Relaxor ferroelectrics are a class of dielectric materials characterized by local chemical disorder and polar nanoregions, with typical dielectric responses manifested as broadened dielectric peaks and pronounced frequency dispersion. Benefiting from their large dielectric tunability, high dielectric permittivity, substantial electric-field-induced strain, and electro-optic and photorefractive effects, relaxor ferroelectrics show great promise for applications in microwave tunable devices, high-energy-density energy storage capacitors, solid-state cooling systems, piezoelectric sensors, and actuators.
High-entropy engineering has recently emerged as an effective strategy for tailoring structural disorder and local polarization behavior in ferroelectric ceramics. In many ferroelectric systems, introducing multiple cations is expected to enhance compositional disorder, disrupt long-range ferroelectric order, and promote relaxor behavior. However, recent studies have shown that the influence of high entropy on relaxor behavior is not always positive. In some high-entropy systems, relaxor characteristics are absent or weakened, accompanied instead by enhanced ferroelectricity. This suggests that high entropy does not regulate relaxor behavior solely through compositional disorder; rather, more complex local structural evolution may be involved.
Among various ferroelectric systems, tetragonal tungsten bronze (TTB) oxides, with flexible site occupancy and compositional diversity, provide an ideal structural platform for exploring the relationship between high-entropy design and relaxor behavior. In TTB systems, polarization mainly originates from the displacement of B-site cations along the [001] direction, while A-site cations regulate the tilting and distortion of BO 6 octahedra through different A–O bonding environments. These local distortions can further give rise to commensurate or incommensurate modulation structures, thereby influencing the macroscopic dielectric response. In high-entropy TTB systems, configurational entropy, local distortion, modulation structure, and polar nanoregion dynamics are strongly coupled, making it difficult to distinguish the dominant factors governing diffuse phase transition and relaxor-ferroelectric evolution.
Recently, a research team led by Zhenxing Yue from Tsinghua University, China reported an entropy-tunable TTB ceramic system, K(NaPr) 1- x (SrBa) x Nb 5 O 15 , with x = 0.1, 0.3, 0.4, 0.5, 0.6, 0.7, and 0.8. Unlike studies focused on a single high-entropy composition, this work constructed a continuous composition series to systematically decouple the effects of configurational entropy, crystal structure, relaxor dynamics, local structural distortion, and modulation-structure evolution.
The team published their work in Journal of Advanced Ceramics on August 1 2 , 202 6 .
“In this work, we designed K(NaPr) 1- x (SrBa) x Nb 5 O 15 tetragonal tungsten bronze ceramics with continuously varying configurational entropy through A-site Sr/Ba co-substitution. By systematically tracking the evolution of crystal structure, dielectric relaxation, polarization switching, and modulation structure, we identified the key factors governing diffuse phase transition and relaxor-ferroelectric evolution,” said Zhenxing Yue, professor at the School of Materials Science and Engineering at Tsinghua University (China), a senior expert whose research interests focus on the field of functional ceramics material.
“The results show an unexpected trend. With increasing Sr/Ba substitution, the electrical response evolves from an ergodic relaxor state with slim P - E loops and four current peaks to a ferroelectric-like state with double current peaks, fatter hysteresis loops, and increased remanent and maximum polarizations. This behavior is opposite to the common expectation that higher configurational entropy should simply enhance relaxor behavior through increased compositional disorder,” said Zhenxing Yue.
“Structural and dielectric analyses further reveal the origin of this evolution. The lattice parameter c and tetragonality c / a increase continuously, while Raman results indicate a more uniform BO 6 local environment. These structural changes favor enhanced ferroelectric polarization. Vogel–Fulcher analysis shows increased freezing temperature and decreased activation energy, indicating strengthened coupling among polar nanoregions. Together, these findings show that the relaxor-ferroelectric evolution is mainly controlled by crystal-structure evolution, local BO 6 environment, and polar nanoregion dynamics. In contrast, the diffuse phase transition is closely related to modulation-structure evolution, as supported by the incommensurate modulation observed in SAED and the similar U-shaped variations of the incommensurability parameter δ and the diffuseness coefficient γ ,” said Zhenxing Yue.
This work demonstrates that configurational entropy does not directly determine the relaxor characteristics in this high-entropy TTB system. Instead, configurational entropy mainly affects diffuse phase-transition behavior through regulation of A-site occupation and modulation structure, while relaxor-ferroelectric evolution is more directly governed by crystal structure, BO 6 local environment, and polar nanoregion coupling.
The study provides a mechanistic framework for understanding high-entropy effects in structurally complex TTB ferroelectrics. It also offers guidance for the rational design of lead-free dielectric materials with relaxor properties.
Other contributors include Chongyang Zhang, Weijia Guo, Xingchen Zhang, Bowen Yin, Yutian Lu and Hui Zhang from the School of Materials Science and Engineering at Tsinghua University in Beijing, China.
About Author
Zhenxing Yue is a professor at the School of Materials Science and Engineering, Tsinghua University, China. His research interests include ferroelectric and piezoelectric ceramics, microwave dielectric ceramics, microwave magnetic materials, low-temperature co-fired ceramic (LTCC) materials and integrated ceramic components, as well as functional ceramic thin- and thick-film materials.
DOI LINK： https://doi.org/10.26599/JAC.2026.9221359
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 2025 IF is 14, ranking in Top 1 (1/34, Q1) among all journals in “Materials Science, Ceramics” category, and its 2025 CiteScore is 24.6 (6/133) in Scopus database. ResearchGate homepage: https://www.researchgate.net/journal/Journal-of-Advanced-Ceramics-2227-8508
Journal of Advanced Ceramics
Decoupling the factors governing diffuse phase transition and relaxor–ferroelectric evolution in high-entropy tetragonal tungsten bronze ceramics
12-Aug-2026