High-temperature Phase Research Articles

Performance investigation and optimization of latent heat exchanger with pin fins based on non-uniform deployment strategy

Latent heat storage technology is an essential way of efficiently utilizing industrial residual heat, which helps to the objective of carbon neutrality in all countries. In this work, latent heat exchangers with pin fins are numerically investigated based on non-uniform deployment strategy and then optimized according to response surface method. The influences of rotation angle, non-uniform fin pitch, non-uniform fin length and combination of phase change materials with different melting temperatures on thermal storage performance are studied. Results show that the increment of rotation angle facilitates the reduction of complete melting time, and the optimal angle accelerates the melting speed by 10.3% compared to the 0° angle. The arrangements of gradually decreasing fin pitch and gradually increasing fin length along flow direction of heat transfer fluid improve the heat storage performance, which can reduce the complete melting time by 7.3% and 22.2% respectively, compared to the uniform arrangement. The multiple phase change materials latent heat exchanger with high melting temperature phase change material placed in high temperature region and low melting temperature phase change material in low temperature region can make better utilization of heat from heat transfer fluid, which can improve the melting speed by 16.8% compared with the single phase change material latent heat exchanger. The optimized latent heat exchanger based on response surface method reduces the complete melting time by 23.4% compared to the original model. In conclusion, the heat storage performance of latent heat exchanger with pin fins effectively improved by adopting the non-uniform deployment strategy.

(Invited) Interlayer Excitons in Two-Dimensional Perovskite/Monolayer Transition Metal Dichalcogenide Heterostructures

The emergence of two-dimensional (2D) materials has intrigued a great deal of research on novel physical phenomena and various functional applications due to their particular crystal structures and reduced dimensionality. Unlike 3D materials, bulks of 2D materials can be easily thinned to atomic thickness by mechanical exfoliation and atomically thin 2D materials can be arbitrarily stacked to form vertical van der Waals (vdW) heterostructures, which could inherit the unique characteristics of the constituent layers and even exhibit new properties not possessed by them. Particularly, when type-Ⅱ vdW heterostructures are excited, the positive and the negative charges would reside in the different layers after the charge transfer but be limited within a short distance due to the strong quantum confinement effect of 2D materials, leading to strong Coulomb interaction and the formation of interlayer excitons (IXs). IXs are generally equipped with orientated dipole moment and long lifetime, making them ideal media for the future interconnects between optical transmission and electronic computation. Currently, studies on IXs are mainly focused on the vdW heterostructures formed by monolayers of transition-metal dichalcogenides (TMDs). Here, I will first talk about vdW heterostructures formed by 2D perovskites and TMDs for studying IXs. Stacking different kinds of 2D perovskites and TMDs, formation of IXs is confirmed by excitation-power-, temperature-, electric-field-dependent and time-resolved photoluminescence (PL) studies. Notably, robust IX emission can be observed regardless of the stacking sequence and geometric alignment of the constituent layers, showing great advantages over the TMD/TMD vdW heterostructures, which require special twist-angle and thermal annealing. Then, I would like to give a brief introduction on widely tuning the IX emission energy by changing the layer number of the 2D perovskite or the TMD, which shed light on the application of 2D perovskite/TMD vdW heterostructures in broad-spectrum optoelectronics. Furthermore, I would like to next talk about how the selection of organic chains in 2D perovskites influences the properties of the IXs. By using chiral 2D perovskites, the IX emission shows substantial circular polarization and the polarization direction is only related to the chirality of the molecules regardless of the excitation scheme or any other external field, which could open up new passages for controlling valley- or spin-polarization of IXs. By introducing molecules with different dielectric constants, the dielectric screening strength in the vdW heterostructure is changed and hence the binding energy of the IXs is also modified, which offers great opportunities for exploiting tunable excitonic devices and studying exciton condensation. Finally, I will also introduce IX as a non-destructive tool for probing the local phase transition at the surface of the 2D perovskite (BA)2PbI4 flakes. By spatially PL mapping of the (BA)2PbI4/WSe2 heterostructure, two different IX species can be observed to distinguish the low-temperature and the high-temperature phase respectively.

Modeling and parametric analysis of low-temperature oxidative self-heating in coal stockpiles driven by natural convection

To accurately ascertain the behavior of oxidation heating and emission of oxidation products in fully enclosed coal storage yards under the influence of natural convection, comprehensive adiabatic oxidation experiments were conducted, encompassing coal particles of multiple grain sizes. Linear regression analysis was applied to deduce the heating characteristics of coal particles within real coal stockpiles from the experimental data. Subsequently, numerical simulations were executed, leveraging the acquired oxidation parameters specific to the stored coal. These simulations unveiled that natural convection triggers the formation of spiral airflow on both sides of the stockpile, with the strength of this airflow increasing in tandem with rising temperatures. An inflection point becomes evident during the impact assessment of porosity on maximum temperature variation, whereby its augmentation improves the heating rate when below the critical threshold, but conversely diminishes it when surpassing that threshold. Furthermore, coal particles smaller than 3 mm effectively isolate oxygen. As the degree of metamorphism increases, the rate of temperature rise decreases, and the high-temperature region penetrates deeper into the coal stockpile. The genetic algorithm-optimized random forest algorithm emerges as a highly effective tool for the precise prediction of the efficient storage duration of the coal stockpile. Keeping porosity below 0.25 proves effective in oxygen isolation. Lower heights and steeper slope angles exhibit the capacity to decelerate oxidation during high-temperature phases, thereby minimizing the loss of coal calorific value and greenhouse gas emissions. This study is paramount for the achievement of secure, efficient, and environmentally friendly coal storage practices in the context of natural convection.

Synthesis and tunable photoluminescence properties of Er3+/Eu3+ co-doped Na5La(MoO4)4 phosphors

The tunable emission characteristics of Er3+ doped and Er3+/Eu3+ co-doped Na5La(MoO4)4 phosphors prepared via high-temperature solid phase method were investigated. The microstructure of the modified phosphor was studied by X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy, and its luminescence properties were analyzed by photoluminescence excitation and photoluminescence spectra. The energy transfer mechanism of Er3+ ions to Eu3+ ions was investigated by changing the concentration of Eu3+ ions to induce the spectral changes, and the photoluminescence decay lifetime was measured to validate the findings. Notably, under excitation at 380 nm, the co-doped phosphors exhibited tunable emission ranging from green to orange-red. Furthermore, Na5La(MoO4)4:0.04Er3+/0.04Eu3+ phosphor, when combined with a 380 nm chip, achieved desired warm white light emission. These promising results underscore the potential application of Na5La(MoO4)4:0.04Er3+/0.04Eu3+ phosphor in solid-state lighting.

Composite phase change materials with thermal-flexible and efficient photothermal conversion properties for solar thermal management

Composite phase change material (CPCM) with the advantages of high enthalpy and constant temperature phase change, has been widely used in many fields, such as photovoltaic thermal system, building envelope structure and so on. However, conventional CPCM is often rigid, poor light absorption and low thermal conductivity, which limits the application of solar energy utilization. In this paper, a novel Paraffin wax/Thermoplastic elastomer/Carbon nanotube(PA/SEBS/CNT) with shape stability, thermos-flexibility and high photothermal conversion efficiency was prepared, PA as the phase change material, SEBS as the flexible material and CNT as the light-absorbing material. The results show that the addition of CNT increases the absorbance of PA/SEBS from 0.3 to 1.0, and the photothermal conversion efficiency of PA/SEBS/CNT-10 % is as high as 96.17 %. In addition, the CPCM also has a high enthalpy value of 180 J/g, and a high thermal conductivity of >0.3403 W/(m·K), and also exhibits shape-driven memory. At the same time, outdoor photothermal experiments show that PA/SEBS/CNT has excellent photothermal conversion performance under real sunlight, and the highest temperature can reach 99.51 °C. The new CPCM developed has a broad application prospect in solar thermal systems.

Three-dimensional observation of porous materials prepared from iron tailings and their pore wall site adsorption function

Porous materials are widely used to treat phosphorus-containing wastewater due to their structural characteristics and loading site functionality. The use of iron tailings as a raw material during the preparation of these materials can effectively reduce production costs. In this study, a porous material was prepared according to a one-step method using solid waste iron tailings. High-temperature phase transition technology was used to construct crystallographic sites on the pore walls of the material to improve the phosphorus removal efficiency. The pore structure, pore wall characteristics, and internal crystal growth in the three-dimensional space of the material were characterized using X-ray microscopy (micro-CT) scanning, and the voxel data for the internal structural were analyzed. The results showed that the material had a clear internal skeletal structure, a uniform distribution of internal pores, and crystal phases in three-dimensional space. The pore ratio in the three-axis direction was greater than 50%, with connected pores accounting for more than 95% of the pores. The wall thickness distribution was uniform, but the pore size distribution and ellipticity ratio varied significantly due to the different pore structures and quantities. A connected structure was formed when the thin walls of adjacent pores ruptured, and there were magnesioferrite and hematite crystal sites with fractal growth in the pore wall framework. The adsorption capacity of the porous material for phosphorus pollutants was investigated using photometry, and the highest removal rate was found to be 68.13%. This analysis suggests that the presence of rough pore walls, a high specific surface area, and crystal sites within the pore walls enhance the adsorption performance of the material. Further research along this line could explore the potential of developing new low-cost materials for pollution treatment.

Phase separation of a magnetic fluid: Asymptotic states and nonequilibrium kinetics.

We study self-assembly in a colloidal suspension of magnetic particles by performing comprehensive molecular dynamics simulations of the Stockmayer (SM) model, which comprises spherical particles decorated by a magnetic moment. The SM potential incorporates dipole-dipole interactions along with the usual Lennard-Jones interaction and exhibits a gas-liquid phase coexistence observed experimentally in magnetic fluids. When this system is quenched from the high-temperature homogeneous phase to the coexistence region, the nonequilibrium evolution to the condensed phase proceeds with the development of spatial as well as magnetic order. We observe density-dependent coarsening mechanisms-a diffusive growth law ℓ(t)∼t^{1/3} in the nucleation regime and hydrodynamics-driven inertial growth law ℓ(t)∼t^{2/3} in the spinodal regimes. [ℓ(t) is the average size of the condensate at time t after the quench.] While the spatial growth is governed by the expected conserved order parameter dynamics, the growth of magnetic order in the spinodal regime exhibits unexpected nonconserved dynamics. The asymptotic morphologies have density-dependent shapes which typically include the isotropic sphere and spherical bubble morphologies in the nucleation region, and the anisotropic cylinder, planar slab, cylindrical bubble morphologies in the spinodal region. The structures are robust and nonvolatile, and exhibit characteristic magnetic properties. For example, the oppositely magnetized hemispheres in the spherical morphology impart the characteristics of a Janus particle to it. The observed structures have versatile applications in catalysis, drug delivery systems, memory devices, and magnetic photonic crystals, to name a few.

New Minerals from Inclusions in Corundum Xenocrysts from Mt. Carmel, Israel: Magnéliite, Ziroite, Sassite, Mizraite-(Ce) and Yeite.

Our nanomineralogical investigation of melt inclusions in corundum xenocrysts from the Mt. Carmel area, Israel has revealed seven IMA-approved new minerals since 2021. We report here four new oxide minerals and one new alloy mineral. Magnéliite (Ti3+2Ti4+2O7; IMA 2021-111) occurs as subhedral crystals, ~4 μm in size, with alabandite, zirconolite, Ti,Al,Zr-oxide, and hibonite in corundum Grain 767-1. Magnéliite has an empirical formula (Ti3+1.66Al0.13Ti4+0.15Mg0.10Ca0.01Sc0.01)Σ2.06 (Ti4+1.93Zr0.08)Σ2.01O7 and the triclinic P1¯ Ti4O7-type structure with the cell parameters: a = 5.60(1) Å, b = 7.13(1) Å, c = 12.47(1) Å, α = 95.1(1)°, β = 95.2(1)°, γ = 108.7(1)°, V = 466(2) Å3, Z = 4. Ziroite (ZrO2; IMA 2022-013) occurs as irregular crystals, ~1-4 μm in size, with baddeleyite, hibonite, and Ti,Al,Zr-oxide in corundum Grain 479-1a. Ziroite has an empirical formula (Zr0.72Ti4+0.26Mg0.02Al0.02Hf0.01)Σ1.03O2 and the tetragonal P42/nmc zirconia(HT)-type structure with the cell parameters: a = 3.60(1) Å, c = 5.18(1) Å, V = 67.1(3) Å3, Z = 2. Sassite (Ti3+2Ti4+O5; IMA 2022-014) occurs as subhedral-euhedral crystals, ~4-16 μm in size, with Ti,Al,Zr-oxide, mullite, osbornite, baddeleyite, alabandite, and glass in corundum Grain 1125C1. Sassite has an empirical formula (Ti3+1.35Al0.49Ti4+0.08Mg0.07)Σ1.99(Ti4+0.93Zr0.06Si0.01)Σ1.00O5 and the orthorhombic Cmcm pseudobrookite-type structure with the cell parameters: a = 3.80(1) Å, b = 9.85(1) Å, c = 9.99(1) Å, V = 374(1) Å3, Z = 4. Mizraite-(Ce) (Ce(Al11Mg)O19; IMA 2022-027) occurs as euhedral crystals, <1-14 μm in size, with Ce-silicate, Ti-sulfide, Ti,Al,Zr-oxide, ziroite, and thorianite in corundum Grain 198-8. Mizraite-(Ce) has an empirical formula (Ce0.76Ca0.10La0.07Nd0.01)Σ0.94(Al10.43Mg0.84Ti3+0.60Si0.09Zr0.04)Σ12.00O19 and the hexagonal P63/mmc magnetoplumbite-type structure with the cell parameters: a = 5.61(1) Å, c = 22.29(1) Å, V = 608(2) Å3, Z = 2. Yeite (TiSi; IMA 2022-079) occurs as irregular-subhedral crystals, 1.2-3.5 μm in size, along with wenjiite (Ti5Si3) and zhiqinite (TiSi2) in Ti-Si alloy inclusions in corundum Grain 198c. Yeite has an empirical formula (Ti0.995Mn0.003V0.001Cr0.001)(Si0.996P0.004) and the orthorhombic Pnma FeB-type structure with the cell parameters: a = 6.55(1) Å, b = 3.64(1) Å, c = 4.99(1) Å, V = 119.0(4) Å3, Z = 4. The five minerals are high-temperature oxide or alloy phases, formed in melt pockets in corundum xenocrysts derived from the upper mantle beneath Mt. Carmel.

High-temperature phase stability of Y2O3 and SiO2 co-doped ZrO2 powder

High-temperature phase stability of Y2O3 and SiO2 co-doped ZrO2 powder

Effect of the high temperature phase transition on the tribological behavior of atmospheric plasma sprayed AlCoCrFeNi-Bi2O3 coating

Owing to the brittleness of the body-centered cubic (BCC) structure and lack of self-lubrication, plasma-sprayed AlCoCrFeNi high-entropy alloy (HEA) coatings undergo severe abrasive wear, resulting in high friction and wear. In this study, the substrate surface temperature was increased (800 °C) to promote the phase transition from BCC to ductile FCC during spraying. As a result, the prepared AlCoCrFeNi HEA coating contained BCC and FCC phases, exhibiting a higher adhesive strength, lower friction coefficient and wear rate at room temperature (RT)–800 °C. In addition, the elevated substrate surface temperature enabled the transition of the low-temperature stable phase α-Bi2O3 to the high-temperature stable phase δ-Bi2O3. δ-Bi2O3 promoted the formation of low shear strength planes owing to its low interaction parameter and defect-fluorite structure with 25 % anionic vacancies similar to that of the Magnéli phase, which facilitated friction reduction in a wide temperature range. This study confirms that δ-Bi2O3 can effectively improve the anti-wear performance of the AlCoCrFeNi-Bi2O3 coating at RT, 200, 600 and 800 °C. However, at 400 °C, the low melting point and soft nature of the Bi2O3 weakened the mechanical strength of the coating and inhibited the construction of a solid and tough tribo-layer, resulting in a relatively high wear rate for AlCoCrFeNi-Bi2O3 coating. At 800 °C specifically, under the thermal coupling effect, δ-Bi2O3 migrated and aggregated on the worn surface with the oxidation product Al2O3 of the AlCoCrFeNi HEA matrix, and jointly promoted the formation of a compact and smooth tribo-layer with lubricating capability, which not only effectively reduced friction but also inhibited wear.

Novel lithium ion-sieve spinning fiber composite of PVDF-HMO for lithium recovery from geothermal water

With the increasing application of the industrialization of lithium and its derivatives, there has been a surge of interest in recovering this resource from liquid sources. However, synthesizing adsorbents with industrial significance is still a significant challenge. Herein, the precursor Li1.6Mn1.6O4 of H1.6Mn1.6O4 powder absorbent with the highest theoretical adsorption capacity and the lowest Mn dissolution loss rate was first synthesized by hydrothermal or high-temperature solid phase method. The commercialized wet spinning apparatus, which has convenient operation and a simple process, was used to prepare PVDF/HMO spinning fiber to recover lithium resources from geothermal water. It has a large specific surface area of 31.45 m2 g−1 and a pore size of 9.04 nm, and the adsorption capacity was 14.95 mg g−1, with the distribution coefficient of Li+ being 1404.96 mL g−1. Furthermore, the equilibrium was reached within just 2 h at pH 12, and the elution time was just 1 h. Even after the fifth cycle, the adsorption capacity remained high at 14.21 mg g−1. These characteristics indicate that the new material has excellent application potential for lithium recovery from geothermal water.

Experimental investigation of the phase equilibria of CaO–Al2O3–TiO2 slag system at 1500 °C with p(O2)=10−3 atm

The phase diagram CaO–Al2O3–TiO2 slag system is of great importance for metallurgical processes, such as the utilization of Ti-bearing slag and optimization in Al–Ti alloy steel smelting process. In the present work, the high-temperature phase equilibrium experimental technique was adopted, and the type and composition of equilibrium phases were identified by Electron Probe Micro Analysis (EMPA) and X-ray diffraction (XRD). The iso-thermal section of CaO–Al2O3–TiO2 system at 1500 °C in Ar atmosphere was constructed for the first time. There are 10 three-phase fields (Liquid + CaO+3CaO·2TiO2, Liquid+3CaO·2TiO2+4CaO·3TiO2, Liquid + CaO·Al2O3+4CaO·3TiO2, CaO·TiO2+CaO·Al2O3+CaO·2Al2O3, CaO·2Al2O3+CaO·TiO2+CaO·6Al2O3, Liquid + Al2O3+Al2O3·TiO2, Liquid + CaO·TiO2+CaO·6Al2O3, Liquid + CaO·6Al2O3+Al2O3, Liquid + TiO2+Al2O3·TiO2, 4CaO·3TiO2+CaO·TiO2+CaO·Al2O3), 13 two-phase fields (Liquid + CaO, CaO+3CaO·2TiO2, Liquid + Al2O3, Liquid+3CaO·2TiO2, Liquid+4CaO·3TiO2, Liquid + TiO2, Liquid + CaO·TiO2, Liquid + Al2O3·TiO2, CaO·TiO2+CaO·2Al2O3, Liquid + CaO·6Al2O3, Liquid + CaO·Al2O3, 4CaO·3TiO2+CaO·TiO2, 4CaO·3TiO2+3CaO·2TiO2), 3 single-phase solid solution fields (4CaO·3TiO2(ss), 3CaO·2TiO2(ss), TiO2(ss)), and 2 independent single liquid phase fields. Besides, taking the Ti-bearing slag system as an example, the influence of oxygen potential on the activity of (TiOx) was discussed; furthermore, the reasonability of the valence state approximation of element Ti was farther evaluated.

In situ XRD and Raman study of the phase transition in V2O5 xerogels

Vanadium oxide xerogel samples (V2O5∙nH2O) were successfully synthesized using a liquid phase reaction between α-V2O5 and H2O2, as well as through the interaction of amorphous V2O5 films with atmospheric water. The samples were systematically investigated by X-ray diffraction and Raman spectroscopy. Temperature-dependent studies confirmed the existence of two distinct phases. Depending on synthesis and processing protocols, either phase can be stabilized in ambient conditions. It was proved that the formation of a high-temperature phase from amorphous vanadium oxide previously led to some misinterpretations associated with the high-pressure δ-V2O5 polymorph. While current structural models of vanadium oxide xerogel provide some insights, our findings underscore the exciting potential for refining and expanding these models in future research endeavors.

Deep machine learning, molecular dynamics and experimental studies of liquid Al-Cu-Co alloys

Understanding the correlations between liquids and solids opens the way to predict by investigating liquids, the domains of thermodynamic parameters favoring intriguing solid phases. This approach is especially urgent for the design of multicomponent systems working with a continuous array of component concentrations (most modern materials of practical interest are multicomponent). Here we address an Al-Cu-Co system experimentally and theoretically using molecular dynamics and machine learning interaction potentials on top of the first-principles training data in a composition range of 15 at.% Co and 10 to 30 at.% Cu, and 25 at.% Cu and 2.5 to 20 at.% Co. The selected concentration sections contain different high-temperature solid phases. Differential thermal analysis has uncovered the features of solid phase formation at slow cooling and normal pressure. The boundaries of different phase regions correlate with the extrema on the one hand in undercooling and on the other hand in viscosity in the concentration area. The theoretical calculations have uncovered the correlations between the extrema and the readjustment of the chemical short-range order in the liquid, with the nonmonotonicity of the concentration dependence of the glass transition temperature and the specific volume.

Tuning the growth of intermetallic compounds at Sn-0.7Cu solder/Cu substrate interface by adding small amounts of indium

The void defect in intermetallic compounds (IMCs) layer at the joints caused by inhomogeneous atomic diffusion is one of the most important factors limiting the further development of Sn-based solders. In this work, the thermodynamic stability of IMCs (high-temperature η-Cu6Sn5 and o-Cu3Sn phases) was improved by adding small amounts of indium (In), and the IMCs layers with moderate thickness, low defect concentrations and stable interface bonding were successfully obtained. The formation order of compounds and the interfacial orientation relationships in IMCs layers, the atomic diffusion mechanism, and the growth tuning mechanism of In on η-Cu6Sn5 and Cu3Sn, after In adding, were discussed comprehensively by combining calculations and experiments. It is the first time that the classic heterogeneous nucleation theory and CALPHAD data were used to obtain the critical nucleus radius of η-Cu6Sn5 and Cu3Sn, and to explain in detail the main factors affecting the formation order and location of IMCs at joints during the welding process. A novel and systematic growth model about IMCs layers in the case of doping with alloying elements was proposed. The growth tuning mechanism of In doping on η-Cu6Sn5 and Cu3Sn was further clarified based on the proposed model using first-principles calculations. The growth model used in this study can provide insights into the development and design of multielement Sn-based solders.

Combined passive enhancement techniques improve the thermal performance of latent heat storage system: A design anomaly?

Poor heat transfer rate due to low thermal conductivity of phase change material limits the wide application of latent heat storage (LHS) systems. Thermal performance enhancement techniques can be potential methods to address this major limitation of LHS systems. In this context, the present numerical study examines the individual and cumulative impact of two passive heat transfer enhancement techniques (the orientation of the domain and position of the heat transfer fluid (HTF) tube) on the thermal performance of the latent heat storage (LHS) system consisting of high-temperature (HT) phase change medium (PCM). The individual effect of orientation decreases the charging duration of θ = 0° (horizontal configuration) by 10.5 %, 15 %, and 19.04 % than θ = 30°, θ = 60° and θ = 90° (vertical configuration), respectively. However, the discharging duration remains unchanged for all inclinations (11.5–12 h). The individual effect of eccentricity decreases the charging duration of horizontal (θ = 0⁰, ey = −5 mm,-10 mm,-20 mm) system by 6.25 %,12.8 %, and 18.75 % than concentric horizontal (θ = 0°, ex = ey = 0) system. Moreover, the combined effect of orientation and eccentricity (θ = 0⁰,ey = −5 mm,-10 mm,-20 mm) reduces charging duration by 28.75 %, 33.33 %, and 38.1 % than vertical concentric domain (θ = 90°, ex = ey = 0), respectively. However, eccentricity in vertically upward and downward directions increases the discharging duration compared to the concentric domain. Hence, the combined effect results in a design anomaly for HT-LHS system. The charging and discharging performances are observed to be predominantly sensitive to the Rayleigh number than the Reynolds number.

Ni2+-doped MgTa2O6 phosphors capable of near-infrared II and III emission under blue-light excitation

Presently, Ni2+-activated near-infrared (NIR) phosphors still have disadvantages such as relatively short emission wavelength and narrow half-peak width, mismatched excitation wavelength to that of commercially available high-efficiency blue chips. Here, Ni2+-doped tetragonal MgTa2O6 NIR phosphor was successfully prepared by high-temperature solid phase method. The matrix material provided an octahedral lattice for Ni2+ to replace Ta5+ in the [TaO6] octahedron of the crystal lattice. Under the excitation of 470 nm blue light, Ni2+ was excited through 3T2(F)→3A2(F) spin-allowed transition and emitted an ultra-broadband NIR light that was 1300–2000 nm in wavelength, peaked ∼ 1620 nm, covered the NIR-II and NIR-III regions, had a full width at half maximum reached 297 nm, and a PLQY of 25.62 %. The unique ultra-broadband and long wavelength NIR emission by this phosphor was derived from Ni2+ which is situated in a weak crystal field environment due to space asymmetric distortion caused by a high charge polarization surrounding the center of the [TaO6] octahedron in a MgTa2O6 matrix. A NIR pc-LED was constructed using Ni2+-doped near-infrared phosphors packaged with a commercial high-efficiency blue LED chip (@ 470 nm), and its application prospect was demonstrated by NIR night vision monitoring and nondestructive imaging of venous in human fingers.

Polar topological superdomain arrays in PMN-PT crystals engineered via a voltage-free method

Domain engineering is an active field of research that aims to enhance the functional properties of ferroelectric materials for various applications. This work presents a voltage-free method for fabricating topological superdomain arrays in 0.72Pb(Mg1/3Nb2/3)O3-0.28PbTiO3 (PMN-28PT) crystals. During the cooling process from high-temperature paraelectric phase to room temperature ferroelectric phase, the out-of-plane polarization of PMN-28PT crystals in contact with aluminum can be fully regulated downward, attributed to the difference in the work function of aluminum and PMN-28PT. In conjunction further with photolithography and ultraviolet light illumination, it is easy to obtain periodic strip domain structures with alternating up and down polarization. Moreover, this method can also control in-plane polarization, resulting in a large-scale central divergent/convergent topological superdomain array. These findings provide insights into ferroelectric domain engineering and have implications for the development of electromechanical, piezoelectronic, and photonic devices.

High-temperature phase stability and phase transformations of Niobium-Chromium Laves phase: Experimental and first-principles calculation studies

The high-temperature phase stability of the NbCr2 Laves phase has not yet been established beyond disagreement. The well accepted C14 phase field has been eliminated from the Nb-Cr phase diagram in a recent study that claimed that the NbCr2 alloy shows the C15 structure up to melting. The present study was conducted to address these ambiguities. The experimental investigations show the presence of C14, C15, and C36 structures in the as-cast alloy. Differential scanning calorimetry studies of the as-cast alloy show the transformation of the eutectic mixture of bcc + NbCr2 to single-phase NbCr2 at 1338 K. An in-situ X-ray diffraction (XRD) study of as-cast alloy shows a phase transformation of C36 → C14 below 1273 K. Density functional theory (DFT) calculations confirm two phase transformations: (a) a metastable transformation of C36 → C14 at 783 K and (b) an equilibrium transformation of C15 → C14 at 1971 K, which was validated by high temperature DTA and TEM studies. Further, extended DFT calculations on supercells with four compositions of NbCr1.9, NbCr2, NbCr2.1, and NbCr2.2 also corroborated the presence of the C14 phase, and consequently, the Nb-Cr phase diagram is modified. This finding resolves the controversy regarding the existence of an equilibrium C14 phase field before melting.

A new mineral cuprodobrovolskyite Na4Cu(SO4)3 from the Tolbachik volcano (Kamchatka, Russia) and relationships in the family of natural anhydrous Na–Cu sulfates

AbstractA new mineral cuprodobrovolskyite, ideally Na4Cu(SO4)3, was found in sublimates of the Arsenatnaya fumarole at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. It is associated with petrovite, saranchinaite, euchlorine, krasheninnikovite, langbeinite, calciolangbeinite, anhydrite, sanidine, tenorite and hematite. Cuprodobrovolskyite occurs as coarse hexagonal tabular or equant, typically skeletal crystals up to 1 mm and their clusters or crusts up to 1.5 cm × 2.5 cm in area. The mineral is transparent, light blue or greenish-bluish to almost colourless with vitreous lustre. Cuprodobrovolskyite is optically uniaxial (+) with ω = 1.509(3) and ε = 1.528(3). The empirical formula calculated on the basis of 12 O apfu is (Na3.64K0.09Pb0.03)Σ3.76(Cu0.51Ca0.22Mg0.16Zn0.07Al0.01Mn0.01)Σ0.98S3.04O12. The unit-cell parameters of cuprodobrovolskyite calculated from the powder X-ray diffraction data are: a = 15.702(2), c = 22.017(5) Å, V = 4701.0(2) Å3, space group R3 and Z = 18. The crystal structure was studied using the Rietveld method, Rp = 0.0246, Rwp = 0.0325, R1 = 0.0521 and wR2 = 0.0770. Cuprodobrovolskyite is an isostructural analogue of dobrovolskyite Na4Ca(SO4)3 with Cu prevailing over Ca. One of the main features of cuprodobrovolskyite is Cu2+ in 7-fold coordination. On the basis of relationships with saranchinaite Na2Cu(SO4)2 and petrovite Na12Cu2(SO4)8 in the Arsenatnaya fumarole and the results of heating experiments, cuprodobrovolskyite is considered as the highest-temperature phase among anhydrous Na–Cu sulfate minerals.