Milling and quite-fast sintering as key production steps to obtain fully dense PZTN-CF particulate composites

In the near future (within ten years) magnetoelectric multiferroics could be implemented into the emerging technologies such as wireless power, internet of things, machine-to-machine communication services, mesh network, etc. Remarkable efforts have been done to develop laminated bi-layer and multilayer multiferroic composites as bulk or thin films. These structures lead to remarkable magneto-electric coupling coefficients of a few Volts / cm∙Oe because the ferroic layer is a “full dielectric” which can be completely poled in the conventional way. On the other hand in the particulate ceramic composites the requirement for “full dielectric” is no longer applicable, since the ferroic phases are fully separated within the composite. The strengths of particulate ceramic composites are low cost, simple production technology, higher strain mediated magneto-electric coupling (since electric order phase/magnetic phase interface density can be higher) and easy control of electrical and magnetic properties if the ferroelectric phase (generally a perovskite) and the ferromagnetic one (a ferrite with spinel structure) are mixed in a favourable proportion under the percolation threshold of the ferromagnetic phase. A great research effort is in progress to improve the fabrication of PZT–CoFe2O4 (PZT– CF) composites in order to avoid the unwanted reactions, which occur during densification of PZT–CF materials at 1100–1200 °C, and to achieve the electric saturation during the poling. Up to date, by setting a quite-fast sintering, full densification and prevention of unwanted reactions were achieved for the PZT:CF 74:26 composites,1 but achieving electric saturation is still a challenge. Further important results were: the understanding that the main cause of reactions is the PbO loss;1 the proposal of an equation to calculate the PbO loss through XRD analysis, considering the amount of ZrO2 and variation of perovskite’s tetragonality;1 and the ability to design the ceramic process (milling of the CF powers in particularly) to control the CF grain size distribution, which can be mono- or bi-modal, and overgrowth.1,2 References 1. P. Galizia, C.E. Ciomaga, L. Mitoseriu and C. Galassi, “PZT-cobalt ferrite particulate composites: Densification and lead loss controlled by quite-fast sintering”, J. Eur. Ceram. Soc., 37, pp. 161–168, 2016. 2. P. Galizia, C. Baldisserri, C. Capiani and C. Galassi, “Multiple parallel twinning overgrowth in nanostructured dense cobalt ferrite”, Mater. Design, 109, pp. 19–26, 2016.