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Thermal barrier coating (TBC) materials employ ceramics with low thermal conductivity and excellent thermal durability. Recently, the gas turbine market has been increasing demand for a thermally insulating material applicable at higher operating temperatures above 1200 °C for greater thermal conversion efficiency. In this study, synthesized high-entropy A 2 Zr 2 O 7 zirconate ceramics incorporated five cations of a similar ionic radius into the A3+ cation site through a conventional solid-state reaction, and their superior thermophysical properties demonstrate. The HEO ceramics exhibited overall low thermal conductivity (from room temperature to 1000 °C) due to inducing lattice distortion in the crystal structure. In addition, divalent cations were added to the A3+ cation site to increase the oxygen vacancy at the structure, thereby suppressing the heat transfer caused by phonon. A 2 Zr 2 O 7 zirconate HEOs show enhanced thermal barrier performance than yttria-stabilized zirconia (YSZ), conventional TBC material, demonstrating a possibility of application as next-generation TBC materials. [ABSTRACT FROM AUTHOR]

Herein, we propose a new multidisciplinary approach for investigating the corrosion behavior of thermal barrier coatings, combining the thermal-gradient mechanical fatigue method with hot corrosion tests. Corrosive salts (Na 2 SO 4 ; V 2 O 5) of varying concentrations (10−20 mg/cm2) were deposited on the surface of yttria-stabilized zirconia (YSZ) coatings to evaluate the microstructural changes occurring during the reaction, via thermal graded mechanical fatigue tests. The tests were conducted at a surface temperature of 1150 °C in 10 min cycles and underwent applied uniaxial tensile loads. The corrosion tests show that the ZrV 2 O 7 plays an important role as an intermediate in the collapse of the lamellar structures during the reaction, which results from the repetitive precipitation of V 2 O 5 and m -ZrO 2 from the ZrV 2 O 7. The microstructure of corroded YSZ coatings exhibited a different degradation mechanism under a thermomechanical environment, compared with the testing under isothermal atmospheric conditions. [ABSTRACT FROM AUTHOR]

In this study, a high-entropy approach was employed to design a new single-phase A 2 B 2 O 7 oxide for thermal insulation applications. Multicomponent high-entropy oxides, containing up to seven different cations, were successfully synthesized in a single defective fluorite structure. We observed that the incorporation of the functional cation, Zn2+, effectively blocked the heat radiation phenomenon by reducing the photon mean free path, and further reduced the high-temperature thermal conductivity owing to the larger free carrier concentration originated from the large number of oxygen vacancies. Although a large concentration of Zn2+ caused a slight reduction in thermal expansion, this study suggests that functional cations can be easily incorporated; thus, expanding the material diversity beyond the typical doping levels to develop new thermal barrier materials. [ABSTRACT FROM AUTHOR]

• Thermal-insulating performance of fluorite ceramic as a new TBC material. • Synthesis of YYNT ceramics via a solid-state reaction. • Glass-like low thermal conductivity and excellent thermophysical properties compatible with YSZ. The effects of substituting A and B cations in A 3 BO 7 compounds on their thermophysical properties were studied by imposing a significant mass difference on the substituents. Specifically, (Yb 1−x Y x) 3 (Nb 1−y Ta y)O 7 (YYNT) ceramics were synthesized, and their structural characteristics were investigated. All the YYNT ceramics had defective fluorite structures and exhibited glass-like low thermal conductivity (1.19 W/m K at 25 °C), which was derived from the highly distorted crystal structure and cation substitution. In addition, their excellent thermophysical properties, such as compatible thermal expansion, high elastic modulus, and hardness, make them promising candidates for new thermal barrier materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel high-entropy oxide (YYHEO) was engineered with significant mass disorder. • YYHEO exhibited glass-like low thermal conductivity (1.27 W/m∙K). • YYHEO exceeded typical substitutional solid solubility limit even with a significant atomic size difference (>50%). • YYHEO shows thermal stability even at elevated temperature (1500 ° C) without any phase degradation. • Thermophysical properties were compatible with YSZ (CTE: 10.08 × 10−6 K−1, E : 218.21 ± 3.64 GPa and H : 14.42 ± 0.5 GPa). An entropy-stabilization strategy was applied to engineer a novel thermal insulating material by establishing a single-phase solid solution with the formula of (Y 1/2 Yb 1/2) 2 (Ti 1/3 Zr 1/3 Hf 1/3) 2 O 7 (YYHEO). Structural analysis revealed that this material exceeded the typical substitutional solubility limit, even with a significant atomic size difference, where the conventional determination rule was defied. YYHEO exhibited a lower glass-like thermal conductivity due to its highly disordered crystal structure and the specific design strategy. The coefficient of thermal expansion and mechanical properties (e.g. elastic modulus and hardness) were comparable to conventional materials, suggesting that YYHEO is a promising candidate for application as a new thermal insulating material. [ABSTRACT FROM AUTHOR]

• B-SiO 2 exhibits unique properties, such as Lewis neutrality, a uniform and dense morphology, and solubility in YSZ. • B-SiO 2 Lewis neutral layer was successfully applied on conventional YSZ by a sol–gel-based glassification process. • B-SiO 2 layer significantly improved the corrosion resistance and chemical stability of conventional YSZ. • A protection mechanism based on the electronic structure and the Lewis acid–base mechanism was suggested. A boron-doped silica (B-SiO 2) layer was coated on the surface of conventional plasma-sprayed yttria-stabilized zirconia (YSZ) coating to improve the hot corrosion resistance and chemical stability against Na 2 SO 4 + V 2 O 5 salts by glassification based on sol-gel process. The YSZ surface was successfully covered by the glassificated B-SiO 2 with Lewis neutrality. Further destabilization of YSZ was prevented by the formation of a solid solution. Consequently, the B-SiO 2 layer improved the hot corrosion resistance and chemical stability of YSZ. [ABSTRACT FROM AUTHOR]

• Hot corrosion behavior of YSZ/LZO blended TBC was investigated. • YSZ/LZO blended layer produced LaVO 4 , m -ZrO 2 , and t -ZrO 2 in a hot corrosive environment. • The blended layer showed a shallow infiltration depth and a severely degraded microstructure. • The corrosion mechanism has been suggested in the blended TBC with a heterogeneous interface. In the present study, layered thermal barrier coatings (TBC) were fabricated with different surface layers with lanthanum zirconate (LZO), yttria-stabilized zirconia (YSZ), and YSZ/LZO blended layer. Their hot corrosion behaviors were investigated in the molten salt of Na 2 SO 4 + V 2 O 5 at 1100 °C. TBC with the YSZ/LZO blended layer showed a different hot corrosion behavior with a relatively shallow depth and densified reaction layer compared with those with the LZO and YSZ layers. The blended layer showed the most severely degraded microstructure above the planar reacted area, which can be more appropriate for a sacrificial layer to protect the substrate. [ABSTRACT FROM AUTHOR]

Sintering behavior and phase transformations in yttria-stabilized zirconia (YSZ)-based thermal barrier coatings (TBCs) control their applications in gas turbines operated at high working temperatures required for improved fuel efficiency. In this work, to control the sintering behavior and reduce phase transformations in YSZ-based TBCs, lanthanum zirconate (LZ) powder was blended with the YSZ feedstock powder, and YSZ-LZ composite coatings were fabricated using the air plasma spraying method. The influence of mixture weight ratio of YSZ to LZ (75:25, 50:50, and 25:75) on the sintering behavior and phase stability of the composite coatings was investigated through the isothermal exposure test at 1100, 1300, and 1400 °C. The as-coated composites showed the pyrochlore and tetragonal phases, indicating that the phases are LZ and YSZ, respectively. As the exposure temperature was increased, the phase transformation of YSZ from the tetragonal phase to the monoclinic phase was accelerated. The content of monoclinic phase was changed with the increasing LZ content after thermal exposure at 1300 and 1400 °C. In addition, the composites showed different sintering and bridging behaviors at the adjacent splats with the LZ content. The composites prepared with the blended feedstock powders of LZ and YSZ produced an obvious effect on the phase stability and mechanical properties. [ABSTRACT FROM AUTHOR]

• FMMO–NR is introduced as a catalytic host for lithium sulfur batteries. • Fast conversion reactions LiPSs and immobilization of LiPSs are enabled by FMMO–NR. • FMMO–NR presents outstanding rate capability and stable cyclability. • FMMO–NR shows outstanding cyclability with a high sulfur loading of 5 mg cm–2. Lithium sulfur (Li–S) batteries have been intensively studied as promising energy storage devices due to their high theoretical specific capacity and cost effectiveness. However, the poor cycle life and low Coulombic efficiency caused by the insulating nature of sulfur and shuttle effect of lithium polysulfides (LiPSs) still hinder the practical implementation of Li–S batteries. Here, we report Fe 2 (MoO 4) 3 decorated MoO 3 nanorod (FMMO–NR) heterostructure as an efficient catalytic host for Li–S batteries. Fe 2 (MoO 4) 3 has low electrical conductivity, but excellent catalytic activity, and MoO 3 has high electrical conductivity but low catalytic activity. With the synergistic advantages of the high electrical conductivity of one-dimensional MoO 3 nanorod and strong catalytic activity of Fe 2 (MoO 4) 3 with a redox potential of ∼2.9 V, FMMO–NR enables fast conversion reactions of long-chain LiPSs to Li 2 S 2 /Li 2 S and suppresses the shuttle effect by immobilization of LiPSs with strong binding. The FMMO–NR electrode shows a high discharge capacity of 1588 mAh g −1 and stable cycle performance with a capacity retention of 70% at 2 C over 500 cycles. Even with a high sulfur loading of 5 mg cm–2, the FMMO–NR electrode presents outstanding cycling stability with a capacity retention of 73% over 100 cycles. [ABSTRACT FROM AUTHOR]