Open Access Research Article Just accepted
Suppressing the phase transition of ZrP2O7 by defect and entropy regulation for high-temperature wave-transparent material application
Journal of Advanced Ceramics
Available online: 12 June 2024

ZrP2O7 is a promising wave-transparent material candidate due to the low dielectric constant and low dielectric loss, while the inherent phase transition characteristic at about 300 ℃ limits its high-temperature application. Therefore, suppressing the phase transition is necessary for ZrP2O7 to serve in extremely harsh environments. In this work, introducing Ti and Hf into ZrP2O7 causes significant lattice distortion and an increase in entropy, both of which synergistically limit the crystal structure transformation. In addition, enhanced phonon scattering by mismatch of atomic mass and local distortion leads to a reduction in the thermal conductivity. Lattice distortions also cause changes in both bond length and tilting angle, so that (Ti1/3Zr1/3Hf1/3)P2O7 does not undergo a sudden expansion like ZrP2O7. (Ti1/3Zr1/3Hf1/3)P2O7 maintains excellent dielectric properties, which highlights it as a promising high-temperature wave-transparent material.

Open Access Research Article Issue
(Ho0.25Lu0.25Yb0.25Eu0.25)2SiO5 high-entropy ceramic with low thermal conductivity, tunable thermal expansion coefficient, and excellent resistance to CMAS corrosion
Journal of Advanced Ceramics 2022, 11 (8): 1279-1293
Published: 15 June 2022

Low thermal conductivity, compatible thermal expansion coefficient, and good calcium- magnesium-aluminosilicate (CMAS) corrosion resistance are critical requirements of environmental barrier coatings for silicon-based ceramics. Rare earth silicates have been recognized as one of the most promising environmental barrier coating candidates for good water vapor corrosion resistance. However, the relatively high thermal conductivity and high thermal expansion coefficient limit the practical application. Inspired by the high entropy effect, a novel rare earth monosilicate solid solution (Ho0.25Lu0.25Yb0.25Eu0.25)2SiO5 was designed to improve the overall performance. The as-synthesized (Ho0.25Lu0.25Yb0.25Eu0.25)2SiO5 shows very low thermal conductivity (1.07 W·m-1·K-1 at 600 ℃). Point defects including mass mismatch and oxygen vacancies mainly contribute to the good thermal insulation properties. The thermal expansion coefficient of (Ho0.25Lu0.25Yb0.25Eu0.25)2SiO5 can be decreased to (4.0-5.9)×10-6 K-1 due to severe lattice distortion and chemical bonding variation, which matches well with that of SiC ((4.5-5.5)×10-6 K-1). In addition, (Ho0.25Lu0.25Yb0.25Eu0.25)2SiO5 presents good resistance to CMAS corrosion. The improved performance of (Ho0.25Lu0.25Yb0.25Eu0.25)2SiO5 highlights it as a promising environmental barrier coating candidate.

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