Small Thermal Hysteresis Research Articles

MAGNETOCALORIC EFFECT AROUND CURIE TEMPERATURE IN Ni50-x CuxMn38Sn12B3 SHAPE MEMORY RIBBONS

The magnetocaloric effect in Ni50-xCuxMn38Sn12B3 ribbons depending on the Cu substitution (x= 0, 1, 3) was investigated around the Curie temperature. The purpose of the present study was to analyze the magnetocaloric effect around a second order phase transition (around the Curie temperature) which has a smaller thermal hysteresis compared to a first order phase transition (Martensitic transition). The Curie temperature of the ribbons shifted to higher temperatures with increasing Cu content. A conventional magnetocaloric effect (MCE) was observed around the Curie temperature when the ribbons are subjected to a magnetic field change of 5 T. The magnetic entropy changes were calculated based on the isothermal magnetization data using thermodynamic Maxwell equation. The highest magnetic entropy change and the refrigerant capacity was obtained for the x=1 ribbon.

Effect of Heat Treatment Temperature on Martensitic Transformation and Superelasticity of the Ti49Ni51 Shape Memory Alloy

The martensitic transformation and superelasticity of Ti49Ni51 shape memory alloy heat-treatment at different temperatures were investigated. The experimental results show that the microstructures of as-cast and heat-treated (723 K) Ni-rich Ti49Ni51 samples prepared by rapidly-solidified technology are composed of B2 TiNi phase, and Ti3Ni4 and Ti2Ni phases; the microstructures of heat-treated Ti49Ni51 samples at 773 and 823 K are composed of B2 TiNi phase, and of B2 TiNi and Ti2Ni phases, respectively. The martensitic transformation of as-cast Ti49Ni51 alloy is three-stage, A→R→M1 and R→M2 transformation during cooling, and two-stage, M→R→A transformation during heating. The transformations of the heat-treated Ti49Ni51 samples at 723 and 823 K are the A↔R↔M/A↔M transformation during cooling/heating, respectively. For the heat-treated alloy at 773 K, the transformations are the A→R/M→R→A during cooling/heating, respectively. For the heat-treated alloy at 773 K, only a small thermal hysteresis is suitable for sensor devices. The stable σmax values of 723 and 773 K heat-treated samples with a large Wd value exhibit high safety in application. The 773 and 823 K heat-treated samples have large stable strain–energy densities, and are a good superelastic alloy. The experimental data obtained provide a valuable reference for the industrial application of rapidly-solidified casting and heat-treated Ti49Ni51 alloy.

Reversible adiabatic temperature change in the shape memory Heusler alloyNi2.2Mn0.8Ga: An effect of structural compatibility

The large magnetocaloric effect (MCE) observed in Ni-Mn based shape-memory Heusler alloys put them forward to use in magnetic refrigeration technology. It is associated with a first-order magnetostructural (martensitic) phase transition. We conducted a comprehensive study of the MCE for the off-stoichiometric Heusler alloy Ni$_{2.2}$Mn$_{0.8}$Ga in the vicinity of its first-order magnetostructural phase transition. We found a reversible MCE under repeated magnetic field cycles. The reversible behavior can be attributed to the small thermal hysteresis of the martensitic phase transition. Based on the analysis of our detailed temperature dependent X-ray diffraction data, we demonstrate the geometric compatibility of the cubic austenite and tetragonal martensite phases. This finding directly relates the reversible MCE behavior to an improved geometric compatibility condition between cubic austenite and tetragonal martensite phases. The approach will help to design shape-memory Heusler alloys with a large reversible MCE taking advantage of the first-order martensitic phase transition.

Observation of Room-Temperature Range Magnetocaloric Effect in PrSr1−xPbxMn2O6 (0.4 ≤ x ≤ 0.6) Double-Perovskite Manganite System

The Pr(Sr1−xPbx)Mn2O6 (0.4 ≤ x ≤ 0.6) double-perovskite manganite samples have been produced by using a sol-gel method. The Rietveld refinement method has been used to analyse the structural properties, and the results show that all samples are crystallized in monoclinic structure with P21/n space group without any impurity phase. The temperature dependence of magnetization measurement shows that samples exhibit paramagnetic to ferromagnetic phase transition by decreasing temperature. The values of the $T_{\mathrm {C}}$ are determined as 286, 280 and 278 K for $x =$ 0.4, 0.5 and 0.6 in Pr(Sr1−xPbx)Mn2O6 samples, respectively. Isothermal applied magnetic field-dependent magnetization curves are used to determine both order of magnetic phase transition and magnetic entropy change (ΔSM) value. $-$ ΔSM values are found as 3.68, 3.15 and 2.85 J kg− 1 K− 1 for PSPM-4, PSPM-5 and PSPM-6 samples, respectively. Additionally, magnetic phase transition of the samples is identified as second-order magnetic phase transition that indicates accompanying small thermal and magnetic hysteresis to the samples during the phase transition. Relative cooling power (RCP) values are determined as 282, 233 and 268 J kg− 1 for PSPM-4, PSPM-5 and PSPM-6 samples, respectively.

Conductive thermal diode based on the thermal hysteresis of VO2 and nitinol

We theoretically demonstrate that the junction between a phase-change material with a phase-invariant one can efficiently function as a conductive thermal diode. Analytical expressions for the heat flux and optimal rectification factor are derived and analyzed for junctions whose operations are driven by the thermal conductivity hysteresis of both VO2 and nitinol. It is shown that phase-change materials with higher thermal conductivity contrast, smaller thermal hysteresis, and faster phase transitions yield a conductive thermal diode with higher rectification of heat currents. Rectification factors of up to 19.7% and 18.8% are found for thermal diodes based on VO2 and nitinol, operating with a temperature difference between their terminals of 369.5 − 300 = 69.5 K and 388.2 − 273 = 115.2 K, respectively. These similar rectification factors could be enhanced by increasing the thermal conductivity variations of the diode terminals, and hence, the results obtained will be useful for guiding the development of phase-change materials capable of optimizing the rectification of conductive heat fluxes.

Mononuclear Fe(II) Complexes Based on the Methylpyrazinyl-Diamine Ligand: Chemical-, Thermo- and Photocontrol of Their Magnetic Switchability.

Two new mononuclear Fe(II) complexes, [Fe(2MeLpz)(NCX)2] (L = N,N'-dimethyl-N,N'-bis((pyrazin-2-yl)methyl)-1,2-ethanediamine and X = S (1), BH3 (2)), have been synthesized and characterized by single-crystal X-ray diffraction, magnetic, optical reflectivity, and photomagnetic measurements. They have similar FeN6 coordination environments offered by the tetradentate ligand with a cis-α conformation and two NCX- coligands in cis positions. However, 1 and 2 have different molecular arrangements and crystal packings, and are isolated in orthorhombic Pbnb and monoclinic C2/c space groups, respectively. 1 remains in a high spin state (S = 2) over all temperatures while 2 undergoes a spin transition around 168 K with a small thermal hysteresis of about 0.4 K (at a temperature scan rate of 1.3 K min-1). This phase transition, which can also be optically detected due to the associated marked change of the sample color, occurs between two structurally characterized phases, which exhibit Fe(II) complexes in their high spin and low spin states at high and low temperatures, respectively. The reversible photoswitching between these two states has also been confirmed at low temperatures using well separated wavelength irradiations.

Discovery of Rapid and Reversible Water Insertion in Rare Earth Sulfates: A New Process for Thermochemical Heat Storage.

Thermal energy storage based on chemical reactions is a prospective technology for the reduction of fossil-fuel consumption by storing and using waste heat. For widespread application, a critical challenge is to identify appropriate reversible reactions that occur below 250 °C, where abundant low-grade waste heat and solar energy might be available. Here, it is shown that lanthanum sulfate monohydrate La2 (SO4 )3 ⋅H2 O undergoes rapid and reversible dehydration/hydration reactions in the temperature range from 50 to 250 °C upon heating/cooling with remarkably small thermal hysteresis (<50 °C), and thus it emerges as a new candidate system for thermal energy storage. Thermogravimetry and X-ray diffraction analyses reveal that the reactions proceed through an unusual mechanism for sulfates: water is removed from, or inserted in La2 (SO4 )3 ⋅H2 O with progressive change in hydration number x without phase change. It is also revealed that only a specific structural modification of La2 (SO4 )3 exhibits this reversible dehydration/hydration behavior.

Giant caloric effect of low-hysteresis metamagnetic shape memory alloys with exceptional cyclic functionality

Solid-state caloric cooling is currently under extensive study owing to its great potential to replace the conventional vapor-compression technique. The search for refrigeration materials displaying a unique combination of pronounced caloric effect, low hysteresis and high reversibility on phase transformation, as well as multiferroic behavior is nowadays very active. Here we report a singular Ni50Mn31.5In16Cu2.5 metamagnetic shape memory alloy exhibiting giant adiabatic temperature changes of 13 K upon loading and −10 K upon unloading. This value significantly exceeds any previously reported data of ferroic materials. Simultaneously, a small thermal hysteresis of 3 K and an exceptional phase transformation stability over 105 magnetic field cycles have been achieved by ensuring the compatible kinematic conditions of specific lattice interface. Moreover, we propose a strategy to further reduce hysteretic losses and improve the reversibility of magnetocaloric effect by manipulating transformation paths evoked by magnetic field and stress, and therefore such a multicaloric approach is attractively beneficial for reaching high energetic utilization efficiency.

Structure, magnetism and magnetocalorics of Fe-rich (Mn,Fe)1.95P1-Si melt-spun ribbons

Abstract Single phase Mn 0.66 Fe 1.29 P 1- x Si x (0 ≤ x ≤ 0.42) compounds were synthesized using the melt-spinning (rapid solidification) technique. All the compounds form in the Fe 2 P-type hexagonal structure, except a Co 2 P-type orthorhombic structure of the Si-free Mn 0.66 Fe 1.29 P compound. The compounds with 0.24 ≤ x ≤ 0.42 present a FM-PM phase transition, while the compounds with lower Si content show an AFM-PM phase transition. In the Mn 0.66 Fe 1.29 P 1- x Si x compounds, T C and Δ T hys are not only Si content dependent, but also magnetic field dependent. By increasing the Si content from x = 0.24 to 0.42, T C increases from 195 to 451 K and Δ T hys is strongly reduced from ∼61 to ∼1 K. T C increases and Δ T hys decreases with increasing magnetic field, Δ T C /Δ B is about 4.4 K/T. Mn 0.66 Fe 1.29 P 1- x Si x compounds show large saturation magnetic moments with values up to 4.57 μ B /f.u.. A large MCE with a small thermal hysteresis is obtained simultaneously in Fe-rich Mn 0.66 Fe 1.29 P 1- x Si x melt-spun ribbons.

The influence of hydrostatic pressure on the magnetic and magnetocaloric properties of DyRu2Si2

We report the magnetic and magnetocaloric properties of the tetragonal rare-earth compound DyRu2Si2 under applied hydrostatic pressure. The isothermal entropy change (ΔS) and the adiabatic temperature change (ΔTad) were calculated from magnetization data collected at different applied pressures and from heat capacity measurements conducted at atmospheric pressure, respectively. The application of hydrostatic pressure significantly modified the multi-step magnetization curve and the saturation magnetization. A suppression of the magnetization was observed for P = 0.588 GPa and P = 0.654 GPa whereas, at about P ≈1 GPa, the saturation magnetization increased and the magnetization isotherms again resembled the curves measured at atmospheric pressure. A small thermal hysteresis was observed between the heating and cooling M(T) curves at Tt=3.4 K, with an applied magnetic field of H = 0.1 T. This thermal hysteresis indicates a first-order like transition which was also supported by the Arrott plot analysis. The volume magnetostriction was estimated from the pressure-dependent magnetization measurements using a Maxwell relation.

Comparative study of R-phase martensitic transformations in TiNi-based shape memory alloys induced by point defects and precipitates

We studied the influence of point defects (Fe) and precipitates (Ti3Ni4) on the characteristics of R-phase martensitic transformation by comparing the transport and thermal properties of as-quenched Ti50Ni46Fe4 and annealed Ti48.7Ni51.3 shape memory alloys. Both alloys undergo a weak first-order R-phase transformation with a small thermal hysteresis (less than 7 K) and non-zero transformation strain, suggesting the introduction of point defects and precipitates lead to a stable R-phase in these alloys due to the defects induced local lattice deformations. Furthermore, our study revealed that the transition temperature, transformation width, and transformation strain of the investigated R-phase TiNi-based alloys are strongly affected by the induced defects. As a result, the annealed Ti48.7Ni51.3 has a higher transition temperature than that of Ti50Ni46Fe4, as expected.

High-temperature antiferroelectric and ferroelectric phase transitions in phase pure LaTaO4

Phase-pure LaTaO4 ceramics was prepared by solid-state reaction. Dielectric spectroscopic data as well as differential scanning calorimetric experiments showed the existence of a sequence two high-temperature first-order structural phase transitions. The first phase transition occurs above 160°C (on heating), from the monoclinic P21/c space group at room temperature to the polar orthorhombic Cmc21 group, exhibiting a very large thermal hysteresis probably linked to the reconstructive nature of the structural transition. The second transition occurs around 225°C to the orthorhombic Cmcm space group, with a small thermal hysteresis. Vibrational Raman spectroscopic analyses confirmed these two sequential phase transitions, as well as the thermal hysteresis observed for both first-order transitions in repeated heating and cooling cycles. The existence of a strong monoclinic distortion at room temperature could be related to the presence of defects (oxygen vacancies) in LaTaO4 ceramics, after sintering. Dielectric spectroscopy showed a strong influence of the electric conductivity on the dielectric response with activation energy of dc component of conductivity (0.62eV) compatible with the presence of oxygen vacancies. Far-infrared data confirmed that the extra modes observed in the Raman spectra are forbidden bands, which were activated by defects into the structure.

Magnetic feature and near-infrared absorption of a [Pt(mnt)2]--based H-bond supramolecular crystal

A new salt [H2DABCO][Pt(mnt)2]2 (1) (mnt2-=maleonitriledithiolate and H2DABCO2+ is diprotonated 1,4-diazabicyclo[2.2.2]octane) has been synthesized; its crystal structure, magnetic and near-IR absorption properties have been investigated. Two different [Pt(mnt)2]- anions form the strong π-dimers, labeled as Pt(1)-dimer and Pt(2)-dimer, with quite shorter Pt…Pt and S…S distances and molecular plane-to-plane distance (<3.5Å) within a dimer. The [Pt(mnt)2]22- π-dimers are connected through the cations in the strong H-bond manner to form three-dimensional H-bond supramolecular crystal. The salt shows weak paramagnetism in 1.99–300K and this is due to the existence of strong antiferromagnetic coupling within a π-dimer. In addition, a small thermal hysteresis loop is observed at ca. 120K, indicating that a phase transition probably occurs that is further confirmed by variable-temperature IR spectra. Another fascinating functionality of 1 is the intense near-IR absorption in the region of 750–2500nm, and this near-IR absorption feature makes it to be a promising optical material.

Design of High Temperature Ti-Pd-Cr Shape Memory Alloys with Small Thermal Hysteresis

The large thermal hysteresis (ΔT) during the temperature induced martensitic transformation is a major obstacle to the functional stability of shape memory alloys (SMAs), especially for high temperature applications. We propose a design strategy for finding SMAs with small thermal hysteresis. That is, a small ΔT can be achieved in the compositional crossover region between two different martensitic transformations with opposite positive and negative changes in electrical resistance at the transformation temperature. We demonstrate this for a high temperature ternary Ti-Pd-Cr SMA by achieving both a small ΔT and high transformation temperature. We propose two possible underlying physics governing the reduction in ΔT. One is that the interfacial strain is accommodated at the austenite/martensite interface via coexistence of B19 and 9R martensites. The other is that one of transformation eigenvalues equal to 1, i.e., λ2 = 1, indicating a perfect coherent interface between austenite and martensite. Our results are not limited to Ti-Pd-Cr SMAs but potentially provide a strategy for searching for SMAs with small thermal hysteresis.

Effect of Hf content on martensitic transformation, microstructure, and mechanical properties of Cu50Zr50−xHfx alloys

The effect of Hf substituting for Zr of Cu50Zr50−xHfx alloys on the microstructure, martensitic transformation behavior, and mechanical properties is investigated. It is demonstrated that Cu50Zr50−xHfx alloys exhibit higher transformation temperature with a peak martensite reverse transformation temperature of 594 K for Cu50Zr42Hf8 alloy, smaller thermal hysteresis and better thermal stability in comparison to those of Cu50Zr50 alloy. Due to the appearance of hard brittle second phase (Zr,Hf)2Cu, the elastic modulus increases while the plasticity reduces with Hf substituting for Zr.

Electro-sinter-forged Ni–Ti alloy

An innovative powder metallurgical process (Electro-Sinter-Forging – ESF) has been applied to a gas atomized Ni–Ti powder to avoid the typical drawbacks of the conventional industrial processing of this material: oxygen pick up, high processing temperature and slow cooling rate. At the same time, the ESF allows to overcome the low sintering activity of the Ni–Ti powders. Sintered materials, produced by using different processing conditions, are characterized and compared. Results concerning the thermal, structural, microstructural and mechanical analyses are reported and discussed. The density of the sintered samples increases by increasing the amount of applied energy and final pressure during the sintering process. The sample showing the highest density has a direct phase transformation on heating and cooling, with broad DSC peaks, and small thermal hysteresis; it is austenitic at room temperature, with a low amount of coarse (micrometric) precipitates, Ti4Ni2Ox nanometric precipitates and high hardness. The ESF sintering at highest energies induces a “band-type” microstructure with a preferential crystallographic orientation; the crystallographic texture of the sintered samples has been investigated through Electron Back Scattering Diffraction (EBSD) analysis and a fiber texture <100> has been evidenced. The ion release from the sintered samples has been investigated: it is comparable to commercial Ni–Ti alloys currently used and it is correlated to the sample porosity. The biocompatibility has been demonstrated towards fibroblasts.

Design of a MEMS piezoresistive differential pressure sensor with small thermal hysteresis for air data modules.

The design, fabrication, and evaluation results of a MEMS piezoresistive differential pressure sensor fabricated by the dry etching process are described in this paper. The proposed sensor is designed to have optimal performances in mid-pressure range from 0 psi to 20 psi suitable for a precision air data module. The piezoresistors with a Wheatstone bridge structure are implanted where the thermal effects are minimized subject to sustainment of the sensitivity. The rectangular-shaped silicon diaphragm is adopted and its dimension is analyzed for improving pressure sensitivity and linearity. The bridge resistors are driven by constant current to compensate temperature effects on sensitivity. The designed differential pressure sensor is fabricated by using MEMS dry etching techniques, and the fabricated sensing element is attached and packaged in a Kovar package in consideration of leakage and temperature hysteresis. The implemented sensors are tested and evaluated as well. The evaluation results show the static RSS (root sum square) accuracy including nonlinearity, non-repeatability, and pressure hysteresis before temperature compensation is about 0.09%, and the total error band which includes the RSS accuracy, the thermal hysteresis, and other thermal effects is about 0.11%, which confirm the validity of the proposed design process.

Influence of Ultrasonic Vibrations on Shape Memory Effect

The results of studies on the influence of ultrasonic vibrations (UVs) on shape memory effect (SME) in NiTi alloys are presented. The appearance of shape memory effect is due to changes in the temperature and mechanical stress. They can operate simultaneously under the ultrasonic treatment. It has been found that the ultrasonic vibrations can initiate shape recovery processes in a material with shape memory effect. The reversion of the accumulated deformation occurs at the direct and reverse martensite transformations under the influence of ultrasonic vibrations. Since the process is accompanied by ultrasonic heating, small thermal mechanical hysteresis loops have been observed during the direct transformation. The deformation reversion can be explained by ultrasonic heating of the sample due to the dissipation of vibrations and the formation of austenite.

Electronic and magnetic properties of manganite thin films with different compositions and its correlation with transport properties: An X-ray resonant magnetic scattering study

Here, we present x-ray resonant magnetic dichroism and x-ray resonant magnetic scattering measurements of the temperature dependence of magnetism in Pr-doped La-Ca-Mn-O films grown on (110) NdGaO3 substrates. We observed thermal hysteresis of the ferromagnetism in one film that also showed large thermal hysteresis of ∼18 K in transport measurements. While in a second film of a different nominal chemistry, which showed very small thermal hysteresis ∼3 K in transport measurements, no thermal hysteresis of the ferromagnetism was observed. These macroscopic properties are correlated with evolution of surface magnetization across metal insulator transition for these films as observed by soft x-ray resonant magnetic scattering measurements.

Calorimetric and magnetic study for Ni50Mn36In14 and relative cooling power in paramagnetic inverse magnetocaloric systems

The non-stoichiometric Heusler alloy Ni50Mn36In14 undergoes a martensitic phase transformation in the vicinity of 345 K, with the high temperature austenite phase exhibiting paramagnetic rather than ferromagnetic behavior, as shown in similar alloys with lower-temperature transformations. Suitably prepared samples are shown to exhibit a sharp transformation, a relatively small thermal hysteresis, and a large field-induced entropy change. We analyzed the magnetocaloric behavior both through magnetization and direct field-dependent calorimetry measurements. For measurements passing through the first-order transformation, an improved method for heat-pulse relaxation calorimetry was designed. The results provide a firm basis for the analytic evaluation of field-induced entropy changes in related materials. An analysis of the relative cooling power (RCP), based on the integrated field-induced entropy change and magnetizing behavior of the Mn spin system with ferromagnetic correlations, shows that a significant RCP may be obtained in these materials by tuning the magnetic and structural transformation temperatures through minor compositional changes or local order changes.