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
Enhanced piezoelectric performance of Cr/Ta non-equivalent co-doped Bi4Ti3O12-based high-temperature piezoceramics
Journal of Advanced Ceramics 2024, 13 (3): 263-271
Published: 21 February 2024

In this study, (Cr1/3/Ta2/3) non-equivalent co-doped Bi4Ti3O12 (BIT) ceramics were prepared to solve the problem that high piezoelectric performance, high Curie temperature, and high-temperature resistivity could not be achieved simultaneously in BIT-based ceramics. A series of Bi4Ti3−x(Cr1/3Ta2/3)xO12 (x = 0–0.04) ceramics were synthesized by the solid-state reaction method. The phase structure, microstructure, piezoelectric performance, and conductive mechanism of the samples were systematically investigated. The B-site non-equivalent co-doping strategy combining high-valence Ta5+ and low-valence Cr3+ significantly enhances electrical properties due to a decrease in oxygen vacancy concentration. Bi4Ti2.97(Cr1/3Ta2/3)0.03O12 ceramics exhibit a high piezoelectric coefficient (d33 = 26 pC·N−1) and a high Curie temperature (TC = 687 ℃). Moreover, the significantly increased resistivity (ρ = 2.8×106 Ω·cm at 500 ℃) and good piezoelectric stability up to 600 ℃ are also obtained for this composition. All the results demonstrate that Cr/Ta co-doped BIT-based ceramics have great potential to be applied in high-temperature piezoelectric applications.

Open Access Research Article Issue
In-situ observation and mechanism of calcium–magnesium–alumina–silicate (CMAS) melts-induced degradation of RE2SiO5 (RE = Tb, Dy, Ho, Y, Er, Tm, and Yb) ceramics at 1500 °C
Journal of Advanced Ceramics 2023, 12 (12): 2315-2330
Published: 04 January 2024

Rare earth (RE) silicate is one of the most promising environmental barrier coatings for silicon-based ceramics in gas turbine engines. However, calcium–magnesium–alumina–silicate (CMAS) corrosion becomes much more serious and is the critical challenge for RE silicate with the increasing operating temperature. Therefore, it is quite urgent to clarify the mechanism of high-temperature CMAS-induced degradation of RE silicate at relatively high temperatures. Herein, the interaction between RE2SiO5 and CMAS up to 1500 ℃ was investigated by a novel high-temperature in-situ observation method. High temperature promotes the growth of the main reaction product (Ca2RE8(SiO4)6O2) fast along the [001] direction, and the precipitation of short and horizontally distributed Ca2RE8(SiO4)6O2 grains was accelerated during the cooling process. The increased temperature increases the solubility of RE elements, decreases the viscosity of CMAS, and thus elevates the corrosion reaction rate, making RE2SiO5 fast interaction with CMAS and less affected by RE element species.

Open Access Research Article Issue
Ultrahigh electrostrain with excellent fatigue resistance in textured Nb5+-doped (Bi0.5Na0.5)TiO3-based piezoceramics
Journal of Advanced Ceramics 2023, 12 (3): 487-497
Published: 15 February 2023

(Bi0.5Na0.5)TiO3 (BNT)-based lead-free piezoceramics exhibit excellent electric field-induced strain (electrostrain) properties, but often suffer from large hysteresis and poor fatigue resistance, which strongly limit their applications. Here, <00l> textured Nb5+-doped 0.8(Bi0.5Na0.5)TiO3–0.2(Bi0.5K0.5)TiO3 (0.8BNT–0.2BKT) ceramics with a high degree of texturing (~80%) were prepared by the reactive template grain growth (RTGG) method using Bi4Ti3O12 as a template. By the combination of donor doping in the B-site and the RTGG method, the electrostrain performance achieves a significant enhancement. A high electrostrain of 0.65% and a piezoelectric coefficient ( d33*) of 1083 pm/V with reduced hysteresis at an electric field of 6 kV/mm are obtained. No electrostrain performance degradation is observed after unipolar electric field loading of 105 cycles, showing excellent fatigue endurance. These results indicate that the texturing BNT-based lead-free piezoceramics by the RTGG method is a useful approach to developing eco-friendly actuators.

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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