Large Entropy Research Articles

Optimizing Room‐Temperature Thermoelectric and Magnetocaloric Performance via Constructing Multi‐Scale Interfacial Phases in LaFeSi/BiSbTe Thermo‐Electro‐Magnetic Refrigeration Materials

AbstractFabricating a thermo‐electro‐magnetic material that exhibits simultaneously excellent magnetocaloric (MC) and thermoelectric (TE) performance is challenging since the interfacial reaction causes severe deterioration of MC and TE performance. In this work, a construction of multi‐scale interfaces in LaFe10.4Co0.8Si1.8/Bi0.5Sb1.5Te3 (LFS/BST) composites is realized by adopting a low‐temperature high‐pressure sintering strategy. It is revealed in the atomic‐scale that the interfacial reaction between LFS and BST leads to the formation of (Fe,Co)(Sb,Te)2 micro‐grains and LaTe2 nano‐grains, and the latter form low‐mismatch phase boundaries with LFS matrix. Benefiting from the multi‐scale interfacial phases, excellent MC performance of LFS is preserved alongside a minor impact on TE properties, e.g., a peak zT of 1.04 and a small decrease of 3.0% in relative cooling power are achieved in the 2%LFS/BST composite. Compared with other thermo‐electro‐magnetic materials, a good trade‐off between MC and TE performance is realized in LFS/BST composites with simultaneously high MC and TE performance. The 20%LFS/BST composite exhibits a room‐temperature zT of 0.46 with large maximum magnetic entropy change and relative cooling power of 0.81 J kg−1 K−1 and 44.83 J kg−1, respectively. This work provides an effective material design for developing the all‐solid‐state MC/TE hybrid refrigeration technique.

Magnetocaloric effect, magnetotransport and magnetic properties of polycrystalline Pr(0.65-x)GdxSr0.35MnO3 (x ≤ 0.3) compounds

Polycrystalline Pr0.65-xGdxSr0.35MnO3 (x = 0.01, 0.05, 0.1, 0.2, 0.3) manganites were prepared by conventional solid-state method. Structural analysis has revealed a change in structure with x = 0.2, from Rhombohedral (R-3c) to Orthorhombic (Pbnm) symmetry. Small oxygen deficiency was found in the samples. The electrical measurements revealed typical colossal magnetoresistance (CMR) behavior, with single metal–insulator peak at Tp for all investigated samples. The small polaron hopping (SPH) and variable-range hopping (VRH) models were used to describe the electrical conduction above Tp. Magnetic measurements show an increase in magnetization below the Curie temperature, TC. Values of Tc diminish with increasing Gd3+ content. Isothermal measurements around critical points suggest a possible interaction between the 4f-ions and Mn-sublattice The magnetic critical behavior analysis established the tri-critical mean-field model to be the governing model for the series. Large magnetic entropy change ΔSM at near room temperature (278 K) was exhibited by the x = 0.01 sample at 2.2 J/kgK in μ0ΔH = 1 T and 5.36 J/kgK in μ0ΔH = 4 T. The largest |ΔSM| value was shown by the x = 0.1 sample. The values of the relative cooling power (RCP) and the temperature-averaged entropy change (TEC) increased with substitution qualifying these compounds as magnetocaloric materials.

Large cryogenic magnetocaloric effect in Na5Gd4F(SiO4)4

The adiabatic demagnetization refrigeration based on the magnetocaloric effect of magnetic materials has been regarded as an effective technology to attain sub-Kelvin temperature. In this article, the magnetic properties and MCE of Na5Gd4F(SiO4)4 compound are investigated. Due to the high Gd3+ ion/anion ligand ratio and weak magnetic interaction, Na5Gd4F(SiO4)4 exhibits a large magnetic entropy change of 49.6 J·kg−1·K−1 under magnetic field change of 0–7 T at 2.6 K, which surpasses the commercial magnetic refrigerant Gd3Ga5O12 under the same conditions. Besides, its refrigeration capacity and the relative cooling power under magnetic field change of 0–7 T reaches up to 308.9 J·kg−1 and 406.7 J·kg−1, respectively. These properties indicate that Na5Gd4F(SiO4)4 compound is a promising magnetic refrigeration material.

Magnetostructural transformation and magnetocaloric response in Mn(Fe)NiSi(Al) alloys

An efficient magnetocaloric refrigerant must have certain characteristics such as a sharp transition near the desired working temperature, a large cyclic magnetocaloric response, and the use of raw materials with reduced costs and low environmental consequences. In this sense, this work focuses on a series of rare-earth- and Co-free Mn0.5Fe0.5NiSi1-xAlx alloys (x = 0.0525, 0.060, 0.0685) with promising magnetocaloric properties. The alloys were synthesized using combined arc melting and induction melting techniques, as this synthesis route provides improved control on the sample composition and homogeneity. We investigated how the heat treatment temperature and Al content affect the magnetostructural and magnetocaloric properties of the alloys. On the one hand, it is found that annealing at 1173 K for 7 days leads to a sharp magnetostructural transformation with no traces of impurities for the alloy with x = 0.0525. Under these conditions, a large isothermal entropy change of –11.5 J kg−1 K−1 for 1 T is obtained near room temperature, significantly improving the value of the as-cast sample. On the other hand, following this optimal heat treatment, the influence of Al content is studied: upon increasing the Al concentration the magnetostructural transformation shifts to lower temperatures, ranging from 320 K for x = 0.0525 to 220 K for x = 0.0685 (measured upon heating).

Nano‐High Entropy Materials in Electrocatalysis

AbstractHigh entropy materials (HEMs) compositing of at least five elements have gained widespread attention in the field of electrocatalysis due to their tunable activities and high stability. These intrinsic properties can be further highlighted when the size of HEMs comes to the nanoscale. In nanostructured HEMs, the fascinating properties including large composition space, multi‐element synergy, and high configuration entropy are expected to endow nano‐HEMs with excellent catalytic activity and stability, thus providing greater potential for the design of advanced electrocatalysts. In this review, nano‐HEMs are differentiated in detail in dimensions and the common synthesis methods are summarized. Additionally, from the perspective of the complex nanostructure‐performance relationship, the applications of nano‐HEMs in electrocatalysis systems, including water‐splitting (hydrogen evolution reaction (HER), oxygen evolution reaction (OER)), hydrogen oxidation reaction (HOR), oxygen reduction reaction (ORR), carbon dioxide reduction reaction (CO2RR), nitrogen reduction reaction (NRR) and alcohol oxidation reaction (AOR) are discussed. Finally, the main challenges faced by nano‐HEMs electrocatalysis are underscored. This review is expected to provide more insights into understanding and developing efficient electrocatalytic materials for practical applications.

Low-temperature magnetic refrigeration in Gd20Tb20Er20Al20M20 (M = Fe, Co) high-entropy metallic glasses

This paper focuses on the magnetocaloric effect (MCE) of Gd20Tb20Er20Al20M20 (M = Fe, Co) high-entropy metallic glasses (HE-MGs). XRD and TEM results indicate that both HE-MGs are amorphous. Magnetic studies show that both HE-MGs display spin-glass behavior, undergo a second-order phase transition from ferromagnetic to paramagnetic, and exhibit soft magnetic properties at the Curie temperature (TC). Notable large and broad table-like magnetic entropy change characteristics of Gd20Tb20Er20Al20Fe20 (Gd20Tb20Er20Al20Co20) appear near a TC of 92 (51) K. Hence, under 7 T magnetic field, |-∆SMmax|, ∆ TFWHM, and RCP are 7.83 (10.10) J·kg-1·K-1, 120.07 (71.88) K, and 1008.26 (805.70) J·kg-1, respectively. Furthermore, the modulation of the magnetic and magnetocaloric properties of the samples after substitution of Fe for Co was revealed by the intricate 3d-3d and 3d-4f exchange interactions within the system. The magnetic phase transition critical behaviors in both HE-MGs were analyzed using the scaling law to clarify the deviation of amorphous materials from the mean-field theory. Thus, this study not only highlights the potential of this material for low-temperature magnetic refrigeration applications, but also expands our understanding of its physical properties.

Infinite-Volume Gibbs States of the Generalized Mean-Field Orthoplicial Model

The generalized mean-field orthoplicial model is a mean-field model on a space of continuous spins on Rn\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathbb {R}^n$$\\end{document} that are constrained to a scaled (n-1)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(n-1)$$\\end{document}-dimensional ℓ1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\ell _1$$\\end{document}-sphere, equivalently a scaled (n-1)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(n-1)$$\\end{document}-dimensional orthoplex, and interact through a general interaction function. The finite-volume Gibbs states of this model correspond to singular probability measures. In this paper, we use probabilistic methods to rigorously classify the infinite-volume Gibbs states of this model, and we show that they are convex combinations of product states. The predominant methods utilize the theory of large deviations, relative entropy, and equivalence of ensembles, and the key technical tools utilize exact integral representations of certain partition functions and locally uniform estimates of expectations of certain local observables.

Temperature-dependent lattice dynamics study on phase stability, martensitic transformation mechanism, and vibrational entropy properties of B2-type Ni–Mn–Ti Heusler alloy

The all-d-metal Ni–Mn–Ti Heusler alloy with its good mechanical properties and colossal caloric effects has attracted significant attention for mechanocaloric refrigeration. However, the phase stability of the B2-type disordered structure at finite temperatures and the physical origin of large phase transformation entropy change in theoretical calculation remain unclear. In view of thermal and strongly anharmonic effects, we combined the first-principles and temperature dependent effective potential calculations to systematically study the phase stability, martensitic transformation mechanism, and vibrational entropy properties of B2 partial disordered structures for Ni8Mn5Ti3 and Ni8Mn6Ti2. Our results showed the austenitic structures of Ni8Mn5Ti3 and Ni8Mn6Ti2 both exhibit antiferromagnetic interaction behaviors at targeted temperatures, resolving the contradiction between previous calculations and experiments. By the analysis of phonon dispersion relations and Helmholtz free energies at low and high temperatures, we provided a deeper explanation for the underlying mechanism of martensitic transformation. Meanwhile, the phase transformation temperatures and vibrational entropy changes were accurately predicted compared with the experiment results. Specifically, we demonstrated that the large vibrational entropy change of Ni–Mn–Ti material originates from the contributions of both the tetragonal distortion ratio and volume change, which provides important theoretical guidance and has great practical significance for designing the solid-state material with large vibrational entropy change in the application of solid-state refrigeration.

Magnetocaloric effect of topological excitations in Kitaev magnets

Traditional magnetic sub-Kelvin cooling relies on the nearly free local moments in hydrate paramagnetic salts, whose utility is hampered by the dilute magnetic ions and low thermal conductivity. Here we propose to use instead fractional excitations inherent to quantum spin liquids (QSLs) as an alternative, which are sensitive to external fields and can induce a very distinctive magnetocaloric effect. With state-of-the-art tensor-network approach, we compute low-temperature properties of Kitaev honeycomb model. For the ferromagnetic case, strong demagnetization cooling effect is observed due to the nearly free Z2 vortices via spin fractionalization, described by a paramagnetic equation of state with a renormalized Curie constant. For the antiferromagnetic Kitaev case, we uncover an intermediate-field gapless QSL phase with very large spin entropy, possibly due to the emergence of spinon Fermi surface and gauge field. Potential realization of topological excitation magnetocalorics in Kitaev materials is also discussed, which may offer a promising pathway to circumvent existing limitations in the paramagnetic hydrates.

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.

Charge Redistribution in High-Entropy Perovskite Oxide Porous Nanotubes Boosts Nitrate Electroreduction to Ammonia.

High-entropy perovskite oxides are promising materials in the field of electrocatalysis due to their advantages such as large spatial composition regulation, entropy effects, and tunable material properties. However, the preparation of high-entropy perovskite oxides with stable and controllable structures still remains challenging. Herein, we fabricated a series of high-entropy perovskite oxide porous nanotubes (PNTs) by electrospinning as efficient electrocatalysts for the nitrate reduction reaction (NO3RR). We further revealed that the different diffusion and decomposition behaviors of metal ions and polymers during the calcination process are the key to the formation of high-entropy perovskite oxide PNTs. Especially, LaSrNiCoMnFeCuO3 PNTs show excellent performance of the NO3RR, achieving the maximum NH3 Faradaic efficiency of almost 100%, yield rate of 1657.5 μg h-1 mgcat.-1, and durable stability after successive cycling, being one of the best electrocatalysts for the NO3RR. The mechanism studies show that the charge redistribution induced by the multisite synergistic effect and abundant unsaturated sites in the high-entropy perovskite oxide PNTs favors the adsorption of NO3- and key intermediates and reduces the catalytic energy barrier, thus further achieving high NO3- conversion efficiency.

Achieving Magnetic Refrigerants with Large Magnetic Entropy Changes and Low Magnetic Ordering Temperatures.

Adiabatic demagnetization refrigeration (ADR) is a promising cooling technology with high efficiency and exceptional stability in achieving ultralow temperatures, playing an indispensable role at the forefront of fundamental and applied science. However, a significant challenge for ADR is that existing magnetic refrigerants struggle to concurrently achieve low magnetic ordering temperatures (T0) and substantial magnetic entropy changes (-ΔSm) at ultralow temperatures. In this work, we propose the combination of Gd3+ and Yb3+ to effectively regulate both -ΔSm and T0 in ultralow temperatures. Notably, the -ΔSm values for Gd0.1Yb0.9F3 (1) and Gd0.3Yb0.7F3 (2) in the 0.4-1.0 K range exceed those of all previously reported magnetic refrigerants within this temperature interval, positioning them as the most efficient magnetic refrigerants for the third stage to date. Although the -ΔSm values for Gd0.5Yb0.5F3 (3) in 1-4 K are less than those of the leading magnetic refrigerant Gd(OH)F2, the -ΔSm values for Gd0.7Yb0.3F3 (4) in 1-4 K at 2 T surpass those of all magnetic refrigerants previously documented within the same temperature range, making it the superior magnetic refrigerant for the fourth stage identified thus far.

Effect of Fe on the microstructure and magnetic transition of Mn-Fe-P-Si Microwires

This work systematically investigated the effect of Fe content on the microstructure and magnetic transition behaviors of melt-extracting Mn-Fe-P-Si microwires. It was shown that the Fe content does not change the main phase of the samples, i.e. Fe2P compound, which decreased with the increasement of Fe content. The transition temperature (Ttran) decreased from 311 to 245.5 K while the thermal hysteresis (Thys) increased from 9.5 to 22.5 K increasing Fe from 0.90 to 1.05. The samples realized the first order magnetic transition at x = 1.00 and 1.05, correspondingly the samples demonstrated large magnetic hysteresis losses (Wy,) and isothermal magnetic entropy change (−∆Sisopeak) at 5 T, 59.1 J kg−1 and 14.5 J kg−1 K−1 for the sample x =1.00, 58.4 J kg−1 and 15.8 J kg−1 K−1 for the sample x = 1.05. In contrast, the samples at x = 0.90 and 0.95 indicated second order transition character, and the Wy and −∆Sisopeak were much smaller, i.e. 14.8 J kg−1 and 10.3 J kg−1 K−1, 9.7 J kg−1 and 10.7 J kg−1 K−1 respectively for the samples x = 0.90 and 0.95. The largest effective refrigerant capacity (RCE, 293.7 J kg−1, 5 T) is found at x = 0.90. The reduced hysteresis and maintained competitive isothermal magnetic entropy change make the melt-extracting Mn-Fe-P-Si microwires with optimized Fe content as a promising magnetocaloric material family applied in real magnetic refrigeration applications.

Colossal Barocaloric Effect near Ambient Temperature in 1-Dodecanol under a Low Pressure.

Solid-state refrigeration based on the barocaloric effect is an effective alternative to traditional vapor compression refrigeration. Here 1-dodecanol has been studied due to its large latent heat at a solid-liquid phase transition point around room temperature. The transition temperature will vary with the applied hydrostatic pressure, exhibiting with a sensitivity of 0.14 K MPa-1, which indicates its potential for refrigeration. A pressure of 40 MPa can result in a large isothermal entropy change of 520 J kg-1 K-1 (equivalent to that obtained in vapor compression refrigeration) at 297 K. A large adiabatic temperature change of >20 K in 1-dodecanol was acquired by direct measurement. A wide temperature window of ∼50 K (288-337 K) can be obtained in 1-dodecanol, which demonstrates broad application prospects. These discoveries offer promising prospects for barocaloric cooling and high-efficiency refrigeration technologies relying on solid-liquid phase transitions.

Effect of Cu addition on the physical and mechanical properties of a Ni–Mn–In–Co polycrystalline shape memory alloy

The martensite transformation (MT), magnetocaloric effect (MCE), and mechanical properties of the polycrystalline Ni46Mn36In14Co4 (Co4) alloys with doping of 4 at.% Cu were examined. A large magnetization change (ΔM, 92 emu/g), large magnetic entropy change (ΔSM, 37.3 J kg−1K−1), high refrigerant capacity (RC, 261 J kg−1), relatively high sensitivity to magnetic fields (2.8 K/T), and two-way magnetic-field-induced MT were attained at approximately room temperature. Moreover, the compressive fracture strength and strain of the alloy reached 335 MPa and 7.4 %, respectively. Finally, the mechanism of the excellent combination properties of the Ni42Mn36In14Co4Cu4 (Co4Cu4) alloy was discussed. This study can aid in the development of high-performance magnetic refrigeration and intelligent actuator materials.

Intelligent Fault Diagnosis Method for Transformer Driven by Multiple Vibration Data

Abstract Early monitoring and early warning of transformer failure are crucial to ensure the safe and dependable functioning of the power system, as transformers are essential equipment within the system. On multivariate vibration data, this work presents a sophisticated approach for diagnosing faults in transformers which integrates entropy model and machine learning. Firstly, a new coarse-grained method is introduced into the improved multiscale fuzzy entropy to improve the disadvantage of the traditional entropy model with large entropy fluctuation under high-scale factors. Furthermore, the features of transformer multivariate vibration signals are extracted by the entropy model. Finally, the extreme learning machine is utilized to achieve efficient detection of transformer defects. This method provides a useful method reference for fault diagnosis of power equipment with multi-vibration signal, and has good reference value.

Avionics Module Fault Diagnosis Algorithm Based on Hybrid Attention Adaptive Multi-Scale Temporal Convolution Network.

Since the reliability of the avionics module is crucial for aircraft safety, the fault diagnosis and health management of this module are particularly significant. While deep learning-based prognostics and health management (PHM) methods exhibit highly accurate fault diagnosis, they have disadvantages such as inefficient data feature extraction and insufficient generalization capability, as well as a lack of avionics module fault data. Consequently, this study first employs fault injection to simulate various fault types of the avionics module and performs data enhancement to construct the P2020 communications processor fault dataset. Subsequently, a multichannel fault diagnosis method, the Hybrid Attention Adaptive Multi-scale Temporal Convolution Network (HAAMTCN) for the integrated functional circuit module of the avionics module, is proposed, which adaptively constructs the optimal size of the convolutional kernel to efficiently extract features of avionics module fault signals with large information entropy. Further, the combined use of the Interaction Channel Attention (ICA) module and the Hierarchical Block Temporal Attention (HBTA) module results in the HAAMTCN to pay more attention to the critical information in the channel dimension and time step dimension. The experimental results show that the HAAMTCN achieves an accuracy of 99.64% in the avionics module fault classification task which proves our method achieves better performance in comparison with existing methods.

Structural Order in the Hydration Shell of Nonpolar Groups versus that in Bulk Water.

The poor solubility of nonpolar compounds in water around room temperature is governed by a large and negative entropy change, whose molecular cause is still debated. Since the Frank and Evans original proposal in 1945, the large and negative entropy change is usually attributed to the formation of ordered structures in the hydration shell of nonpolar groups. However, the existence of such ordered structures has never been proven. The present study is aimed at providing available structural results and thermodynamic arguments disproving the existence of ordered structures in the hydration shell of nonpolar groups.

Inhomogeneous quenches as state preparation in two-dimensional conformal field theories

The nonequilibrium process where the system does not evolve to the featureless state, that without quantum properties, is one of the new central objects in the nonequilibrium phenomena. In this paper, starting from the short-range entangled state in the two-dimensional conformal field theories (2D CFTs), the boundary state with a regularization, we evolve the system with the inhomogeneous Hamiltonians called Möbius/sine-square-deformed (SSD) ones. Regardless of the details of CFTs considered in this paper, during the Möbius evolution, the entanglement entropy exhibits the periodic motion called quantum revival. During SSD time evolution, except for some subsystems, in the large time regime, entanglement entropy and mutual information are approximated by those for the vacuum state. We argue the time regime for the subsystem to cool down to vacuum one is t1≫O(LlA), where t1, L, and lA are time, system, and subsystem sizes. This finding suggests the inhomogeneous quench induced by the SSD Hamiltonian may be used as the preparation for the approximately vacuum state. We propose the gravity dual of the systems considered in this paper, furthermore, and generalize it. In addition to them, we discuss the relation between the inhomogeneous quenches and continuous multiscale entanglement renormalization ansatz (cMERA). Published by the American Physical Society 2024

Designing Advanced Amorphous/Nanocrystalline Alloys by Controlling the Energy State.

Amorphous alloys, also known as metallic glasses, exhibit many advanced mechanical, physical, and chemical properties. Owing to the nonequilibrium nature, their energy states can vary over a wide range. However, the energy relaxation kinetics are very complex and composed of various types that are coupled with each other. This makes it challenging to control the energy state precisely and to study the energy-properties relationship. This brief review introduces the recent progresses on studying the enthalpy relaxation kinetics during isothermal annealing, for example, the observation of two-step relaxation phenomenon, the detection of relaxation unit (relaxun), the key role of large activation entropy in triggering memory effect, the influence of glass energy state on nanocrystallization. Based on the above knowledge, a new strategy is proposed to design a series of amorphous alloys and their composites consisting of nanocrystals and glass matrix with superior functional properties by precisely controlling the nonequilibrium energy states. As the typical examples, Fe-based amorphous alloys with both advanced soft magnetism and good plasticity, Gd-based amorphous/nanocrystalline composites with large magnetocaloric effect, and Fe-based amorphous alloys with high catalytic performance are specifically described.