Résumé:
The Pb-free piezoceramics are currently considered as an alternative to Pb-based ceramics due to the harmful effects of lead on the environment and human health. In this thesis, two families of Pb-free piezoelectric ceramics were studied, including Ba(1-x)CaxTiO3 (BCT) and (1-y)BiFeO3-yBaTiO3 (BFO-BT).
In the first part, the incorporation mechanism of Ca into BaTiO3 were investigated using differential scanning calorimetry (DSC) technique at multiple heating rates. The DSC and the X-ray diffraction technique (XRD) has demonstrated the complete incorporation of Ca into BaTiO3 structure. Incorporation kinetics was analyzed by Freidman (FR), Ozawa-Flynn-Wall (OFW) and Kissinger-Akahira-Sunose (KAS) isoconversional methods. The results indicate that the incorporation process was carried out through a single-step. The kinetic parameters, i.e. Activation energy (Ea), preexponential factor (A) and the kinetic model (f(α)), were determined through the combined kinetic analysis method. The BCT ceramic samples were then synthesized using the conventional solid-state reaction method in order to study the effect of Ca doping on the structural, microstructural and electrical properties of BaTiO3. Different characterization techniques, such as XRD, Raman, SEM and electrical measurements, were used in order to study the influence of Ca on the properties of BaTiO3.
In the second part, the (1-y)BiFeO3-yBaTiO3 (BFO-BT) ferroelectric ceramic was prepared by Reactive Flash Sintering (RFS). This preparation technique combines synthesis and sintering in a single Flash experiment. The starting oxides reacted during the flash to produce a stoichiometric well-sintered solid solution at a temperature of 858 °C by applying a modest field of 35 V cm− 1. The process takes place in a matter of seconds, which allows obtaining a pure perovskite structure without secondary phases. X-ray diffraction (XRD) results show the mixture of rhombohedral and pseudocubic phases expected for a composition that lies within a morphotropic phase boundary (MPB) region. The microstructure exhibits a peculiar bimodal grain size distribution that determines the electrical properties. As compared to previous results, flash-prepared 0.67BiFeO3-0.33BaTiO3(BFO-33BT) evidences smaller grain size as well as slightly lower remanent polarization (Pr) and smaller coercive field (Ec) under similar electric fields. It is also demonstrated that the preparation by RFS provides benefits regarding electrical energy consumption
