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(Mg 0.2 Al 0.2 Ce 0.2 Y 0.2 Zr 0.2)O 1.6 high entropy ceramics powders have been prepared by co-precipitation method with two calcination temperatures (1000 °C and 1200 °C). The microstructure, phase composition and phase stability after repeated calcination at 1400 °C with various times of the powders have been investigated. The powder calcined at 1200 °C has the better crystallinity and the stronger diffraction peak of t-ZrO 2 phase at room temperature. The existence of Ce4+ and Y3+ with large radius in the ZrO 2 lattice can enhance the tetragonality of the powders. The Mg2+ and Al3+ with small radii can exist in the lattice gap of ZrO 2 or replace the position of Zr4+, causing lattice contraction, offsetting the lattice expansion which caused by Ce4+ and Y3+, and reducing the negative effects induced by the large ion doping. Thus, (Mg 0.2 Al 0.2 Ce 0.2 Y 0.2 Zr 0.2)O 1.6 has a good phase stability after repeated calcination at 1400 °C for 80h. [ABSTRACT FROM AUTHOR]

In the study, we synthesized the (BiO 1.5) 0.88 (ErO 1.5) 0.08 (HoO 1.5) 0.04 and (BiO 1.5) 0.88 (ErO 1.5) 0.04 (HoO 1.5) 0.08 ternary compositions using the solid–state reactions in an atmosphere of air. All compositions were then heated to 650, 700, 750, and 800 °C to observe how the calcination temperature impacts phase stability and conductivity. All XRD patterns suggested that the cubic δ–phase, a high–ion conductor, became stable at room temperature. Depending on the temperature, the DTA curves revealed that some compositions had an endothermic peak at around 600 °C, indicating an order–disorder transition wholly related to anion sublattice arrangement without a phase transition. At 700 °C, the highest conductivity was found to be 0.482 S/cm for the (BiO 1.5) 0.88 (ErO 1.5) 0.04 (HoO 1.5) 0.08 composition calcined at 800 °C, and this conductivity is greater than that of a single–doped (BiO 1.5) 0.80 (ErO 1.5) 0.20 system. The FE–SEM images indicated that calcination at 650 °C and 700 °C, which are below the phase transition temperature (729 °C) from α–phase to cubic δ–phase, results in atom aggregation and porosity on the surface. Besides, the calcination temperature was shown to significantly impact grain sizes, with compositions produced with a calcination at 800 °C exhibiting bigger grains than lower ones. [ABSTRACT FROM AUTHOR]

A series of cathode materials of Pr 2-x Sr x NiO 4 (x = 0, 0.3, 0.5, 0.7, 1, 1.5) are synthesized by the EDTA-citric acid route. The results show that the Pr 1.7 Sr 0.3 NiO 4 , Pr 1.5 Sr 0.5 NiO 4 , Pr 1.3 Sr 0.7 NiO 4 and PrSrNiO 4 exhibit excellent structural stability and carbon dioxide resistance, and also exhibit good chemical compatibility and thermal matching with the SDC electrolyte. It is also found that the Sr doping is beneficial in improving the high temperature conductivity of Pr 2-x Sr x NiO 4. At 800 °C, the electrical conductivity of Pr 1.5 Sr 0.5 NiO 4 and Pr 1.3 Sr 0.7 NiO 4 reaches 185 S cm−1 and 317 S cm−1, respectively. In addition, the area-specific resistance (ASR) value increases significantly with Sr doping, which reduces the catalytic activity of the material. Acceptable ASR values are obtained for Pr 1.5 Sr 0.5 NiO 4 and Pr 1.3 Sr 0.7 NiO 4 , with ASR values of 0.079 Ω cm2 and 0.082 Ω cm2 at 800 °C, respectively. Additionally, the most interesting result is the ASR value obtained after high-temperature thermal decomposition of Pr 2 NiO 4 , where Pr 2 NiO 4 * (decomposed) has the lowest ASR value of only 0.027 Ω cm2 at 800 °C, showing the best catalytic activity. The maximum power densities of Pr 2-x Sr x NiO 4 (x = 0.5 and 0.7) and Pr 2 NiO 4 * are found to be 515, 430, and 548 mW cm−2 at 800 °C, respectively. These results show that when the Sr doping amount is less than 1.5, the stability of the Pr 2-x Sr x NiO 4 cathode material can be effectively improved, but its catalytic performance is partially sacrificed. [ABSTRACT FROM AUTHOR]

Notwithstanding the impressive phase stability and low thermal conductivity exhibited by lanthanum zirconate (LZ), its low coefficient of thermal expansion is deemed a paramount limitation. In the present study, (La 1-x Y x) 2 Zr 2 O 7 with x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, as new TBCs, were synthesized by reverse co-precipitation and calcination method. The XRD and Raman analyses elucidated that the substitution of Y3+ ions occurred exclusively at the La3+ positions. In addition, in accordance with FESEM and DTA findings, the incorporation of Y 2 O 3 has induced a reduction in particle size and an enhancement in crystallization resistance. The evaluation of the coefficient of thermal expansion (CTE) demonstrated a notable improvement following the introduction of Y 2 O 3. Specifically, the CTE of LZ increased from 9.34 × 10−6 °C-1 to 10.5 × 10−6 °C-1 in the case of (La 0.5 Y 0.5) 2 Zr 2 O 7 at 1100oC. Investigations of phase stability following a 50 h heat treatment at 1300oC indicated that Y 2 O 3 had no impact on phase stability. All compounds, similar to LZ, exhibited excellent phase stability. Furthermore, the addition of Y 2 O 3 significantly amplified the grain boundary diffusion mechanism during heat treatment, leading to an accelerated grain growth rate. The grain growth rate increased from 1.7 nm/h at LZ to 2.2 nm/h in the case of (La 0.6 Y 0.4) 2 Zr 2 O 7. [ABSTRACT FROM AUTHOR]

Single stabilizer-doped ZrO 2 has drawbacks such as inferior mechanical properties and thermal stability, making it difficult to obtain ZrO 2 ceramics with good density and high crystallinity. Thus, it is expected that ZrO 2 is doped and modified by two or more stabilizers. In this paper, the Sc 2 O 3 –Y 2 O 3 –ZrO 2 nanocomposite ceramic powders were prepared using ZrOCl 2 ⋅8H 2 O, ScCl 3 ⋅6H 2 O, and YCl 3 ⋅6H 2 O as raw materials and polyvinylpyrrolidone as dispersant. They calcined at diverse temperaturesby the pressureless sintering-assisted co-precipitation method after being pressed into disc shape. Sc 2 O 3 and Y 2 O 3 were added as ZrO 2 stabilizers to ameliorate the lack of insufficient mechanical properties and high-temperature stability of ZrO 2 ceramics caused by single doping. To study the stability of the phases at high temperatures, the specimens were characterized by TG-DTG, XRD, Raman, SEM, FT-IR, etc. The effects of different pH valuesand different calcination temperatures on the Sc 2 O 3 –Y 2 O 3 –ZrO 2 nanocomposite ceramics were investigated. It was demonstrated that ternary doping has very excellent phase stability. After calcination no monoclinic phase appeared, and the precursor samples were transformed from amorphous to a large amount of tetragonal phases and a few cubic phases. The samples at pH = 10 and calcination temperature of 1000 °C showed the best stabilization, the most uniform grain development, the best crystallinity, the most regular morphology, the highest tetragonal phase content of 89.2 %, the stabilization rate of 94.58 %, and the highest relative density of 98.75 %. The results show that this nanocrystalline powder can be used to prepare high-density nanoceramics. Furthermore, the activation energy for grain growth of Sc 2 O 3 –Y 2 O 3 –ZrO 2 nanocomposite ceramics was calculated as 13.87 kJ/mol. This paper provides a theoretical and experimental research basis for the controlled synthesis of Sc 2 O 3 –Y 2 O 3 –ZrO 2 nanocomposite ceramics using a pressureless sintering-assisted co-precipitation method. [ABSTRACT FROM AUTHOR]

As a promising material for the advanced thermal barrier coatings (TBCs), scandium oxide (Sc 2 O 3) and yttrium oxide (Y 2 O 3) co-stabilized zirconia (ScYSZ) has been given increasing attention during the past decade. In this study, three types of TBCs including YSZ, ScYSZ and ScYSZ-YSZ double ceramic layer (DCL) coatings were deposited by a wide-velocity range high-energy plasma spraying technology. The thermal physical property, phase stability and thermal cycling performance of TBCs were comparatively studied. The results suggested that the thermal conductivity from 200 °C to 1000 °C of ScYSZ coating was reduced by approximately 30 % compared to the YSZ coating. After exposure at 1400 °C for 1000 h, the ScYSZ coating still kept the initial tetragonal phase structure, while the tetragonal phase was completely disappeared in the YSZ coating after 300 h at 1400 °C. Notably, the ScYSZ-YSZ DCL coating demonstrated the highest thermal cycling life within the temperature range of 1320∼1370 °C, exhibiting a remarkable 43 % increase over the single ScYSZ coating and doubling that of the single YSZ coating. The outcomes of this study hold significant promise for practical applications in the realm of high-performance TBCs. [ABSTRACT FROM AUTHOR]

Developing cathodes that are both phase-stable and tolerant to carbon dioxide (CO 2) is a crucial and challenging task for solid-oxide fuel cells (SOFCs) operating at reduced temperatures. The activity of oxygen reduction reaction (ORR) in SOFC cathodes is typically influenced by factors such as geometric features and oxygen vacancies. In this study, new and robust cathodes for SOFCs, Sr 2 Co 1.5 Fe 0.4 Ta 0.1 O 5+δ (SCFT) and Sr 2 Co 1.5 Fe 0.4 Nb 0.1 O 5+δ (SCFN) are developed by doping a small amount of niobium (Nb) and tantalum (Ta) into Sr 2 Co 1.6 Fe 0.4 O 5+δ (SCF) using a simple solid-state reaction technique. The effects of Nb/Ta doping on the crystal structure, oxygen vacancies, electrical conductivity, and electrochemical properties of SCFT and SCFN are investigated. The results reveal that these materials possess a fully cubic structure in the Fm-3m space group, with improved oxygen vacancy and electrical conductivity. They also exhibit good chemical compatibility with electrolytes at 1100 °C for 8 h and remain thermally stable when exposed to air and CO 2 at 700 °C, without any additional phase formation. The area-specific resistance (ASR) of the SCFT cathode is found to be only 0.06 Ω cm2, whereas the SCFN cathode has an ASR of 0.10 Ω cm2. The superior performance of SCFT can be attributed to the higher oxygen vacancy, which enhances oxygen surface exchange kinetics and diffusivity compared to SCFN. When tested in a single cell using humidified H 2 as the fuel and ambient air as the oxidant, the SCFT cathode achieves a power density of 656 mW cm−2 at 700 °C, while the SCFN cathode reaches 559 mW cm−2, indicating the potential of SCFT as a promising cathode material for SOFCs. The excellent performance of these materials can be attributed to their mixed electronic-ionic conduction properties, unique structural features, and high observed oxygen vacancy, which contribute to their remarkable electronic conductivity and significant ionic mobility. [ABSTRACT FROM AUTHOR]

[Display omitted] To significantly improve phase photostability, CsPbI 3 absorber films were modified by introducing isonipecotic acid. This has resulted in remarkable long-term operational stability of CsPbI 3 -based perovskite solar cells with optimally modified light absorbers. [ABSTRACT FROM AUTHOR]

After the discovery of the prototypical high-entropy oxide with formula Cu 0.2 Zn 0.2 Mg 0.2 Co 0.2 Ni 0.2 O, the research on these materials has shown a dramatic boost. While many studies were devoted to exploring their possible applications, only few addressed the effective reasons behind their stability. The possibility to achieve a single-phase structure is usually hastily attributed to configurational entropy. This resulted in an extensive misuse of the terms "entropy-stabilized oxides" and "high-entropy oxides", often employed as synonyms. However, the effective role of entropy in the stabilization should be demonstrated for each system, and even for Cu 0.2 Zn 0.2 Mg 0.2 Co 0.2 Ni 0.2 O it is still under debate. Moreover, many effects concur to the stabilization, i.e. the relative concentration, the valence state and the ionic radii of the cations involved. We will here discuss the role of configurational entropy in the phase stability, considering the main classes of crystal structures and providing a guide to critically discern between entropy and non-entropy stabilized oxides. [ABSTRACT FROM AUTHOR]

The incorporation of a few amount of MnO 2 into 0.88NaNbO 3 -0.12SrTiO 3 lead-free ceramics was found to effectively stabilize the antiferroelectric orthorhombic P phase before its transition into antiferroelectric orthorhombic R phase, consequently featuring completely reversible electric field-induced antiferroelectric-ferroelectric phase transition. Not only reproducible double polarization hysteresis loops but also repeated sprout-like strain-field curves ensure great application potentials in large-displacement lead-free actuators owing to both large repeatedly-utilized strains of ∼0.33% and low driving field of ∼11 kV/mm. Combined results of XPS, Raman spectroscopy and dielectric properties indicate that the stabilized antiferroelectric P phase was closely related to the reduced B-site cation polarizability and oxygen vacancy concentration, while a slight change in antiferrodistortive degree would discourage the P-R phase transition. These results indicate that ionic doping is an alternative method to alter the antiferroelectric P phase stability of NaNbO 3 -based lead-free ceramics by synergistically considering the influencing factors of phase and crystal structure stability. [ABSTRACT FROM AUTHOR]

The high sintering resistance of multi-cation zirconates has attracted a lot of research interest in new generation of thermal barrier coatings. For this purpose, La3+, Gd3+, and Yb3+ cations were selected for placement in the A-site of A 2 Zr 2 O 7 structures to synthesize (La 0.33 Gd 0.33 Yb 0.33) 2 Zr 2 O 7 powder using co-precipitation method at 1000 °C for 3 h. The high-temperature properties of the prepared powder were evaluated at 1300 °C for 50 h. The results indicated an increase in the tendency to change the crystallographic structure from defect fluorite to pyrochlore during the heat treatment process. Compared to the single-cation zirconates, La 2 Zr 2 O 7 (⁓ 4 nm.h−1), Gd 2 Zr 2 O 7 (⁓ 3.5 nm.h−1), and Yb 2 Zr 2 O 7 (⁓ 12 nm.h−1) powders, the (La 0.33 Gd 0.33 Yb 0.33) 2 Zr 2 O 7 multi-cation zirconate powder exhibited a lower growth rate of crystallite size (⁓ 3 nm.h−1). This suggests that the use of multiple cations in the A-site of A 2 Zr 2 O 7 structures can be more beneficial in improving sintering resistance than using a single cation. [ABSTRACT FROM AUTHOR]

Thermal barrier coatings (TBCs) are critical for the reliability and lifespan of aircraft engine turbine blades. In this study, a novel quaternary rare-earth oxide (La 2 O 3 , Gd 2 O 3 , Yb 2 O 3 , and Y 2 O 3) co-doped ZrO 2 solid solution, referred to as 1La-xGd-2Yb-3.5YSZ, was synthesized by varying the doping amount of Gd 2 O 3 from 0 to 6 mol. %. The impact of co-doping-induced lattice distortion on the phase composition, high-temperature phase stability, sintering resistance, and mechanical and thermal properties of the solid solution has been explored. It is found that the addition of Gd 2 O 3 stabilizer effectively increased the lattice distortion of the solid solution, which led to improved phase stability and sintering resistance, enhanced mechanical properties, and low thermal conductivity. Our findings highlight the promising properties of the 1La-xGd-2Yb-3.5YSZ solid solution, making it an attractive candidate for TBC materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • Number of experimentally reported MAX phases has doubled since 2019 to more than 342. • Elemental combinations expanded via alloying, high-entropy and top-down synthesis routes. • Article introduces a MAX phase classification based on how they are synthesized. • New MAX phases for future synthesis are identified by phase stability predictions. The MAX phases are a class of nanolaminated materials composed of an early transition-metal (M), an A-group element (A) and C, N, B and/or P (X). Progress in MAX phase research in recent years has increased their number from the original 50 or so, to more than 300 phases. Since half of the 342 MAX phases have been discovered after 2018, an overview of the progress made in the field is timely. Currently, 28 M elements, 28 A elements, and 6 X elements have been incorporated in the MAX phases, alloys included. We further categorize MAX phases based on the synthesis route used to make them; if made via a one-step approach in bottom-up synthesis or formed through elemental replacement reactions in top-down synthesis. This classification is also correlated to theoretical phase stability predictions, that in turn, can be used to identify novel synthesizable MAX phase compositions as well as to suggest suitable synthesis routes. Furthermore, using phase stability predictions we identify 182 new theoretically stable MAX phases awaiting experimental confirmation. Notably, as MAX phases are precursors for MXenes, the dramatically increased interest in the latter for a large host of potential applications renders the former even more valuable. [ABSTRACT FROM AUTHOR]

In this work, the Ce4+ and Ti4+ co-doped YSZ powders (Ce 0.08-x Ti x Y 0.08 Zr 0.88 O 2.04) with various additions of Ti4+ substitution Ce4+ are prepared by the co-precipitation method. The microstructure, phase and chemical composition, phase transformation process, and phase stability after repeated calcination at 1300 °C of the powders have been investigated. The crystal structure of co-doping YSZ depends on the addition of Ti4+ substitution Ce4+ in the Ce 0.08-x Ti x Y 0.08 Zr 0.88 O 2.04. When the doping molar ratio of Ce4+ to Ti4+ is 3:1 or 1:1, the ZrO 2 can be stabilized to form the t′-phase and show better thermal stability, according to the TG-DSC and XRD results. Ti4+ enters the ZrO 2 lattice in the form of substitution or interstitial. The oversized radius cation and undersized-radius cation co-stability can be induced by co-doping of Ti4+ and Ce4+. Thereby, the t′-ZrO 2 is stabilized after repeated calcination at 1300 °C for 120 h. The co-doping of oversized radius cations and undersized-radius cations can further improve the t′-ZrO 2 stability of YSZ, while the role of oversized radius cations is dominant. [ABSTRACT FROM AUTHOR]

High-temperature stability, including sintering resistance and phase stability, is critical for thermal barrier coatings (TBCs) applied at ultra-high temperature over 1500 °C. In this work, we reported a high-entropy rare-earth zirconate (Y 0 2 La 0.2 Nd 0.2 Sm 0.2 Eu 0.2) 2 Zr 2 O 7 (YLNSE) synthesized by solid-state reaction method. X-ray diffraction (XRD), transmission electron microscopy (TEM), and energy dispersive spectrometer (EDS) mapping results confirmed that YLNSE formed a single-phase pyrochlore structure with uniform rare earth elements distribution. YLNSE maintained more uniform microstructure, higher porosity retention, lower grain growth rate and better thermomechanical properties during sintering at 1500 °C, as the results of the ordered crystal structure and sluggish diffusion effect, indicating a better sintering resistance than conventional TBC material yttria-stabilized zirconia (YSZ). In addition, YLNSE also demonstrated high coefficient of thermal expansion (CTE, 11.04 × 10-6K-1, 25–1500 °C) and low thermal conductivity (1.95 W m-1 K-1, 1500 °C), as well as good phase stability at 1500 °C. In view of the excellent high-temperature stability of YLNSE, it is a promising candidate for ultra-high temperature TBCs. [ABSTRACT FROM AUTHOR]

The phase instability of 6–8 wt% Y 2 O 3 partially stabilized ZrO 2 (YSZ) in high temperature and molten salt corrosion environment seriously limits its application above 1200 °C. In this study, the chemical co-precipitation method prepared Yb 2 O 3 and CeO 2 co-doping YSZ (YbCeYSZ) ceramic materials to improve the above issues. It was proposed to improve the defect of high-temperature phase instability of CeO 2 -doped YSZ materials by adding Yb 2 O 3. The phase stability, thermal insulation properties, and Na 2 SO 4 + V 2 O 5 molten salt corrosion behavior of YbCeYSZ ceramic materials were studied. The results showed that 2.5 mol% Yb 2 O 3 -4 mol% CeO 2 -YSZ material (2.5Yb4CeYSZ) had no monoclinic phase (m-ZrO 2) after holding at 1500 °C for 120 h due to forming more defect clusters in the system. Meanwhile, the 2.5Yb4CeYSZ had excellent thermal insulation performance and molten salt corrosion resistance, which was attributed to the strong phonon scattering in the 2.5Yb4CeYSZ material system and the low reactivity between the stabilizer and the corrosive salt. [ABSTRACT FROM AUTHOR]

The mismatch of thermal expansion coefficient (CTE) between thermal barrier coatings (TBCs) and environmental barrier coatings (EBCs) is the key factor that affects the durability of T/EBCs in aero-engine environments. To alleviate the CTE mismatch, the novel TBC materials with relatively low CTE are needed. In this study, Lu 4 Hf 3 O 12 with δ-phase rhombohedral structure was synthesized by solid-state reaction using Lu 2 O 3 and HfO 2 as the raw materials. Lu 4 Hf 3 O 12 ceramics exhibited outstanding phase stability up to 1600 °C and comparable mechanical properties to 8 wt% Y 2 O 3 stabilized ZrO 2 (8YSZ) as well as great resistance against water-vapour/oxygen corrosion. Additionally, it possessed the thermal conductivity of 1.20 W/m·K at 1000 °C, about 43% lower compared to traditional 8YSZ material (2.1–2.22 W/m·K), and coefficient of thermal expansion (CTE) of 8.46 × 10−6 K−1 (10.38 × 10−6 K−1 for 8YSZ). These results preliminarily reveal that Lu 4 Hf 3 O 12 could be considered as a potential material for thermal insulation top-coat in the field of T/EBCs. [ABSTRACT FROM AUTHOR]

The possibility of altering the phase equilibria of multicomponent oxide systems through precise control of configurational entropy has opened a platform with unlimited possibilities to fine-tune material properties. The current work is aimed at tailoring the mechanical and thermal properties of (MgNiCoCuZn)O by an intelligent design of constituent phase structure resulting from controlled cooling from the stabilization temperature. Based on the cooling rates, the amount of CuO nucleation was found to vary between 5.4 and 12.3 wt%, along with a corresponding decrease in Cu2+ content in the matrix. It was observed that with the decrease in Cu2+ ion concentration in the matrix, the Young's modulus and hardness increased by 33% and 26%, respectively, along with a corresponding decrease in the coefficient of thermal expansion by 15%. Similarly, an increased nucleation of CuO precipitates led to the improvement of fracture toughness of the material by 15%, while its thermal conductivity remained unaltered. [Display omitted] [ABSTRACT FROM AUTHOR]

A series of 16 mol% CeO 2 -2 mol% Re 2 O 3 co-stabilised zirconia (ZrO 2) (16Ce4ReSZ, Re Eu, Gd, Dy, Y, Er, Yb) ceramic materials were synthesised using a chemical coprecipitation– high-temperature roasting method. Their phase structure, high-temperature phase stability, mechanical properties, thermal conductivity and coefficient of thermal expansion (CTE) were investigated. The results show that the ZrO 2 tetragonal phase co-stabilised by CeO 2 and Re3+ with a smaller radius has better stability. The 16Ce4ReSZ (Re Dy, Y, Er, Yb) materials have high fracture toughnesses, low thermal conductivities, and high CTE values. As the radius of the Re3+ ions decreases, the lattice energy increased, while the lattice distortion decreases, the CTE decreases slightly and the thermal conductivity of the material increases slightly. Owing to the high phase stability of 16Ce4YbSZ, its mechanical properties are best after 100 h of sintering at 1400 °C. [ABSTRACT FROM AUTHOR]

The present study aims to investigate the influence of grain growth during heat treatment on the phase stability of AZO: A 2 Zr 2 O 7 compounds at 1300°C. To this end, three cations of La3+, Gd3+, and Yb3+ (corresponding to large, medium and small cations, respectively) were placed in the A-site of the AZO compounds through co-precipitation–calcination technique at 1000°C for 3 h to achieve LaZO: La 2 Zr 2 O 7 , GdZO: Gd 2 Zr 2 O 7 , and YbZO: Yb 2 Zr 2 O 7 , respectively. The phase stability of LaZO, GdZO, and YbZO was assessed under 50 h of heat treatment at 1300°C. Characterization techniques such as conventional and high-temperature XRD, Raman and Fourier transform infrared (FTIR) spectroscopies, simultaneous thermal analysis (DTA/TG), and field-emission scanning electron microscopy (FESEM) were employed to assess the synthesized compounds. FESEM results of LaZO, GdZO and YbZO calcinated powders indicated orderly particles, uniform in shape and size, with a relative tendency of agglomeration and with an average particle size of less than ∼100 nm. XRD results of LaZO and YbZO powders after calcination indicated the formation of pyrochlore and defect fluorite structures, respectively. The placement of Gd3+ (GdZO) led to the formation of a dual pyrochlore-defect fluorite structure. The current research also indicated an enhancement in the tendency to form pyrochlore structure in GdZO and YbZO compounds along with the growth of the grains after 20 (mean grain size of ∼250 nm) and 50 h (mean grain size of ∼800 nm) of exposure to the temperature of 1300°C, respectively. [ABSTRACT FROM AUTHOR]

Phase stability and equilibrium calculations are very significant in the process industries, ranging from process simulation, equipment design, operation and design. These problems involve several systems of complex and nonlinear equations, which are mathematically challenging. An alternative solution is formulating the problems into a global optimisation problem. A robust and reliable optimisation technique is required to solve these global optimisation problems. In this study, two recently developed stochastic global optimisation algorithms, POA and GTO were applied to phase stability and equilibrium problems. The need to enhance their performance necessitated the development of two modified algorithms, PGOA1 and PGOA2, which are the hybridisation of POA and GTO. All the algorithms' abilities were explored for solving computationally challenging and multidimensional phase stability and equilibrium problems, and their performances were compared. The implementation of POA and GTO was good in solving most problems, though GTO slightly outperformed POA. The hybridisation of both to develop PGOA1 and PGOA2 was worthwhile as both outperformed the POA and GTO. PGOA2 is more robust and reliable in solving phase stability and equilibrium, and its performance superseded the performances of the other algorithms. • Pelican and Gorilla troops algorithms applied to phase problems. • Phase stability and equilibrium for non-reactive and reactive benchmark problems. • Hybrid of Pelican and Gorilla troop algorithms outperformed the parent algorithms. • The inclusion of a local optimizer improved the algorithms. [ABSTRACT FROM AUTHOR]

The non-transformable tetragonal zirconia (t- ZrO 2) in ZrO 2 -RETaO 4 systems offers significant promise in the development of next generation thermal barrier coatings. This work focuses on the effects of rare-earth dopants on phase equilibria and phase stability of tetragonal zirconia in ZrO 2 -RETaO 4 systems. Precursor-derived oxides were heat treated at 1500 °C to elucidate phase constitution by X-ray diffraction. The composition ranges of non-transformable t- ZrO 2 in ZrO 2 -YbTaO 4 , ZrO 2 -DyTaO 4 and ZrO 2 -GdTaO 4 are measured to be about 30–41, 22–29 and 16–19 mol% RE 0.5 Ta 0.5 O 2 , respectively. However, non-transformable t -ZrO 2 cannot be found in ZrO 2 -NdTaO 4 and ZrO 2 –LaTaO 4. Formation abilities of t -ZrO 2 in ZrO 2 -RETaO 4 systems are determined to be inversely proportional to the ionic radius of RE3+. Based on our calculations, stabilization mechanisms of non-transformable t -ZrO 2 were considered to be related to degree of strain energy release and high-temperature decomposed reactions of the doped t -ZrO 2. Firstly, RE-Ta pair dopants could relieve the strain energy of the strained tetragonal zirconia structure, which would prevent the displacive transformation of t -ZrO 2 → m -ZrO 2. Secondly, the solid solubilities of RE-Ta dopants should be large enough to ensure the doped t -ZrO 2 phase cannot decompose before inhibiting t -ZrO 2 → m -ZrO 2. For large ionic radius of Nd3+ and La3+ dopants, the decomposed reactions of doped t -ZrO 2 can take place even at very low dopant concentration, which explains the observations that t -ZrO 2 cannot be detected in their whole compositions. The emerging results are useful to the development of appropriate thermal barrier coatings. [ABSTRACT FROM AUTHOR]

A mixed perovskite titanate-aluminate [(1- x)(Sr 0.6 La 0.2 Ce 0.2 Ti 0.8 Mg 0.2 O 3)- x NdAlO 3 for x = 0.1 to 0.4] solid solution was successfully synthesized. X-ray diffraction patterns (XRD) and Rietveld refinement results indicated a stable perovskite phase with a cubic structure, in which Nd3+ occupies the A-site randomly while Al3+ occupies the B-site. No additional reflection spots (superlattice reflections) were detected in the HRTEM pattern (see SAED), confirming the cubic symmetry. All samples showed small Urbach tails, mainly due to compositional disorder. Microstructural analysis based on atomic force microscopy (AFM) showed no traces of impurity phases. For x = 0.4, excellent microwave dielectric properties (MWD) are obtained with a quality factor (Q × f) of 37,131 GHz at f = 5.2801 GHz, relative permittivity (ε r) of 43, and temperature coefficient of resonant frequency (τ f) of +1.3 ppm/°C. Variations in ε r , Q × f values, and τ f may be related to changes in relative density (ρ rel), ion polarizability, optical band gap, and tolerance factor, respectively. [ABSTRACT FROM AUTHOR]

This study concerns the cryogenic hydrogen combustion in subcritical pressure conditions, with practical relevance to rocket engine applications. A cryogenic two-phase flame in the counterflow configuration is calculated and analyzed with the consideration of real-fluid effects and heat/mass transfer across the liquid-gas interface. The effects of pressure, strain rate, fuel inlet temperature, and heat loss on the flame characteristic behaviors are examined. It is found that the vaporization rate of liquid oxidizer scales with the square-root of pressure (p) times strain rate (a st), and is not a limiting factor for combustion. The total heat release scales with p a s t at lower strain rates while with p 4 / 5 a s t 1 / 3 at higher strain rates. The significant results on the phase-stability of cryogenic flame are also established. It is found that the unstable phase, in terms of vapor-liquid equilibrium, arises in the vicinity of the liquid-gas interface; however, all unstable-phase states still stay in the metastable region of the phase diagram. For all the flame solutions considered in this study, no thermochemical state enters the spinodal region. • Identify two distinct scalings for total heat release at lower and higher strain rates. • Establish scalings of oxidizer vaporization rate and flame-interface distance. • Identify the region of unstable phase in physical space and the scaling of its size. • Find that all unstable phase states remain in the metastable region. [ABSTRACT FROM AUTHOR]

This study designed a series of TiVNbMoCr alloys under the VEC constraint. Based on the thermodynamic calculation, the precipitation behavior was predicted, and the precipitation strengthening was experimentally investigated and discussed. The results showed that below 600 °C, the designed alloys with VEC from 4.30 to 4.60 are metastable at a single β phase state. With low VEC, the HCP-structured α phase precipitates from the BCC-structured β phase with a coherent interface between them. With high VEC, TiCr 2 (C15-Laves phase) precipitates from the β phase companying with the α phase. The prediction results are well consistent with the experimental results. Aged at 400 °C for 60 h, the alloys with VEC of 4.30 and 4.35 contained large volume fraction of the large-sized α phase, playing a great role in strengthening. The alloys with VEC of 4.55 and 4.60 exhibited small-sized precipitation particles acting in strengthening in terms of the Orowan mechanism, and the yield strength depends mainly on the volume fraction and size of precipitation particles, as well as the intrinsic strength of the β matrix that can be predicted by the Varvenne model based on the MD calculation. To some extent, the intrinsic ductility of the β matrix determines the tensile plasticity of the alloys with high VEC. Although favoring for strengthening, more TiCr 2 precipitates are not conducive to tensile plasticity. [ABSTRACT FROM AUTHOR]

• As-cast HEA displays a triple phase structure comprising fcc, Chi (χ) and TiC. • Ti addition enhanced mechanical properties via solid solution and precipitation. • Homogenization decomposes χ phase, increasing TiC volume and thus YS and UTS. • Decomposition of χ phase after annealing enhanced the strength-ductility properties. This research investigates the effects of adding 2 at.% Ti on the microstructure, phase transformation, and mechanical properties of FeMn 40 Co 10 Cr 10 C 0.5 high-entropy alloy (HEA) in both as-cast and homogenized conditions. The incorporation of Ti increased the lattice parameter of the FCC matrix and caused greater lattice distortion (∼5.9 %) due to the larger atomic radius of Ti. The negative mixing enthalpy of Ti resulted in segregation at interdendritic regions, forming a Ti-rich Chi (χ) phase during solidification. The as-cast structure displayed a dendritic microstructure consisting of 77.9 % FCC, 20.6 % χ, and 1.5 % TiC phases. After homogenization at 1200 °C for 2 h, the χ phase was dissolved, increasing the volume fraction of TiC to 24 %. The homogenized sample exhibited a substantial improvement in tensile properties, i.e., with the ultimate tensile strength (UTS) rising from 631 MPa in the as-cast condition to 689 MPa, and yield strength (YS) increasing from 346 MPa to 419 MPa, while maintaining an elongation of ∼ 54 %. These enhancements are attributed to solid solution strengthening, increased carbide precipitation, and the dissolution of the χ phase into the FCC matrix. [ABSTRACT FROM AUTHOR]

Formation of the W 2 Zr intermetallic is the key reason for the low relative density and brittleness of W-Zr alloys. In this study, 65 W-Zr-Ti-Nb alloys with different Ti and Nb content were prepared by powder metallurgy. With the increase of Ti and Nb content, the proportion of the W 2 Zr in the alloy decreases, causing the densification of 65 W-Zr-Ti-Nb alloys. The thermodynamic calculation shows that the addition of both Ti and Nb results in a narrowing stabilized temperature range of W 2 Zr and an expanding stabilized temperature range of BCC-WTi x Nb y , respectively, ultimately causing the disappearance of the W 2 Zr and formation of the WTi x Nb y during non-equilibrium cooling. Both high ductility and strength can be achieved in the W-Zr-Ti-Nb alloys by assistance of the disappearance of the brittle W 2 Zr phase and the formation of the ductility WTi x Nb y. The first principle calculation indicates that the co-doping Ti and Nb results in a larger expansion on the spacing of the {110} close-packed plane and a smaller expansion or even shrinkage on the atomic spacing along the close-packed direction of the WTi x Nb y. Further, integrated crystal orbital Hamilton population (ICOHP) results proved that the bonding strength of W-Ti and W-Nb was weaker than that of W-W in WTi x Nb y. Both increased spacing of {110} plane and decreased interatomic bonding strength aid in reducing Peierls-Nabarro stress, promoting plastic deformation. This study provides a new method for improving mechanical properties by tailoring the phase constitution in W-Zr alloys through co-doping Ti and Nb. • W-Zr alloys with high plasticity and strength was achieved by tailoring the stability and deformability of W-rich phases. • The mechanism of Ti and Nb addition on the inhibition of the W 2 Zr in W-Zr alloy phase is revealed. • P-N stress reduction mechanism was revealed by analyzing lattice structure and interatomic bonding of W-rich phases. [ABSTRACT FROM AUTHOR]

• Systematic experimental studies and thermo-kinetic simulations have been used to delineate the effect of prior microstructure on the carbide precipitation during tempering of a Cr-Mo-V pressure vessel steel. • Steel with two different initial microstructures, produced by cooling it at 10 °C/min and water quenching from austenitization temperature, was investigated. • Multiscale characterization revealed the presence of carbon-rich martensite/austenite (M/A) islands in the steel cooled at 10 °C/min. • M 7 C 3 and MC carbides precipitated in both the samples during tempering at 650 °C, while M 23 C 6 carbide formed only in the 10 °C/min cooled sample. • Thermo-kinetics simulations showed that the carbon enrichment in the M/A constituents was responsible for the enhanced precipitation kinetics of M 23 C 6 carbide. Cr-Mo-V steels are key materials used for constructing thick reactor pressure vessels (RPV) owing to an impressive combination of their mechanical properties and weldability. Conventionally, these steels are subjected to a quality heat treatment that comprises austenitization, quenching and tempering. Owing to its large thickness, an RPV experiences widely different cooling rates across its thickness during quenching, leading to considerable variation in the microstructure from the surface to the centre of the vessel. In this study, a Cr-Mo-V steel was austenitized at 950 °C for 1 h and cooled at two rates (water quenching and 10 °C/min), representative of the cooling rates at the surface and centre of a typical RPV, to study the effect of prior microstructure on the carbide precipitation during tempering of the steel at 650 °C. Electron microscopy of the as-cooled samples revealed the presence of martensitic microstructure in water quenched sample and predominantly granular bainitic microstructure in slow cooled sample. Synchrotron studies revealed the presence of retained austenite containing ∼0.8% carbon in the slow-cooled sample. Tempering of the steel at 650 °C for 200 h precipitated M 7 C 3 and MC (VC) carbides in the water-quenched sample, while the slow cooled samples precipitated M 23 C 6 as an additional constituent. This difference in the carbide precipitation in the two samples has been attributed to the excess carbon in the martensite/austenite (M/A) regions in slow cooled samples and explained on the basis of carbide precipitation sequence predicted using Thermo-kinetic simulations. This analysis has shown that M 23 C 6 and M 7 C 3 carbides in the slow cooled sample precipitate simultaneously as critical radii of their nucleation as well as their incubation time become comparable when the matrix contains more than 0.25% C. The present study has demonstrated that the microstructure prior to tempering may significantly affect the precipitation sequence of carbides during tempering. [ABSTRACT FROM AUTHOR]

Thermal barrier coating materials require high phase stability, low thermal conductivity, and a thermal expansion coefficient that matches the bonding layer. Cation doping is a highly efficient method for enhancing the thermophysical and mechanical characteristics of materials used in thermal barrier coatings. The thermophysical and mechanical properties, as well as the phase stability at high temperatures of ceramic materials doped with Yb3+ in gadolinium zirconate, are examined by utilizing first principles calculations and solid-state reaction methods. As the Yb3+ content increases, the grain average particle size of gadolinium zirconate ceramics first decreases and then increases. Given that a smaller grain size results in more grain boundaries, thereby reducing the thermal conductivity of the material, it can be inferred that Yb0.20 ((Gd 0.8 Yb 0.2) 2 Zr 2 O 7) with the smallest grain size exhibits lower thermal conductivity. As the Yb3+ content increases, both the calculated and experiment results suggest the Young's modulus of gadolinium zirconate initially declines to its minimum value when the Yb3+ content is 0.5 and subsequently experiences a little increase. Furthermore, as the concentration of Yb3+ increases, the material initially experiences a drop in both hardness and fracture toughness, followed by a subsequent increase. Both the calculation and experimental results indicate that the thermal conductivity of gadolinium zirconate initially decreases and then increases. Among the different compositions, Gd 1.5 Yb 0.5 Zr 2 O 7 demonstrates the minimum thermal conductivity, measuring 1.029 W/(m⸱K) according to the Clark model and 1.152 W/(m⸱K) according to the Cahill model. At a temperature of 1273 K, the experimental results demonstrated that (Gd 0.8 Yb 0.2) 2 Zr 2 O 7 has the lowest thermal conductivity of 1.415 W/(m·K). Furthermore, both the calculated and experimental thermal expansion coefficients of the material decrease first until the Yb3+ concentration is 0.5 and then increase slightly when the Yb3+ content increases. Moreover, gadolinium zirconate ceramics have demonstrated a consistent single-phase fluorite structure, excellent stability at high temperatures, and remarkable structural integrity during repeated heating and cooling cycles. The calculation results exhibit strong congruence with the experimental data. The objective of this work is to improve the thermophysical and mechanical properties of gadolinium zirconate ceramics for their application as materials for thermal barrier coatings. • Yb3+ decreases the H v , K IC , κ and TEC of Gd 2 Zr 2 O 7 firstly and then increases. • Gd 1.5 Yb 0.5 Zr 2 O 7 has the lowest minimum thermal conductivity. • Gd 1.6 Yb 0.4 Zr 2 O 7 displays the lowest thermal conductivity of 1.415 W/(m·K) at 1273 K. • Yb3+-doped Gd 2 Zr 2 O 7 ceramics have demonstrated excellent stability at high temperatures. • The experimental results have a good consistent trend with the calculated results. [ABSTRACT FROM AUTHOR]

High-temperature structural alloys are urgently desired for refractory applications. In this work, we conceived a facile route to achieve an excellent combination of high-temperature strength and room-temperature ductility in a NbMoTaWHf refractory high-entropy alloy (RHEA). The idea is to break up the stable single body-centered cubic (BCC) phase in NbMoTaW RHEA to introduce the tiny secondary phase by alloying appropriate hafnium (Hf) that can stall and accumulate dislocations. The dual-BCC-phase structure and the dislocations for the NbMoTaWHf RHEA were characterized. The compressive yield strengths of the NbMoTaWHf RHEA at room temperature, 1200, 1600, and 1800 °C were 1730, 1088, 390, and 312 MPa, respectively. The alloy displayed plastic deformation behaviors and dual-BCC-phase structure stability after compressing at 1600 and 1800 °C. The superb high-temperature strength was mainly ascribed to the high softening temperature, second-phase strengthening, and solid-solution strengthening. This work provides a promising high-temperature structural material with improved room-temperature ductility and high strength at elevated temperatures and enriches the database of the NbMoTaW-based RHEAs. [Display omitted] • NbMoTaWHf RHEA with high strength at elevated temperatures were designed. • The dual-BCC-phase NbMoTaWHf RHEA was stronger than the NbMoTaW RHEA by forming the tiny Hf-rich secondary phase. • The high-temperature strengthening mechanism was discussed. [ABSTRACT FROM AUTHOR]

The linear accelerator (LINAC) system currently under construction at the Hefei Advanced Light Facility (HALF) employs acceleration tubes to accelerate the electron beam to 2.2 GeV. The RF field within the acceleration tube is controlled by an MTCA.4-based low-level radio frequency (LLRF) prototype system to meet stringent phase stability requirements. This paper introduces the structure of the LLRF system, encompassing both its hardware and software components. The LLRF system uses the non-IQ-sampling method to suppress odd harmonics through digital filters, achieving a signal-to-noise ratio (SNR) of approximately 73 dB. Given that the power sources of most acceleration tubes operate in a saturated state, the radio-frequency (RF) control algorithm within the software is based on a separate amplitude open-loop and phase close-loop to maintain stable phase control during amplitude disturbances. The design of the RF control logic, including digital filters, the REF phase tracking method, the close-loop feedback controller, and the output pulse mode control algorithm, is detailed. Offline pulse-to-pulse test results demonstrate that it achieves a phase stability of 0.0176° rms with a solid-state amplifier, meeting the facility's requirements. [ABSTRACT FROM AUTHOR]

Most properties of crystalline materials are closely associated with their structures. The theoretical prediction of crystal structures at finite temperatures is a formidable task, but significant progress has been made recently. In this work we employ the open source SLUSCHI (Solid and Liquid in Ultra Small Coexistence with Hovering Interfaces) package interfaced with the first-principles VASP code for prediction of high temperature structures from ab initio molecular dynamics. The approach is tested by prediction of the stable and metastable phases for tungsten (W) and titanium (Ti) and by analysis of high temperature and high pressure phases of Y 2 O 3. The high temperature phase of Y 2 O 3 is stable for 100 K below the melting temperature (2712 K). It is proposed to possess either cubic or hexagonal symmetry but has never been experimentally refined due to the low quality of high temperature diffraction data. The prediction with SLUSCHI indicated that Y 2 O 3 crystallizes from the melt in hexagonal structure, with the P6 3 /mmc space group. The refinement of Y 2 O 3 high temperature synchrotron diffraction data using predicted coordinates produces realistic atomic displacement parameters, corroborating fast oxygen diffusion evident from computations. These findings demonstrate the efficacy of our computational method in predicting material behavior across a wide range of conditions, supporting the development of new ultra-high temperature materials. [Display omitted] [ABSTRACT FROM AUTHOR]

• Emergence of soft patterns and soft phonon behaviour under pressure. • Pressure-induced martensitic transformation. • The smaller the C′ , the easier the martensitic phase transformation is. First-principles calculations are used to investigate the phase stability and martensitic transformation of two new all- d -metal Heusler alloys Fe 2 VIr and Fe 2 TaIr at 0–50 GPa. The difference in phase stability between Fe 2 VIr and Fe 2 TaIr is due to the effect of d - d orbital hybridisation between different atoms and the appearance of triply degenerate in the pressure-induced phonon optical modes. The softening behaviour of the transverse phonon mode along the high symmetry point X is responsible for the martensitic transformation of Fe 2 TaIr. We also observed the softening of the shear elastic constant C ′ = (C 11 - C 12)/2. Strong Fe-Fe magnetic coupling, softening of transverse acoustic phonon modes and anomalous softening of C′ awaken the martensitic transformation. Low-frequency phonon hybridisation of the heavy elements Ta and Ir is the driving force behind the softening. A surprising phenomenon is found during tetragonal deformation of the structure of Fe 2 TaIr at 45 GPa, whereby the structure break through the energy barrier of the leap and produced a tetragonal martensitic phase with a much lower energy. It may imply that pressure-induced Fe 2 TaIr produced a premartensitic phase. This work presents a detailed analysis of the anomalous softening behaviour of Fe 2 TaIr and the mechanism of the pressure-induced martensitic transformation. A new idea is proposed for an in-depth study of the martensitic phase transition precursor reaction. [ABSTRACT FROM AUTHOR]

In present study, the strengthening mechanism of friction-stir welded Fe-17Mn binary alloy was quantitatively investigated by means of the electron microscopic observation in stir zone center and the dislocation-based constitutive equation. As the rotation speed increased from 440 to 760 rpm, both fraction of thermal ε martensite and prior γ austenite size were elevated due to the severely frictional heat, whereas the dislocations were annihilated. Though different microstructural feature of welds, the stir zone center had similar hardness and yield strength regardless of rotation speed. It was because of notable increase in ε martensite hardening as well as marginal decreases in hardening in grain boundary and dislocation with increasing rotation speed. [Display omitted] • FSW in Fe-17Mn alloy is performed by increasing rotation speeds from 440 to 760 rpm. • There are no huge differences in hardness and yield strength of welds. • Strengthening mechanism is estimated by constitutive equation including ε hardening. • Faster speed improves hardening for grain boundary and ε phase. • Faster speed reduces dislocation hardening. [ABSTRACT FROM AUTHOR]

• The structural stability, optoelectronic properties, and photovoltaic performance of lead-free mixed-valence Cs 2 AgIAuIIIX 6 (X = Cl, Br, I) are firstly disclosed. • The structural stability is validated by comprehensive theoretical calculations. • The studied perovskites exhibit appropriate optical band gaps (1.2 − 1.5 eV) for photovoltaic applications. • The predicted maximum efficiency of 30.3 % is achieved for Cs 2 AgIAuIIII 6. In light of their suitability for optoelectronic and photovoltaic devices, lead-free halide double perovskites (HDPs) have been extensively concerned in recent years. However, most HDPs have large and indirect band gaps (> 2 eV), which is unfavorable for perovskite solar cells. Here, the structural stability, optoelectronic response, and photovoltaic performance of mixed-valence HDPs Cs 2 AgIAuIIIX 6 (X = Cl, Br, I) have been theoretically examined. The thermodynamic, dynamical, and mechanical stability are verified in terms of the decomposition energy, phonon dispersion, and elastic constants. The computed indirect-gaps are 1.44 eV for Cs 2 AgIAuIIICl 6 , 1.25 eV for Cs 2 AgIAuIIIBr 6 , and 1.22 eV for Cs 2 AgIAuIIII 6 , respectively. These mixed-valence Cs 2 AgIAuIIIX 6 (X = Cl, Br, I) HDPs possess more suitable optical band gaps in comparison with that of Cs 2 AuIAuIIIX 6. The role of different metal cations in determining electronic properties is further elucidated. Furthermore, the optical analysis discloses that three mixed-valence HDPs exhibit high visible-light absorption coefficients. Additionally, the photovoltaic response of Cs 2 AgIAuIIIX 6 (X = Br, I) is further substantiated since the predicted efficiency is beyond 28 %. Overall, our study reveals that mixed-valence Cs 2 AgIAuIIIX 6 (X = Cl, Br, I) HDPs shows good stability and superior photovoltaic performance, which is an efficient candidate for single-junction perovskite solar cells. [ABSTRACT FROM AUTHOR]

Due to the excellent mechanical properties, TiZrNb-based refractory high entropy alloys (RHEAs) show great potential application prospects in aviation, aircraft and petrochemical. However, the RHEAs are usually thermally metastable and brittle phases can be precipitated in intermediate temperature (such as 500–700℃), which severely limit the preparation of large-sized RHEAs ingots in industrial production. In this paper, we propose an alloy optimization strategy to suppress the precipitation of TiZrNb-based RHEAs by adding interstitial atomic oxygen (O). The results show that the precipitation temperature region of brittle phases can be reduced from 500°C∼650°C to 550°C∼600°C after adding oxygen, and the temperature region is reduced by more than 66 %. Moreover, the growth rate of precipitated phase decrease from 4.1 × 10−23 m3/s to 1.9 × 10−24 m3/s after adding oxygen, which is reduced by more than ten times. The analysis shows that adding oxygen inhibits the diffusion rate of Zr at intermediate temperature, thus delaying the formation of Zr-rich phase. Based on this, TiZrNb-based RHEAs with oxygen can well keep the outstanding ductility even after annealing at intermediate temperature for 4 hours, while the TiZrNb-based RHEAs without oxygen show ∼50 % ductility loss after the same annealing treatment. Our results not only provide new insights into the phase stability and mechanical stability of RHEAs, but also provide a new strategy for improving the phase stability of large-size ingots for engineering applications. • Adding oxygen significantly inhibited the phase precipitation at intermediate temperature. • Adding oxygen reduces the principal element diffusion rate and thus inhibits the phase precipitation. • Adding oxygen avoids the sharp deterioration of ductility after isothermal annealing. [ABSTRACT FROM AUTHOR]

• The structural features and photophysical properties of Cs 2 HgPdX 6 (X = Cl, Br) under pressure are systematically studied. • The structural stability is verified for both compounds. • The fundamental properties of both compounds are more sensitive to an external pressure. • The excellent optoelectronic properties of pressure-induced Cs 2 HgPdX 6 (X = Cl, Br) are disclosed for photovoltaics. As viable alternative light-harvesting materials in perovskite solar cells (PSCs), halide double perovskites (HDPs) Cs 2 BBʹX 6 with B = monovalent cation and Bʹ = trivalent cation have gathered extensive attention thanks to their excellent chemical stability and tunable properties. Unfortunately, most of these HDPs typically exhibit large optical bandgap and weak visible-light absorption, which seriously limits their application in single-junction PSCs. In this research, we theoretically report two novel Cs 2 HgPdX 6 (X = Cl, Br) HDPs for the first time, and their interesting physical properties are scrutinized. According to our predictions, novel Cs 2 HgPdX 6 (X = Cl, Br) is an experimentally synthesizable compound since its stability is carefully examined. Our calculations disclose that Cs 2 HgPdX 6 (X = Cl, Br) is an indirect and large band gap compound (> 2 eV), and the band edges of valence and conduction bands mainly involve the strong orbital hybridization between Pd-4d and X-p. Additionally, under the application of pressure, the band gaps of both compounds are narrowed to an optimal value at moderate pressure, making them ideal alternatives for single-junction PSCs. The band gap reduction is due to the contraction of long Pd–X bond length and the increase of atomic orbital overlap. Meanwhile, the remarkable photochromic response of Cs 2 HgPdX 6 (X = Cl, Br) with pressure is presented from the observations of the red-shift optical absorption spectra, thus it shows an obvious improvement for efficient visible-light absorption. Our study ensures the possibility of the application of pressure-induced Cs 2 HgPdX 6 (X = Cl, Br) in the field of PSCs. [ABSTRACT FROM AUTHOR]

The development of microreactor technology presents an efficient solution for providing portable electricity, catering to both human space exploration needs within our solar system and supplying power to remote Earth-bound areas. The miniaturization of nuclear reactors poses immediate new challenges for materials science with respect to the capability for controlling nuclear reactions via thermalization of highly-energetic neutrons. In a microreactor, neutron moderation takes place in compact geometries, thus new moderator materials are required to exhibit high moderating power per unit of volume. This challenge is currently being addressed through the development of transition metal hydrides, known for their strong nuclear moderation capability but to date, research on their irradiation response is limited, specifically regarding phase stability, hydrogen in-lattice retention, and their dependence on irradiation temperature and dose. Herein, we present a detailed investigation on the response of yttrium dihydride (YH 2) to heavy ion irradiation. The experiments indicate that YH 2 is stable up to an irradiation dose of 2 dpa and below 800 ° C, identified herein as a critical temperature for YH 2. Our study detected the nucleation and growth of voids as a function of the irradiation temperature. They were the predominant type of radiation damage present in the microstructure of YH 2 that was distinguishable from pre-existing defects in the pristine YH 2 samples. Below the critical temperature, no phase transformation (degassing/dehydriding) nor amorphization occurred. Experimental results with concomitant density functional theory calculations allowed us to elaborate and propose new strategies to enhance the metal hydride performance in extreme environments. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Double perovskites are stable in cubic structure with Fm3m space group. • Materials are ductile and exhibit indirect band gaps of 1.12 eV, 0.77 eV, and 0.084 eV. • The absorption bands exist in the visible region and are suitable for solar energy harvesting. • ZT values suggest their capability for thermoelectric device applications. The current study effort primarily focuses on the computational investigation of the physical properties of Li 2 AuBiX 6 (X = Cl, Br, and I) double perovskites (DPs) utilizing the Density Functional Theory (DFT) framework. The structural and elastic characteristics have been evaluated to reveal phase and mechanical stability. The assessed formation energy and elasticity constants calculations validate that the examined DPs possess cubic phase, exhibit stability, and demonstrate ductility. The band structure analysis has been accomplished with a modified Becke-Johnson (mBJ) potential. The band structure simulations reveal that Li 2 AuBiCl 6 , Li 2 AuBiBr 6 , and Li 2 AuBiI 6 possess an indirect energy gap, with values of 1.12 eV, 0.77 eV, and 0.084 eV, respectively. We further examined the optical parameters in the spectrum of incoming photons from 0 to 4 eV. Considerable absorbance in the visible spectrum has been observed for Li 2 AuBiX 6 (X = Cl, Br, and I), suggesting that these DPs are compatible with photovoltaics. Finally, we have computed thermoelectric (TE) characteristics in relation to temperatures within the range of 100 to 600 K. The investigated DPs might be suitable for thermoelectric systems, as indicated by the moderate values of the figure of merit, which needs to be improved. The obtained absorption and figure of merit values surpass similar perovskites Rb 2 AuBiX 6. Hence, the current work might be advantageous for developing novel photovoltaic and TE systems. [ABSTRACT FROM AUTHOR]

Metal-doped iron silicides (β-FeSi 2) are promising thermoelectric materials for high-temperature applications. However, the addition of metal dopants usually causes the formation of secondary metallic phases, resulting in the degradation of thermopower. Here we report the stability of semiconducting β-phase (higher than 95 %) of Mn-doped β-FeSi 2 obtained at Mn concentration from 1 % to 5 %, where the samples were prepared through direct arc melting and heat treatment process. The carrier density remarkably increases with Mn content, but the mobility decreases. The electrical resistivity significantly decreases with Mn content. The Seebeck coefficient of Mn-doped samples is improved and stable at high-temperature regions because of the reduction of the bipolar effect and β-phase stability. The thermal conductivity slightly increases with Mn. As a result, the maximum thermoelectric power factor PF = 970 μWm−1K−2 and dimensionless figure of merit ZT = 0.12 at 800 K are obtained in a 3 % Mn-doped sample. The stability of β-phase and the improved carrier density are the origins of enhanced thermoelectric properties, where the Seebeck coefficient is improved, and the electrical resistivity is reduced. Our study provides insight into the importance of phase stability for enhancing thermoelectric transport in Mn-doped β-FeSi 2. [Display omitted] • We investigate phase stability and thermoelectric properties of β-Fe 1− x Mn x Si 2. • 95 % of semiconducting phase β-FeSi 2 is stabilized for Mn content up to 5 %. • The addition of Mn significantly increases the carrier density. • β-FeSi 2 stability and increased carrier density improve thermoelectric properties. [ABSTRACT FROM AUTHOR]

• Soft modes and soft phonon behaviour leads to a change in phase stability. • Pressure-induced Fe 2 NbIr produces the pre-martensite phase. • This work presents an analysis of the pressure-induced martensitic transformat. The martensitic transformation of the new all- d -metal Heusler alloy Fe 2 NbIr is investigated using first-principles. The structure undergoes softening and hardening under pressure, which corresponds to the two phases of the martensitic phase transformation, i.e. C′ softening of the austenite and C′ hardening of the pre-martensite phase, implying that the pressure may induces to produce a cubic pre-martensite phase. An exciting phenomenon is found in the tetragonal deformation of the pre-martensite phase, where the pre-martensite phase overcome the energy barrier of the jump to produce a tetragonal martensite phase with a much lower energy. It explains the presence of a pre-martensite phase in shape memory alloys, i.e., it provides a conduit for the phase change. This work presents an analysis of the anomalous softening behaviour of Fe 2 NbIr and the mechanism of the pressure-induced martensitic transformation, and provides a new idea for study of the precursor effect of martensitic phase transformation. [ABSTRACT FROM AUTHOR]

Energy efficiency demands finding new materials for applications at elevated temperatures. Refractory multicomponent alloys with a BCC/B2 microstructure promise to serve as alternatives to the current state-of-the-art, Ni-based superalloys for applications at higher temperatures. With the vast compositional space of these alloys, the first fundamental question is whether the B2 phase can form among refractory metals. In this study, we span through the periodic table to investigate the potential for creating ordered B2 intermetallics among the refractory metals, using first principles calculations, and establish the correlation between the nature of the atomic bonds and stability of the B2 structure. We use our newly developed Multi-Cell Monte Carlo method to explore the extensive compositional space of these alloys, refine the trends in ordering, and pinpoint the most promising combinations for detailed analysis. We discover that B2 phases form exclusively with the inclusion of elements from groups VII and VIII, such as Re, Ru, and Os, and we identify these phases among a total of eleven elements. Further analysis of the electronic structure and bonding characteristics of these B2 systems reveals a pseudogap in the electronic density of states at the Fermi level. This pseudogap is attributed to the hybridization of d orbitals, leading to the formation of strong covalent bonds in the most stable compounds. This finding explains why B2 formation is restricted to elements from groups IV-VIII and V-VII refractory metals. [Display omitted] [ABSTRACT FROM AUTHOR]

"Suzuki segregation" of Mo to planar defects was proposed to contribute to secondary hardening after post-deformation annealing in the MP35N alloy, a CrCoNi-based single-phase superalloy. However, a direct proof of this proposal is challenging and reported observations are controversial. Here, we prepared nanocrystalline MP35N thin films by co-deposition on a microtip array of pre-sharpened Si tips. This enabled a direct investigation of the Mo distribution in a nanoscale structure with many grain boundaries (GBs) after annealing by atom probe tomography. We observed that no Mo but Cr segregates to GBs between 360 and 460 °C. Additionally, we found that MP35N is thermally more stable than a (Mo-free) Cr-Co-Ni medium-entropy alloy under the same conditions. Factors that influence the kinetics of phase decomposition and thermal stability, including grain size, Mo addition, and the loss of Cr due to oxidation at GBs were addressed. [Display omitted] • The effect and the distribution of Mo at planar defects in the MP35N alloy remains unclear. • Thin films coated on Si-tips enables direct atomic-scale investigation. • Nanocrystalline MP35N alloy facilitates the investigation of Mo distribution. • No Mo but Cr was observed to segregate at grain boundaries. • Mo slows down the kinetics of phase decomposition and improves phase stability. [ABSTRACT FROM AUTHOR]