Large Entropy Change Research Articles

Rational design of high performance metal organic framework stationary phase for gas chromatography

Metal organic frameworks (MOFs) are assembled from metal ions or clusters and organic ligands. The high tunability of these components offers a solid structural foundation for achieving efficient gas chromatography (GC) separation. This review demonstrates that the design of high performance MOFs with suitable stationarity should consider both the thermodynamic interactions provided by these MOFs and the kinetic diffusion of analytes. Thermodynamic parameters are basic indicators for describing the interactions between various analytes and the stationary phase. Thermodynamic parameters such as retention factors, McReynolds constants, enthalpy changes, and entropy changes can reflect the relative intensity of thermodynamic interactions. For example, a larger enthalpy change indicates a stronger thermodynamic interaction between the analytes and stationary phase, whereas a smaller enthalpy change indicates a weaker interaction. In addition, the degree of entropy change reflects the relative degrees of freedom of analytes in the stationary phase. A larger entropy change indicates that the analytes have fewer degrees of freedom in the stationary phase. The higher the degree of restriction, the closer the adsorption of the analytes and, thus, the longer the retention time. Thermodynamic interactions, such as metal affinity, π-π interactions, polarity, and chiral sites, can be rationally introduced into MOF structures by pre- or post-modifications depending on the target analytes. These tailored thermodynamic interactions create a favorable environment with subtle differences for efficient analyte separation. For example, MOF stationarity may require large conjugation centers to provide specific π-π interactions to separate benzenes. Chiral groups may be required in the MOF structure to provide sufficient interactions to separate chiral isomers. The kinetic diffusion rate of the analytes is another critical factor that affects the separation performance of MOFs. The diffusion coefficients of analytes in the stationary phase (Ds) can be used to evaluate their diffusion rates. The chromatographic dynamics equation illustrates that the chromatographic peak of analytes tends to be sharper and more symmetrical when the Ds is large, whereas a wider trailing peak may appear when the Ds is small. The Van Deemter equation also proves that a low Ds may lead to a high theoretical plate height and low column efficiency, whereas a high Ds may lead to a low theoretical plate height and increased column efficiency. Analyte diffusion can be significantly influenced by the pore size, shape, particle size, and packing mode of MOFs. For instance, an excessively small pore size results in increased mass transfer resistance, which affects the diffusion of analytes in the stationary phase, probably leading to serious peak trailing. Thus, a suitable pore size is required to enhance the kinetic diffusion of analytes and improve the separation performance of MOFs. Theoretically, the design of a high performance MOF stationary phase requires the creation of routes for the rapid diffusion of analytes. However, the separation ability of an MOF is determined by not only the kinetic diffusion rate of the analytes but also the thermodynamic interactions it provides. An excessively fast diffusion rate may lead to insufficient interactions between the analytes and MOFs, compromising their ability to effectively separate different analytes. The thermodynamic interactions and kinetic diffusion of analytes are synergistic and mutually essential. Therefore, this review concludes with research on the influence of both the thermodynamic interactions and kinetic diffusion of analytes on the performance of MOF stationary phases. Based on the findings of this review, we propose that high performance MOF stationary phases can be achieved by balancing the thermodynamic interactions and kinetic diffusion of analytes in these phases through the rational design of the MOF structure. We believe that this review provides useful guidelines for the design of high performance MOF stationary phases.

Evaluation of calf thymus DNA binding of newly synthesize five 9 [sbnd]O[sbnd] Imidazolyl alkyl berberine derivative: A comparative multi-spectroscopic and calorimetric study

DNA binding with small molecule plays an important role in the designing of various anticancer drugs with greater efficacy. The five 9-O-imidazolyl alkyl berberine derivatives (BI) of different chain length has been synthesized and fully characterized. The binding study of calf thymus DNA with these newly synthesized berberine derivative was performed using various biophysical techniques. The binding affinity of BI to calf thymus DNA increased with increasing the chain length. The binding constant value obtained from UV–Vis spectral analysis was 1.84x105for BI1, 2.01x105for BI2, 1.51 × 106 for BI3, 3.66 × 106 for BI4, 6.68 × 106. Partial intercalative binding with strong stabilization of the DNA helix was revealed from circular dichroism spectral study and viscosity measurement. From the ITC experiment it was revealed that the bindings of BI1, BI2, BI3, BI4 and BI5 to calf thymus DNA were favoured by a large positive favourable entropy and negative enthalpy change and the highest spontaneity found for BI5. With the increase in chain length the binding was driven by a stronger entropy term with a higher binding constant indicates involvement of hydrophobic force for all these interaction. High binding affinities of calf thymus DNA with berberine-imidazole derivatives might be helpful for new drug design.

Direct Conversion of Phase-Transition Entropy into Electrochemical Thermopower and Peltier Effect.

Thermocell generates thermopower from a temperature difference (ΔT) between two electrodes. The converse process of thermocells is an electrochemical Peltier effect, which creates a ΔT on the electrodes by applying an external current. The Seebeck coefficient (Se ) of the electrochemical system is proportional to the entropy change of the redox reaction; therefore, a redox system having a significant entropy change is expected to increase the Se . In this study, a thermo-responsive polymer having a redox-active moiety, poly(N-isopropyl acrylamide-co-N-(2-acrylamide ethyl)-N'-n-propylviologen) (PNV), is used as the redox species of a thermocell. PNV2+ dication undergoes the coil-globule phase transition upon the reduction to PNV+ cation radical, and a large entropy change is introduced because water molecules are freed from the polymer chains. The Se of PNV thermocell drastically increased to +2.1mV K-1 at the lower critical solution temperature (LCST) of PNV. The entropy change calculated from the increment of Se agreed with the value evaluated by differential scanning calorimetry. Moreover, the electrochemical Peltier effect was observed when the device temperature was increased above the LCST. This study shows that the large entropy change associated with the coil-globule phase transition can be used in electrochemical thermal management and refrigeration technologies. This article is protected by copyright. All rights reserved.

Ultralow-field magnetocaloric materials for compact magnetic refrigeration

Magnetic refrigeration around the liquid-helium temperature plays a critical role in many technological sectors. Even if gallium gadolinium garnet (GGG) has been regarded as the benchmark, its application is highly limited by the small magnetic entropy changes, the requirement of superconducting magnets, and the large device sizes. Here, we report that LiREF4 (RE = rare earth) single crystals exhibit significantly superior magnetocaloric performance levels to commercial GGG. Under a small magnetic field of 5 kOe, which can be easily achieved by a permanent magnet, the magnetic entropy change reaches a record-high value of 16.7 J kg−1 K−1 in LiHoF4 in contrast to the value of 1.0 J kg−1 K−1 in GGG. The combination of small driving fields, large entropy changes, and excellent thermal and/or magnetic reversibility enables this series to be employed as the ideal working material for compact magnetic refrigeration around the liquid-helium temperature.

High-performance LaFe11.6Si1.4Hy/Al composites for magnetic refrigeration: A good combination of magnetocaloric effect, mechanical properties, and thermal conductivity

Bulk LaFe11.6Si1.4Hy/Al composites with the saturated hydrogen content were prepared by hot pressing and subsequent hydrogenation. Al particles were dramatically deformed when pressed at 773 K, and a reaction of La(Fe,Si)13 and Al phases took place at 873 K. The reinforced skeleton structure consisting of malleable Al phases in the composites allows brittle La(Fe,Si)13Hy particles to be well bonded after hydrogen absorption. As a result, these LaFe11.6Si1.4Hy/Al hydrides show a good comprehensive performance for magnetic refrigeration, i.e., large entropy changes of 9.8–12.5 J/kg K under 2 T, large adiabatic temperature changes of 3.36–3.97 K under 1.9 T, high thermal conductivity of 11.4–45.6 W/m K, and high bending strength of 16.8–48.2 MPa. Particularly, the 20 wt% Al composite possesses a compressive strength of 122 MPa and plastic deformation of 4.6 %.

Reversible heat effects of lithium metal- and porous lithium iron phosphate electrodes

We report Peltier heats and reaction entropy of cells with lithium metal- and near fully lithiated lithium iron phosphate (LFP) electrodes. The Peltier heats were measured through the Seebeck coefficient of thermogalvanic cells. The value obtained for the Peltier heat of Li-metal, -32 ± 3 kJ/mol at 298 K, supports previously reported values. When close to being fully lithiated, LFP goes through a phase transition from a two-phase mixture to a solid solution. The value of Peltier heats obtained for LFP vary from -15 ± 1 to -72 ± 9 kJ/mol. The variation is explained by large entropy changes of lithium iron phosphate, near the phase transition. The cell entropy difference of lithium iron phosphate against lithium metal varied from -64 ± 3 to +50 ± 20 J/K mol. The negative Peltier heats means that the electrodes generates heat when acting as an anode, which leads to a temperature rise in the electrode compartment, and absorbs heat when acting as a cathode. The local reversible heat effect is equal to or larger in magnitude than the net reversible heat effect. The time-dependence of the Seebeck coefficient, the Soret effect, was found to differ between the cells with planar Li-metal electrodes to porous LFP.

Giant magnetocaloric effect in the Co-doped Tb5Si2Ge2 by establishing magnetostructural coupling

The magnetostructural coupling materials exhibit excellent magnetocaloric properties, making them ideal candidates for magnetic refrigerants. Tb5Si2Ge2 reveals diverse phase transition behaviors, but its structural and magnetic phase transitions are decoupled, which restricts its potential applications in magnetic refrigeration technology. Here, we demonstrate that upon the addition of Co into the Ge site of Tb5Si2Ge2, the compound can obtain a strong magnetostructural coupling between the structural and the magnetic transition, which can significantly improve the magnetocaloric properties. It is observed that the magnetic entropy change under a magnetic field change of 5 T is increased from − 18.30 Jkg−1K−1 to − 31.34 Jkg−1K−1 after adding the magnetic element Co into the compound. The temperature-averaged entropy change (TEC) at the working range of 3 K under 1 T is also improved 2.1 times, exhibiting an enhanced low-field magnetocaloric performance. In addition, theoretical calculations show that a large lattice entropy change of 21.5 Jkg−1K−1 can be achieved after the magnetostructural transformation in the Co-doped compound. The results demonstrate that Co doping can be used to construct a stable magnetostructural transition, transforming Tb5Si2Ge2 into an excellent magnetic refrigerant.

Room temperature giant magnetocaloric effect in Pd doped FeRh and the effect of martensitic transition

FeRh 0.8 Pd 0.2 is known to exhibit near room-temperature first-order antiferromagnetic (AF)–ferromagnetic (FM) transition, typical of chemically ordered FeRh system. In addition, it is also reported to show martensitic transition at a lower temperature. In this work, the effect of sample history on transition temperature (Tt) and the magnetocaloric effect (MCE) have been studied. The experimentally determined MCE parameters across FM to AF transition induced either by isothermal magnetic field sweep or by temperature sweep showed a large isothermal change in entropy around room temperature, i.e., 14 J/kg K for 50 kOe magnetic field change, whereas MCE corresponding to AF–FM transition depends on cooling history. Our study shows that in the presence of martensite phase, the peak value of MCE is shifted to higher temperatures but with significantly reduced magnitude.

Magnetocaloric and Magneto-transport Properties in Polycrystalline Ni<sub>56</sub>Mn<sub>20</sub>Ga<sub>24</sub> Heusler Alloy

Polycrystalline ingots of Ni-rich Ni56Mn20Ga24 alloy were prepared by conventional arc melting procedure. The magnetocaloric and magnetotransport properties of the alloy were investigated within a temperature range from 4.2-300 K and up to a magnetic field of 8 T. A large magnetocaloric effect (∆SM ~ 29 J/Kg K) was observed in the alloy in the vicinity of magneto-structural transition temperature at a change of 5 T magnetic field. From magnetic measurements, it was observed that the martensite to austenite transition was accompanied by higher to lower magnetization in higher magnetic fields. The large entropy change was explained by considering the first-order magneto-structural transition in this alloy. A high negative magnetoresistance (⁓7 %) associated with magnetic field induced first order magneto-structural transition was also observed near room temperature due to a change of 8 T magnetic field for this alloy.

Effect of hydrophilic atenolol and lipophilic propranolol β-blockers on the surface and bulk aggregation of quaternary ammonium bromide surfactants: A comparative study

The variations in the surface and bulk properties of alkyltrimethylammonium bromide (ATAB) surfactants (C12 to C16) in presence of a hydrophilic β-blocker drug atenolol (ATL) and a lipophilic β-blocker drug propranolol (PPL), have been investigated using three independent techniques, viz; electrical conductivity, surface tension and cyclic voltammetry. Electrical conductivity measurement indicates that both ATL and PPL at low concentrations of 0.5 mM and 1.0 mM brings about almost equal changes to the critical micelliastion concentration of all ATAB surfactants. However, at higher concentrations (3 mM to 10 mM), PPL seems to be more effective, than ATL, in reducing the cmc and hence favouring micellization. Various interfacial parameters at the air–water interface have been determined through the measurements of surface tension of the surfactants in varying concentrations of ATL and PPL ranging from 0.5 mM to 10 mM. The thermodynamic parameters of micellization are evaluated from the temperature dependence of cmc. The variation of Gibbs energy with temperature is small while large changes in enthalpy and entropy of micellization are observed in the temperature range studied. The effect of TTAB on the electrolytic solutions of ATL and PPL on the voltametric response of glassy carbon electrode (GCE) was examined. TTAB enhanced the current signal of ATL while opposite effect was observed for PPL. The experimental results have been analysed in terms of the difference in the hydrophobicities of the two β-blocker drug molecules.

Electrocaloric effect in BaTiO3 multilayer capacitors with first-order phase transitions

Electrocaloric (EC) materials, presenting large adiabatic temperature change or isothermal entropy change under the application (or removal) of electric fields, offer an efficient alternative to caloric heat pumps for replacing hazardous gases used in traditional vapor-compression systems. Recently, a large EC temperature change of 5.5 K have been reported in Pb(Sc0.5Ta0.5)O3 multilayer ceramic capacitors (Nair et al 2019 Nature 575 468) thanks to its strong first-order phase transition and a temperature span of 13 K has been reported in a prototype based on these capacitors (Torelló et al 2020 Science 370 125). However, the toxicity of lead forces researchers to find eco-friendly materials exhibiting competitive EC performances. Here, we study the EC effect in lead-free BaTiO3 multilayer capacitors using an infrared camera. Unlike commercial BaTiO3 capacitors, we prepared our samples without sacrifying the first-order phase transition in BaTiO3 while a low amount of 0.2 mol% Mn was added as an acceptor dopant to improve electrical resistivity. Their EC adiabatic temperature variations show two peaks versus temperature, which match BaTiO3 two first-order phase transitions, as observed by differential scanning calorimetry. We measured a temperature drop of ∼0.9 K over a temperature range of 70 K under 170 kV cm−1, starting at 30 °C near the tetragonal-to-orthorhombic phase transition. Under the same electric field, a maximum temperature change of 2.4 K was recorded at 126 °C, at BaTiO3’s Curie temperature. Our findings suggest that further optimized BaTiO3 capacitors could offer a path for designing lead-free caloric cooling prototypes.

Magnetocaloric properties of a wire composite of La (Fe,Mn,Si)13-H alloy powders in a Gd cylindrical tube

The enhancement of magnetocaloric effect (MCE) and the extension of effective magnetic refrigeration temperature region near room temperature are critical requirements for highly efficient and environment friendly cooling technologies. The large isothermal entropy change of the first-order phase transition material and broader temperature range of the second-order phase transition material are combined into the composite form of La(Fe,Mn,Si)13-H and Gd with their transition temperatures close to room temperature. In this work, wire composites were fabricated using the La (Fe,Mn,Si)13-H powders filled inside the Gd tube. The magnetocaloric properties of the wire composite are convoluted from individual constituents. The dual transitions temperature were observed at 287 K and 292 K. The isothermal entropy change response of the wire composite can be obtained by using the simulation with the combined weight of the Gd tube and La (Fe,Mn,Si)13-H powders. The maximum isothermal entropy change (−ΔSiso) at μoH= 5 T calculated from isothermal magnetization measurements are 8.7 for Gd tube, 16.9 for La(Fe,Mn,Si)13-H powders, and 10.2 J/kg•K for a wire composite. The magnetocaloric properties including the order of phase transition of the wire composite are close to second-order type due to the higher weight fraction of Gd tube.

Structural, magnetic, magnetocaloric and critical studies of Sm-substituted La0.67-xSmxPb0.13Ca0.2MnO3 perovskite manganites

The structural, magnetic, magnetocaloric, and critical behaviors for Sm substituted La0.67-xSmxPb0.13Ca0.2MnO3 manganites with x = 0, 0.1, and 0.2 were investigated in this work. Based on Rietveld refinement of XRD patterns, all samples have an orthorhombic structure with the Pnma space group. With Sm substitution, the average ionic radii of A-site cation (<rA>), the unit cell volume (V), the Goldschmidt tolerance factor (tG), and the average <θMn-O-Mn> bond angle decrease. Whereas the average bond distance, <dMn-O>, and the variance disorder parameter (σ2) increase. Ferromagnetic (FM) to paramagnetic (PM) phase transitions with second-order type were revealed for all samples from magnetization measurements and Arrott plots. Curie temperature (TC) decreases with Sm substitution from 298 K for x = 0–256 K for x = 0.2. Large maximum entropy change and relative cooling power (6.20 J Kg−1 K−1 and 236 J Kg−1, respectively) have been observed for the undoped sample (x = 0), but the values of these parameters are suppressed due to the disorder caused by Sm doping. The estimated critical exponents (β, γ, and δ) for the x = 0 sample are consistent with tricritical mean-field theory. However, for x = 0.1 and 0.2, they are close to the 3D- Ising model. The change in this universality class can be associated with the increase of disorder by substituting the Sm3+ cations in La0.67-xSmxPb0.13Ca0.2MnO3 manganites.

Magnetostress and multicaloric effect in Ni44.1Co5.0Mn36.1In13.4Cu1.4 polycrystalline alloy

In this Letter, we report on a large magnetic field-induced stress of 14.4 MPa/T and a low stress hysteresis of 50 MPa in a polycrystalline Ni44.1Co5.0Mn36.1In13.4Cu1.4 alloy, rendering it as a promising candidate for high-energy output and high-efficient actuators. The large magnetostress mainly originates from the large transformation entropy change of 15.4 J/(kg K) and the high sensitivity of phase transformation temperature to the magnetic field of −9.2 K/T. Furthermore, we have explored the possibility by adopting multicaloric strategy to enhance the transformation reversibility and widen the cooling temperature window. Unexpectedly, the application of the magnetic field has little impact on the elastocaloric temperature change, which might be ascribed to the large magnetization character of ferromagnetic austenite phase and the non-synergic spin-lattice transformation behavior in the Ni44.1Co5.0Mn36.1In13.4Cu1.4 alloy.

Pressure-freezing of dodecane: exploring the crystal structures, formation kinetics and phase diagrams for colossal barocaloric effects in n-alkanes.

Barocaloric (BC) materials provide cheaper and more energy efficient alternatives to traditional refrigerants. Some liquid alkanes were recently shown to exhibit a colossal BC effect, matching the entropy changes in commercial vapour-liquid refrigerants. Dodecane was predicted to have the largest entropy change among the studied alkanes. Using synchrotron powder and single-crystal X-ray diffraction, Raman spectroscopy, and lattice energy calculations, we investigated the BC effects of n-dodecane at high pressures and room temperature. Remarkably, a colossal entropy change |ΔS| of 778 J kg-1 K-1 at 0.15(3) GPa and 295 K was observed. Spectroscopic studies revealed that this entropy change correlates closely with the conformational transition from mixed gauche to all-trans forms during pressure-induced crystallization. Additionally, the usage of a diamond anvil cell allowed the determination of the crystal structures of in situ crystallized n-un- and dodecane, as well as evaluation of the pressure-dependent crystal growth kinetics. Furthermore, our research suggests that the entropy change (per kilogram) upon compression should be similar for all n-alkanes within the range of 9-18 carbon atoms in the molecule, based on their lattice energies. Even-numbered alkanes are predicted to exhibit superior BC properties compared to their odd-numbered counterparts due to the more symmetric crystal structures and lower propensity to form plastic phases with lower transition entropy.

A first-principle assisted framework for designing high elastocaloric Ni–Mn-based magnetic shape memory alloy

• An efficient first-principle-based computational method to predict ΔV/V 0 is proposed • The substitution of Ga for In is beneficial to increase ΔV/V 0 and ∆S vib • The substitution of Cu for Mn is beneficial to reduce ∆M and ∆S mag • A large transformation entropy change is obtained of the proposed alloy • The studied alloy exhibits excellent elastocaloric properties at room temperature A large adiabatic temperature change (∆ T ad ) is a prerequisite for the application of elastocaloric refrigeration. Theoretically, a large volume change ratio ( ∆V/V 0 ) during martensitic transformation is favorable to enhance ∆ T ad . However, the design or prediction of ∆V/V 0 in experiments is a complex task because the structure of martensite changes simultaneously when the lattice parameter of austenite is tuned by modifying chemical composition. So far, the solid strategy to tailor ∆V/V 0 is still urgently desirable. In this work, a first-principles-based method was proposed to estimate ΔV/V 0 for Ni–Mn-based alloys. With this method, the substitution of Ga for In is found to be an effective method to increase the value of ΔV/V 0 for Ni–Mn–In alloys. Combined with the strategies of reducing the negative contribution of magnetic entropy change (via the substitution of Cu for Mn) and introducing strong crystallographic texture (through directional solidification), an outstanding elastocaloric prototype alloy of Ni 50 (Mn 28.5 Cu 4.5 )(In 14 Ga 3 ) was fabricated experimentally. At room temperature, a huge ∆ T ad of -19 K and a large specific adiabatic temperature change of 67.8 K/GPa are obtained. The proposed first-principle-assisted framework opens up the possibility of efficiently tailoring ∆V/V 0 to promote the design of advanced elastocaloric refrigerants.

Cation-Deficient Ce-Substituted Perovskite Oxides with Dual-Redox Active Sites for Thermochemical Applications.

Identifying thermodynamically favorable and stable non-stoichiometric metal oxides is of crucial importance for solar thermochemical (STC) fuel production via two-step redox cycles. The performance of a non-stoichiometric metal oxide depends on its thermodynamic properties, oxygen exchange capacity, and its phase stability under high-temperature redox cycling conditions. Perovskite oxides (ABO3-δ) are being considered as attractive alternatives to the state-of-the-art ceria (CeO2-δ) due to their high thermodynamic and structural tunability. However, perovskite oxides often exhibit low entropy change compared to ceria, as they generally have one only redox active site, leading to lower mass-specific fuel yields. Herein, we investigate cation-deficient Ce-substituted perovskite oxides as a new class of potential redox materials combining the advantages of perovskites and ceria. We newly synthesized the (CexSr1-x)0.95Ti0.5Mn0.5O3-δ (x = 0, 0.10, 0.15, and 0.20; CSTM) series, with dual-redox active sites comprising Ce (at the A-site) and Mn (at the B-site). By introducing a cation deficiency (∼5%), CSTM perovskite oxides with both phase purity (x ≤ 0.15) and high-temperature structural stability under STC redox cycling conditions are obtained. Thermodynamic properties are evaluated by measuring oxygen non-stoichiometry in the temperature range T = 700-1400 °C and the oxygen partial pressure range pO2 = 1-10-4 bar. The results demonstrate that CSTM perovskite oxides exhibit a composition-dependent simultaneous increase of enthalpy and entropy change with increasing Ce-substitution. (Ce0.20Sr0.80)0.95Ti0.5Mn0.5O3-δ (CSTM20) showed a combination of large entropy change of ∼141 J (mol-O)-1 K-1 and moderate enthalpy change of ∼238 kJ (mol-O)-1, thereby creating favorable conditions for thermochemical H2O splitting. Furthermore, the oxidation states and local coordination environment around Mn, Ce, and Ti sites in the pristine and reduced CSTM samples were extensively studied using X-ray absorption spectroscopy. The results confirmed that both Ce (at the A-site) and Mn (at the B-site) centers undergo simultaneous reduction during thermochemical redox cycling.

Effect of the post annealing cooling rate on the martensitic transformation and the magnetocaloric effect in Ni-Mn-Sn ribbons

We report the modification of the martensitic transformation in Ni-Mn-Sn ribbons by controlling the post annealing cooling rate. Isothermal holding above the order-disorder temperature for 24 h ensured homogeneous grain growth and uniform microstructural features in all the samples. However the atomic order was tailored by varying the cooling rate. The furnace-cooled sample exhibited the highest austenite stabilization and the lowest martensitic transformation temperature of 200.2 K, whereas the air-cooled sample exhibited the highest transformation temperature of 298.5 K. The martensite evolved as ferromagnetic clusters in an anti-ferromagnetic matrix in the samples with high atomic disorder, whereas long-range anti-ferromagnetic co-relations developed in the highly ordered samples. The martensitic transformation in the as-spun ribbons generated a significant magnetocaloric effect and a large entropy change of 4.02 J/kg/K, for a ΔH of 2 T. Furthermore, furnace cooling increased the relative cooling power of the ribbons by 23.3 J/kg over the as-spun specimens.

Order-disorder phase transition and molecular dynamics in the hybrid perovskite [(CH3)3NH][Mn(N3)3

We present a temperature-dependent Raman scattering study of a [(CH3)3NH][Mn(N3)3] hybrid organic–inorganic azide-perovskite, in which we have analysed in detail the wavenumber and full width at half-maximum (FWHM) of lattice modes and internal modes of the NC3 skeleton, N3– and CH3 molecular groups. In general, the modes exhibited unusual behaviour during the phase transitions, including discontinuity in the phonon wavenumber, bandwidth, and unconventional shifts upon temperature variation. Spectral features on heating reveal the absence of significant distortions in the NC3 skeleton and a relatively restricted order–disorder process of the TrMA+ cations. On the other hand, linewidth anomalies of the δNC3 and νasNC3 modes have been attributed to the molecular dynamics of encapsulated cations. The unconventional blue shift of the symmetric stretching modes of azide ligands indicates the weakening of the intermolecular interactions between the TrMA+ cations and azido-bridges, and the strengthening of the intramolecular bonds. Additionally, we have used differential scanning calorimetry to confirm the subtle monoclinic to monoclinic (P21/c → C2/c) phase transition at around 330 K; and the phase transition to trigonal structure (R3¯m) above 359 K, whose associated entropy variation turns to be |ΔS| ∼ 22.3 J·kg−1 K−1 and displays a barocaloric (BC) tunability |δTt/δP| ∼ 3.17 K kbar−1, according to our estimations using the Clausius-Clapeyron method. Although the obtained values of entropy change and BC tunability are very close to those reported on formate-perovskites and other important caloric materials, those parameters are much lower than the giant entropy change of ∼80 Jkg−1 K−1 and large BC tunability ∼12 K kbar−1 observed for the analogue azide-perovskite [(CH3)4N][Mn(N3)]3 (TMAMnN3). Very interestingly, our combined study shed light to understand such different behaviour, as they reveal that the hydrogen bonds created between the TrMA+ cations and the framework prevent an extensive order–disorder process that is needed to obtain large entropy changes and large BC coefficients as it occurs in the case of related azide-perovskites with no H-bonds between the A cations (for example TMA) and the framework.

High Energy Storage Performance and Large Electrocaloric Response in Bi0.5Na0.5TiO3-Ba(Zr0.2Ti0.8)O3 Thin Films.

With regard to the global energy crisis and environmental pollution, ferroelectric thin films with unique polarization behavior have garnered considerable attention for energy storage and electrocaloric refrigeration. Herein, a series of (1 - x)Bi0.5Na0.5TiO3-xBa(Zr0.2Ti0.8)O3 (x = 0.3-0.9; (1 - x)BNT-xBZT) films were fabricated on Pt(111)/Ti/SiO2/Si substrates. Incorporating BZT can tune the polarization behavior and phase transition temperature of BNT. A high recoverable energy density ≈ 82 J cm-3 and optimized efficiency ≈ 81% were realized for the (1 - x)BNT-xBZT thin film with x = 0.7. The thin film exhibits excellent stability in energy storage performance, a wide working frequency range (0.5-20 kHz), a broad operating temperature window (20-200 °C), and reduplicative switching cycles (107 cycles). In addition, the 0.5BNT-0.5BZT film exhibits a desirable electrocaloric effect with a large adiabatic temperature change (ΔT ≈ -22.9 K) and isothermal entropy change (ΔS ≈ 33.4 J K-1 kg-1) near room temperature under a moderate applied electric field of 2319 kV cm-1. These remarkable performances signify that the (1 - x)BNT-xBZT system is a promising multifunctional electronic material for energy storage and solid-state cooling applications.