There is always a need for a refrigerant with a large ΔH at operating temperature. On the other hand, refrigeration equipment generally available typically functions near/below RT. Thus, for ferroelectric refrigeration to be practical, a large ΔH at a transition near/below RT is essential. Representative PST ceramics demonstrate substantial promise for EC refrigeration near RT, attracting considerable interest. The highly ordered PST ceramic always has excellent EC properties, while it is difficult to achieve. Previous researchers often employed a heat treatment process combining high-temperature quenching and long-term annealing to obtain highly ordered PST ceramics. However, high-temperature quenching can induce microcracks, leading to reduced breakdown resistance. In fact, the Ω is not just a function of the annealing time from the initial high-temperature quenched state, but also depends in a complex manner upon the thermal history of each individual sample. Therefore, rationally regulating the parameters of the heat treatment process is crucial for obtaining highly ordered PST ceramics.
Recently, a team of material scientists led by Prof. Bai Yang at the University of Science and Technology Beijing, has successfully obtained PST ceramics with a high Ω of 1 by combining initial sintering with a low-temperature and long-time annealing heat treatment process. Besides, they also explored the large-scale modulation of Ω in PST ceramics and systematically investigated its influence on the ferroelectric properties, phase transition characteristics, and ECE. In particular, PST ceramics with tunable Ω showed excellent EC performance in meeting the requirements of near/below RT refrigeration applications.
The team published their work in Journal of Advanced Ceramics on May 4, 2025.
"In this report, we continuously adjust the Ω for PST ceramics on a large scale from 0.51 to 1 by multiple heat treatment processes. Using TEM and HAADF techniques, the PST ceramic with Ω = 0.51 has a coexistence of ordered and disordered configuration for B-site ions, and the sample with Ω = 1 has a fully ordered arrangement of B-site ions." said Bai Yang, professor at the Institute for Advanced Materials and Technology at University of Science and Technology Beijing, a senior expert whose research interests focus on the field of EC refrigeration.
With the increasing Ω, the Curie temperature (TC) shifts to higher temperatures, from -7 °C for Ω = 0.51 to 28 °C for Ω = 1. "The variation range of TC covers RT to below zero, endowing PST ceramics with application potential for the most marketable refrigeration devices." said Bai Yang.
For Ω = 1, it shows a clear feature of normal ferroelectric with first-order phase transition; while samples with low Ω, eg., Ω = 0.59 and Ω = 0.51, demonstrate weakened ferroelectricity with diffused phase transition. In addition, the frequency dispersion becomes more notable in the sample with low Ω. "The ferroelectric properties of PST ceramics can be regulated by adjusting Ω. That is, as the Ω decreases, the PST ceramics undergo a gradual transition towards relaxor ferroelectric." said Bai Yang.
A large ΔH of 1.06 J g-1 and a huge ΔTmax = 4.26 K (@60 kVcm-1) at the Tpeak of 37 °C are achieved in the highly ordered PST ceramics with Ω = 1. With the reduction of Ω, the TC gradually shifts from RT to below 0 °C, and the phase transition is diffused. A fairly large ΔTmax = 1.57 K is obtained at a rather low temperature of 0 °C in the ceramic with Ω = 0.51. "The former is excellent for RT refrigeration, the latter opens up the possibility of low-temperature refrigeration, and the continuous adjusting the operating temperature facilitates a cascade cooling design." said Bai Yang.
This work proves that lattice ordering is another efficient route to modify ferroelectric features i.e. a new method for materials design and optimization. Moreover, the ordering-optimized PST ceramics open a new avenue to explore advanced near/below RT refrigeration systems.
Other contributors include Ruowei Yin, Yuxuan Hou, Rongju Zhong, Yanjing Su, Lijie Qiao, Chuanbao Liu, Lifeng Zhu from University of Science and Technology Beijing, China; Xiaowei Lv, Renchao Che from Fudan University, China; Junjie Li from Chengdu University of Information Technology, China.
This work was supported by grants from National Natural Science Foundation of China (52325208, 92463311, 52173217) and State Key Lab for Advanced Metals and Materials (2024-Z05).
About Author
Yang Bai, Professor, Institute for Advanced Materials and Technology, University of Science and Technology Beijing, National Natural Science Foundation of China for Distinguished Young Scholars. His main research interests are materials genetic engineering, metamaterials for multiple physical fields, ferroelectric ceramics, etc. He serves as PI for 1 project from National Key Research and Development Program of China and 8 projects from National Natural Science Foundation of China. He has published more than 200 SCI-indexed papers, published 5 academic monographs in English/Chinese, and obtained more than 10 national authorized patents. He won 1 first prize and 1 second prize of natural science of the Ministry of Education, and won the 13th Youth Science and Technology Award of the Chinese Ceramic Society. He is the executive director of the Chinese Society of Metamaterials, and a director of the Chinese Advanced Ceramics Society, etc. He also serves as the editorial board of 5 English SCI journals and 3 Chinese journals.
About Journal of Advanced Ceramics
Journal of Advanced Ceramics (JAC) is an international academic journal that presents the state-of-the-art results of theoretical and experimental studies on the processing, structure, and properties of advanced ceramics and ceramic-based composites. JAC is Fully Open Access, monthly published by Tsinghua University Press, and exclusively available via SciOpen . JAC's 2023 IF is 18.6, ranking in Top 1 (1/31, Q1) among all journals in "Materials Science, Ceramics" category, and its 2023 CiteScore is 21.0 (top 5%) in Scopus database. ResearchGate homepage: https://www.researchgate.net/journal/Journal-of-Advanced-Ceramics-2227-8508
About SciOpen
SciOpen is an open access resource of scientific and technical content published by Tsinghua University Press and its publishing partners. SciOpen provides end-to-end services across manuscript submission, peer review, content hosting, analytics, identity management, and expert advice to ensure each journal's development. By digitalizing the publishing process, SciOpen widens the reach, deepens the impact, and accelerates the exchange of ideas.
