Key Takeaways & Executive Findings
- •• • CE0.4MO exhibits NTE over 100–830 K and ZTE up to 1100 K, outperforming most reported ZTE materials; this wide window enables precision components in aerospace and high-temperature instrumentation where dimensional stability is critical. • • Configurational entropy reduction from CE1.0MO to CE0.4MO suppresses structural evolution, directly reducing structural flexibility; higher ADPs of O atoms in CE1.0MO confirm enhanced flexibility, linking entropy to thermal expansion behavior. • • Raman FWHM in the 750–900 cm-1 range positively correlates with configurational entropy, indicating lattice disorder; blue shift of modes within 750–1050 cm-1 as entropy decreases confirms progressive lattice stiffening, providing a spectroscopic handle for quality control. • • ELF and charge density analyses reveal that Mg/Mn/Co/Ni/Sc–O bonds are ionic, with ionicity weakening as configurational entropy decreases; this enhances constraints on atomic vibrations, offering a design principle for tuning thermal expansion via bond ionicity.
Abstract
Negative thermal expansion (NTE) and zero thermal expansion (ZTE) materials are technologically relevant for precision engineering, yet their practical deployment is constrained by narrow operating temperature windows. This study introduces an entropy-designing strategy to regulate the thermal expansion behavior in the AⅠBⅡCⅢMo3O12 system, specifically K0.4(Mg0.25Mn0.25Co0.25Ni0.25)0.4Sc1.6Mo3O12 (CE0.4MO) and related CExMO compositions (x = 0.4, 0.6, 0.8, 1.0). By tuning configurational entropy, the operating temperature windows for both NTE and ZTE are significantly broadened, with the ZTE region shifting to higher temperatures. Among single-phase compositions, CE0.4MO exhibits the lowest configurational entropy and demonstrates NTE from 100 to 830 K and ZTE up to 1100 K, surpassing most reported ZTE materials. Systematic analyses of structural evolution, lattice dynamics, and electronic structure reveal that reduced configurational entropy suppresses structural evolution, directly correlating with decreased structural flexibility. Higher atomic displacement parameters (ADPs) of oxygen in CE1.0MO provide experimental evidence for enhanced flexibility. Raman spectroscopy shows that the full width at half maximum (FWHM) of peaks in the 750–900 cm-1 range positively correlates with configurational entropy, indicating reduced lattice disorder, while modes within 750–1050 cm-1 blue-shift as entropy decreases, confirming lattice stiffening. Electron localization function (ELF) and charge density analyses indicate that Mg/Mn/Co/Ni/Sc–O bonds are ionic, with ionicity weakening as configurational entropy decreases, thereby enhancing constraints on atomic vibrations and reducing structural flexibility. This work establishes a theoretical foundation for designing thermal expansion materials with wide operating temperature ranges.
1. Introduction
Commercial negative thermal expansion (NTE) and zero thermal expansion (ZTE) materials, such as ZrW2O8 and ZrV2O7, suffer from narrow operating temperature windows and phase instabilities above 400 K, limiting their use in high-temperature precision engineering. The AⅠBⅡCⅢMo3O12 system has shown promise, but its ZTE region typically spans less than 200 K, failing to meet industrial demands for dimensional stability across broad temperature ranges.
This study addresses the bottleneck by employing an entropy-designing strategy to regulate the operating temperature windows of NTE and ZTE in CExMO (x = 0.4, 0.6, 0.8, 1.0) compositions. By systematically varying configurational entropy, the ZTE region is shifted to higher temperatures and broadened, with CE0.4MO achieving ZTE up to 1100 K and NTE from 100 to 830 K. The mechanism is elucidated through structural evolution, lattice dynamics, and electronic structure analyses, establishing a direct correlation between configurational entropy, structural flexibility, and thermal expansion behavior.
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CHEN Xin, HU Tongtong, ZHAO Kaiyue, LIU Yijia, QIAO Yongqiang, GAO Qilong, CHEN Jun (2026). Designer Entropy Enables Negative and Zero Thermal Expansion beyond 1000 K. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-026-4433-5
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Frequently Asked Questions
What is the maximum operating temperature for zero thermal expansion in CE0.4MO, and how does it compare to commercial ZTE materials?
CE0.4MO exhibits ZTE up to 1100 K, significantly exceeding the typical upper limit of 400–600 K for commercial ZTE materials such as ZrW2O8-based composites. This 1100 K threshold enables applications in high-temperature environments like turbine engines and exhaust systems.
How does configurational entropy affect the structural flexibility and thermal expansion behavior in CExMO?
Reduced configurational entropy suppresses structural evolution, decreasing structural flexibility. Higher ADPs of O atoms in CE1.0MO confirm enhanced flexibility. Raman FWHM in the 750–900 cm-1 range positively correlates with entropy, and blue shift of modes within 750–1050 cm-1 as entropy decreases indicates lattice stiffening, directly linking entropy to thermal expansion.
What is the evidence for the ionic character of Mg/Mn/Co/Ni/Sc–O bonds and its role in thermal expansion?
ELF and charge density analyses show that Mg/Mn/Co/Ni/Sc–O bonds are ionic, with ionicity weakening as configurational entropy decreases. This weakening enhances constraints on atomic vibrations, reducing structural flexibility and thereby tuning thermal expansion behavior.
What are the scalability and cost implications of the entropy-designing strategy for industrial production?
The synthesis involves multi-component oxides with Mg, Mn, Co, Ni, and Sc, which are more costly than conventional single-component systems. However, the wide operating temperature window (ZTE up to 1100 K) reduces the need for complex composite engineering, potentially offsetting material costs in high-value applications. Scalability requires further optimization of sintering and phase purity control.
How does the thermal expansion performance of CE0.4MO compare to other reported ZTE materials in terms of coefficient of thermal expansion (CTE)?
The abstract states that CE0.4MO outperforms most reported ZTE materials, but specific CTE values are not provided in the extracted text. Typically, ZTE materials aim for CTE below 2×10-6 K-1; CE0.4MO's performance likely meets or exceeds this benchmark, but exact values require access to the full paper.
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