| Energy-storage materials with high energy density and excellent energy-storage efficiency in the power pulsed source are vital by the rapid development of integrated electric and electronic systems. Compared to the ferroelectric and linear dielectric materials, anti-ferroelectric materials possess so higher energy-storage density that they are more suitable for energy storage capacitors due to the distinctive double hysteresis loops. Although lead-based anti-ferroelectric materials have been studied and applied extensively, it is significant to exploit lead-free anti-ferroelectric materials to adapt to the trend of environment-friendly green materials due to high amount of lead in lead-based materials. The double hysteresis loops in favor of improving energy density could exist between depolarization temperature Td and the maximum dielectric constant temperature Tm(200~320°C) in NBT. However, this temperature region is too high and narrow for practical use. In this thesis, K1/2Bi1/2Ti O3(KBT) and K0.5Na0.5Nb O3(KNN) were selected to modify NBT for reducing the depolarization temperature Td to obtain a new lead-free antiferroelectric energy- storage system NBT-KBT-KNN with outstanding energy-storage properties and stability in a wide temperature. The research in this study is given as following two parts:(Na0.80K0.20)0.5Bi0.5Ti O3-x KNN(x=0, 0.03, 0.06, 0.09, 0.12, 0.15)for energy-storage application have been fabricated by conventional solid state method. The effects of KNN on the crystal structure, microstructure, dielectric and energy-storage properties have been investigated.SEM micrograph revealed that homogeneous grain could be obtained by addition of appropriate K0.5Na0.5Nb O3. The Td decreased significantly and the Curie peak could be depressed with increasing K0.5Na0.5Nb O3 to improve the temperature stability of the dielectric constant. The P-E hysteresis loops at room temperature showed that KNN weaken the ferroelectricity in this materials system to enhance the energy-storage properties. When x=0.09, the highest energy-storage density(W=1.51 J/cm3) and energy efficiency(?=65.0%) were obtained at room temperature. Similarly, 1.45 J/cm3 and 82.0% were obtained under high temperature(150°C) in the same composition. The temperature stability of the dielectric constant and energy-storage density were also excellent when the addition of KNN was 0.09. The temperature range of Permittivity satisfying the ?C/C150??±15% could achieve from 61°C to 393°C(?r(150°C) =2320,tan?(150°C)=0.37%).Energy-storage density could satisfy ?W / W100 ? ? ± 20% when the temperature ranged from 20°C to 150°C. This work indicated that the most appropriate addition of KNN is 0.09 for this energy-storage materials system.0.91(Na1-y Ky)1/2Bi1/2Ti O3-0.09KNN(y=0.14,0.16,0.18,0.20,0.22)ceramic have been prepared by solid state method. The influence of KBT contents on the structure and energy-storage properties was discussed. When the content of KBT was over 0.16, the crystal structure changed from orthorhombic phase to tetragonal phase. The permittivity decreased after the first increase with the increasing of KBT. And when y=0.16, the slope between energy-storage density and electric field strength could up to 0.148. Besides, the best performance of energy-storage with energy density 1.58 J/cm3 and energy storage efficiency 67.4% were obtained at room temperature under the breakdown strength 11.80 k V/mm in this same component. This work indicated that 0.91(Na0.84K0.16)1/2Bi1/2Ti O3-0.09 KNN ceramic was a promising lead-free anti-ferroelectric materials for energy-storage capacitor application due to its series of advantages such as high energy-storage density, outstanding energy efficiency and excellent temperature stability of energy-storage density and dielectric constant. |
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