Elastocaloric effect in zinc oxide nanowire

In this work, zinc oxide (ZnO) nanowire is proposed for elastocaloric application which has been overlooked until now. The elastocaloric effect ([Formula: see text]CE) is calculated by Maxwell relation. The large elastocaloric temperature and entropy change evaluated as 17 K and 28 J/kgK, respectively, at 300 K correspond to the stress of 12 GPa or strain of 5.5% by the simulation data. The elastocaloric temperature can be increased to 22 K under the operating tempering of 600 K. However, [Formula: see text]CE estimated from the experimental data is found as 2.6 K at 300 K, which corresponds to stress of 6 GPa. These results are expected to significantly expand the knowledge of ZnO nanomaterials as a potential candidate for [Formula: see text]CE. The results are based on the indirect approximation; hence, a direct measurement is needed to verify the obtained results.

Energy Storage Capacity and Electrocaloric Effect on Sn Modified Barium Titanium Oxide (BaTi0.8Sn0.2O3)

Modified Barium Titanium Oxide ( BaTi 0.8 Sn 0.2 O 3 ) was prepared by using the solid-state reaction method. The crystal structure, energy storage behavior, and electrocaloric properties were studied. The phase purity and structural analysis were investigated using the X-ray diffraction technique and the Rietveld refinement of XRD pattern. The microstructure of the sample was recorded by using the Field Emission Scanning Electron Microscopy (FESEM). The temperature variation dielectric property shows that the ceramic exhibits diffuse phase transition behaviour. The ferroelectric nature in BaTi 0.8 Sn 0.2 O 3 has been depicted from P-E loops analysis. The energy storage behaviour and electrocaloric properties were estimated from the temperature variation P-E loops at 40kV/cm. The electrocaloric effect was studied by an indirect method using Maxwell relation, and the electrocaloric value has been estimated to with 94% of energy storage efficiency.

Magnetocaloric Effect in Nanosystems Based on Ferromagnets with Different Curie Temperatures

The magnetocaloric effect in nanosystems based on exchange-coupled ferromagnets with different Curie temperatures is calculated within the mean-field theory. Good agreement between the results of the mean-field theory and the Landau theory, valid near the critical phase transition temperature, is demonstrated for a flat-layered Fe/Gd/Fe structure. We show that a high magnetic cooling efficiency in this system is attainable in principle and prove the validity of the Maxwell relation, enabling an experimental verification of the predictions made. The theory developed for flat-layered structures is generalized to a granular medium.

Comment on “Giant pyroelectric energy harvesting and a negative electrocaloric effect in multilayered nanostructures” by G. Vats, A. Kumar, N. Ortega, C. R. Bowen and R. S. Katiyar, Energy Environ. Sci., 2016, 9, 1335

In the ferroelectric phase, the change of polarization with temperature from partially switched polarization hysteresis loops has no relation with the electrocaloric effect (ECE) and hence cannot be used in Maxwell relation to deducing ECE.

Magnetic and Magnetocaloric Effect of Laves Phase Compounds Er(Fe0.8−xMn0.2−yCox+y)2 with x, y = 0.0 or 0.1

Magnetic and magnetocaloric effect (MCE) of the Er(Fe0.8−xMn0.2−yCox+y)2 Laves phase-type compounds have been investigated. X-ray diffraction (XRD) analysis has revealed that these compounds crystallize with the C15 type Laves phase structure (Space Group Fd-3m). The magnetization curves indicate a ferri-magnetic-ordering resulting of the antiparallel coupling between the moments of the heavy rare earth Er and the transition metal (TM). The partial substitution of Fe/Mn by Co increases the Curie temperature from 355 K for Er(Fe0.8Mn0.2)2 to 475, 550, and 555 K for Er(Fe0.7Mn0.2Co0.1)2, Er(Fe0.8Mn0.1Co0.1)2, and Er(Fe0.7Mn0.1Co0.2)2, respectively. According to the nature of the TM elements, arguments were presented forwards either Molecular Field or Spin Fluctuation Theory, even Stoner type pictures should be considered for. MCE was calculated according to the Maxwell relation based on isotherm magnetization measurements. The magnetic entropy change (−∆SM) observed on a 300–400 K temperature range can be understood in terms of a Spin Fluctuation Theory picture supported by both the different magnetic polarization levels that were shared by the TM elements and the related interatomic exchange forces.

Enhanced Electrocaloric Effect in 0.73Pb(Mg1/3Nb2/3)O3-0.27PbTiO3 Single Crystals via Direct Measurement

Electrocaloric properties of [110] and [111] oriented 0.73Pb(Mg1/3Nb2/3)O3-0.27PbTiO3 single crystals were studied in the temperature range of 293–423 K. The Maxwell relations and the Landau–Ginsburg–Devonshire (LGD) phenomenological theory were employed as the indirect method to calculate the electrocaloric properties, while a high-resolution calorimeter was used to measure the adiabatic temperature change of the electrocaloric effect (ECE) directly. The results indicate that the directly measured temperature changes of ΔT > 2.5 K at room temperature were procured when the applied electric field was reversed from 1 MV/m to −1 MV/m, which are larger than those deduced pursuant to the Maxwell relation, and even larger than those calculated using the LGD theory in the temperature range of 293–~380 K.

Measurement of the torque in braided DNAs using a thermodynamic Maxwell relation

ABSTRACTBraided DNAs are significant structural intermediates in cellular processes, yet little has been experimentally demonstrated about their higher-order structure and twisting torques. We use magnetic tweezers to measure braid extensions at forces ranging from 0.3 to 8 piconewtons, and then apply a thermodynamic Maxwell relation to calculate the torque. Experimentally inferred torques in unbuckled braids take on values up to 76 pN·nm, which depends on force, and inter-tether distance. As predicted using a statistical mechanical model, the twist modulus of the braids increases with catenation prior to buckling or formation of plectoneme, and is comparable to that of single DNA.

Effect of Hydrogen on the Structure, Magnetic and Magnetocaloric Properties of Laves Phase Type-Compounds RE(Fe0.25Co0.75)2Hy with RE = Ho and Er, y = 0.0, 3.0, 3.5

The crystal structure and overall magnetic properties of RE(Fe0.25Co0.75)2Hywith RE = Ho and Er, were analyzed versus y, the hydrogen content. The single phase C15 type compounds, synthesized using cold crucible HF melting, were hydrogenated and controlled using a PCI apparatus. The impact of hydrogen insertion on the cell parameter, the Curie temperature TCand the magnetization saturation were determined. All compounds and hydrides were found to be ferrimagnets, the magnetic moment of RE and 3d elements being opposite since Ho and Er belong to the 2ndrow of rare earth elements. Depending on the formula, a typical compensation point was in evidence. The 2ndorder character of the ferri ↔ paramagnetic transition was established using the Arrott plot method. Magnetization isotherms vs. magnetic field gives quantified results for the magnetic entropy variation by application of the Maxwell relation. Control of y, the hydrogen content, shows it is interesting for improvement of the MCE of the starting compounds. However increasing y leads to decreased TCat the lowest temperatures, suggesting potential cryogenic uses.