Negative thermal expansion (NTE) is fascinating as it involves a material's volume contraction rather than expansion upon heating. Although NTE lattices typically have highly flexible frameworks, the magnitude of NTE is often very small, and they frequently behave a narrow temperature range for controllable NTE. It remains a great challenge to achieve large NTE while maintaining a wide temperature operation range from the currently available materials. It has been suggested that the perovskite-type (ABO3) ferroelectric of PbTiO3 (PT) is one of the most promising compounds for large NTE applications. Along with piezoelectricity and ferroelectricity, PT also exhibits unusual NTE from room temperature (RT) to its Curie temperature (TC = 763 K), with a pronounced average volumetric CTE of -1.99 ´ 10-5/K. As the volume shrinkage of PT occurs primarily along the polar c axis of the tetragonal phase, an increase in c/a could lead to an increase in NTE. Indeed, enhanced NTEs were obtained in PT-based ferroelectrics with improved tetragonality.
Recently, a team of material scientists led by Zhao Pan and Youwen Long from the Institute of Physics, Chinese Academy of Sciences reported the synthesis, structure, and thermal expansion properties of a new PbTiO3-based perovskite system, (1-x)PbTiO3-xBiYbO3. The system exhibits an unusual enhanced tetragonalities compared to pristine PbTiO3 (c/a = 1.064). Consequently, NTE over an extended temperature range has been realized in 0.95PbTiO3-0.05BiYbO3 ( = -2.18 ´ 10-5/K, 300 - 820 K) and 0.90PbTiO3-0.10BiYbO3 ( = -1.85 ´ 10-5/K, 300 - 850 K), respectively, when compared to that of pristine PbTiO3 ( = -1.99 ´ 10-5/K, 300 - 763 K). Our experimental and theoretical studies indicate that the improved tetragonalities and expanded NTE temperature range result from stronger Pb/Bi-O and Ti/Yb-O bond strengths, and an asymmetrically distributed charge density. The present study presents a new instance of NTE across a broad temperature range, highlighting its potential as an effective thermal expansion compensator.
The team published their work in Journal of Advanced Ceramics on May 19, 2025.
"In this report, we present a novel PbTiO3-based perovskite system, (1-x)PbTiO3-xBiYbO3, synthesized using a distinctive high-pressure and high-temperature technique. The system exhibits an unusual enhanced tetragonalities compared to pristine PbTiO3 (c/a = 1.064). Consequently, NTE over an extended temperature range has been realized in 0.95PbTiO3-0.05BiYbO3 ( = -2.18 ´ 10-5/K, 300 - 820 K) and 0.90PbTiO3-0.10BiYbO3 ( = -1.85 ´ 10-5/K, 300 - 850 K), respectively, when compared to that of pristine PbTiO3 ( = -1.99 ´ 10-5/K, 300 - 763 K)." said Zhao Pan, associate professor at the Institute of Physics, Chinese Academy of sciences, a young researcher whose research interests focus on the field of negative thermal expansion material.
"Materials with large NTE over a wide temperature range are valuable, since they can be used as thermal inhibitors to compensate thermal expansion by forming composites with normal positive thermal expansion materials. However, Although NTE lattices typically have highly flexible frameworks, the magnitude of NTE is often very small, and they frequently behave a narrow temperature range for controllable NTE. It remains a great challenge to achieve large NTE while maintaining a wide temperature operation range from the currently available materials." said Zhao Pan.
"It has been suggested that the perovskite-type (ABO3) ferroelectric of PbTiO3 (PT) is one of the most promising compounds for large NTE applications. Along with piezoelectricity and ferroelectricity, PT also exhibits unusual NTE from room temperature (RT) to its Curie temperature (TC = 763 K), with a pronounced average volumetric CTE of -1.99 ´ 10-5/K. As the volume shrinkage of PT occurs primarily along the polar c axis of the tetragonal phase, an increase in c/a could lead to an increase in NTE. Indeed, enhanced NTEs were obtained in PT-based ferroelectrics with improved tetragonality. The flexible structure of PT allows for enhancement of NTE by modulating its c/a," said Zhao Pan.
"We designed and prepared a new PT-based perovskite system of (1-x)PT-xBiYbO3 by high-pressure and high-temperature method. The samples are of high quality with negligible impurities, and all investigated samples have tetragonal symmetry.According to the Rietveld refinement results, the c axis shows an apparently increase tendency with the substitution of BiYbO3, while the a axis slightly increases as a function of the BiYbO3 content. Consequently, the c/a ratio increases from 1.064 for pristine PT, to 1.066 and 1.069 for 0.95PT-0.05BY and 0.90PT-0.10BY, respectively," said Zhao Pan.
In ferroelectrics based on the PT, the enhanced c/a and large PS could be associated with a large ferroelectric volume effect, or a large NTE. It is proposed that a large c/a of PT-based ferroelectrics indicates a large lattice distortion, which could lead to a significant volume shrinkage when lattice energy is released upon heating. To study the thermal expansion properties of (1-x)PT-xBY (x = 0.05 and 0.10) solid solutions, temperature-dependent SXRD experiments were performed. The temperature dependence of lattice parameters of the (1-x)PT-xBY (x = 0.05 and 0.10) compounds were determined by the Rietveld refinement of the SXRD data.For the 0.95PT-0.05BY compound, in the temperature range of RT to 700 K, the unit cell volume shows little dependence on the temperature with an average CTE of -3.79 ´ 10-6/K. However, a very strong NTE occurs on approaching the TC. The average volumetric CTE in the whole temperature range of 300 to 820 K was = -2.18 ´ 10-5/K, which is even a little stronger than the pristine PT ( = -1.99 ´ 10-5/K, RT ~ 763 K). Similar phenomenon was also observed in the 0.90PT-0.10BY compound. In the temperature range of RT to 700 K, a low CTE of -1.31 ´ 10-6/K was observed, while a sharply decrease of unit cell volume appears with further increasing temperature. The overall volumetric CTE of 0.90PT-0.10BY is = -1.85 ´ 10-5/K in the temperature range of RT to 850 K. Note that even though the magnitude of NTE for the 0.90PT-0.10BY compound decreased, the NTE temperature range was extended from RT to its TC as high as 850 K.
Both experimental and theoretical studies indicate that the improved tetragonalities and expanded NTE temperature range result from stronger Pb/Bi-O and Ti/Yb-O bond strengths, and an asymmetrically distributed charge density.
Other contributors include Fengyi Zhou, Duo Wang from Faculty of Applied Sciences, Macao Polytechnic University in Macao, China; Qiumin Liu, Takumi Nishikubo, Masaki Azuma from the Laboratory for Materials and Structures, Tokyo Institute of Technology in Yokohama, Japan; Shogo Kawaguchi from Research and Utilization Division, Japan Synchrotron Radiation Research Institute (JASRI), SPring-8, Japan; Mengqi Ye, Xubin Ye, Xiao Wang, Jin Liu, Nianpeng Lu, Youwen Long from the Institute of Physics, Chinese Academy of Sciences.
This work was supported by the National Key R&D Program of China (Grant No. 2021YFA1400300), the National Natural Science Foundation of China (22271309, 12304268, 11934017, and 12261131499), the Beijing Natural Science Foundation (Grant No. Z200007), and the Chinese Academy of Sciences (Grant No. XDB33000000). D.W. acknowledges financial support from the Science and Technology Development Fund from Macau SAR (Grant No. 0062/2023/ITP2) and the Macao Polytechnic University (Grant No. RP/FCA-03/2023). The synchrotron X-ray powder diffraction experiments were performed at SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (2024A1506 and 2024A1695). The authors would like to acknowledge Profs. Xi Shen and Richeng Yu in the Institute of Physics, Chinese Academy of Sciences for TEM performance.
About Author
Dr. Zhao Pan is an associate professor in the Institute of Physics, Chinese Academy Sciences. He received his PhD from University of Science and Technology Beijing (USTB) in Jan. 2017 under the supervision of Prof. Jun Chen, and then Joined Tokyo Institute of Technology (present Institute of Science Tokyo) as a postdoc in Prof. Masaki Azuma's group. From Nov. 2021, he joined Prof. Youwen Long's group in the Institute of Physics, Chinese Academy Sciences as an associate professor. His research interest lies in high-pressure synthesis, quantum beam experiments including synchrotron X-ray and neutron, and exploration of novel properties such as negative thermal expansion, ferroelectricity, magnetism, and exotic electronic transitions. He published more than 80 in-peer reviewed papers.
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
