Low-temperature Materials Research Articles

Structural, magnetic, and magnetocaloric characterizations of geometrically-frustrated SrRE2O4 (RE = Gd, Dy, Ho, Er) oxides for low-temperature cooling applications

The magnetocaloric (MC) properties of many rare earth (RE)-based magnetic solids have been intensively investigated. This research aims to develop suitable MC materials for low-temperature cooling application and to better elucidate their intrinsic properties. We have fabricated four single-phase SrRE2O4 (RE = Gd, Dy, Ho, Er) oxides and conducted a systematic experimental investigation into their structural, magnetic, and low-temperature MC properties. All these SrRE2O4 oxides crystallize in an orthorhombic structure (space group Pnma) and exhibit typical geometrical frustration. This frustration arises from the one-dimensional RE ion zigzag ladders along the c-axis, which link the two-dimensional honeycomb lattice in the ab plane. The elements in SrRE2O4 oxides are uniformly distributed and present with valence states of Sr2+, RE3+, and O2−, respectively. Large low-temperature MC effects and notable performances are realized in these SrRE2O4 oxides, determined by the MC parameters of magnetic entropy change, refrigerant capacity, and temperature-averaged entropy change (with a lift of 5 K). These MC parameters under a magnetic field change of 0–70 kOe are as follows: 34.18 J/kgK, 275.88 J/kg, and 30.74 J/kgK for SrGd2O4; 18.13 J/kgK, 253.83 J/kg, and 17.54 J/kgK for SrDy2O4; 18.81 J/kgK, 354.77 J/kg, and 18.61 J/kgK for SrHo2O4; and 22.63 J/kgK, 284.25 J/kg, and 21.97 J/kgK for SrEr2O4. These values are comparable to those of most recently updated low-temperature MC materials with remarkable performances, making these SrRE2O4 oxides highly interesting for practical cooling applications.

Development of Novel Ternary Alloy of CSiSn for Low-Cost Next Generation Photovoltaics

The growing need for highly efficient solar cells calls for significant advancements in the development of a new material system to meet the needs of low-cost and low-cost production. Current multi-junction solar cell alternatives are more costly to produce. This research showcases the development and analysis of a novel ternary material system, The CSiSn (CST) alloy, which shows potential for creating low-cost material with high absorption in of solar spectrum. In this work, the following aspects regarding the CST material are investigated: 1) Material modeling using density functional theory, 2) electronic band structure estimations, 3) low-temperature material growth technique via Plasma Enhanced Chemical Vapor Deposition (PE-CVD) system; 4) advanced material and optical characterizations of CST alloys.

Experimental Study on the Effect of Additives for Phase Change Hysteresis Performance

Phase change energy storage materials are the core of phase change energy storage technology. Phase change hysteresis can cause phase change materials not to store and release thermal energy as expected, and most studies have not focused on this. A low-temperature eutectic phase change material CaCl2·6H2O–MgCl2·6H2Omaterial prepared was investigated, and some influencing factors of the phase change hysteresis phenomenon and its regular characteristics were aspired to be obtained. The melting-solidification curves were obtained using a step-cooling test bench, and the latent heat values and heat absorption and exothermic curves of materials with different proportions were measured by a differential scanning calorimeter. The experimental results show that the temperature difference of the phase change hysteresis tended to increase gradually with the increase of the mass fraction of the nucleating agent, and the hysteresis temperature difference increases from the initial 3.9 °C–15.02 °C when SrCl2·6H2O was added by 2.4%. The temperature difference of the phase change hysteresis increased gradually with the increase of the mass fraction of the thickener. This paper provides a new idea for optimizing the properties of phase change energy storage materials and provides a possibility for realizing the parametric control of phase change hysteresis factors.

Magnetic properties and large low-field magnetocaloric effect of RFe2Si2 (R = Ho, Tm) compounds

Nowadays, magnetic refrigerant technology has drawn much attention for its environmental friendliness. Those magnetic materials possessing giant low-field magnetocaloric effect (MCE) performance are of great importance for practical applications, especially at low temperatures. Herein, we present a detailed study on polycrystalline magnetocaloric compounds HoFe2Si2 and TmFe2Si2. HoFe2Si2 exhibits a transition from antiferromagnetic to paramagnetic phase at 2.2 K, while no long-range magnetic ordering is observed in TmFe2Si2 even temperature down to 2 K. For both compounds, they showed large low-field magnetic entropy change (−ΔSM) with the peak values of 10.6 and 7.9 J kg−1 K−1 under field change of 0–2 T for HoFe2Si2 and TmFe2Si2, respectively, which is comparable or even larger than some low-temperature magnetocaloric materials. In addition, the characteristic of second-order magnetic transitions of both compounds were confirmed on basis of Arrott plots and mean-field theory criterion. The low magnetic ordering temperatures, large low-field MCE performance along with the feature of second order phase transition for HoFe2Si2 and TmFe2Si2 indicate that both compounds are promising candidate for magnetic refrigerant materials at liquid helium temperature.

High power factor and mechanical properties of Bi1-xSbx alloys enabled by redensification of crystal slabs

The low-cost Bi1-xSbx crystal has been considered the best low-temperature material for its high electrical properties, which also can generate high effective thermal conductivity, revealing a high potential in heat dissipation. However, the weak mechanical strength hinders practical applications. Herein, we firstly grew the Bi1-xSbx crystal by the Bridgeman method, then cleaved the crystal into slabs with different sizes for hot-pressing. The obtained materials exhibited a high bending strength of 72 MPa, which is twofold that of Bi1-xSbx [001]-direction. Furthermore, the hot-pressed Bi1-xSbx samples show high electrical conductivities, being similar to those of the single crystals, resulting in the high record power factor of 78 μW·cm-1·K-2 @110 K and 38 μW·cm-1·K-2 @300 K among the hot-pressed poly-crystalline Bi1-xSbx. This high electrical performance is beneficial to the applications of heat dissipation. Therefore, this work proves an effective way to simultaneously improve the mechanical and thermoelectric properties of Bi1-xSbx alloys.

Conjugated Nitroxide Radical Polymer with Low Temperature Tolerance Potential for High-Performance Organic Polymer Cathode.

Low-temperature operation poses a significant challenge for current commercial rechargeable lithium-ion batteries (LIBs). Organic polymer electrode materials, exhibiting a nonintercalation redox mechanism, offer a viable solution to mitigate the decline in electrochemical performance at low temperatures in LIBs. Herein, a radical polymer P(DATPAPO-TPA) with a conjugated nitrogen-rich triphenylamine derivative as the backbone and high-density nitroxide pendants has been synthesized. Due to the large interstitial spaces between adjacent structural units and polymer chains, resulting from the significant torsion angle between the benzene rings in the P(DATPAPO-TPA) skeleton, ions could effectively transport. This structural feature demonstrated a notable discharge capacity of 143.3 mA h·g-1 and a high charge-discharge plateau at ∼3.75 V vs Li+/Li, outperforming most reported radical polymer cathode materials. In addition, its capacity retention could reach 83.1% after 2000 cycles at an ultrahigh current density of 50 C, showing excellent rate capability and promising cyclability. Also notable was P(DATPAPO-TPA)'s favorable low-temperature performance that maintains a high discharge capacity of 139.2 mA h·g-1 at 0 °C. The synthesized P(DATPAPO-TPA) is a tangible illustration of a viable design strategy for low-temperature electrode materials, thereby contributing to broadening applications for radical polymer electrode materials.

Low-Temperature Bonding Materials and Insulation Materials for High-Density 3D Packaging

Low-Temperature Bonding Materials and Insulation Materials for High-Density 3D Packaging

Low-temperature cross-linkable hole-transporting materials with benzocyclobutenes for solution-processed organic light-emitting diodes

Cross-linkable hole-transporting materials with a new cross-linking group, benzocyclobutene, are designed and synthesized. These materials dissolve well in common organic solvents and exhibit excellent solvent resistance after thermal cross-linking. Electroluminescent (EL) devices were fabricated using these two hole-transporting materials.

Sintering behavior, structural evolution, and dielectric properties of Li3Mg3NbO7 + x wt% LiF microwave dielectric ceramics

In this paper, x wt% LiF (1 ≤ x ≤ 10) is utilized to decrease sintering temperature, improve microstructure and enhance Q × f of Li3Mg3NbO7 ceramics. Remarkably, the appropriate addition of LiF leads to the dramatic reduction in sintering temperature (reduced by 300 °C) and the significant improvement in Q × f (increase ratio: 26 %). The addition of LiF causes the generation of cubic oxyfluoride solid solution, which is confirmed by XRD, SEM and TEM. When x ≤ 8, both orthorhombic oxide and cubic oxyfluoride solid solution exist in ceramics. When x = 10, the ceramic is composed of cubic oxyfluoride solid solution and LiF. It is confirmed that the maximum mass percentage of LiF required to fully form a cubic solid solution is between 8 wt% and 10 wt%. The significant improvement in Q × f is mainly attributed to increase in relative density and orthorhombic-cubic phase transition. In this system, Li3Mg3NbO7 + 8 wt% LiF ceramics sintered at 900 °C possess the optimal dielectric properties: εr = 14.10, Q × f = 152,510 GHz and τf = −43.5 ppm/°C. The Li3Mg3NbO7 + 8 wt% LiF ceramics show an outstanding combination of low εr, high Q × f and low sintering temperature, surpassing the performance of most low-temperature dielectric materials. The excellent chemical compatibility with Ag electrodes suggests that the Li3Mg3NbO7 + 8 wt% LiF ceramics are particularly promising for LTCC applications.

Anneal-free ultra-low loss silicon nitride integrated photonics

Heterogeneous and monolithic integration of the versatile low-loss silicon nitride platform with low-temperature materials such as silicon electronics and photonics, III–V compound semiconductors, lithium niobate, organics, and glasses has been inhibited by the need for high-temperature annealing as well as the need for different process flows for thin and thick waveguides. New techniques are needed to maintain the state-of-the-art losses, nonlinear properties, and CMOS-compatible processes while enabling this next generation of 3D silicon nitride integration. We report a significant advance in silicon nitride integrated photonics, demonstrating the lowest losses to date for an anneal-free process at a maximum temperature 250 °C, with the same deuterated silane based fabrication flow, for nitride and oxide, for an order of magnitude range in nitride thickness without requiring stress mitigation or polishing. We report record low anneal-free losses for both nitride core and oxide cladding, enabling 1.77 dB m-1 loss and 14.9 million Q for 80 nm nitride core waveguides, more than half an order magnitude lower loss than previously reported sub 300 °C process. For 800 nm-thick nitride, we achieve as good as 8.66 dB m−1 loss and 4.03 million Q, the highest reported Q for a low temperature processed resonator with equivalent device area, with a median of loss and Q of 13.9 dB m−1 and 2.59 million each respectively. We demonstrate laser stabilization with over 4 orders of magnitude frequency noise reduction using a thin nitride reference cavity, and using a thick nitride micro-resonator we demonstrate OPO, over two octave supercontinuum generation, and four-wave mixing and parametric gain with the lowest reported optical parametric oscillation threshold per unit resonator length. These results represent a significant step towards a uniform ultra-low loss silicon nitride homogeneous and heterogeneous platform for both thin and thick waveguides capable of linear and nonlinear photonic circuits and integration with low-temperature materials and processes.

Thermodynamic modeling of Bi2Te3 in the defect energy formalism

Bi2Te3 is a promising thermoelectric material that is often touted as one of the best-performing low-temperature thermoelectric materials. As a result, it has been widely used commercially, both for clean energy generation and in cooling devices. Like many other thermoelectric materials, defects play a key role in the performance of Bi2Te3. As a result, numerous studies have attempted to experimentally and computationally map out the dominant defects in the phase, these include efforts to determine the dominant defect, estimate defect energies, and predict their concentration. The computer coupling of phase diagrams and thermochemistry (CALPHAD) is one of many tools under the auspices of the materials genome initiative (MGI) that enables the rapid design of new functional materials with improved properties. The Defect energy formalism (DEF) with a charged sublattice, an offshoot of the Compound energy formalism (CEF), provides a way to directly include first-principle defect energy calculations into CALPHAD descriptions of solid phases. The introduction of the charge sublattice enables the estimation of the free carrier concentrations in the phase. Here we apply the DEF to the Bi2Te3 system, emphasizing the robustness of the DEF in describing meaningful endmembers and the elimination of fitting parameters. Unlike previous assessments using the Wagner–Schottky defect model, we include the description of the charged defects in our assessment. The DEF with a charged sublattice provides a good prediction of the non-stoichiometry of the phase when compared with experimental data and also predicts a thermodynamic defect concentration at low temperature that is physically reasonable.

Microstructure evolution and deformation behaviour of Sn-xBi-1Ag Solder alloys: Influences of Bi content

The study of microstructural evolution in ternary Sn–Bi–Ag solder alloys is critical due to its direct impact on the mechanical properties of these low-temperature solder materials. This research compares the solidification and deformation behaviors of two such alloys, Sn–10Bi–1Ag and Sn–57Bi–1Ag, to shed light on the influences of bismuth (Bi) content variations. Experimental results indicate that increasing Bi content alters the solidification process and the degree of undercooling. In the Sn–10Bi–1Ag alloy, the eutectic reaction produces plate-like Ag3Sn with a predominant with {101‾0}hcp facet, considering Ag3Sn as a pseudo-hexagonal structure. Conversely, in the Sn–57Bi–1Ag alloy, Ag3Sn nucleates as the primary phase, exhibiting blocky or extensively branched morphologies, enclosed by various facets including {0001}hcp and {101‾0}hcp. Additionally, two distinct Bi particle sizes were identified in the Sn–10Bi–1Ag alloy: eutectic lamellar Bi (∼200 nm) and Bi precipitates (∼15 nm), when cooled at 10 °C/min, in comparison to typical lamellar β-Sn/Bi eutectics in Sn–57Bi–1Ag. In-situ tensile test revealed that the Sn–10Bi–1Ag demonstrates superior strength and reduced ductility. This is attributed to the reinforcement provided by the smaller-sized Bi particles and the eutectic Ag3Sn structures. In contrast, for the Sn–57Bi–1Ag, the primary Ag3Sn phase tends to fracture during deformation, and the deformation mechanism is predominantly controlled by grain boundary and phase boundary sliding. This study elucidates the significance of Bi precipitates and Ag3Sn in Sn–Bi–Ag solder, providing valuable insights for the alloy design of future low-temperature solders.

Physical and chemical properties of low-temperature nanostructured thermoelectric materials on the basis of Bi2Te2.8Se0.2 and Bi0.5Sb1.5Te3

Nanostructured thermoelectric (TE) materials Bi2Te2.8Se0.2 (0.16 wt% CdCl2) n-type and Bi0.5Sb1.5Te3 (2.2 wt% Te and 0.16 wt% TeI4) p-type were fabricated, and complex investigations of these materials were carried out. The thermoelectric materials were obtained by spark plasma sintering (SPS) of nanodispersed powder ground in planetary ball mill. It was found that the average particle sizes in thermoelectric materials after milling for 60 min were about 30 nm. After SPS of the powders, the average crystallite sizes were from 86 to 96 nm. Thermal stability of materials up to 550 K was observed. The relationship between the composition, structure and properties of TE materials was established. The maximum ZT obtained for nanostructured TE materials were ZT = 1.16 at 380 K for Bi2Te2.8Se0.2 and ZT = 1.35 at 370 K for Bi0.5Sb1.5Te3. Increase in ZT for nanostructured thermoelectric materials is due to the decrease of the lattice thermal conductivity.

Development of Self-Heating Concrete Using Low-Temperature Phase Change Materials: Multiscale and In Situ Real-Time Evaluation of Snow-Melting and Freeze–Thaw Performance

Development of Self-Heating Concrete Using Low-Temperature Phase Change Materials: Multiscale and In Situ Real-Time Evaluation of Snow-Melting and Freeze–Thaw Performance

Novel low-temperature adsorption material Ni0.85Se for efficient removal of elemental mercury from coal-fired flue gas

Abstract Mercury pollution poses a serious hazard to the ecological environment and human well-being. The issue of mercury emissions has always been a hot topic of concern. In this work, spherical Ni0.85Se material was successfully prepared and applied for the first time in the mercury removal of coal-fired flue gas. After a series of experiments and characterization studies, it was found that Ni0.85Se has excellent mercury removal performance in low-temperature environments below 120°C, especially with almost 100% mercury removal efficiency below 60°C. It effectively removes mercury from the coal-fired flue gas at power stations and can be adopted as an effective adsorption material for mercury removal in other industries with coal combustion.

Flexural behaviours of concrete-filled stainless-steel tubular beams under cold-region low temperatures

Applications of concrete-filled square (or circular) stainless-steel tubes keep increasing in cold-region coastal engineering structures. However, their behaviours under low-temperature bending have not been fully investigated, which brings obstacles to their engineering applications. To address this issue, this paper investigated flexural behaviours of concrete-filled square/circular stainless-steel tubular beams (CFSSSTBs/CFCSSTBs) at low temperatures through eight four-point bending tests. The main studied parameters were low temperatures (20∼−60 ℃) and cross-section type (circular or square shape). Test results showed that both CFSSSTBs and CFCSSTBs exhibited flexural failure and exhibited excellent ductility under low-temperature bending benefiting from the excellent ductility of stainless steel; bending resistances of CFSSSTBs and CFCSSTBs were improved by 5% and 22%, respectively. This study also developed finite element models (FEMs) for simulations on flexural behaviours of CFSSSTBs/CFCSSTBs at low temperatures. The FEMs considered both low-temperature material and geometric nonlinearities. Validations against eight tests proved the capacities of FEM simulations on low-temperature flexural behaviours of CFSSSTBs/CFCSSTBs. Finally, the code equations in Eurocode 4 and AISC 360 were used to predict the stiffness and ultimate bending resistances of CFSSSTBs/CFCSSTBs. Validations showed that the code equations underestimated the bending resistances of CFSSSTBs/CFCSSTBs. This study provided fundamental information on the flexural bending mechanism of CFSSSTBs/CFCSSTBs) at low temperatures.

Preparation and properties of activated carbon-based Na3PO4 composites for low-temperature thermochemical heat storage

With the advantages of low heat storage temperature, high heat storage density, and a low price, Na3PO4 has been proposed as a thermochemical heat storage candidate material for use in solar low-temperature heat storage engineering applications. However, the application of pure Na3PO4 is limited due to its propensity for agglomeration. In this study, activated carbon-based Na3PO4 (R-AC@Na3PO4) composites with mass fractions of 30 %, 50 %, and 80 % were synthesized by melt impregnation method using activated carbon as the porous matrix. The morphology and structure of the composites were characterized, and their heat storage performances were investigated. The hydration experiments were carried out in a constant temperature and humidity chamber and dehydration experiments were carried out in thermogravimetric analysis and differential scanning calorimetry simultaneously. The results showed that at 30 °C, 60 % relative humidity, the hydration equilibrium time for the composites were only 30 %–40 % of the pure material. Meanwhile, at a mass fraction of 80 %, material's volumetric heat storage can reach 1793 J·cm−3 without agglomeration, and the performance was stable after 20 cyclic tests. This study provides a reference for the research and development of low-temperature thermochemical heat storage materials and offers more possibilities for R-AC@Na3PO4 composites in future engineering applications.

Influence of cationic vacancy diffusion on the aging behavior of low-temperature SrCo1-xRuxO3 thermosensitive ceramics

The thermosensitive ceramics of negative temperature coefficient (NTC), SrCo1-xRuxO3 (0 ≤ x ≤ 0.8), were synthesized using the solid-phase method. The research systematically explored the phase structure, microstructure, elemental chemical states, electrical properties, and aging performance. X-ray diffraction (XRD) data indicates that with the increase of Ru content, the lattice parameter increases. Scanning electron microscopy (SEM) images reveal a dense and uniform microstructure. X-ray photoelectron spectroscopy (XPS) data indicates the presence of Co2+/Co3+ and Ru4+/Ru5+ ion pairs. Resistive temperature data indicates its potential use as a low-temperature thermosensitive resistance material in the range of 2–300 K. Fitting the resistance-temperature curve using the thermally activated band conduction model and Mott's 3D variable range hopping model. Proposed the Ru–O2--Co hopping model, elucidating the hole hopping transport mechanism in NTC ceramics. Impedance spectroscopy analysis indicates that grain boundary resistance dominates the overall resistance of the sample. After aging at 77 K for 864 h, the maximum aging drift rate of the ceramic material is 1.55 %. Proposed a novel cationic vacancy diffusion model to explain aging phenomena, offering a new perspective for designing high-stability low-temperature NTC thermistors.

Preparation and properties of gel-type low-temperature phase change materials

In the context of the dual‑carbon target, there is a high emphasis on the energy efficiency of traditional mechanical cold storage systems with significant power consumption. Additionally, the implementation of time-of-use electricity pricing has played a crucial role in driving the rapid advancement of energy storage technology. The application of energy storage technology in cold storage can significantly reduce the energy consumption of the refrigeration system, save operating costs by shifting peak demand to valleys, and reduce start and stop frequencies. Therefore, studying phase-change materials with high latent heat, low cost, and good performance for cold storage is of great practical application in cold storage. The paper developed four types of gel-type phase-change cold storage materials with high latent heat, low cost, and good cycle stability. These materials mainly consist of NH4Cl, KCl, and deionized water. The phase transition temperature ranges from −18 to −21 °C, the latent heat of phase change is approximately 260 to 289 J/g, and the thermal conductivity ranges from 0.58 to 0.60 W/(m·K), which can meet the cooling demand of cold storage facilities. Furthermore, by comparing the phase transition temperature, latent heat value of phase change, and cyclic stability, a gel-type PCM with good comprehensive properties was selected for corrosion and corrosion inhibition studies with five common metal samples in welded and non-welded forms. The results showed that material B2 had slight corrosion on 1060 aluminum, 6061 aluminum, and 304 stainless steels, but no obvious corrosion phenomenon was found on 316 stainless steels. The corrosion rate of the material on red copper was the highest, and the corrosion was too strong. In addition, the corrosion of welded parts is more serious than that of non-welded parts, and the welding points are more susceptible to corrosion. Adding the corrosion inhibitor BTA to material B2 can reduce the corrosion rate of red copper by more than 94 %.

Review of the Low-Temperature Acoustic Properties of Water, Aqueous Solutions, Lipids, and Soft Biological Tissues.

Existing data on the acoustic properties of low-temperature biological materials is limited and widely dispersed across fields. This makes it difficult to employ this information in the development of ultrasound applications in the medical field, such as cryosurgery and rewarming of cryopreserved tissues. In this review, the low-temperature acoustic properties of biological materials, and the measurement methods used to acquire them were collected from a range of scientific fields. The measurements were reviewed from the acoustic setup to thermal methodologies for samples preparation, temperature monitoring, and system insulation. The collected data contain the longitudinal and shear velocity, and attenuation coefficient of biological soft tissues and biologically relevant substances-water, aqueous solutions, and lipids-in the temperature range down to -50 °C and in the frequency range from 108 kHz to 25 MHz. The multiple reflection method (MRM) was found to be the preferred method for low-temperature samples, with a buffer rod inserted between the transducer and sample to avoid direct contact. Longitudinal velocity changes are observed through the phase transition zone, which is sharp in pure water, and occurs more slowly and at lower temperatures with added solutes. Lipids show longer transition zones with smaller sound velocity changes; with the longitudinal velocity changes observed during phase transition in tissues lying between these two extremes. More general conclusions on the shear velocity and attenuation coefficient at low-temperatures are restricted by the limited data. This review enhance knowledge guiding for further development of ultrasound applications in low-temperature biomedical fields, and may help to increase the precision and standardization of low-temperature acoustic property measurements.