Evolution of Transformation Strain During Partial Transformation Cycling of an NiTi Shape Memory Alloy

This paper deals with how the magnitude of transformation strain changes on partial transformation cycling of an NiTi shape memory alloy. A near-equiatomic NiTi shape memory alloy was allowed to undergo partial thermal cycling keeping the stress constant at 100 MPa for various upper cycle temperatures (between austenite start and austenite finish), using a custom-built thermomechanical cycling test setup. The displacement and the temperature of the sample during cycling were measured using a LASER extensometer and an optical pyrometer, respectively. The test results show that the recovery strain and thermal hysteresis width decrease with increasing number of cycles during partial cycling. In addition, martensite start and martensite finish temperatures increase during the initial cycles, whereas austenite start and austenite finish temperatures decrease during the initial cycles, followed by their saturation.

Proton switching molecular magnetoelectricity

The convergence of proton conduction and multiferroics is generating a compelling opportunity to achieve strong magnetoelectric coupling and magneto-ionics, offering a versatile platform to realize molecular magnetoelectrics. Here we describe machine learning coupled with additive manufacturing to accelerate the design strategy for hydrogen-bonded multiferroic macromolecules accompanied by strong proton dependence of magnetic properties. The proton switching magnetoelectricity occurs in three-dimensional molecular heterogeneous solids. It consists of a molecular magnet network as proton reservoir to modulate ferroelectric polarization, while molecular ferroelectrics charging proton transfer to reversibly manipulate magnetism. The magnetoelectric coupling induces a reversible 29% magnetization control at ferroelectric phase transition with a broad thermal hysteresis width of 160 K (192 K to 352 K), while a room-temperature reversible magnetic modulation is realized at a low electric field stimulus of 1 kV cm−1. The findings of electrostatic proton transfer provide a pathway of proton mediated magnetization control in hierarchical molecular multiferroics.

Electrical Characterization And Study of Current Drift Phenomena And Hysteresis Mechanism In Junctionless Ion-Sensitive Field-Effect Transistor.

A comprehensive study of the drain current drift mechanism and hysteresis phenomena in fabricated p-channel junctionless ion-sensitive field-effect transistor (JL-ISFET) has been investigated for the first time. The drift measurements have been performed through transient analysis of drain current, under different pH and liquid-gate bias (Vlg). Further, time-dependent gate-capacitance (CG) has also been analyzed to see the effect of hydroxyl ions (OH-) in the sensing film (Al2O3). The hysteresis has also been investigated for different pH loop ( 7 → 3 → 7 → 11 → 7 and 7 → 11 → 7 → 3 → 7) and times (960s, 1500s, and 1920s). It has been observed that the drift of JL-ISFET occurs because of chemical modification of the sensing film, due to OH- . The proposed device exhibits a threshold voltage sensitivity of 58.2 mV/pH that is near to the Nernstian limit. Further, the hysteresis width and maximum drain current drift are measured as ~1.3 mV and 2.4 µA (~75%), respectively.

The Influence of Martensitic Intercalations in Magnetic Shape Memory NiCoMnAl Multilayered Films

Hysteresis and transformation behavior were studied in epitaxial NiCoMnAl magnetic shape memory alloy thin films with varying number martensitic intercalations (MIs) placed in between. MIs consists of a different NiCoMnAl composition with a martensitic transformation occurring at much higher temperature than the host composition. With increasing number of intercalations, we find a decrease in hysteresis width from 17 K to 10 K. For a large difference in the layers thicknesses this is accompanied by a larger amount of residual austenite. If the thicknesses become comparable, strain coupling between them dominates the transformation process, which manifests in a shift of the hysteresis to higher temperatures, splitting of the hysteresis in sub hysteresis and a decrease in residual austenite to almost 0%. A long-range ordering of martensite and austenite regions in the shape of a 3D checker board pattern is formed at almost equal thicknesses.

Unraveling the Guest-Induced Switchability in the Metal-Organic Framework DUT-13(Zn)

A guest-induced flexibility in the framework DUT-13 was investigated in situ to analyze the breathing mechanism upon physisorption of nitrogen (77 K) and n-butane (273 K). The crystal structure of cp phase, solved from PXRD data using the computation-assisted semiempirical approach, shows two times smaller pore volume, compared to the op phase, which is consistent with the corresponding isotherms. The contraction mechanism is mainly based on the conformational isomerism of the benztb4- linker, which transforms from a staggered conformation in op phase to a more eclipsed in cp phase, leading to the contraction of the larger pore. A nearly complete op → cp → op transition was observed in the case of n-butane adsorption at 273 K, while in case of weakly interacting nitrogen molecules a portion of the sample remains in the op phase in the entire pressure range. Apparently, in case of DUT-13 the contraction is crystallite size-dependent, similarly as in a number of other switchable MOFs, which should be investigated more in detail in the future. Methane adsorption at varying temperatures showed a wide hysteresis at the temperatures between 111 K and 140 K. The hysteresis width decreases until it disappears completely at 170 K leading to a reversible isotherm, typical for rigid frameworks. The fact that breathing is observed in a broader temperature range in comparison to DUT‑49 demonstrates that thermodynamics and kinetics favour the DUT-13 contraction. Linker and hinges in DUT-13 are not stiff enough to support the metastable states required for NGA.

Unraveling the Guest-Induced Switchability in the Metal-Organic Framework DUT-13(Zn)

A guest-induced flexibility in the framework DUT-13 was investigated in situ to analyze the breathing mechanism upon physisorption of nitrogen (77 K) and n-butane (273 K). The crystal structure of cp phase, solved from PXRD data using the computation-assisted semiempirical approach, shows two times smaller pore volume, compared to the op phase, which is consistent with the corresponding isotherms. The contraction mechanism is mainly based on the conformational isomerism of the benztb4- linker, which transforms from a staggered conformation in op phase to a more eclipsed in cp phase, leading to the contraction of the larger pore. A nearly complete op → cp → op transition was observed in the case of n-butane adsorption at 273 K, while in case of weakly interacting nitrogen molecules a portion of the sample remains in the op phase in the entire pressure range. Apparently, in case of DUT-13 the contraction is crystallite size-dependent, similarly as in a number of other switchable MOFs, which should be investigated more in detail in the future. Methane adsorption at varying temperatures showed a wide hysteresis at the temperatures between 111 K and 140 K. The hysteresis width decreases until it disappears completely at 170 K leading to a reversible isotherm, typical for rigid frameworks. The fact that breathing is observed in a broader temperature range in comparison to DUT‑49 demonstrates that thermodynamics and kinetics favour the DUT-13 contraction. Linker and hinges in DUT-13 are not stiff enough to support the metastable states required for NGA.