Energy storage performances of (1-y)(0.3BiFeO 3 -0.7SrTiO 3 )-yK(1-x) NaxNbO 3 dielectric capacitors Xiaoding Qi and Kai-Yu Wang Department of Materials Science and Engineering, National Cheng Kung University, Tainan City 70101, Taiwan Most of the renewable energy resources are intermittent by nature. So, the storage of such energies for constant access is equally important as their production. Although dielectric capacitors may not be as well-known as other energy storage devices, such as batteries and electrochemical capacitors, they show a few unique advantages, in particular the high-power density (~10 8 W/Kg), ultrashort charge/discharge duration (100s ns), and long cycle lifetime (~10 5 ). So, they have a great application prospect in high-pulse power supplies. In this work, perovskite- structured BiFeO 3 , which has a very large spontaneous polarisation, was mixed with other oxide ferroelectrics or dielectrics in order to obtain a relaxor-ferroelectric behaviour in the solid-solutions formed, so that a slim ferroelectric hysteresis loop was obtained for achieving high recoverable energy density (W rec ) and efficiency (h). Furthermore, microstructure and defect engineering was carried out to enhance the dielectric breakdown strength, which was equally important for achieving high W rec and h. After such domain and microstructure engineering, high values of W rec (>3.20 J/cm 3 ) and h (>90%) were attained in the solid-solutions (1-y)(0.3BiFeO 3 -0.7SrTiO 3 )- yK (1-x) Na x NbO 3 . Furthermore, the samples also exhibited a very good thermal stability for W rec and η, which varied only 4.0% and 0.8%, respectively, over the temperature range between 25-100°C, which are ideal for practical application. The details about the materials synthesis and various structural and physical characterisations of these energy-storage dielectrics will be given in this presentation.
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