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.
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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.
(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 (
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.