Size-dependent Hysteresis Research Articles

Nucleation site potency distributions in thermoelastic martensitic transformation in Ni43Co7Mn39Sn11 particles

The relationship between the nucleation process and thermal hysteresis width in reversible thermoelastic martensitic transformations remains unclear, particularly as the volume of transforming material decreases. Understanding the number density and nature of defects which serve as nucleation sites in this class of materials requires a quantitative analysis of nucleation site potency distributions in different classes of materials with different intrinsic barriers to nucleation. Here, we investigate the size dependence of hysteresis in microscale ${\mathrm{Ni}}_{43}{\mathrm{Co}}_{7}{\mathrm{Mn}}_{39}{\mathrm{Sn}}_{11}$ alloy particles (radius $4.4\text{--}19.0\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{m}$) during reversible martensitic transformations by collecting temperature-dependent magnetization of 126 individual alloy particles. Size-dependent hysteresis is quantified by a power law model and attributed to friction-induced energy dissipation. In samples with ideal nucleation-limited transformations, martensitic transformation temperatures on cooling decreased with decreasing particle volume due to the low probability of including relatively sparse high-energy nucleation sites. Nucleation site potency distributions are quantified as a function of thermodynamic driving force and compared against potency distributions for thermoelastic martensitic transformations in other classes of materials and for burst martensitic transformations. Across different classes of materials, as the energy barrier associated with the martensitic transformation increases, number densities of defects with sufficient potency to nucleate the transformation decrease dramatically. This finding suggests that very different kinds of defects may be responsible for nucleation of martensitic phase transformations in different material systems.

Size and density controlled Ag nanocluster embedded MOS structure for memory applications

Metal-nanoclusters (NC), deposited by magnetron-based nanocluster source coupled with quadrupole mass filter (QMF) assembly having independent control over their size and density, are used in fabricating NC-based non-volatile memory (NVM) devices. The effect of diameter and density on the NVM charge storage characteristics are presented where Ag is used as the metal NC. The Ag-NC, sandwiched between HfO2 tunnel and control oxides, is deposited by using the combination of the above two instruments. No annealing is performed at any stage of the device fabrication. The largest hysteresis loop area in the capacitance-voltage (C−V) characteristics of metal-oxide-semiconductor (MOS) characteristics is observed for a cluster density of 1×1011cm−2. Further, an NC size dependent hysteresis loop area is observed with the MOS devices where the NC diameter is varied from 3 to 1.5nm keeping the NC density at 1×1011cm−2. The device performance is found to be improved with a reduction of the NC size and shows its best with the NC diameter of 1.5nm. The storage time of the NVM devices also increases with the decrease in the NC diameter and exhibits their best performances for the NCs with a diameter of 1.5nm.

Pore Size Dependent Hysteresis Elimination in Perovskite Solar Cells Based on Highly Porous TiO2 Films with Widely Tunable Pores of 15–34 nm

Pore size and porosity of the porous materials play an important role in catalysis, dye-sensitized solar cells and mesoscopic perovskite solar cells (PSC), etc. Increasing pore size and porosity of mesoporous TiO2 is crucial for facilitating pore-filling of perovskite, charge extraction on TiO2/CH3NH3PbI3 interface and thus cell performance enhancement. Highly porous TiO2 films (TFs) with a large pore size that extends the limit of particle size have been achieved through a novel TiO2 paste using copolymer P123 as a pore-adjusting agent and 2-butoxyethyl acetate as a solvent. A highly porous structure with the pore size of 34.2 nm and porosity of 73.5% has been obtained, the porosity of which is the largest that has ever been reported in the screen-printed TiO2 thick films. The pore size and porosity of TFs can be successively adjusted in a certain range by tuning the P123 content in the pastes. As particle size and surface area of TFs are kept almost constant, the specific investigation on the effect of varied pore size on the performance of bilayer-structured PSCs becomes possible. The hysteresis phenomenon, the notorious problem of PSCs, is found to depend greatly on pore size and porosity of TFs, that is, pore-filling of perovskite. The suppressing effect of highly porous TFs on hysteresis by avoiding charges accumulation on the interface due to enhanced interfacial contact is proved by the invariable photocurrent response after prebias treatment. A hysteresis-free solar cell with an efficiency of 15.47% was achieved by depositing a 242 nm-thick perovskite capping layer upon 350 nm-thick TF with a pore size of 34.2 nm. This method developed for the preparation of highly porous TFs provides a new way to fabricate hysteresis-free PSCs and is widely applicable for the fabrication of other mesoporous metal oxide films with large pore sizes.

Particle size dependent hysteresis loss in La0.7Ce0.3Fe11.6Si1.4C0.2 first-order systems

Here, we report particle size dependent hysteresis loss in La0.7Ce0.3Fe11.6Si1.4C0.2. Hysteresis loss was getting smaller with reducing the particle size. The reduced ratio can be as high as ∼61% as the sample is ground from bulk into small particles (20-50 μm). Such reduction can be ascribed to the notably increased surface area of sample and the partially removed internal strain and grain boundaries, other than nucleation factors and electronic band structure. Meanwhile, entropy change |ΔS| slightly decreases, but the effective refrigeration capacity shows an increase due to the notable reduction of hysteresis loss. Our investigations also reveal particle size limitation. When the size is below 10 μm (average ∼ 4 μm), the sample may lose its stability and the |ΔS| notably reduces.

Size-dependent hysteresis and phase formation kinetics during temperature cycling of metalnanopowders

We present a description of the evolution of a polymorphically transforming metalnanoparticle ensemble subjected to a temperature cycling with constant rates oftemperature change. The calculations of the time dependence of the volume fraction of thenew phase show the existence of size-dependent hysteresis and its main features. Thestatistical analysis makes it possible to introduce and determine the size-dependentsuperheating limit and supercooling limit.

The effect of liquid properties to contact angle hysteresis

Low-rate dynamic advancing and receding contact angles of 21 liquids from two homologous series (i.e. n-alkanes and 1-alcohols) and octamethylcyclotetrasiloxane (OMCTS) on FC-732-coated silicon wafer surfaces were measured by an automated Axisymmetric Drop Shape Analysis-Profile (ADSA-P). The receding contact angle was found to decrease with time, suggesting surface swelling and sorption. An initial receding angle ( θ ri), which theoretically represents the receding angle before sorption starts, was extrapolated back to time of zero contact ( t 0) by least-squares regression in each experiment. The contact angle hysteresis, i.e. the difference between advancing contact angle and θ ri, was found to decrease with increasing chain length of the liquid molecules for both the alkane and alcohol series. Contact angle hysteresis was found to vanish when the chain length was extrapolated to infinity. These results are plausible in terms of liquid sorption by the solid surface: very large molecules are unlikely to penetrate into the solid film. In order to reconfirm that contact angle hysteresis depends on molecular size of the liquid, contact angles of OMCTS, which is a bulky and quasi-spherical molecule, were measured. The hysteresis was found to be 4.1°, which is smaller than for any alkane or alcohol system. The molecular size-dependent hysteresis suggests that contact angle hysteresis phenomena are mainly due to liquid penetration and surface swelling, or at least liquid retention, even on this very hydrophobic surface. The fact that receding contact angles reflect liquid retention by the solid and are therefore not a property of the solid alone, supports the widespread practice of using only the advancing contact angles in studies of surface energetics of solids and disregarding the receding contact angles.

Size-Dependent Hysteresis of Phase Transition in Polymer Gel

Size-Dependent Hysteresis of Phase Transition in Polymer Gel