High-temperature Phase Research Articles

Terahertz Wave Absorption of a Rubidium Manganese‐Iron Prussian Blue Phase Transition Material

AbstractRubidium manganese hexacyanidoferrate, Rb0.97Mn[Fe(CN)6]0.99 ⋅ 0.5H2O, which has a three‐dimensional cyanido‐bridged Mn−Fe framework encapsulating Rb+ ions, shows a terahertz (THz) wave absorption property. This compound undergoes a charge‐transfer phase transition between FeIII‐CN‐MnII [high temperature (HT) phase] and FeII‐CN‐MnIII [low temperature (LT) phase] near room temperature. The HT phase exhibits a THz wave absorption at 1.06 THz due to the slow vibration of the heavy Rb+ ions encapsulated in the three‐dimensional framework. By contrast, the LT phase displays a higher resonance frequency at 1.13 THz. This shift to a higher frequency is attributed to the framework shrinkage, which decreases the space available for the trapped Rb+ ion. Indeed, the void volume accompanying the phase transition decreases by 16.4 % from 41.4 Å3 (HT phase) to 34.6 Å3 (LT phase). Tuning the THz wave absorption frequency is necessary for THz devices such as absorbers, switches, filters, and modulators, especially for THz technology with THz waves in the sub‐THz region or near 1 THz.

Creep-thermal fatigue behavior of thin-walled structures with holes and a creep-thermal fatigue-oxidation phase field model

An experiment was conducted to evaluate the creep-thermal fatigue (CTF) behavior of thin-walled structures with holes. To achieve this, a high-temperature hold phase was added in the testing. The crack propagation of CTF is driven by the combined effects of creep, thermal fatigue, and oxidation. Therefore, a creep-thermal fatigue-oxidation phase field model was developed to simulate CTF behavior. The model accounts for the interaction between creep damage and fatigue damage, as well as the oxidation effect. A creep degradation function was formulated based on classical damage theory, and two creep damage models were compared. Two physically meaningful strategies were proposed to describe oxidation-induced fatigue damage. Finally, the applicability of model to creep-fatigue was validated.

Optical temperature sensing properties of novel RE3+ (RE=Er, Ho) doped BaLa2Ti3O10 phosphors

A novel luminescent material of BaLa2Ti3O10:RE3+ was synthesized by the high-temperature solid phase method, with a typical layered structure belonging to a special crystal system. Under the excitation of 980 nm, BaLa2Ti3O10:4%Er3+ exhibits characteristic emissions centered at 531 nm, 551 nm and 668 nm. It is noteworthy that the color of BaLa2Ti3O10:3%Ho3+ shows a strong green emission at 551 nm and a weak red emission near 664 nm, also represents adjustable yellow-green light with the change of 980nm laser pumped powers. The optical temperature sensing properties were checked by employing different strategies, relating to the thermally-coupled-levels (TCLs) and nonthermally-coupled-levels (NTCLs). The results show that the maximum relative sensitivity of TCLs based on BaLa2Ti3O10:Er3+ is 0.68% K-1(305 K). Similarly, the maximum sensitivity of TCLs is 0.89% K-1(313 K) in BaLa2Ti3O10:Ho3+, which performs well from 313 K to 513 K. It has been found the samples using FIRs of TCLs can produce higher absolute (Sa) and relative (Sr) sensitivities compared with those using Fluorescence Intensity Ratios (FIRs) of NTCLs. The multiple FIRs also achieved superior levels of temperature resolution and repeatability in all cases. Generally, this work provides favorable candidates for the temperature sensors.

Synergistic effect of indium doping on thermoelectric performance of cubic GeTe-based thin films

Germanium Telluride (GeTe) has been widely explored as a promising lead-free thermoelectric material in its rhombohedral and cubic phases. However, the structural transition between these two phases at ∼700 K causes an abrupt change of thermal expansion coefficient, challenging its broader practical applications. Also, as characterized by multi-valence bands and strong anharmonic interaction, the high-temperature cubic phase exhibits a higher power factor, lower thermal conductivity, and ultimately superior thermoelectric performance than its rhombohedral counterpart. Prompted by these, in this work, the cubic phase of Ge0.9Sb0.1Te (presented as GeSbTe in the following content) nanocrystalline thin film is successfully realized by RF sputtering followed by post-annealing treatment. Additionally, Indium, as an electron donor to the germanium site and an effective scattering center, further moderates carrier concentration, enhances the Seebeck coefficient and reduces thermal conductivity. The optimal composition achieves an estimated peak of ∼1.95 and an estimated average of ∼ 1.11 within the temperature range of 300 K to 575 K, showcasing GeTe as a compelling candidate for applications close to room temperature.

Utilization of handheld LIBS and XRF analyzers for impurity detection in 3D-printed ultra-high-temperature ceramics

In this study, we implement handheld laser-induced breakdown spectroscopy (LIBS) and X-ray fluorescence (XRF) analyzers to detect elemental impurities in additively manufactured ultra-high-temperature ceramics (UHTCs). Spectral data were collected from digital light processing (DLP) 3D-printed alumina (Al2O3) samples at various processing stages. These stages included high-temperature debinding and sintering phases used to bake out organic impurities and improve grain cohesion of the ceramic. Spectral analysis revealed the presence of organic impurities such as H and C together, with inorganic impurities such as Na, Si, Ca, and Fe. A reduction in elemental impurities in the spectra was observed as the ceramic samples were processed, validating the effectiveness of handheld analyzers for in situ rapid impurity detection and quality control in the manufacturing of 3D-printed UHTCs.

Dominant role of charge ordering on high harmonic generation in Pr0.6Ca0.4MnO3

High harmonic generation (HHG) is a typical high-order nonlinear optical phenomenon and can be used to probe electronic structures of solids. Here, we investigate the temperature dependence of HHG from Pr0.6Ca0.4MnO3 in the range of 7–294 K, including the charge ordering (CO) transition and magnetic transition temperatures. The high harmonic (HH) intensity remains almost constant in the high-temperature charge-disordered phase. However, as the temperature is lowered, it starts to increase near the CO transition temperature where an optical gap related to the CO appears. The anomalous gap energy dependence resembles the one recently reported in a Mott insulator. We attribute the suppression of the HH intensity at high temperatures to the destructive interference among HH emissions from thermally activated multiple charge configurations. Our results suggest that HHG is a promising tool for probing the fluctuation of local order in strongly correlated systems. Published by the American Physical Society 2024

Temperature stable (1-x)BaAl2Si2O8-xBa3V2O8 (0.2 ≤ x ≤ 0.5) microwave dielectric composite ceramics for LTCC applications

BaAl2Si2O8 microwave dielectric ceramics possess dielectric properties of low permittivity (εr) and low loss, coupled with low synthesis cost, making them promising for commercialization. However, the hexagonal structure undergoes high-temperature phase transitions that deteriorate thermal shock resistance and durability, hindering its practical use. In this work, we report temperature-stable BaAl2Si2O8-Ba3V2O8 low temperature co-fired ceramics (LTCC). The combination of Ba3V2O8 and G9 glass achieved a near-zero τf and a thermal expansion coefficient of ∼ 8.5 ppm/℃, significantly enhancing the temperature stability of BaAl2Si2O8 ceramics. By employing ion substitution and enhancing lattice disorder, the components of G9 glass were strategically designed to successfully induce hexagonal-to-monoclinic transformation of BaAl2Si2O8 phase. The dielectric properties of 0.5BaAl2Si2O8-0.5Ba3V2O8-9 wt% G9 sintered at 900 ℃ were εr ∼9, Q×f ∼22,000 GHz and τf ∼ +1.9 ppm/℃. Good chemical compatibility with silver powders was confirmed by further investigation of the co-firing behavior. This work provides attractive candidate for BaAl2Si2O8-based LTCCs and an available approach for modifying BaAl2Si2O8 ceramics.

High-Temperature Steam Oxidation and Surface Microstructure Evolution of Fe13Cr6Al(1–4)Mo0.15Y Alloys

The current study investigated the microstructure evolution and anti-corrosion behavior of low Y doping alloys of Fe13Cr6Al(1–4)Mo0.15Y subjected to high-temperature steam (800 °C to 1300 °C). The results indicate that steam oxidation induces the growth of high-quality oxidation film that is thermodynamically driven, with rapid increases in the thickness from 800 °C to 1300 °C without film convolution and spallation. The film convolution and spallation were successfully suppressed through on-site formation of the high-temperature stable ternary crystalline phase (Y2Mo3O12) and decreasing of the thickness of α-Al2O3 oxidation film during the fabrication and oxidation scenario. The on-site steam oxidation rate has been significantly suppressed, with lower weight gain and less oxidizing film convolution than monolithic FeCrAlMo alloy, through the addition of a low concentration of Y.

Assessment of former austenite structure in hot rolled steel in terms of its texture after martensitic transformation

Textures of medium carbon steel, hot rolled and then quenched, have been determined by Electron backscatter diffraction (EBSD). To ensure representativeness of results, a rather large treated scan covered about a thousand of prior grains, each containing several thousands of measurement points. Considering inter-phase orientation relationships peculiar to martensitic steels, textures of the high temperature phase (austenite) have been assessed in terms of the transformation textures. Thus, deformed and recrystallized states of austenite dependent on the rolling conditions can be distinguished. To verify EBSD data, martensite textures were measured by an independent method of EBSD whereas morphology of the prior grains was revealed by means of chemical etching.

Improving In Situ Combustion for Heavy Oil Recovery: Thermal Behavior and Reaction Kinetics of Mn(acac)3 and Mn-TO Catalysts

In this research work, the catalytic performances of two manganese-based catalysts, manganese (III) acetylacetonate (Mn(acac)3) and manganese tallate (Mn-TO), were studied during the process of Ashalcha heavy oil oxidation under in situ combustion conditions. DSC analysis shows distinct thermal behavior of both ligated catalysts during low- and high-temperature oxidation phases (LTO and HTO); for example, the shifting in peak temperature (Tp) in the HTO at a heating rate of 10 °C/min was reduced by approximately 5.3% for Mn-TO and 2.24% for Mn(acac)3 when compared with uncatalyzed heavy oil. Combined isothermal kinetic analyses using the Friedman and Kissinger–Akahira–Sunose analytic methods have provided insights about activation energies and frequency factors over the whole conversion range, where the catalytic performance of Mn-TO showed low activation energies in both LTO and HTO (Eα of Mn-TO was approximately 13.33% (LTO) and 7.68% (HTO) less than with the heavy oil alone). In addition, calculations of the effective rate constant confirmed the increased oxidation rate trend of both catalysts, with Mn-TO exhibiting the highest values. The findings highlight the potential of these manganese-based catalysts, the Mn-TO catalyst in particular, in optimizing heavy oil oxidation processes. The overall results further contribute to developing more efficient ligand catalyst complexes for sustainable heavy oil recovery while continuously improving their efficient application during in situ combustion in the petroleum industry.

Quenching high-temperature phase in Cu–Sn alloy system by femtosecond and picosecond laser irradiation

Quenching high-temperature phase in Cu–Sn alloy system by femtosecond and picosecond laser irradiation

Comment on Hajra et al.: “High-temperature phase stability and phase transformations of Niobium-Chromium Laves phase: Experimental and first-principles calculation”

This work comments on a recent publication by Hajra et al. (Mater. Design 236 (2023) 112483), which claims to have presented compelling experimental and theoretical evidence in favour of the existence of an equilibrium C14-NbCr2 high-temperature Laves phase in the Cr-Nb system. In the present comment, evidence and conclusions reported in the paper of Hajra et al. are critically put into context of insight from previous works. From this it is concluded here, that the evidence in favour of an equilibrium C14-NbCr2 high-temperature Laves phase is, by far, not that compelling as claimed by Hajra et al.. Instead, the most direct evidence presented in the literature does not support the existence of an equilibrium C14-NbCr2 high-temperature Laves phase. Alternative interpretations of Hajra et al.’s evidence and conclusions are offered, and it is elaborated, which true gaps in knowledge exist concerning the Laves phases in the Cr-Nb system.

An Investigation of Oxides of Tantalum Produced by Pulsed Laser Ablation and Continuous Wave Laser Heating.

Recent progress has seen multiple Ta2O5 polymorphs generated by different synthesis techniques. However, discrepancies arise when these polymorphs are produced in widely varying thermodynamic conditions and characterized using different techniques. This work aimed to characterize and compare Ta2O5 particles formed at high and low temperatures using nanosecond pulsed laser ablation (PLA) and continuous wave (CW) laser heating of a local area of tantalum in either air or an 18O2 atmosphere. Scanning electron microscopy (SEM) and Raman spectroscopy of the micrometer-sized particles generated by PLA were consistent with either a localized amorphous Ta2O5 phase or a similar, but not identical, crystalline β-Ta2O5 phase. The Raman spectrum of the material formed at the point of CW laser impingement was in good agreement with the previously established ceramic "H-Ta2O5" phase. TEM and electron diffraction analysis of these particles indicated the phase structure matched an oxygen-vacated superstructure of monoclinic H-Ta2O5. Further from the point of laser impingement, CW heating produced particles with a Raman spectrum that matched β-Ta2O5. We confirmed that the high-temperature ceramic phase characterized in previous work by Raman spectroscopy was the same monoclinic phase characterized in different work by TEM and could be produced by direct laser heating of metal in air.

Study on the effect of TiC/B on the performance of laser cladding in-situ fabricating wear-resistant self-lubricating coatings

To improve the wear resistance of IN718, coatings containing the self-lubricating phase h-BN were prepared and the coating properties were analyzed in relation to the variation of laser power. The results show the TiC added to the cladding powder partially decomposes and in-situ fabricates new reinforcing phases TiN, B4C, etc. The lubricating phase h-BN was in-situ fabricated by adding B into the powder. As the laser power increased from 1.6 kW to 2 kW and 2.5 kW, eutectic microstructures of high melting point reinforcing and lubricating phases were observed. Due to the decomposition of TiC and in-situ fabricated of TiC2, TiN and B4C concentrations changing with the laser power, the surface hardness of the coatings prepared at 2.5 kW was the highest at 391.03HV0.5. Which is 1.096 and 1.108 times of 1.6 kW and 2 kW. At room temperature, the coating fabricated by 2 kW has the highest average friction coefficient of 0.537. This is because the self-lubricating phase h-BN is a high-temperature lubricating phase and the wear surface has a low oxide content, and is influenced by the hardness of the coating. At 500°C, the coating fabricated with 2.5 kW has the lowest average friction coefficient due to the best synergistic effect of the lubricating and reinforcing phases at 0.376. The 2.5 kW coating has the best wear resistance, with wear rates 0.69 and 0.54 times at room temperature and 0.82 and 0.8 times at 500°C of 1.6 kW and 2 kW. The wear mechanism at room temperature is abrasive wear, and at 500°C is mainly a combination of h-BN and oxide synergistic lubrication.

ZnO-NaNO3 nanocomposites for solar thermal energy storage systems

High-temperature phase change materials (PCMs) with good energy storage density and thermal conductivity are needed to utilize solar thermal energy effectively to meet industrial thermal energy demands. Composite PCMs containing a material of higher thermal conductivity and an inorganic high-temperature PCM can be explored to meet these requirements. Accordingly, a high-temperature, composite inorganic PCM (ZnO-NaNO3) with enhanced thermophysical properties was prepared, and its energy storage potential was investigated experimentally. A maximum thermal conductivity enhancement of 22.7% was achieved at 200 °C for 2 wt% ZnO-NaNO3 nanocomposite. The increase in thermal conductivity at higher temperatures may be attributed to the formation of ordered sodium nitrate layers on the nanoparticle surfaces. The increase in surface area and surface energy due to the addition of ZnO nanoparticles increased the specific heat of the nanocomposite in both the solid and liquid phases (43.5% in the liquid phase for 2 wt% ZnO-NaNO3). Thus, the addition of ZnO nanoparticles to NaNO3 increased its energy storage capacity. The addition of ZnO nanoparticles to NaNO3 did not affect the onset, peak or endset temperature during melting and freezing. Moreover, 2 wt% ZnO-NaNO3 exhibited cyclic stability even after 500 cycles and thus has potential as an energy storage medium.

Crystallite Size Effects on Electrical Properties of Nickel Chromite (NiCr2O4) Spinel Ceramics: A Study of Structural, Magnetic, and Dielectric Transitions

The effect of sintering temperature on the structural, magnetic, and dielectric properties of NiCr2O4 ceramics was investigated. A powder X-ray analysis indicates that the prepared nanocrystallites effectively inhibit the cooperative Jahn–Teller distortion, thereby stabilizing the high-temperature cubic phase structure with space group Fd-3m. Multiple transitions are confirmed by temperature-dependent magnetization M(T) data. Moreover, the magnetization value decreases and the Curie temperature increases with a decrease in the crystallite size. The low-temperature-dependent real permittivity (ε′-T) for a NiCr2O4 crystallite size of 78 nm exhibits a broad maximum at 40 K that is independent of frequency. This establishes a correlation between electric ordering and the underlying magnetic structure. The temperature dependency of the dielectric constant at fixed frequencies for both NiCr2O4 crystallite sizes rises with temperature for a certain range of frequencies. A significant improvement is evident: the dielectric constant (ε’) at room temperature reaches approximately 5738 for the sample with 28 nm crystallites, while the 78 nm crystallite sample shows a noticeable drop to ε’~174. The frequency-dependent conductivity curves for both types of NiCr2O4 nanocrystallites have different conductivity values. The lower-crystallite-size sample demonstrates higher conductivity values than the 78 nm crystallite size one. This observation is attributed to the decrease in crystallite size, which increases the number of grain boundaries and, consequently, scatters a higher number of charge carriers.

Disclosing the magnetic ground state of PrBaMn2O6

In this work, we report a neutron diffraction study on a single crystal of the layered PrBaMn2O6 perovskite. This compound undergoes two consecutive magnetic transitions with decreasing temperature. At TC ≈ 309 K, a long-range ferromagnetic ordering is established with the Mn magnetic moments oriented along the c axis. Below TN ≈ 240 K, a spin reorientation gives rise to a sudden decrease of the magnetization and the formation of an antiferromagnetic order. This magnetic transition is also accompanied by an electronic localization caused by a structural phase transition from a high-temperature tetragonal phase (P4/mmm) into a low-temperature orthorhombic one (P21am). Our neutron diffraction study at 12 K has unambiguously identified that the ground magnetic structure for this compound is a layered antiferromagnetic structure along the c axis with the Mn moments oriented in the ab plane along one diagonal of the primitive tetragonal cell. No sign of magnetic scattering associated to a CE-type magnetic structure was found in our study, discarding its occurrence in this compound. This result excludes the occurrence of a charge order transition to account for the electronic localization and it is fully consistent with previous structural studies showing a unique crystallographic site for Mn atom in the low-temperature phase. A symmetry analysis was carried out to identify the magnetic space group of the ferromagnetic order above TN and the two possible groups for the antiferromagnetic ordering below TN.

High temperature environmental scanning electron microscopy characterization of transient phase formation during conversion of simulated nuclear waste feed to glass

In-situ High-Temperature Environmental Scanning Electron Microscopy (HT-ESEM) is used to characterize the transient phases formed during the melting of complex glass batch mixtures representing simulated nuclear waste feeds. The first phenomenon that occurs is the formation of oxyanionic salt melt, followed by the reaction of oxyanionic salts with refractory grains containing Si, Al, or Mg through surface reactions to form a molten alkali-alumino-boro-silicate phase. The onset temperatures of gas bubble formation and primary foaming are directly determined from the HT-ESEM measurements. The formation of sulfate lakes as well as the formation of high-temperature transient phases floating at the sample surface are also directly observed and identified. Convection currents are observed and their consequences on glass homogenization are discussed.

Assessment of thermofluidic behaviour of a Medium-High-Temperature shell and tube latent heat storage through experimental and computational investigation

The study envisages a holistic experimental methodology encompassing the entire spectrum of formulation, characterization, and thermal response evaluation of a medium–high-temperature (MHT) phase change material (PCM). The heating rate in melting is significantly less than the cooling rate during solidification until PCM reaches phase transition temperature. For q“ = 1000 W/m2, charging duration of vertical domain (θ = 90°) is 15 % slower than horizontal domain (θ = 0°). However, with increase in flux to 2000 W/m2 the charging duration is only 6 % slower for θ = 90° than θ = 0°. Melting/charging duration for thermocouple positioned at A (r = 18 mm, top side of prototype) is 15.38 % lower than at F (r = 18 mm, bottom side of prototype) and positioned at C (r = 38 mm, top side) is 8 % lower than at D (r = 38 mm, bottom side) for horizontally orientated LHTES system. A substantial decrease (by 17.64 %) in discharging duration was observed with increase in the inlet flow rate and the inlet temperature by 2.5 times and 3.3 times, respectively. The total energy accumulated in the LHTES demonstrates an approximately 11 % increase with the escalation of electric flux from 1000 W/m2 to 2000 W/m2 during the charging process for θ = 0° orientation. In contrast to charging, faster solidification rate is observed in the bottom half of the prototype (points D, E, F) compared to the top half (points A, B, C) which has implications for the design and operation of LHTES systems.

Realizing multiorbital Hubbard model with commensurate fillings in the paramagnetic phase of triangular magnets (X = Mn, Co, Ni)

The multiorbital Hubbard model is renowned for its rich phase diagram, characterized by various filling-dependent Mott transitions. However, controlling electron filling to explore the complete phase diagram within a single material remains challenging. In this study, we investigate three members of a correlated magnet family: Na2BaX(PO4)2 (where X = Mn, Co, Ni). Our focus is on revealing their unusual electronic structure related to the different electron fillings. Despite differences in their effective angular momentum, our first-principles calculations reveal a strikingly similar flat-band electronic structure across all three systems. Remarkably, we found that their distinct valence configurations lead to a similar response to electronic correlations in the high-temperature paramagnetic phases, which nicely realizes Mott states with different electron concentrations. Thus, these systems can be conceptualized as multiorbital Hubbard models with differing electron fillings. Our work unifies the understanding of these structurally similar systems and opens new avenues for exploring correlated electronic structures with distinct fillings.