@article{Song2024, 
author = {Chuanqi Song and Feifan Zheng and Yuan Zhang and Hongbo Cheng and Long Teng and Kun Wang and Hanfei Zhu and Chao Liu and Li Wang and Zhengyan Liang and Jun Ouyang},
title = {Dielectric ultracapacitors based on columnar nano-grained ferroelectric oxide films with gradient phases along the growth direction},
year = {2024},
journal = {Journal of Advanced Ceramics},
volume = {13},
number = {7},
pages = {1072-1079},
keywords = {ferroelectric, energy storage, silicon, thin films, phase coexistence, nanograin},
url = {https://www.sciopen.com/article/10.26599/JAC.2024.9220920},
doi = {10.26599/JAC.2024.9220920},
abstract = {In this work, dielectric ultracapacitors were designed and fabricated using a combination of phase boundary and nanograin strategies. These ultracapacitors are based on submicron-thick Ba(Zr0.2Ti0.8)O3 ferroelectric films sputter-deposited on Si at 500 °C. With a composition near a polymorphic phase boundary (PPB), a compressive strain, and a high nucleation rate due to the lowered deposition temperature, these films exhibit a columnar nanograined microstructure with gradient phases along the growth direction. Such a microstructure presents three-dimensional polarization inhomogeneities on the nanoscale, thereby significantly delaying the saturation of the overall electric polarization. Consequently, a pseudolinear, ultraslim polarization (P)–electric field (E) hysteresis loop was obtained, featuring a high maximum applicable electric field (~5.7 MV/cm), low remnant polarization (~5.2 μC/cm2) and high maximum polarization (~92.1 μC/cm2). This P–E loop corresponds to a high recyclable energy density (Wrec ~208 J/cm3) and charge‒discharge efficiency (~88%). An in-depth electron microscopy study revealed that the gradient ferroelectric phases consisted of tetragonal (T) and rhombohedral (R) polymorphs along the growth direction of the film. The T-rich phase is abundant near the bottom of the film and gradually transforms into the R-rich phase near the surface. These films also exhibited a high Curie temperature of ~460 °C and stable capacitive energy storage up to 200 °C. These results suggest a feasible pathway for the design and fabrication of high-performance dielectric film capacitors.}
}