Large Entropy Change Research Articles

On the structural and thermo-magnetic study of the magnetocaloric Heusler alloy Ni2Mn1-x Cu x Ga0.8Al0.2

Full Heusler alloys present martensitic transition and shape memory effect related phenomena and several technological applications can be envisaged. One promising area is the magnetocaloric effect (MCE) as the magnetic and structural transitions combine to produce a large isothermal entropy and adiabatic temperature change useful for heating and cooling applications. In this work, we study a Ni–(Mn, Cu)–(Ga, Al) Heusler alloy family which has a giant MCE when the chemical composition is fine-tuned to bring the temperature of the second-order magnetic transition close the first-order structural one. Our results show that, for a certain range of copper concentration, the samples show interesting physical properties captured by calorimetric, microscopy imaging, and magnetization measurements, leading to a high MCE with minimized hysteresis.

Reversible colossal barocaloric effects near room temperature in 1-X-adamantane (X=Cl, Br) plastic crystals

Plastic crystals undergo phase transitions with unusually large volume and entropy changes related to strong molecular orientational disordering. These features have led to a resurgent interest in these materials because recently they have shown great potential in solid-state cooling applications driven by pressure. Here we demonstrate that two plastic crystals derived from adamantane -1-Br-adamantane and 1-Cl-adamantane- undergo colossal reversible barocaloric effects under moderate pressure changes in a wide temperature span near room temperature thanks to a relatively small hysteresis and very high sensitivity of the transition temperature to pressure. In particular, 1-Cl-adamantane displays an optimal operational temperature range covering from ~40 K below and up to room temperature, and under a pressure change of 1 kbar this compound outperforms any other barocaloric material known so far. Our work gives strong support to plastic crystals as best candidates for barocaloric cooling. We also provide insight into the physical origin of the entropy changes through the analysis of the disorder on the involved phases.

Colossal Barocaloric Effect by Large Latent Heat Produced by First‐Order Intersite‐Charge‐Transfer Transition

AbstractMaterials which show novel thermal properties can be used to make highly efficient and environmentally friendly energy systems for thermal energy storage and refrigeration through caloric effects. An A‐site‐ordered quadruple perovskite‐structure oxide, NdCu3Fe4O12, is found to release significant latent heat, 25.5 kJ kg−1 (157 J cc−1), at the intersite‐charge‐transfer transition temperature near room temperature. The transition is first‐order and accompanied by an unusual magnetic ordering and a large negative‐thermal‐expansion‐like volume change, and thus, it causes a large entropy change (84.2 J K−1 kg−1). The observed entropy change is comparable to the largest changes reported in inorganic solid materials, and more importantly, it is utilized through a colossal barocaloric effect. The adiabatic temperature change by applying 5.1 kbar pressure is estimated to reach 13.7 K, which means efficient refrigeration can be realized through this effect.

Supramolecular Thermocells Based on Thermo-Responsiveness of Host–Guest Chemistry

Abstract Molecular machines leverage sub-nanometer level intermolecular forces and host–guest interactions to perform useful work observable at the macroscopic level. The development of molecular machines for the past three decades has resulted in successful applications from molecular switches, chemical sensing, to actuators. However, the application of molecular machines and supramolecular chemistry in energy production is rare and has been highly anticipated. This review introduces the advancement of supramolecular thermocells, initially proposed by our research group, which use thermo-responsive host–guest interaction to regenerate electrochemical energy from low-grade heat sources. The selective transport of a redox species carried by the host molecule from the cooled to the heated electrode creates a concentration gradient of the guest redox species and provides an additional voltage to the thermocell. The key properties of useful host molecules for the supramolecular thermocells are: (1) high selectivity of the host molecule to capture either the oxidized or reduced species as the guest, (2) inhibition of the redox activity after the encapsulation, (3) large entropy change at the release of the guest molecule in response to the temperature changes. Design principles and promising candidates of molecular machines for the future development of supramolecular thermocells are presented here.

Spreading Dynamics of a Precursor Film of Ionic Liquid or Water on a Micropatterned Polyelectrolyte Brush Surface.

Time evolution of the microscopic wetting velocity of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMI-TFSI) or water on a micrometer-scale line-patterned surface with a poly(3-sulfopropyl methacrylate) brush and a hydrophobic perfluoroalkyl monolayer was precisely measured by direct observation using optical microscopy and a selective dyeing method over a long period (178 days). When a liquid droplet was placed on the dyed line-patterned brush surface, the liquid penetrated and spread into the polymer brush layer, forming a precursor thin film that extended beyond the macroscopic contact line. The elongation proceeded in two stages by an adiabatic process followed by a diffusive process. The elongation distance X increased with time in proportion to t2.6 for water and t0.81 for EMI-TFSI during the adiabatic process. In a diffusive process, the advancing velocity of the precursor film was markedly reduced to be expressed as X ∝ t0.66 for water and X ∝ t0.21 for EMI-TFSI, indicating that the diffusive process was affected by the energy dissipation of the wetting system. The high viscosity and the strong molecular interaction of EMI-TFSI with the polymer brush gave a large entropy change during the wetting process to result in a slower spreading velocity.

High-efficiency magnetic refrigeration using holmium

Magnetic refrigeration (MR) is a method of cooling matter using a magnetic field. Traditionally, it has been studied for use in refrigeration near room temperature; however, recently MR research has also focused on a target temperature as low as 20 K for hydrogen liquefaction. Most research to date has employed high magnetic fields (at least 5 T) to obtain a large entropy change, which requires a superconducting magnet and, therefore, incurs a large energy cost. Here we propose an alternative highly efficient cooling technique in which small magnetic field changes, Δμ0H ≤ 0.4 T, can obtain a cooling efficiency of −ΔSM/Δμ0H = 32 J kg−1K−1T−1, which is one order of magnitude higher than what has been achieved using typical magnetocaloric materials. Our method uses holmium, which exhibits a steep magnetization change with varying temperature and magnetic field. The proposed technique can be implemented using permanent magnets, making it a suitable alternative to conventional gas compression–based cooling for hydrogen liquefaction.

Large magnetocaloric entropy change in ferrimagnetic Er1-xCo2 systems at cryogenic temperatures: the role of erbium deficiency

Large magnetocaloric entropy change in ferrimagnetic Er1-xCo2 systems at cryogenic temperatures: the role of erbium deficiency

Statics and dynamics of ferroelectric domains in molecular multiaxial ferroelectric (Me3NOH)2[KCo(CN)6

Statics and dynamics of ferroelectric domains in molecular perovskite multiaxial ferroelectric (Me3NOH)2[KCo(CN)6].

Properties and structural coloured film preparation of some chiral dopants derived from D-Isosorbide

A series of chiral dopants derived from D-isosorbide were synthesized. Some of them exhibita monotropicsmecticA phase. Comparison of the melting points of these chiral dopants, the decrease of them is mainly driven by the large entropy change. The helical twisting power (HTP) values of these chiral dopants with branched alkyl chains, lateral fluoro-substituents and double bonds are lower than those of the chiral dopants with hexyloxy chains. Structural colored polymer films with a right-handed helix are prepared using these chiral dopants.

Biophysical and Thermodynamic Investigations on the Differentiation of Fluorescence Response towards Interaction of DNA: A Pyrene-Based Receptor versus Its Fe(III) Complex.

The Fe(III) complex [Fe(L)(NO3)(H2O)]+ (1) was prepared using a structurally characterized Schiff base ligand, 1-((pyren-1-ylimino) methyl) naphthalen-2-ol (HL), to develop an optical probe for fluorimetric recognition of DNA. An electrospray ionization-mass spectrometry (ESI-MS) study was carried out to ascertain the composition of 1 and the geometry of 1 was optimized by density functional theory (DFT) calculations. Compared to the strong intrinsic fluorescence of the ligand (HL), 1 was only weakly fluorescent. The interaction of 1 with DNA was investigated through different biophysical techniques. The fluorescence emission of 1 appeared to increase progressively in the presence of calf thymus (CT) DNA and this was utilized for the fluorimetric recognition of DNA. In comparison with 1, in the presence of DNA, the ligand HL showed quenching in its emission. The selectivity of 1 towards DNA was also confirmed in the presence of a large number of environmentally pertinent anions (NO3-, SO42-, Cl-, Br-, I-, OAC-, PO43-, ClO4-, HCO3-, H2PO4-, HPO42-, CO32-). Comprehensive DNA-binding experiments also showed that complex (1) and HL interacted with CT-DNA with different efficacies; the affinity of 1 was about six times higher than that of HL. Calorimetric studies showed that the 1-DNA association progressed with large positive entropy changes. In contrast, the association of HL with DNA was an enthalpy-driven process. Molecular docking results confirmed that the binding of 1 with CT-DNA progressed by intercalation and other noncovalent interactions.

Effect of Cu and B Co-doping on magnetocaloric effect, phase transition, and mechanical properties of Mn1.05Fe0.9P0.5-xSi0.5Cu0.10Bx alloys

With large entropy changes and flexible preparation processes, (Mn, Fe)2(P, Si) alloys have attracted wide interest from researchers for magnetic refrigeration. Cu doping can compensate for the mechanical properties, but will increase thermal hysteresis (ΔThys) and decrease the Curie temperature (TC) of (Mn, Fe)2(P, Si) alloys. To tune the TC to room temperature while maintaining low thermal hysteresis and good mechanical properties, Cu-B co-doping is applied to (Mn, Fe)2(P, Si) alloys. The results demonstrated that as the amount of B increases in Mn1.05Fe0.9P0.5-xSi0.5Cu0.10Bx alloys, the TC continuously increases from 261 K to 344 K, and the ΔThys decreases by 76%. Contour plots of XRD patterns show the shifts in Bragg angles near the Curie temperature, which are ascribed to the increase in the lattice parameters during phase transitions, leading to high internal stress. After long-term annealing, Cu tends to segregate at the grain boundaries to act as a buffer between the Fe2P-type main phase. Therefore, stress from lattice deformation during first-order phase transitions can be absorbed. This study presents a new technical route to obtain magnetic refrigeration materials with high magnetocaloric effects and good mechanical properties by co-doping Cu and B, which is instructive for engineering applications.

Elastocaloric effect in bamboo-grained Cu71.1Al17.2Mn11.7 microwires

Bamboo-grained Cu71.1Al17.2Mn11.7 microwires with diameter ∼150 μm were created by Taylor-Ulitovsky method and subsequent annealing. The grain architecture dependent superelasticity (SE) and elastocaloric effects (eCE) were confirmed. The bamboo-grained microwires exhibited low stress hysteresis loss during SE due to the reduced constraints caused by grain boundary, which is favorable for the mobility of martensite-austenite interface. Consequently, a large isothermal entropy change ∼21 J/kg K with a wide temperature range 90 K was achieved. The produced adiabatic temperature change (ΔTad) reached −11.9 K under a maximum stress 400 MPa. A stable ΔTad of −5.6 K showing little degradation in 200 eCE cycles was found with applied stress 325 MPa. This work reveals a fact that the bamboo-grained Cu–Al–Mn microwire may act as a desirable material for miniature solid-state refrigeration devices.

Enhancing giant magnetocaloric effect near room temperature by inducing magnetostructural coupling in Cu-doped MnCoGe

High performance magnetocaloric materials are crucial to realize the energy efficient and environment friendly magnetic cooling/refrigeration technology. We have designed Mn1-xCuxCoGe compounds possessing a giant magnetocaloric effect near room temperature. The magnetic and structural degree of freedom have been coupled by substituting Cu for Mn leading to a first-order magnetostructural phase transformation resulting in a giant magnetocaloric effect over a wide temperature window of 100 K (250–350 K). A very large entropy change value of 58 J.kg−1.K−1 corresponding to a magnetic field change of 5 T near room temperature has been obtained for Mn0.89Cu0.11CoGe exhibiting a maximum effective refrigerant capacity of 258.2 J.kg−1. The first-order magnetostructural phase transformation which is essential for the giant magnetocaloric effect has been confirmed by a combinatorial master-curve and Arrott-plot analyses. The results of giant magnetocaloric effect realized in Mn1-xCuxCoGe are comparable to or better than that of the other reported high performing materials, and this material can be of significant importance for the development of environment friendly and energy efficient cooling devices. The approach of magnetostructural coupling by tuning the structural and magnetic transitions for a giant magnetocaloric effect can also be adopted for other materials to design the best solid-state magnetic refrigerant.

Double-Propeller-like Heterometallic 3d-4f Clusters Ln18Co7.

Two high-nuclearity lanthanide-transition metal clusters with the general formula [Ln18CoIICoIII6(OH)14(CO3)9(CH3CH2COO)6(dea)12(H2O)30]·(NO3)8·Cl4·(CH3CH2OH)6·(H2O)12 (Ln18Co7, Ln = Gd (1) and Dy (2)) have been obtained by reacting CoCl2·6H2O, Ln(NO3)3·6H2O, and a mixture of ligands consisting of propionate and diethanolamine (H2dea). Crystal structural analysis exhibits two three-blade propellers composed of the CoIII3Ln9 units connected by one CoII ion and three CO32- ions, which assemble into a double-propeller-like structure (Ln18CoIICoIII6). Magnetocaloric effect (MCE) studies indicate that Gd18Co7 exhibits a large entropy change (-ΔSm) of 36.9 J kg-1 K-1.

Large tunable elastocaloric effect in additively manufactured Ni–Ti shape memory alloys

High-efficiency elastocaloric refrigeration requires high-performance elastocaloric materials with both large surface areas to promote heat exchange rate and large elastocaloric effects to increase the amount of heat transfer. Ni–Ti shape memory alloys (SMAs) are the most promising elastocaloric materials but they are difficult to process by conventional methods due to their poor manufacturability. Here, we successfully developed Ni–Ti SMAs with large elastocaloric effects by additive manufacturing which has the capability to fabricate complex geometries with large surface areas. The phase transformation temperatures of these additively manufactured Ni–Ti SMAs, fabricated by selective laser melting (SLM), can be tuned by varying the SLM processing parameters and/or post heat treatments and thus tunable large elastocaloric effects were achieved at different temperatures, which can be used for different applications. Owing to its large transformation entropy change and high yield strength as a result of precipitation hardening, the aged SLM fabricated alloy exhibits a remarkably large elastocaloric effect with an adiabatic temperature change as high as 23.2 K, which is among the highest values reported for all Ni–Ti SMAs fabricated by both conventional methods and additive manufacturing. Furthermore, by virtue of the high yield strength and low stress hysteresis of the aged alloy, this large elastocaloric effect shows good stability during cycling. The achievement of such large elastocaloric effects in alloys fabricated by near-net-shape additive manufacturing may accelerate the implementation of high-efficiency elastocaloric refrigeration. This study is instructive for the development of advanced high-performance solid-state refrigeration materials by additive manufacturing.

Printing (Mn,Fe)2(P,Si) magnetocaloric alloys for magnetic refrigeration applications

The fabrication of brittle magnetocaloric materials into heat exchangers is currently challenging for conventional manufacturing techniques. In the present study, we demonstrated that selective laser melting (SLM), an emerging 3D printing technique, offers a new and promising solution to fabricate the (Mn,Fe)2(P,Si) magnetocaloric alloys for magnetic refrigeration applications. The hexagonal (Mn,Fe)2(P,Si) phase, which shows a first-order magnetic transition, is successfully formed in the SLM-printed samples with a very small amount of impurity phase (less than 2% in volume fraction). The SLM processing parameters (e.g., the laser power and scanning speed) have a strong influence on the microstructure, magnetic phase transition and magnetocaloric properties of the printed samples. The microscopic mechanism underlying the changes in the microstructure and phase transition temperature has also been discussed. Besides that, a large isothermal entropy change, more than three times higher than that of the benchmark Gd material in a field change of 1 and 2 T, has been obtained in the SLM-printed samples.

Enhanced cyclic stability of elastocaloric effect in oligocrystalline Cu–Al–Mn microwires via cold-drawing

The cyclic stability of the elastocaloric effect (eCE) is an important performance for elastocaloric refrigeration. Our previously work showed that Cu-Al-Mn microwires with bamboo grains exhibited favorable eCE with small hysteresis. Here, we demonstrated that oligocrystalline grain architecture in Cu-Al-Mn microwires created via multi-step cold-drawing having favorable eCE cyclic stability. The oligocrystalline grains exhibited a preferential 〈101〉 orientation along the wire axis. The annealed microwire with diameter 130 µm showed stress-induced entropy change (ΔSσ) of 5.0 J kg−1 K−1 but degraded rapidly after ~ 15 cycles. On the other hand, the as-drawn microwire with diameter 130 µm showed a large entropy change (ΔSσ) of 10.3 J kg−1 K−1 and a temperature change (ΔT) of 4.5 K with fast fatigue rate. Moreover, the microwire exhibited a smaller ΔT = 3.0 K with stability up to 275 cycles for further cold-drawn to diameter 80 µm. The enhanced cyclic stability of elastocaloric effect in as-drawn microwire was attributed the favorable grain orientation and enhanced yield strength induced by cold-drawing. This work is instructive for designing high-performance Cu-based elastocaloric materials for solid-state cooling applications.

Large barocaloric effects in thermoelectric superionic materials

We predict the existence of large barocaloric effects above room temperature in the thermoelectric fast-ion conductor Cu$_{2}$Se by using classical molecular dynamics simulations and first-principles computational methods. A hydrostatic pressure of $1$ GPa induces large isothermal entropy changes of $|\Delta S| \sim 15$-$45$ Jkg$^{-1}$K$^{-1}$ and adiabatic temperature shifts of $|\Delta T| \sim 10$ K in the temperature interval $400 \le T \le 700$ K. Structural phase transitions are absent in the analysed thermodynamic range. The causes of such large barocaloric effects are significant $P$-induced variations on the ionic conductivity of Cu$_{2}$Se and the inherently high anharmonicity of the material. Uniaxial stresses of the same magnitude, either compressive or tensile, produce comparatively much smaller caloric effects, namely, $|\Delta S| \sim 1$ Jkg$^{-1}$K$^{-1}$ and $|\Delta T| \sim 0.1$ K, due to practically null influence on the ionic diffusivity of Cu$_{2}$Se. Our simulation work shows that thermoelectric compounds presenting high ionic disorder, like copper and silver-based chalcogenides, may render large mechanocaloric effects and thus are promising materials for engineering solid-state cooling applications that do not require the application of electric fields.

Quadrupolar ordering and exotic magnetocaloric effect in RB4 (R\u2009=\u2009Dy, Ho)

The interplay of charge, spin, orbital and lattice degrees of freedom has recently received great interest due to its potential to improve the magnetocaloric effect (MCE) for the purpose of magnetic cooling applications. Here, a new mechanism for a large entropy change with low magnetic fields in rare-earth tetraborides, especially for Ho1-xDyxB4 (x = 0.0, 0.5, and 1.0), is proposed. For x = 0.0, 0.5, and 1.0, the maximum entropy changes of the giant inverse MCE are found to be 22.7 J/kgK, 19.6 J/kgK, and 19.0 J/kgK with critical fields of 25 kOe, 40 kOe, and 50 kOe, respectively. For all compounds, systematic study on how the entropy changes as a function of the field and temperature is performed to investigate their correlation with consecutive double transitions, i.e., the magnetic dipolar order at T = TN and the quadrupolar order at T = TQ (TQ < TN). Based on Landau theory, it is found that this behaviour is attributed to the strong coupling between magnetic dipoles and quadrupoles in the presence of strong spin-orbit coupling and geometric frustration. Our work offers new insights into both academic and industrial interests in the discovery of giant MCE with various applications for magnetic cooling systems.

Giant elastocaloric effect in a Mn-rich Ni44Mn46Sn10 directionally solidified alloy

The superelastic and elastocaloric properties of a Mn-rich Ni44Mn46Sn10 polycrystalline alloy prepared by directional solidification were studied. Owing to the coarse columnar shaped grains with strong ⟨001⟩A preferred orientation, a large superelastic strain up to 8% and a transformation strain of 5.6% can be obtained through compressive stress induced martensitic transformation. Moreover, a giant adiabatic temperature variation up to –18 K was achieved on removing the stress. Such a remarkable elastocaloric effect is attributed to the large transformation entropy change through composition modification and the enhanced mechanical properties due to the formation of a highly textured microstructure in the directionally solidified alloy.