Considering the full utilization of energy and pursuing thin-film capacitors with high energy-storage density, the grain size engineering is used to adjust domain size, in order to enhance the energy-storage efficiency and energy-storage density of thin-film capacitors. Therefore, in this work, lead-free Bi_0.5Na_0.5TiO₃ (BNT) films with designed grain size were grown on Nb-doped SrTiO₃ (Nb:STO) (001) single-crystalline substrates by modulating the mineralizer concentrations via hydrothermal synthesis. The nature of epitaxial growth near the single-crystalline substrates was proved by transmission electron microscopy (TEM). In addition, the phenomenon of the decrease of grain size and the increase of [100] in-plane orientation with the decline of mineralizer concentrations were clarified by grazing-angle incidence X-ray diffraction (GIXRD) and field emission scanning electron microscope (FESEM). By reducing the grain size, an ultrahigh energy-storage efficiency (η) of 75.56% and superior the recoverable energy-storage density (W_rec) of 16.47 J/cm³ were acquired in pure Bi_0.5Na_0.5TiO₃ films. Furthermore, the fine-grained film exhibits weak dependence on the frequency and has excellent anti-fatigue property. Therefore, hydrothermal synthesis is an efficient, inexpensive, and easy method, which is the most promising way to adjust grain size and energy storage of the film capacitor.

考虑到能量的充分利用，追求高储能密度的薄膜电容器，通过晶粒尺寸工程来调整畴尺寸，以提高薄膜电容器的储能效率和储能密度。因此，在这项工作中，在 Nb 掺杂的 SrTiO ₃上生长了具有设计晶粒尺寸的无铅 Bi _0.5 Na _0.5 TiO ₃ (BNT)薄膜。(Nb:STO) (001) 单晶基质通过水热合成调节矿化剂浓度。透射电子显微镜 (TEM) 证明了单晶衬底附近外延生长的性质。此外，通过掠角入射X射线衍射（GIXRD）和场发射扫描电子显微镜（FESEM）阐明了随着矿化剂浓度的降低晶粒尺寸减小和[100]面内取向增加的现象。 ）。通过减小晶粒尺寸，在纯 Bi _0.5 Na _0.5中获得了 75.56%的超高储能效率 ( η ) 和16.47 J/cm ^{3 的}优异可恢复储能密度 ( W _rec )TiO ₃薄膜。此外，细粒薄膜对频率的依赖性较弱，具有优异的抗疲劳性能。因此，水热合成是一种高效、廉价、简便的方法，是调整薄膜电容器晶粒尺寸和储能最有前途的方法。