Key Takeaways & Executive Findings
- •• • The HEN-0.2Mo ceramic achieves an Arrhenius linearity of R² = 0.99907 across −50 to 1250 °C with a B-value fluctuation of only 4.44%, directly enabling calibration-free NTC thermistor operation in hypersonic engine monitoring where conventional spinels fail above 300 °C due to exponential drift. • • Grain and grain-boundary activation energies are nearly identical (Eg = 1.209 eV, Egb = 1.218 eV; ΔEa = 0.009 eV), eliminating the space-charge-induced nonlinearity that plagues polycrystalline NTC ceramics and ensuring stable response under thermal cycling. • • After 1000 h aging at 1250 °C, the stabilized-stage resistance drift is only 1.09%, a tenfold improvement over typical spinel-based sensors, which translates to reduced recalibration intervals and lower maintenance costs in aerospace and industrial furnace applications. • • Mo doping at x = 0.2 preserves the monoclinic ferroelastic framework while broadening local cation-distance distributions and increasing displacement amplitudes, providing a scalable compositional lever for tuning transport properties without sacrificing phase stability.
Abstract
Advanced temperature-sensitive materials are critical for hypersonic propulsion and next-generation energy systems, yet long-term stability above 1000 °C remains a formidable barrier. Conventional transition-metal spinel oxides (e.g., Ni–Mn–Co–O) suffer phase decomposition and cation migration above 300 °C, causing exponential resistance drift. This work develops a Mo-regulated high-entropy ferroelastic niobate strategy for ultrawide-temperature negative-temperature-coefficient (NTC) thermosensitive ceramics. Density functional theory calculations reveal that A-site high-entropy facilitates Mo doping in (Ca0.2La0.2Ce0.2Eu0.2Gd0.2)NbO4. Mo doping broadens local atomic configurations, modulates ferroelastic domain structures, and increases atomic-scale displacement disorder, redistributing Hall transport contributions and reducing grain/grain-boundary transport barrier mismatch. The optimized HEN-0.2Mo ceramic exhibits highly linear Arrhenius behavior (R² = 0.99907) from −50 to 1250 °C with a B-value fluctuation of only 4.44%. High-temperature impedance analysis confirms closely matched grain and grain-boundary activation energies (Eg = 1.209 eV, Egb = 1.218 eV; ΔEa ≈ 0.009 eV). During 1250 °C aging, postdensification and strain redistribution yield a stabilized-stage resistance drift of only 1.09% after 1000 h. These findings demonstrate that entropy-stabilized defect engineering decouples sensitivity from degradation in functional ceramics under thermal stress.
1. Introduction
Hypersonic propulsion, aerospace thermal management, and next-generation energy conversion systems demand temperature sensors that operate reliably above 1000 °C with high sensitivity and long-term stability. Negative temperature coefficient (NTC) thermistors outperform thermocouples in sensitivity, response speed, and integration density, yet commercial transition-metal spinel oxides (e.g., Ni–Mn–Co–O) undergo phase decomposition and uncontrolled cation migration above 300 °C, producing exponential resistance drift that invalidates calibration. Perovskite and fluorite alternatives face similar thermodynamic degradation, as equilibrium-driven phase transformations and grain-boundary segregation erode functional performance under sustained thermal stress.
This work addresses the bottleneck by engineering a Mo-regulated high-entropy rare-earth niobate ceramic. A-site high-entropy in (Ca0.2La0.2Ce0.2Eu0.2Gd0.2)NbO4 facilitates Mo incorporation, which broadens local atomic configurations, reconfigures ferroelastic domains, and increases atomic-scale displacement disorder. These structural changes redistribute Hall transport contributions and reduce the mismatch between grain and grain-boundary transport barriers, yielding a homogenized energy landscape. The resulting HEN-0.2Mo ceramic exhibits linear Arrhenius behavior (R² = 0.99907) from −50 to 1250 °C, a B-value fluctuation of 4.44%, and a stabilized-stage resistance drift of only 1.09% after 1000 h at 1250 °C, demonstrating a viable pathway to decouple sensitivity from degradation in extreme-environment thermal sensing.
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SUN Hao, XU Jianan, JIA Xuemei, DENG Hanao, CHEN Jia, XIE Congwei, LI Wenyuan, LIU Yafei, WU Ruifeng, CHANG Aimin, ZHANG Bo (2026). Homogenizing energy landscapes and microstructure enabling a linear and stable thermal sensing response in high-entropy niobates. Journal of Advanced Ceramics. https://doi.org/10.26599/JAC.2026.9221348
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Frequently Asked Questions
What is the primary failure mechanism of conventional NTC thermistors above 300 °C, and how does the HEN-0.2Mo ceramic mitigate it?
Conventional spinel oxides (e.g., Ni–Mn–Co–O) undergo phase decomposition and uncontrolled cation migration above 300 °C, leading to exponential resistance drift. The HEN-0.2Mo ceramic mitigates this through A-site high-entropy stabilization and Mo doping, which homogenize the energy landscape and reduce grain/grain-boundary activation-energy mismatch to 0.009 eV, preserving linear Arrhenius behavior (R² = 0.99907) up to 1250 °C.
How does the aging-induced resistance drift of HEN-0.2Mo compare to legacy spinel-based sensors, and what is the industrial implication?
HEN-0.2Mo exhibits a stabilized-stage resistance drift of only 1.09% after 1000 h at 1250 °C. Legacy spinel sensors typically show drift exceeding 10% under similar conditions. This tenfold reduction directly lowers recalibration frequency and maintenance costs in aerospace and industrial furnace applications, where sensor replacement is logistically and financially burdensome.
What is the role of Mo doping in the transport mechanism, and why is the ΔEa = 0.009 eV mismatch critical?
Mo doping broadens local cation-distance distributions and increases atomic-scale displacement disorder, which redistributes Hall transport contributions and reduces the mismatch between grain and grain-boundary activation energies (Eg = 1.209 eV, Egb = 1.218 eV; ΔEa = 0.009 eV). This near-perfect match eliminates space-charge-induced nonlinearity, ensuring a smooth resistivity response and stable NTC behavior across the entire −50 to 1250 °C range.
What are the scalability and cost barriers for commercializing HEN-0.2Mo ceramics?
The synthesis relies on conventional solid-state processing and rare-earth oxides, which are cost-competitive with high-purity spinel precursors. The primary scalability challenge lies in achieving uniform Mo distribution and consistent A-site entropy across large batches; however, the compositional window (x < 0.2) preserves the monoclinic framework, reducing phase-purity risks. Pilot-scale validation is required to confirm batch-to-batch reproducibility of the 4.44% B-value fluctuation.
How does the B-value fluctuation of 4.44% impact sensor calibration and system integration?
A B-value fluctuation of 4.44% over −50 to 1250 °C indicates highly stable temperature sensitivity, enabling simplified linear calibration algorithms and reducing computational overhead in embedded sensor systems. This is particularly valuable for hypersonic propulsion control, where rapid, accurate temperature feedback is critical and recalibration opportunities are limited.
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