Flux Method Research Articles

Luminescence properties of zircon single crystals doped with europium and vanadium

Crystals of ZrSiO4; ZrSiO4: Eu3+; and ZrSiO4: (Eu3++V) have been grown by the flux method. Their structural and luminescent properties have been studied demonstrating heterogeneity in cathodoluminescence (CL) for all samples. Such a heterogeneity of CL in ZrSiO4; ZrSiO4: Eu3+ is related to irregular distribution of point defects associated presumably with oxygen vacancies. Uneven distribution of vacancies as assumed led to the formation of different sites for europium ion. Moreover, in different areas of the crystal matrix the number of sites and their types vary. Activation of zircon with europium and vanadium simultaneously caused an increase of europium incorporation in comparison with zircon doped with europium only. It was found that heterogeneity of CL properties of ZrSiO4: (Eu3++V) is related to the irregular distribution of vanadium in crystal matrix. Polarization studies of CL spectra suggest that there are at least four europium sites in ZrSiO4: (Eu3++V).

Magnetic properties of the RNiIn4 (R = Ce, Pr, Nd) series of intermetallic compounds grown by the metallic flux method

This work focuses on the synthesis, structural and magnetic characterization, and the effects of the Crystal Electric Field (CEF) of RNiIn4 (R = Ce, Pr, Nd) compounds. By using the metal flux technique, high-quality single crystals were obtained and analyzed X-ray diffraction and confirmed the formation of a single phase for all compounds and revealed their crystallization in a orthorhombic structure. Magnetic susceptibility measurements revealed antiferromagnetic in order ing temperatures (TN) at 4.02 K, 2.37 K and 4.06 for Ce, Pr, and Nd, respectively. Specific heat data corroborated these findings. The results indicate the easy axis of magnetization lies in the ab-plane for Ce and Nd, and along the c-axis for Pr.

Boiling critical characteristics in narrow rectangular channel under local heat flux concentration conditions

For the establishment of predicting method of local concentrated critical heat flux (CHF) in narrow rectangular channels, and also technical support for the preparation of long-life and high-performance dispersive plate fuel, this work simulates Dry-out type CHF under local concentration of heat flux condition by using Eulerian multiphase model and Enhanced near-wall treatment. The distribution of near-wall temperature and void fraction under different heat flux was calculated by Computational Fluid Dynamics (CFD) method. Dry-out CHF was predicted based on highly and quickly wall temperature rise. The influence of system pressure, mass flow rate and inlet subcooling degree were discussed on Dry-out CHF. Compared with uniform heating, the predicted average heat flux on CHF is lower under local heat flux concentration, and location of CHF is related to the position of heat flux concentration area. This work’s research method in Ansys Fluent could be applied to forecast Dry-out CHF in narrow rectangular channel under local concentration of heat flux condition.

Single crystal zircon doped with europium and vanadium simultaneously in order to support intensive luminescence under UV-light

Crystals of zircon, ZrSiO4, doped with Eu and V simultaneously have been grown for the first time by the flux method. The use of both (Eu + V) has supported higher Eu3+ incorporation into zircon lattice and respective increase of luminescence intensity under UV-light (220 and 365 nm) in comparison with zircon doped with Eu3+ only. The irregular distribution of vanadium and appearance of blue color in some zones of crystal matrix have been observed and studied using optical and scanning electron microscopy, electron probe microanalysis, cathodoluminescence imaging and spectroscopy. Further research is proposed on study of valence states of vanadium in zircon lattice and possible improvement of synthesis conditions in order to avoid formation of blue color suppressing the luminescence.

3R-CuCrO2 delafosite: crystal growth, crystal structure, dielectric and DC conductivity properties

Single-crystal samples of the 3R-CuCrO2 phase (R3m, a = 2.9613(2) Å, c = 17.098(2) Å) with a delafossite structure were grown by the flux method. Structural parameters were refined by X-ray structural analysis. The elemental composition of the grown crystals was confirmed by Auger electron spectroscopy. A threshold electric field switching effect from a high-resistance to a low-resistance state was discovered. The effect is characterized by a jump in electrical resistance (up to 5 orders of magnitude at E = 4.7 kV/cm, T = 120 K) and S-shaped current–voltage characteristics with a region of negative differential resistance. The temperature dependences of dielectric permittivity and dielectric loss tangent exhibit a Debye-type relaxation process with an activation energy of 0.51(3) eV. The observed features of dc conductivity, current–voltage characteristics, and dielectric properties interpreted on the basis of the existence of charge carriers in a small polaron state and the destruction of this state by the electric field.

The Role of Growth Conditions in Modulating Nitrogen Diffusion During Gallium Nitride Crystal Growth by Sodium Flux Method

The Role of Growth Conditions in Modulating Nitrogen Diffusion During Gallium Nitride Crystal Growth by Sodium Flux Method

Quantitative Defect Analysis in CVD‐Grown Monolayer MoS2 via In‐Plane Raman Vibration

ABSTRACTThe synthesis of two‐dimensional transition metal dichalcogenide (2D‐TMD) materials gives rise to inherent defects, specifically chalcogen vacancies, due to thermodynamic equilibrium. Techniques such as chemical vapor deposition (CVD), metal‐organic chemical vapor deposition (MOCVD), atomic layer deposition (ALD), flux growth method, and mechanical exfoliation produce large‐scale, uniform 2D TMD films, either in bulk or monolayers. However, defects on the film surface impact its quality, and it is necessary to measure defect density. The phonon confinement model indicates that the first‐order Raman band frequency shift depends on defect density. Monolayer Molybdenum disulfide (MoS2) exhibits three phonon dispersions at the Brillouin zone edge (M point): out‐of‐plane optical phonon vibration (ZO), in‐plane longitudinal optical phonon vibration (LO), and in‐plane transverse optical phonon vibration (TO). The LO and ZO modes overlap with Raman in‐plane vibration (𝐸12g) and Raman out‐of‐plane vibration (𝐴1g), respectively, causing peak broadening. In the presence of defects, the Raman 𝐸12g vibration energy decreases due to a reduced restoring force constant. The Raman 𝐴1g vibration trend is random, influenced by both restoring force constant and mass. The study introduces a quantitative defect measurement technique for CVD‐grown monolayer MoS2 using Raman 𝐸12g mode, employing sequential data processing algorithms to reveal defect density on the film surface.

Low-temperature flux synthesis of potassium hexatitanate whiskers: Growth mechanism and applications in high-temperature infrared thermal insulation

Potassium hexatitanate whiskers (PHWs, K2Ti6O13)are a promising functional material with high thermal insulation capacity. In this study, PHWs were successfully synthesized using the flux method at temperatures ranging from 725 °C to 1100 °C. The crystal growth mechanism of PHWs in the KCl flux follows a series-parallel pattern. The synthesized PHWs have a near-infrared reflectivity (NIR) exceeding 95%, and the cause of high reflectivity was theoretically analyzed based on the Kubelka-Munk equation. The high temperature stability of near-infrared reflectivity and the thermal stability of the PHWs were further assessed using TG-DSC, XRD, SEM, and UV–VIS-NIR analysis. It was found that PHWs prepared at 800 °C begin to decompose into TiO2 at approximately 1375 °C. Nevertheless, the near-infrared reflectivity remains stable even after heat treatment. Additionally, PHWs were prepared as a composite thermal insulating coating, showing thermal conductivity between 0.177 and 0.569 W/(m K) across the temperature range of 200 °C to 900 °C. The temperature difference between the hot and cold surfaces of the composite coating was significantly greater compared to the control groups at various temperatures, with a p-value of less than 0.01 in the paired t-test. This result demonstrates the great application potential of PHWs as a high-temperature near-infrared thermal insulation material.

Reconfigurable dual-mode meta-waveguide

With the rapid growth of information flux, integrating more channels in limited spaces has been a critical requirement for highly-integrated long-range parallel transmissions. Although meta-waveguides, such as spoof surface plasmon polariton (SSPP) waveguides, can suppress crosstalk between adjacent channels, it is still urgent to seek new methods to further increase the number of channels without occupying additional space. Here, we propose a reconfigurable dual-mode meta-waveguide (RDMMW) by integrating diodes into meta-units, which supports two independent channels using two orthogonal modes. The RDMMW can be switched among dual-mode, even-mode, odd-mode and cutoff states by controlling the diodes, which provides more freedom to manipulate the channel features. The RDMMW possess two outstanding merits in highly-integrated long-range parallel transmissions, including lower coupling between two channels than conventional single-mode waveguides and constant mode coupling in longer waveguides. Thus the proposed RDMMW has advantages of multi-mode, reconfiguration, low coupling and high integration density, providing a new avenue to realize highly-integrated multi-functional systems.

Efficient photocatalytic degradation of methylene blue via synergistic dual co-catalyst on SrTiO3@Al under visible light: Experimental and DFT study

BackgroundPhotocatalytic oxidation is a green method for water purification. However, the operation of traditional photocatalysts depends on exposure to UV radiation, which only forms a small portion of the spectrum comprising sunlight. The expansion of photocatalyst absorption to the visible range of light could greatly improve the efficiency and economic viability of the process. MethodsThe photocatalyst was prepared by first synthesising SrTiO3 nanoparticles by chemical precipitation followed by calcination. Then, SrTiO3 was doped with aluminium using a flux method with Al2O3 and SrCl2 at 1150 °C. Finally, the dual co-catalysts, Rh/Cr2O3 and CoOOH, were photodeposited onto SrTiO3@Al via sequential irradiation. Significant findingsThe Rh/Cr2O3/SrTiO3@Al/CoOOH nanocomposite degraded 87% of methylene blue (MB) (10 mg/L) under visible light in 1 h, a 3.3-fold improvement over pure SrTiO3 and 2.1-fold over a similar commercial composite. This enhancement is due to efficient charge separation resulting from Al doping and improved carrier transport as a result of the anisotropic deposition of the co-catalysts. Optimisation showed that 20 mg of photocatalyst in 50 mL of MB solution (5 mg/L) degraded 100% thereof within 45 min. DFT calculations showed uneven electron distribution in SrTiO3′s conduction band and structural changes with Al doping, further enhancing photocatalytic activity.

Synthesis of europium-based crystals containing As or P by a flux method: Attempts to grow EuAgP single crystals

Europium-based materials are highly attractive due to their diverse range of physical properties. In these studies, we aimed to synthesize single crystals of the potentially topological semimetallic compound EuAgP, which up to this day has only been obtained in polycrystalline form. The flux method was employed for the syntheses, using fluxes such as: Bi, Sn, Pb, and In, in their various ratios. The purpose of using Bi flux was to try synthesizing an analog of EuAgAs single crystals, by fully substituting arsenic with phosphorus. The obtained crystals were characterized by x-ray diffraction and scanning electron microscopy. Despite many unsuccessful attempts to synthesize EuAgP single crystals, the study provides valuable insights into how different fluxes and their ratios influence the final synthesis product. It also underscores the complexity of designing analogs between arsenides and phosphides.

In-situ measurement of thermal transmittance of building walls: Evaluation of stored heat flux in heavy-weight walls during the cooling season

The conventional heat flow meter (HFM) method is used to measure the thermal performance of building walls. Typically, this method is applicable for measurements on lightweight walls and when the difference between the indoor and outdoor temperatures exceeds 10 °C. However, modern buildings are constructed using highly insulated high-performance heavy-weight walls. Therefore, an in-situ measurement method is required to overcome the limited measurement environment of the conventional HFM method. In this study, a novel stored heat flux (SHF) method is proposed to overcome the limitations of the existing HFM method. This method estimates the stored heat flux in the wall using the thermal energy-conservation equation of the enclosed system and uses a decrement factor and time lag to calculate the thermal transmittance (U-value). The proposed method can be applied to heavy-weight walls in the cooling season when the difference between the indoor and outdoor temperatures is less than 10 °C. Furthermore, the design U-value can be estimated with higher accuracy than that observed in the conventional HFM method. The results of the relative error analysis for the U-values show that the conventional HFM method was approximately 68 % of the design U-value, while the proposed SHF method was approximately 15 %.

Insight into γ-Irradiation-Induced Structure Evolution of Uranium(IV) Germanates as Crystalline Nuclear Waste Forms.

New kinds of crystalline waste forms with improved structural stability are desirable for actinide immobilization. In this work, using a molten salt method, two uranium(IV) germanate compounds, namely, K2UGe3O9 (1) and K2UGe2O7 (2), were synthesized, whose compositions consisted of trimeric and dimeric units of germanate, as well as tetravalent uranium, as proved by bond valence calculation and X-ray absorption spectra. Radiation stability assessment is further performed by γ-irradiation to assess the potential of as-synthesized uranium germanate compounds as nuclear waste forms. Powder X-ray diffraction and single-crystal diffraction analyses reveal that 1 remains stable within 1 MGy dosage and undergoes a significant structural change with increasing dosage at 2 MGy, leading to a transformation of 1 to 1-ir analogous to 2 in chemical structure. The underlying mechanism was further studied through a combination of different characterization techniques, including Raman, UV-vis, and electron paramagnetic resonance spectroscopies. Density functional theory calculations of 1 and 2 were also conducted to probe the coordination interaction of germanium and uranium with oxygen atoms. This work reports new crystalline uranium germanates by flux growth and, most importantly, provides insights into the irradiation stability of these materials, which will be beneficial to developing waste forms for long-term immobilization of radionuclides.

A hybrid experimental configuration for emissivity measurement at cryogenic temperatures

Abstract In cryogenic and high vacuum systems, radiation mode of heat transfer is the primary source of energy interaction owing to the wide temperature differentials and very low temperatures and pressures. Measurement of radiative properties such as emissivity is crucial in the design of cryogenic systems. Emissivity measurement at cryogenic temperatures requires careful consideration of the sample preparation and measurement conditions to ensure accuracy and reliability. Most experimental techniques developed so far are complex in their design and equipment, and they work only on a single measuring method. To address these challenges, this research has proposed a simpler and hybrid experimental setup that could employ both calorimetric and heat flux methods to directly measure the total hemispherical emissivity in the range 90 K–180 K. Experiments were conducted with five types of materials (black paint, stainless steel, aluminum foil, aluminized mylar foil, and copper sheet) by using both methods, and the results were validated with the literature data. The data obtained by calorimetric and heat flux methods for each sample showed a high level of consistency with each other, with a variation of only ±1.5%. Moreover, the discrepancy between the measured and literature data was within the acceptable range of 0.3%–10%. The total hemispherical emissivity of mechanically treated copper was higher than that of chemically polished copper by 11%. This simplified setup has incorporated all possible means to minimize heat leakages into and from the cryostat while maintaining accuracy. The obtained data can be used to accurately estimate the radiation heat loads in cryopumps and other cryogenic systems that use similar components.

Preparation of Single-Crystal Li-Rich Mn-Based Layered Oxides with Excellent Electrochemical Performance via Simple Stepwise High-Temperature Sintering.

Li-rich Mn-based layered oxides have attracted extensive attention in lithium-ion battery cathode materials due to their high specific capacity, wide operating voltage, and low cost. However, the large-scale production of single-crystal Li-rich Mn-based layered oxides remains a significant challenge. Herein, the morphology, structure, and electrochemical properties of a series of samples (Li1.2Ni0.13Co0.13Mn0.54O2) prepared by the solid-state method and the molten-salt flux method were assessed. Single-crystal particles exactly could be prepared by potassium chloride (KCl), but its electrochemical performance was inferior and the molten-salt flux method was too complicated for industry. Surprisingly, we found that water washing and annealing processes could enhance the cycling performance. Furthermore, single-crystal Li1.2Ni0.13Co0.13Mn0.54O2 with a particle size of 536 nm was successfully prepared by simple stepwise sintering (950 °C for 7 h, 1000 °C for 1 h, and 850 °C for 2 h), which delivered a specific capacity of 274.9 mAh·g-1 between 2.0 and 4.8 V at 0.1 C with 77.4% initial Coulombic efficiency and 82.1% capacity retention after 100 cycles at 0.1 C. This study may provide theoretical guidance for the industrial production of single-crystal Li-rich Mn-based layered oxides.

Single-photon and multi-photon Fano lines for helium and neon using tRecX-haCC

Abstract Single-photon and multi-photon ionization of helium and neon atoms by ultrashort extreme ultraviolet radiation is studied. The wavelength of radiation is chosen to excite a set of doubly excited states. We analyse the lineshapes arising from the presence of doubly excited states and numerically demonstrate the sensitivity of the Fano q parameter to the order of multi-photon process. The computations were performed using the tRecX-haCC package developed by the authors. The tRecX-haCC package solves the time-dependent Schrödinger equation in the presence of a laser pulse and computes the photoelectron spectra including the narrow resonance peaks using the time-dependent surface flux method (tSurff) and iSurf techniques.

Flux growth of Cs1-xRbxBF3 (B = Ca, Sr) crystals by the micro-pulling-down method

The possibility of growing Cs1-xRbxBF3 (B = Ca, Sr) crystals by micro-pulling-down was investigated due to their potential for application in ultrafast scintillation detectors. A LiF flux was applied to lower the melting point and therefore suppress evaporation of CsF from the melt. Suitable growth conditions were obtained through careful choice of the hot zone elements. A crucible with minimal nozzle length improved mass transport and an afterheater with four windows provided a steep temperature gradient. Inclusion and crack-free crystals of Cs1-xRbxCaF3 (x = 0, 0.1, 0.25, 0.5, 0.75, 0.9, and 1) and CsCa1-xSrxF3 (x = 0, 0.1, and 0.25) were grown under optimized conditions. Despite the hygroscopic nature of the heavy alkali metal fluorides, all the grown crystals are non-hygroscopic which significantly improves their application potential. Growth of CsCa1-xSrxF3 crystals with higher Sr concentration was complicated by the low solubility of SrF2 in the LiF-CsF melt and the hygroscopic nature of the CsSrF3. The formation of solid solution in the Cs1-xRbxCaF3 and CsCa1-xSrxF3 systems was investigated through the dependence of lattice parameters on nominal composition.

Crystal Structure and Li-Fe Order in Synthetic Mg(2-2x)LixFe3+x(SiO4) Olivine Structure.

Olivines are naturally occurring silicates consisting of isolated (SiO4)4- tetrahedra linked through M1O6 and M2O6 octahedra. In this study, we report the structural and crystal-chemical characterization of synthetic olivine crystals containing up to 25% Li-Fe3+ synthesized using the flux growth technique. Based on site scattering, <M1-O> and <M2-O> mean bond lengths, and charge neutrality of the chemical formula, we found a perfect ordering of Li and Fe3+ at the two distinct M1 and M2 sites. Unrestrained linear extrapolation to a hypothetical isostructural LiFe3+(SiO4) composition aligns well with the tabulated ionic radii of Li and Fe3+. Comparison made with the isostructural LiSc(SiO4) reveals that the Li-centered M2O6 octahedron has a significant capacity to distort in order to accommodate structural stresses, due to the relatively weak Li-O bond, while still achieving a bond valence sum that closely matches the formal charge of Li+. This behavior suggests the potential feasibility of an extended Li + Fe3+ for 2 Mg coupled substitution within the olivine structure. The reported structure of the LiFe3+(SiO4) endmember in the literature, despite its apparent matching of cell dimensions and space group with olivine, exhibits extremely unconventional crystal chemical features, raising questions about its validity. Given the importance of the suitability of Li-insertion in LiFeSiO4 as electrodes in rechargeable Li-ion batteries, further studies are needed to investigate its crystal structure and crystal chemistry.

Equilibrium densities of intrinsic defects in transition metal diselenides of molybdenum and tungsten.

Point defects are thermodynamically stabilized in all crystalline materials, with increased densities negatively impacting the properties and performance of transition metal dichalcogenides (TMDs). While recent point defect reduction methods have led to considerable improvements in the optoelectronic properties of TMDs, there is a clear need for theoretical work to establish the lower limit of defect densities, as represented by thermal equilibrium. To that end, an abinitio and thermodynamic analysis of the equilibrium densities of intrinsic point defects in MoSe2 and WSe2 is presented. The intrinsic defect formation energies at the limits of the selenium and metal-rich regimes are determined by density functional theory (DFT) and then augmented with elemental chemical potential functions to determine temperature- and pressure-dependent formation energies. Equilibrium defect densities are determined for MSe, SeM, vM, and vSe, where M and v, respectively, represent the metal and the vacancy, as a function of synthesis temperature and pressure. The effects of vibrational free energy contributions and treatment of the DFT exchange-correlation potential are found to be non-negligible. Calculated equilibrium densities are several orders of magnitude below reported defect densities in TMDs made by chemical vapor deposition, chemical vapor transport, and flux methods, thereby establishing that current synthesis methods are either kinetically limited or impurity dominated.

Energy Flux Method for Wave Energy Converters

Hydrodynamic tools reveal information as to the behaviour of a device in the presence of waves but provide little information on how to improve or optimise the device. With no recent work on the transfer of power (energy flux) from a wave field through the body surface of a wave energy converter (WEC), we introduce the energy flux method to map the flow of power. The method is used to develop an open-source tool to visualise the energy flux density on a WEC body surface. This energy flux surface can also be used to compute the total power capture by integrating over the surface. We apply the tool to three WEC classes: a heaving cylinder, a twin-hulled hinged barge, and pitching surge devices. Using the flux surfaces, we investigate power efficiency in terms of power absorbed to power radiated. We visualise the hydrodynamic consequence of sub-optimal damping. Then, for two pitching surge devices with similar resonant peaks, we reveal why one device has a reduced power performance in a wave spectrum compared to the other. The results show the effectiveness of the energy flux method to predict power capture compared to motion-based methods and highlight the importance of assessing the flux of energy in WECs subjected to different damping strategies. Importantly, the tool can be adopted for a wide range of applications, from geometry optimisation and hydrodynamic efficiency assessment to structural design.