High-entropy oxides (HEOs) are considered promising thermal barrier coating (TBC) materials due to their unique thermophysical performances induced by the entropy effects. In this work, (La 0.2 Ce 0.2 Pr 0.2 Sm 0.2 Eu 0.2 ) 2 Hf 2 O 7 high entropy hafnate, as a thermal barrier coating (TBC) material, was successfully synthesized by solution combustion method for the first time. From the X-ray diffraction, scanning electron microscopy, and transmission electron microscopy results, it is confirmed that (La 0.2 Ce 0.2 Pr 0.2 Sm 0.2 Eu 0.2 ) 2 Hf 2 O 7 has pure single-phase ordered pyrochlore structure with highly homogeneous composition at both micrometer and nanometer scales. The synthesized (La 0.2 Ce 0.2 Pr 0.2 Sm 0.2 Eu 0.2 ) 2 Hf 2 O 7 possesses excellent phase stability at 1600 °C and demonstrates a low thermal conductivity (1.0–1.24 W·m −1 ·K −1 ) which is lower than those of rare earth hafnates (RE 2 Hf 2 O 7 , RE = La, Ce, Pr, Sm, Eu). Therefore, it provides a new perspective and potential to prompt the next generation TBC materials with better performance.
Ling Pan,Ling He,Zibo Niu,Peng Xiao,Wei Zhou,Yang Li
In this work, Yb 4 Hf 3 O 12 ceramic, a typical rare-earth hafnate, was exposed to water vapor with Al(OH) 3 impurities at 1400 ℃, and microstructural evolution and corrosion mechanisms were investigated. The long-term corrosion can be divided into initial hydration and gasification of Hf 4+ and steady-state corrosion after the formation of Al 5 Yb 3 O 12 . In the initial stage, Hf 4+ and the surrounding O 2- tend to be hydrated and then volatilized in the form of Hf(OH) 4 , causing a metastable state of Yb 4 Hf 3 O 12 on the surface. Besides, the preferential corrosion of small grains, grain boundary, and specific crystal plane on the surface and sintered and densified grains result in varied corrosion behavior from the early linear law to the later parabolic law. In the steady-state corrosion stage, due to the consumption of Hf 4+ , more vacancies promote bonding and diffusion of Al 3+ to form corrosion product (Al 5 Yb 3 O 12 ), and during this stage, regrowth and shedding of the corrosion layer reach a dynamic balance.
Near-infrared phosphor-converted light-emitting diodes (NIR-pc-LEDs) are superior to traditional NIR-LEDs in spectral modulation, volume, and cost, and their optoelectronic properties are dominantly controlled by the NIR phosphors, which thus boosts the search for high efficiency and broadband NIR phosphors. In this work, we attempt to realize ultra-broadband NIR phosphors by doping Cr 3+ in self-emitting SrHfO 3 with a weak crystal field. Dual emission bands centered at 770 (host) and 1000 nm (Cr 3+ ) are observed, leading to a wide spectral range of 700–1400 nm. The Cr 3+ ions enter the HfO 6 octahedron and thus produce an NIR emission with a full width at half maximum of 190 nm and an internal quantum efficiency of 24% under 460 nm excitation. A prototype NIR-pc-LED surface light is demonstrated for machine vision by using NIR-pc-LEDs that combine the blue LED with SrHfO 3 :Cr. The work paves an avenue for designing super-broadband NIR phosphors by doping Cr 3+ or other ions into hosts with self-trapped exciton emission (e.g., halide perovskites).
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