Defect-Engineered Ceramic Material for Enhanced Energy Storage

In a recent study published in the Journal of Advanced Ceramics, a research group led by Prof. Dr. Zong-Yang Shen from Jingdezhen Ceramic University explored dielectric materials for energy storage capacitors. They disclosed aliovalent rare earth ion Sm³⁺-doped relaxor ferroelectric Ba_0.12Na_0.3Bi_0.3Sr_0.28-1.5x□_0.5xSm_xTiO₃ (abbreviated as Sm_x-BNBST) solid solutions through defect-engineered phase/domain structure competition.

High discharge density was achieved in high-quality relaxor ferroelectric BNT-based ceramics through a combination of chemical doping, hierarchical structure design, advanced sintering technology, and defect structure engineering.

However, the energy efficiency of BNT-based ceramics remains low, at 60 to 70%, meaning a significant portion of stored energy is lost, generating additional joule heat. Low energy efficiency is a critical, yet often overlooked, issue that requires proper solutions.

Sm_0.07-BNBST ceramics outperform other documented dielectric materials under the same electric field, achieving a high energy efficiency of 91% and a recoverable energy density of 2.1 J/cm³ at a low electric field of 114 kV/cm.

In this work, we proposed that defect-induced phase competition between tetragonal phase P4bm and pseudo-cubic phase Pm3m not only strengthens polarization switching ability but also improves dielectric temperature stability via thermal evolutions. More importantly, a high 91% energy efficiency with discharge density of 2.1 J/cm³ was achieved in Sm_0.07-BNBST ceramics at a low electric field of 114 kV/cm, which is closely related to a reduced P_r demonstrated by PFM measurement.

Prof. Zong-Yang Shen, Study Corresponding Author and Vice Dean, School of Materials Science and Engineering, Jingdezhen Ceramic University

His research interests include dielectric ceramics for high power density energy storage capacitors, as well as piezoelectric ceramics with high Curie temperatures.

“Reduced domain size determines the remanent polarization (P_r), while the competition between tetragonal phase and pseudo-cubic phase determines the maximum polarization (P_max). For the x=0 composition, it exhibits obvious ferroelectricity with increasing voltage; and after the electric field is removed, the polarization direction is still maintained and difficult to return to the initial state, corresponding to a high P_r,” Prof. Zong-Yang Shen added.

He added, “For the x=0.07 composition, the ferroelectricity is significantly weakened; when the external voltage is removed, the polarization direction can quickly return to the initial state, corresponding to a low P_r. The rapid response of polarization switching in Sm0.07-BNBST ceramics indicates that it has highly active polar nanoregions (PNRs), which produce low P_r and moderate P_max, contributing to enhanced energy density and efficiency.”

“As the Sm concentration increases, the P-E loops of Sm_x-BNBST ceramics gradually become slimmer, and both P_max and P_r gradually decrease, indicating that Sm doping weakens the ferroelectricity. When the Sm equals to 0.07 mol, P_max shows a sudden increase, which may be related to the synergistic contributions of tetragonal/pseudo-cubic phase competition and reduced domain size,” added Zong-Yang Shen.

He continued, “Compared with pure BNBST ceramics with one dielectric peak of <100 °C, Sm_x-BNBST ceramics exhibit a new weak dielectric peak near ~200 °C, which should be related to the thermal evolution of defect-induced phase competition between tetragonal phase and pseudo-cubic phase in BNT ceramics. As the Sm concentration increases, the dielectric peaks gradually broaden, and the corresponding transition temperature Tm1 shifts towards lower temperatures, strengthening the dielectric temperature stability.”

Prof. Zong-Yang Shen concluded, “In the following work, we will do research on designing and analyzing the influence of defect structure on dielectric and ferroelectric behaviors of BNT-based ceramics.”

He wants to develop BNT-based ceramics with high discharge density and energy efficiency at low electric fields, which he will subsequently construct into multi-layer ceramic capacitors (MLCCs) to help progress the development of dielectric materials for practical applications.

Dong-Xu Li, Wei Deng, Zhipeng Li, Xuhai Shi, You Zhang, Wenqin Luo, and Fusheng Song from School of Materials Science and Engineering, Jingdezhen Ceramic University in Jingdezhen, China; Deng Wei from Research Center for Advanced Functional Ceramics at Wuzhen Laboratory, Jiaxing, China; You Zhang from Ceramic Research Institute of Light Industry of China, Jingdezhen, China; Chao-Feng Wu from Center of Advanced Ceramic Materials and Devices at Yangtze Delta Region Institute of Tsinghua University, Zhejiang province, China are the other study contributors.

National Natural Science Foundation of China (52267002), Natural Science Foundation of Jiangxi Province (20212ACB204010), and the Science & Technology Research Project of Jiangxi Provincial Education Department (GJJ211301) supported the study.

Journal Reference:

Li, D.-X. et. al. (2024) Aliovalent Sm-doping enables BNT-based realxor ferroelectric ceramics with > 90% energy efficiency. Journal of Advanced Ceramics. doi.org/10.26599/JAC.2024.9220999