Electromechanically active materials are crucial for applications in sensors, actuators, and transducers. Unfortunately, the most popular electromechanically active materials are lead-based, e.g., PbMg1/3Nb2/3O3 –PbTiO3 (PMN-PT), which pose considerable health risks. To address this issue, “giant” electrostrictors, such as Zr- and Gd-doped ceria ceramics, have been researched as alternatives. “Giant” electrostrictors exhibit longitudinal electrostriction coefficient (M33) at least twice as high as the values predicted by Newham’s scaling law. This is noteworthy because electrostriction is a ubiquitous phenomenon, unlike piezoelectricity, it is not restricted to polar structures. Moreover, piezoelectricity is an interconvertible phenomenon between mechanical and electrical counterparts, whereas electrostrictors do not polarize when mechanically tensioned, which can be advantageous. Finally, unlike lead-based materials, ceria-based ceramics can fit seamlessly into current Si microchip technology. Unfortunately, in aliovalent-doped ceria, exceptional performance is only maintained up to a 100 Hz frequency. However, recent research shows that isovalent-doped ceria can offer a solution to this problem. In the case of Ce0.9Zr0.1O2 (ZDC), exceptional performance extends over a wide range of frequencies, from 0.15 to 3000 Hz, and a strain greater than 200 ppm can be achieved without reaching saturation. This improvement is potentially attributed to the mechanism behind electrostriction: in aliovalent-doped ceria, it involves “static” elastic dipoles associated with oxygen vacancies, while in isovalent-doped ceria, “dynamic” elastic dipoles arise from bond anharmonicity. Our investigation focuses on electromechanical coupling in CeO2-ZrO2-HfO2 mixed oxides. We employed a green-chemistry synthesis route for ZDC. 10-hour high-energy milled ZDC displays the fluorite structure and homogeneous distribution of Zr in CeO2, as confirmed by Transmission Electron Microscopy allied to Energy-Dispersive X-ray Spectroscopy (EDS) mapping in scanning mode and Selected Area Electron Diffraction. Moreover, the impact of sintering parameters on the electromechanical coupling of Ce0.95Zr0.04Hf0.01O2 (ZHDC) synthesized by solid-state synthesis was investigated. For ZDC and ZHDC, dense samples were obtained after sintering at 1500 oC, and the fluorite structure was obtained. Raman and X-ray diffraction combined with Rietveld refinement support the hypothesis of solid-solution formation, with no secondary phases detected. The reduction in unit cell volume compared to CeO2 indicates cationic substitution at the A site, as does the blueshift and broadening of the F2g Raman mode corresponding to the eightfold oxygen-coordinated cerium cation in the cubic crystal. X-ray absorption spectroscopy using synchrotron radiation through XANES analysis (Ce M4,5 and O K-edges) indicates the predominance of Ce4+ species and low oxygen vacancy concentration for both compositions. Scanning Electron Microscopy with EDS shows an apparently homogeneous dispersion of dopant atoms in the ceria matrix and average grain sizes in the micrometer scale for all sintered samples. For Ce0.9Zr0.1O2, two hours of sintering led to adequate densification, 93.7%. For Ce0.95Zr0.04Hf0.01O2, different dwell times were tested, and only samples sintered for more than 2.5 hours showed adequate densification (93.1% for 2.5 and 94.4% for 3 hours). What has been observed in this system is a composition-over-microstructure electromechanical response. For Ce0.9Zr0.1O2, M33 reaches 1.7?10 ?17 m2V?2 at 1 kHz. For Ce0.95Zr0.04Hf0.01O2, it lies in the range of 4.20 – 9.03?10-18 m2 V?2.
Comissão Organizadora
Pedro Alves da Silva Autreto
Comissão Científica
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