field of ±12 V, confirming the ferroelectricity in the BDF/KNN composite film.