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Thermal shock damage is a key issue for the stable service of SiC/SiC with environmental barrier coating (EBC) in aero‐engines. The thermal shock damage behavior of SiC/SiC with barium‐strontium aluminosilicate (BSAS)‐based EBC in an air atmosphere quenched by air and water media between RT and 1200 °C is systematically investigated. After 600 thermal shock cycles, cracks form in the EBC due to a sharp increase in the internal thermal stresses, and a SiO2 TGO layer is formed on the Si bonding coat. Based on the TGO thickness, damage within BSAS/mullite coatings is quantified by the oxygen permeability (2.541 × 10−11 mol·(atm cm s)−1), which is increased by 2.5 times compared to static oxidation. Despite cracking damage occurring in the SiC matrix of SiC/SiC substrates, the load‐bearing capability of SiC fibers is improved due to the modulus matching of the fiber/matrix. Oxidation damage is dominated the degradation of the performance of SiC/SiC substrates, whose flexural strength is decreased by 15% after 600 cycles. In the thermal shock test quenched by water media, the strength retention of SiC/SiC‐EBC is below 60%, and an increase in internal defects and even delamination of the SiC/SiC substrate are the main reasons for the thermal shock failure of SiC/SiC‐EBC. [ABSTRACT FROM AUTHOR]

The introduction of porosity into ferroelectric ceramics can decrease the effective permittivity, thereby enhancing the open circuit voltage and electrical energy generated by the direct piezoelectric effect. However, the decrease in the longitudinal piezoelectric coefficient (d33) with increasing porosity levels currently limiting the range of pore fractions that can be employed. By introducing aligned lamellar pores into (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3, this paper demonstrates an unusual 22–41% enhancement in the d33 compared to its dense counterpart. This unique combination of high d33 and a low permittivity leads to a significantly improved voltage coefficient (g33), energy harvesting figure of merit (FoM33) and electromechanical coupling coefficient (k332$k_{33}^2$). The underlying mechanism for the improved properties is demonstrated to be a synergy between the low defect concentration and high internal polarizing field within the porous lamellar structure. This work provides insights into the design of porous ferroelectrics for applications related to sensors, energy harvesters, and actuators. [ABSTRACT FROM AUTHOR]

Tetrathiatriarylmethyl radicals have found wide applications in electron paramagnetic resonance (EPR) spectroscopy and imaging as well as dynamic nuclear polarization (DNP). Recently, intense effort has been devoted to the derivatization of trityl radicals, but there is still a lack of highly efficient methods for access to these radicals. Herein, we report novel acid‐mediated protocols for straightforward and selective synthesis of the hydroxymethyl, aldehyde and methyl derivatives of trityl radicals from the sole substrate hydroxymethyl‐substituted tetrathiatriarylmethanol. The resulting trityl radicals exhibit various redox properties as shown by their cyclic voltammetric results. Importantly, the use of these protocols enables site‐specific deuteration of the three trityl radicals, which show unique EPR spectral properties. Overall, our study reveals the crucial effect of the acids on the synthesis of these trityl radicals and provides a new approach for selective access to different trityl radicals, thus enriching their synthetic chemistry. [ABSTRACT FROM AUTHOR]

Two structured ytterbium monosilicate environmental barrier coatings (Si/Yb2SiO5 and Si/mullite/Yb2SiO5) were prepared on SiC/SiC composites and their performance in wet oxygen at 1350°C was investigated. After 300 h of corrosion, coating peeling occurred for Si/Yb2SiO5–SiC/SiC, while it was intact for Si/mullite/Yb2SiO5–SiC/SiC system due to the mullite intermediate coating well alleviating the thermal expansion mismatched stress. During the assessment, Yb2SiO5 and mullite gradually densified, and a thin layer of ytterbium disilicates (Yb2Si2O7) was formed at their junction as a new protective layer, which pinned into the mullite layer and significantly improved their interface bonding strength and resistance against wet oxygen. The strength retention of SiC/SiC, Si/Yb2SiO5–SiC/SiC, and Si/mullite/Yb2SiO5–SiC/SiC was 64%, 72%, and 97%, respectively, after corrosion in wet oxygen at 1350°C/300 h. Their corrosion mechanism was proposed. [ABSTRACT FROM AUTHOR]

Bi2O3 is a promising sintering additive for YSZ that not only decreases its sintering temperature but also increases its ionic conductivity. However, Bi2O3 preferably grows into large-sized rods. Moreover, the addition of Bi2O3 induces phase instability of YSZ and the precipitation of monoclinic ZrO2, which is unfavorable for the electrical property. In order to precisely control the morphology and size of Bi2O3, a microemulsion method was introduced. Spherical Bi2O3 nanoparticles were obtained from the formation of microemulsion bubbles at the water–oil interface due to the interaction between the two surfactants. Nanosized Bi2O3–YSZ composite powders with good mixing uniformity dramatically decreased the sintering temperature of YSZ to 1000 °C. Y2O3-stabilized Bi2O3 (YSB)–YSZ composite powders were also fabricated, which did not affect the phase of YSZ but decreased its sintering temperature. Meanwhile, the oxygen vacancy concentration further increased to 64.9% of the total oxygen with the addition of 5 mol% YSB. In addition, its ionic conductivity reached 0.027 S·cm−1 at 800 °C, one order of magnitude higher than that of YSZ. This work provides a new strategy to simultaneously decrease the sintering temperature, stabilize the phase and increase the conductivity of YSZ electrolytes. [ABSTRACT FROM AUTHOR]

An iron‐catalyzed trifluoromethylation of indole‐tethered alkene with Togni's reagent to construct CF3‐containing spiro[indole‐3,3′‐pyrrolidine] and tetrahydrocarbazole derivatives under mild and convenient conditions has been disclosed. Mechanistic studies indicate that the reaction proceed through a CF3 radical addition to the alkene, followed by sequential dearomatizing spiocyclization of the indole and oxidation to afford the spiro[indole‐3,3′‐pyrrolidine] derivatives. Meanwhile, when the substituent at the C2 position of the indole is hydrogen, the CF3‐containing tetrahydrocarbazole is obtained through trifluoromethylation of alkene and cyclization of indole. [ABSTRACT FROM AUTHOR]

Hafnia doping is expected to improve the performance of the silicon‐bond layer of environmental barrier coatings (EBCs) for SiC‐based ceramic matrix composites. The optimal doping ratio, distribution of HfO2, and oxidation mechanism of the bond layer have not yet been fully addressed. A prototype Si–HfO2 bond layer with a designed HfO2‐rich area was used to examine its oxidation behavior. A random dispersion model was developed to calculate the optimal HfO2 doping ratio and its appropriate distribution state. The simulation results recommended that 20–30 vol% is the optimal doping ratio, where HfO2 is well dispersed inside Si without forming networks. This enables HfO2 to react with and consume SiO2 without accelerating oxygen diffusion inside the bond layer. This was confirmed by oxidation experiments on Si–xHfO2 tablets, in which the thinnest thermally grown oxide was achieved for the 20 vol% HfO2‐doped Si tablet. Both the microstructure design and material composition selection are highly important to further boost the performance of the EBCs. [ABSTRACT FROM AUTHOR]

Bismuth oxide (Bi2O3) is a promising additive to decrease the sintering temperature of yttria‐stabilized zirconia (YSZ)‐based electrolyte for solid oxide fuel cell application. However, Bi2O3 tends to grow into large column bars (>50 µm) in a chemical coprecipitation method, which dramatically limits the mixing uniformity of Bi2O3 and YSZ, even much worse than that of mechanical mixing. In this study, the reaction temperature was increased from room temperature to 90°C to increase the number of nucleation during the violate reaction between Bi3+ solution and YSZ suspension in NaOH. On this basis, the violence of the reaction was further moderated by adding half of NaOH first, then YSZ powders and the other half of an NaOH solution. The size of Bi2O3 was further decreased to sub‐micrometer and Bi2O3 was homogeneously mixed with YSZ particles, even when its addition amount was as large as 20 mol%. These composite powders effectively promoted the sintering behavior of YSZ. The sintering temperature of YSZ was decreased to 900 and 1000°C with 10 and 5 mol% Bi2O3 doping, respectively. Increasing the doping ratio induced severe volatilization of Bi2O3 and pore formation. Raising the sintering temperature (no more than 1200°C) enhanced the doping effect of Bi2O3 into the YSZ lattice but induced instability in the YSZ crystal structure. [ABSTRACT FROM AUTHOR]