Processing issues and their influence in the magnetoelectric performance of (K,Na)NbO3/CoFe2O4-based layered composites

Low temperature processing of environmentally-friendly (K,Na)NbO3- and CoFe2O4-based layered composites has been accomplished by hot pressing, and their electrical, piezoelectric and magnetoelectric properties have been characterized. High quality composite three-layer CoFe2O4/K0.5Na0.5NbO3/CoFe2O4 structures with defect-free interfaces were obtained by hot pressing at only 1000 °C, when highly reactive CoFe2O4 powders obtained by Pechini were used. Negligible chemical reactions at interfaces or interdiffusion across them took place during processing, while alkali volatilization was minimized. Dense, crack-free CoFe2−zGazO4/(K0.5Na0.5)1−xLixNb1−yTayO3/CoFe2−zGazO4 structures incorporating phases with enhanced piezoresponses have been also obtained, though in this case magnetoelectric coefficients were lower than expected. This is shown to be related with the presence of a core-shell type microstructure within the piezoelectric layer characteristic of (K0.5Na0.5)1−xLixNb1−yTayO3, which is stabilized by the low temperature processing. Procedures for further enhancement of the magnetoelectric response are proposed.