Reversible Phase Transformation Research Articles

Compressive-Strain-Facilitated Fast Oxygen Migration with Reversible Topotactic Transformation in La0.5Sr0.5CoOx via All-Solid-State Electrolyte Gating

Modifying the crystal structure and corresponding functional properties of complex oxides by regulating their oxygen content has promising applications in energy conversion and chemical looping, where controlling oxygen migration plays an important role. Therefore, finding an efficacious and feasible method to facilitate oxygen migration has become a critical requirement for practical applications. Here, we report a compressive-strain-facilitated oxygen migration with reversible topotactic phase transformation (RTPT) in La0.5Sr0.5CoOx films based on all-solid-state electrolyte gating modulation. With the lattice strain changing from tensile to compressive strain, significant reductions in modulation duration (∼72%) and threshold voltage (∼70%) for the RTPT were observed, indicating great promotion of RTPT by compressive strain. Density functional theory calculations verify that such compressive-strain-facilitated efficient RTPT comes from significant reduction of the oxygen migration barrier in compressive-strained films. Further, ac-STEM, EELS, and sXAS investigations reveal that varying strain from tensile to compressive enhances the Co 3d band filling, thereby suppressing the Co-O hybrid bond in oxygen vacancy channels, elucidating the micro-origin of such compressive-strain-facilitated oxygen migration. Our work suggests that controlling electronic orbital occupation of Co ions in oxygen vacancy channels may help facilitate oxygen migration, providing valuable insights and practical guidance for achieving highly efficient oxygen-migration-related chemical looping and energy conversion with complex oxides.

Conductive metal organic framework mediated Sb nanoparticles as high-capacity anodes for rechargeable potassium-ion batteries

The natural abundance of K in the earth crust and ocean and its low redox potential make potassium-ion batteries (PIBs) a feasible substitute for lithium-ion batteries. However, PIB anodes are still limited by slow reaction kinetics due to a large K-ion radius. Herein, for the first time, Sb@Ni3(HHTP)2 (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene) composites are utilised as high-capacity anodes for rechargeable PIBs. In the composites, Sb nanoparticles are homogenously enveloped by a conductive metal–organic-framework (MOF), namely, Ni3(HHTP)2. The empirical results demonstrate that the composites undergo a consecutive reversible phase transformation from Sb to KSb2, KSb, K5Sb4, and K3Sb at different potentials during the potassiation–depotassiation phenomenon. An optimised Sb@Ni3(HHTP)2–10 electrode delivers high reversible capacities of 590 and 431 mAh g−1 at specific currents of 100 and 1000 mA g−1 after 100 and 300 cycles, respectively. The full cell, which is composed of the Sb@Ni3(HHTP)2 anode and a potassium ferrous ferricyanide cathode, provides a reversible capacity of 514 mAh g−1 at a specific current of 500 mA g−1. The excellent capacity performances of the Sb@Ni3(HHTP)2 anode prove that it is among the best PIB anodes reported until now. The exceptional performance of Sb@Ni3(HHTP)2 is attributed to the efficient coating of Sb nanoparticles by the conductive Ni3(HHTP)2 MOF as well as the formation of a strong KF-rich solid electrolyte interphase layer on the Sb@Ni3(HHTP)2 electrode in a concentrated electrolyte of 3 M potassium bis(fluorosulfonyl)imide in ethylene carbonate/diethyl carbonate.

Molecular Dynamics Simulations of PtTi High-Temperature Shape Memory Alloys Based on a Modified Embedded-Atom Method Interatomic Potential.

A new second nearest-neighbor modified embedded-atom model-based PtTi binary interatomic potential was developed by improving the pure Pt unary descriptions of the pre-existing interatomic potential. Specifically, the interatomic potential was developed focusing on the shape memory-associated phenomena and the properties of equiatomic PtTi, which has potential applications as a high-temperature shape memory alloy. The simulations using the developed interatomic potential reproduced the physical properties of the equiatomic PtTi and various intermetallic compound/alloy compositions and structures. Large-scale molecular dynamic simulations of single crystalline and nanocrystalline configurations were performed to examine the temperature- and stress-induced martensitic transformations. The results show good consistency with the experiments and demonstrate the reversible phase transformation of PtTi SMA between the cubic B2 austenite and the orthorhombic B19 martensite phases. In addition, the importance of anisotropy, constraint and the orientation of grains on the transformation temperature, mechanical response, and microstructure of SMA are presented.

Synthesis and characterization of Nickel-rich layered LiNi1-xMnxO2 (x=0.02,0.05) cathodes for lithium-ion batteries

In this paper, LiNi0.98Mn0.02O2 and LiNi0.95Mn0.05O2 binary materials were synthesized by chemical co-precipitation method. The phase characterization and electrochemical performance analysis of Ni-Mn binary materials were carried out by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and electrochemical tests, and the action of Mn element on the material was studied. XRD analysis shows that LiNi0.95Mn0.05O2 material has the better layered structure (1.47 of the (003)/(104) peak intensity ratio), and the lower Li-Ni mixing ratio (1.98%). The initial discharge capacity of LiNi0.95Mn0.05O2 material at 1 C is 189.6 mAh/g, and the capacity retention rate is 89.93% after 100 cycles at 1 C, which is much higher than LiNiO2 of 177.4 mAh/g and 60.26%. In addition, the initial discharge specific capacity of LiNi0.95Mn0.05O2 can reach 205.8 mAh/g at 0.5 C under the high temperature of 50 °C, and the capacity retention rate is 78.7% at 0.5 C for 100 cycles, while the discharge specific capacity of LiNiO2 is 191.1 mAh/g at 0.5 C and the capacity retention rate is only 63.9%. Excellent electrochemical properties of Ni-Mn materials than LiNiO2 at room and high temperature is because Mn4+ without electrochemical activity is stabilized in the transition metal layer during the charge and discharge process of the materials, alleviating the structural collapse caused by the Li/Ni mixing. By comparing the cross-section of the materials before and after 100 cycles at 1 C, LiNi0.95Mn0.05O2 has fewer microcracks due to the high reversible phase transformation of H2-H3 according to the analysis of the dQ/dV versus voltage curves. Meanwhile, the stable layered structure and lithium-ion diffusion channel also make LiNi0.95Mn0.05O2 has the better lithium-ion conductivity.

Stabilizing and accessing across ternary phase cesium lead bromide perovskite nanocrystals: thermodynamic and kinetic controls

Lead halide perovskites with fascinating optoelectronic properties have enabled rapid advancement and development in photovoltaics and light-emitting diodes. However, accessing and stabilizing the complex ternary phase space diagram (Cs-Pb-Br) of perovskites including 3 D nanocrystals, 2 D nanoplatelets, and 0 D hexagonal platelets with desirable optoelectronic properties further requires a deeper understanding of the thermodynamic and kinetic aspects regarding the growth of lead halide perovskite nanocrystals. In this work, we have mapped out the multivariant synthetic design spaces observed in the ternary phase diagram of Cs-Pb-Br to evaluate the effect of controlling thermodynamic equilibrium state (e.g. chemical potentials of the Cs:Pb ratio) and growth kinetics with ligand concentration (oleylamine). Further in-situ tracking of reversible phase transformation with the addition of oleylamine (forward) and PbBr2 (reverse) exhibiting distinctive spectroscopic signatures between 3 D and 0 D phases (vice versa) can provide insight into the reversible phase transformation mechanism and important role of PbBr2 species that can modify the bonding motif and connectivity of [PbBr6]4- octahedral frameworks.

Fluffy-Like Cation-Exchanged Prussian Blue Analogues for Sodium-Ion Battery Cathodes.

Prussian blue (PB) and its analogues are considered as promising cathode materials for sodium-ion batteries (SIBs) owing to their low cost and high capacity. However, it is still a huge challenge to avoid obvious capacity decay during cycling due to the structural collapse. Herein, we design a method to replace parts of Fe ion sites in PB with Ni ions to prepare fluffy-like nickel PB (PB-Ni) by cationic solution immersion, which improves cycling stability for sodium storage. The content of Ni in PB-Ni is explored by regulating the soaking time in the Ni-containing solution, which results in different effects on the electrochemical performance as cathodes of SIBs. Especially, PB-Ni-1d (soaking in NiCl2 solution for 1 day) exhibits an initial capacity of 114.2 mA h g-1 at 50 mA g-1 and a stable cycling performance of 800 cycles at 300 mA g-1. Furthermore, the reversible phase transformation and small volume variation for PB-Ni-1d are revealed by in situ X-ray diffraction characterization. The nickel hexacyanoferrate in outer layer maintains the cubic phase to stabilize the crystal structure. The cation-exchange strategy provides a facile idea to fabricate high-quality PB cathodes with superior stability for high-performance SIBs.

Phase Transitions in Amorphous Germanium under Non-Hydrostatic Compression

As the pioneer semiconductor in transistor, germanium (Ge) has been widely applied in information technology for over half a century. Although many phase transitions in Ge have been reported, the complicated phenomena of the phase structures in amorphous Ge under extreme conditions are still not fully investigated. Here, we report the different routes of phase transition in amorphous Ge under different compression conditions utilizing diamond anvil cell (DAC) combined with synchrotron-based X-ray diffraction (XRD) and Raman spectroscopy techniques. Upon non-hydrostatic compression of amorphous Ge, we observed that shear stress facilitates a reversible pressure-induced phase transformation, in contrast to the pressure-quenchable structure under a hydrostatic compression. These findings afford better understanding of the structural behaviors of Ge under extreme conditions, which contributes to more potential applications in the semiconductor field.

Atomistic simulations of AuTi high-temperature shape memory alloys

Herein, the atomic-scale phase transformation and deformation processes of AuTi shape memory alloys for high-temperature applications were investigated using molecular dynamics simulations based on a newly developed interatomic potential for the Au-Ti binary system. The developed second nearest-neighbor modified embedded-atom method potential exhibited good accuracy and transferability to reproduce various physical properties of the target alloy system, particularly in properties related to the reversible phase transformation of AuTi high-temperature shape memory alloys. As a conceivable application of the interatomic potential, the temperature-induced phase transformation of AuTi single-crystal shape memory alloys and the effect of off-stoichiometry on the phase transformation behavior were examined. Molecular dynamics simulations revealed that the transformation temperature and thermal hysteresis decreased with increasing Ti content, consistent with the reported experimental trend, suggesting that the reduced volume difference between the austenite and martensite phases was closely related to the reduced thermal hysteresis. We further examined the mechanical response and resultant superelasticity of nanocrystalline AuTi alloys to demonstrate that the cyclic deformation of nanocrystalline alloys exhibited a transformation ratcheting behavior caused by the plastic deformation of amorphous-like grain boundary region.

Recycling spent lead acid batteries into aqueous zinc-ion battery material with ultra-flat voltage platforms

The harmless disposal of lead paste in the spent lead-acid batteries (LABs) remains an enormous challenge in traditional pyrometallurgical recycling. Here, we introduced a hydrometallurgical method for the recycling of the spent LABs’ waste to obtain the β-PbO as a novel zinc ion batteries (ZIBs) active material. The obtained β-PbO exhibits ultra-flat charge/discharge voltage platforms (0.21 mV/(mAh g−1)) and stable specific capacity. During the charge/discharge, the β-PbO spontaneously triggers the formation of (ZnSO4)[Zn(OH)2]3·5H2O (ZHS) micro-sheets as a surface passivation layer. Moreover, the ex-situ X-ray spectra reveal that the reversible phase transformation occurs between PbSO4 and Pb with the assistance of ZHS by adjusting the PH value on the electrode-electrolyte interface. The synergistic two-phase-reaction mechanism generates ultra-flat voltage platforms upon the charge/discharge. This “energy-saving and environment-friendly” recycling route eliminates the major source of emission of pollution particulates/gases compared to the traditional pyrometallurgical recycling, while at the same time replacing energy-consuming and environmentally detrimental processes of synthesis of current ZIBs cathodes.

Domain memory effect in the organic ferroics

Shape memory alloys have been used extensively in actuators, couplings, medical guide wires, and smart devices, because of their unique shape memory effect and superelasticity triggered by the reversible martensitic phase transformations. For ferroic materials, however, almost no memory effects have been found for their ferroic domains after reversible phase transformations. Here, we present a pair of single-component organic enantiomorphic ferroelectric/ferroelastic crystals, (R)- and (S)-N-3,5-di-tert-butylsalicylidene-1-(1-naphthyl)ethylamine SA-NPh-(R) and SA-NPh-(S). It is notable that not only can their ferroic domain patterns disappear and reappear during reversible thermodynamic phase transformations, but they can also disappear and reappear during reversible light-driven phase transformations induced by enol–keto photoisomerization, both of which are from P1 to P21 polar space groups. Most importantly, the domain patterns are exactly the same in the initial and final states, demonstrating the existence of a memory effect for the ferroic domains in SA-NPh-(R) and SA-NPh-(S). As far as we are aware, the domain memory effect triggered by both thermodynamic and light-driven ferroelectric/ferroelastic phase transformations remains unexplored in ferroic materials. Thermal and optical control of domain memory effect would open up a fresh research field for smart ferroic materials.

Self-supported VO(PO3)2 electrode for 2.8 V symmetric aqueous supercapacitors

Improving the voltage window of aqueous supercapacitors beyond 2.5 V without diminishing their capacitance performance is a big challenge to achieve excellent energy density because of the undesirable water decomposition. Herein, this study developed a novel vanadium phosphate (VPO) of the VO(PO3)2 aerogel as the electrode to enlarge the device voltage, which could effectively raise HER/OER overpotentials and thus achieving a stable wide electrochemical window of −1 ∼ 1 V (vs. SCE) with remarkably improved capacitance. The VPO microstructure is organized by nanowire-stacked lamellar bricks via engineering a controllable phase-transformation using the V-P-citric acid-aerogel as the precursor. Examined as the supercapacitor electrode, in-situ X-ray powder diffraction analysis uncovers that the VO(PO3)2 undergoes a reversible phase-transformation reaction associated with Na+ intercalation/de-intercalation in Na2SO4 and a typical redox pseudocapacitance process in KOH. For the first time, a 2.8 V symmetric aqueous supercapacitor was further assembled with an energy density of 123.1 Wh kg−1 at the power density of 580 W kg−1, which is much superior to those of all reported V-base supercapacitors. The underlying mechanisms of the VO(PO3)2 on ultrahigh voltage window and charge storage are further elucidated, which provide the fundamental guidance for structuring VPO-based electrodes used for commercial energy storage devices.

Role of point defects in stress-induced martensite transformations in NiTi shape memory alloys: A molecular dynamics study

Shape-memory properties of equiatomic NiTi rely on the thermal- or stress-induced reversible martensitic phase transformation between the $B2$ and $B{19}^{\ensuremath{'}}$ phases. Irradiation defects suppress thermal-induced transformations, but their effects on stress-induced transformations are poorly understood. We use molecular dynamics to investigate the effect of vacancies, vacancy clusters, interstitials, and antisite defects on stress-induced transformations. All defects suppress the transformation, but vacancy clusters do so to the greatest extent, while antisite defects do so to the least extent. The responsible mechanisms are grain boundary pinning and chemical disordering.

Two-dimensional Mg0.2V2O5·nH2O nanobelts derived from V4C3 MXenes for highly stable aqueous zinc ion batteries

Aqueous zinc ion batteries (ZIBs) are of great concern for their low cost, high safety and eco-friendliness. Vanadium oxides are the underlying cathode materials for ZIBs because of their high theoretical capacity. However, the slow kinetics of multivalent charged Zn2+ in the host structure and unstable structure induce inferior cycling stability and rate performance. Herein, Mg2+ pre-intercalated V2O5·nH2O nanobelts derived from conductive V4C3 MXenes are devised and prepared as cathodes for ZIBs, delivering a high reversible capacity of 346 mAh g−1 at 0.1 A g−1 and preeminent ultra-long cycling stability with capacity retention of 83.7% after 10,000 cycles at 5 A g−1. Using this material as cathode, the soft-packed battery also represents favourable rate and cycling performance. The stable structure originated from pre-intercalated Mg2+ and interlayered water, splendid reversible phase transformation and high pseudocapacitive behavior boost the preeminent cycling stability and rate capacity.

Strain Glass State, Strain Glass Transition, and Controlled Strain Release

Strain glass is a new strain state discovered recently in ferroelastic systems that is characterized by nanoscale martensitic domains formed through a freezing transition. These nanodomains typically have mottled or tweed morphology depending on the elastic anisotropy of the system. Strain glass transition is a broadly smeared and high order–like transition, taking place within a wide temperature or stress range. It is accompanied by many unique properties, including linear superelasticity with high strength, low modulus, Invar and Elinvar anomalies, and large magnetostriction. In this review, we first discuss experimental characterization and testing that have led to the discovery of the strain glass transition and its unique properties. We then introduce theoretical models and computer simulations that have shed light on the origin and mechanisms underlying the unique characteristics and properties of strain glass transitions. Unresolved issues and challenges in strain glass study are also addressed. Strain glass transition can offer giant elastic strain and ultralow elastic modulus by well-controlled reversible structural phase transformations through defect engineering.

Electric Field Effects on Charge Conduction for LaMnO3 Controlled La0.7Ca0.3MnO3 Manganite

Control over the different electronic states in mixed valent manganites advances the development of oxide based electronic devices. In this context, carrier density is one of the key aspects that controls the electronic ground states of manganites in a sparkling way since it does not create any impurity within the manganite lattice, unlike chemical doping process. LaMnO3–δ / La0.7Ca0.3MnO3 / LaAlO3 (LMO / LCMO / LAO) manganite based heterostructure was fabricated by low cost chemical solution deposition (CSD) method where thickness of LMO ∼ 50 nm and LCMO ∼ 100 nm were grown on (100) single crystalline substrate. Structural quality and epitaxial nature of heterostructure was verified by performing X–ray diffraction (XRD) ϕ–scan measurement on grown La0.7Ca0.3MnO3 / LaAlO3 (LCMO / LAO) 100 nm thin film and LMO / LCMO / LAO heterostructure. Understanding of few other structural, morphological and chemical aspects of presently studied LMO / LCMO interface and LMO / LCMO / LAO heterostructure has been presented through grazing incidence X–ray diffraction (GIXRD), Rocking curve XRD, cross sectional scanning electron microscopy (SEM), atomic force microscopy (AFM) and X–ray photoelectron spectroscopy (XPS) measurements. Electric field modulated charge conduction for LCMO manganite channel has been understood in the context of field effect configuration (FEC) based transport measurements where temperature dependent LCMO channel resistance was recorded under different control electric fields applied across LMO / LCMO interface in LMO / LCMO / LAO heterostructure. Thermal hysteretic resistance measurements for LCMO manganite channel under zero control electric field exhibit metal to insulator phase transition at TP with finite width of the hysteretic resistance behaviours between two thermal cycles, i.e. cooling and heating. This has been understood on the basis of phase separation scenario, freezing effect and non–reversible electronic phase transformation. Applied control electric field induced improvement in resistance of LCMO manganite channel and reduction in value of TP have been understood on the basis of charge injection process, strain induced disorder dependent charge conduction, phase separation based movements of metal–insulator interface and negligibly small Joule heating effect. Realization of insulating phase fraction, arrested during thermal cycles, has been discussed for the explanation of reduced width of the hysteretic resistance behaviours of LCMO channel upon increase in control electric field applied across LMO / LCMO interface. Possible charge conduction mechanisms have been understood on the basis of Zener double exchange (ZDE) polynomial law for obtained metallic state of LCMO channel. Variation in electroresistance (ER) of LCMO manganite channel with temperature under different control electric fields (applied across LMO / LCMO interface) has been discussed on the basis of charge injection process with an effective role of phase separation scenario of LCMO channel in LMO / LCMO / LAO heterostructure.

Standard mechanical testing is inadequate for the mechanical characterisation of shape-memory alloys: Source of errors and a new corrective approach

Thanks to its unique behaviour characterised by a superelastic response, Nitinol has now become the material of preference in a number of critical applications, especially in the area of medical implants. However, the reversible phase transformation producing its exceptional comportment is also responsible for a number of phenomena that make its mechanical characterisation particularly complex, by hindering the assumptions at the very basis of common uniaxial tensile testing. This necessarily reduces the level of safety and design optimization of current applications, which rely on incorrect mechanical parameters. In this study, the spurious effects introduced by the unconventional material behaviour during uniaxial tensile testing are analysed by means of digital image correlation (DIC), identifying the onset of undesirable material inhomogeneities and bending moments that are dependent on the test setup and strongly limit the reliability of standard characterisation. Hence, a more accurate and systematic testing approach, exploiting the ability of DIC to analyse the local mechanical response at specific regions of the test specimen, is presented and discussed.

Reversible Hydrogen-Induced Phase Transformations in La0.7Sr0.3MnO3 Thin Films Characterized by In Situ Neutron Reflectometry.

We report on the mechanism for hydrogen-induced topotactic phase transitions in perovskite (PV) oxides using La0.7Sr0.3MnO3 as a prototypical example. Hydrogenation starts with lattice expansion confirmed by X-ray diffraction (XRD). The strain- and oxygen-vacancy-mediated electron-phonon coupling in turn produces electronic structure changes that manifest through the appearance of a metal insulator transition accompanied by a sharp increase in resistivity. The ordering of initially randomly distributed oxygen vacancies produces a PV to brownmillerite phase (La0.7Sr0.3MnO2.5) transition. This phase transformation proceeds by the intercalation of oxygen vacancy planes confirmed by in situ XRD and neutron reflectometry (NR) measurements. Despite the prevailing picture that hydrogenation occurs by reaction with lattice oxygen, NR results are not consistent with deuterium (hydrogen) presence in the La0.7Sr0.3MnO3 lattice at steady state. The film can reach a highly oxygen-deficient La0.7Sr0.3MnO2.1 metastable state that is reversible to the as-grown composition simply by annealing in air. Theoretical calculations confirm that hydrogenation-induced oxygen vacancy formation is energetically favorable in La0.7Sr0.3MnO3. The hydrogenation-driven changes of the oxygen sublattice periodicity and the electrical and magnetic properties similar to interface effects induced by oxygen-deficient cap layers persist despite hydrogen not being present in the lattice.

Super-hydrophobic Cs4PbBr6@PDB composites with water-driven photoluminescence enhancement and dehydration recovery

All-inorganic perovskite quantum dots (QDs) are very promising materials for their potential applications in water-related photoluminescence due to their sensitive properties to water. This work initiatively attempts to absorb Cs4PbBr6 QDs into a super-hydrophobic polydivinylbenzene (PDB) porous framework. Under the protection of PDB, the non-luminescent Cs4PbBr6 and luminescent CsPbBr3 transform reversibly by alternate water treatment (excess or small amount) and removal of water. The extraction of CsBr by water and reinsertion of CsBr by evaporation from/into the QDs make up a reversible phase transformation process. The super-hydrophobic porous structure of PDB not only provides the confined space for dissolved CsBr but also inhibits the overflow of trapped CsBr, thereby reducing the adverse impact of excess water on reversible hydrochromism. This work provided a new perspective to understand the phase conversion between Cs4PbBr6 and CsPbBr3. Furthermore, the Cs4PbBr6@PDB in waterborne luminescent inks by screen printing opens a way in the field of anti-counterfeiting owing to the excellent stability of encryption and decryption.

Inorganic‐Cation Pseudohalide 2D Cs2Pb(SCN)2Br2 Perovskite Single Crystal (Adv. Mater. 7/2022)

2D Perovskites Cs2Pb(SCN)2Br2, an inorganic-cation pseudo-halide 2D phase perovskite single crystal, is grown by a simple antisolvent vapor-assisted crystallization method, as reported by Chu-Chen Chueh, Anita W. Y. Ho-Baillie, and co-workers in article number 2104782. Cs2Pb(SCN)2Br2 exhibits a reversible first-order phase transformation to CsPbBr2 at 450 K and has a low exciton binding energy amongst the 2D perovskites. Demonstration for photodetector application shows respectable responsivity and detectivity.

Ultrahigh cycle fatigue of nanocrystalline NiTi tubes for elastocaloric cooling

Elastocaloric cooling using superelastic NiTi shape memory alloy with reversible phase transformation is a promising environmentally friendly technology, but the limited fatigue life of conventional coarse-grained NiTi remains a crucial bottleneck. Here, we report the ultrahigh fatigue life of nanocrystalline NiTi tubes, exceeding 120 million cycles under a compressive stress of 800 MPa. The NiTi tubes demonstrate stable cyclic stress-strain responses and a stable adiabatic temperature drop of 6.6 K in the lifespan. The material coefficient of performance increases from the initial 8.8 to 11.6 of the 108th compressive cycle. The high resistance to nucleation and growth of compression-parallel cracks results in the ultrahigh fatigue life of the tubes. Our research shows the great potentials of nanocrystalline NiTi tubes with both stable thermomechanical properties and long compressive fatigue lives for reliable elastocaloric cooling.