Materials Science (cond-mat.mtrl-sci)

Abstract: Solubility and interfacial energy are two fundamental parameters underlying the competitive nucleation of polymorphs. However, solubility measurement of metastable phases comes with a risk of solventmediated transformations which can render the results unreliable. In this work, we present a rapid microfluidic technique for measuring aqueous solubility of the metastable form using KDP Phase IV as a model system. This bracketing approach involves analyzing the dissolution behavior of crystals in contact with supersaturated microdroplets generated via evaporation. Then, with the help of our recently developed nucleation time measurement technique, together with Mersmann calculation of interfacial energies from solubilities, we were able to access the interfacial energies of both metastable and stable phases. To gain further insights into the observed nucleation behavior, we employed the Classical Nucleation Theory (CNT) to model the competition of polymorphs using our measured solubility and calculated interfacial energies. The results show that the stable form is favored at lower supersaturation while the metastable form is favored at higher supersaturation, in good agreement with our observations and experimental reports in the literature. Overall, our microfluidic approach allows access to unprecedentedly deep levels of supersaturation and reveals an interesting interplay between thermodynamics and kinetics in polymorphic nucleation. The experimental methods and insights presented herein can be of great interest, notably in the mineral processing and pharmaceutical industry.

Abstract: Two dimensional materials are attracting new research for optoelectronics and spintronics due to their unique physical properties. A wide range of emerging spintronic devices are achieved from parent and doped two dimensional materials. First-principles electronic structure calculations of a two-dimensional monolayer of borophene in its P6/mmm form is explored in this study. The electronic, magnetic, and optical properties of doped borophene are analyzed for doping with lithium, sodium, and magnesium. Density functional theory calculations advocate their good dynamical and thermal stability. Spin-polarized electronic properties of these materials are observed to be useful for predicting new spintronic materials. Additionally optical analysis exhibits the absorption peaks in monolayers along the in-plane direction. These properties of doped magnetic borophene suggest the material to be a suitable candidate for designing optoelectronic devices. The most competent spintronic material among three different doped borophenes is lithium doping that can imply a promising avenue for the fast-growing electronics industry.

Abstract: Vitreous silica is the most versatile material for scientific and commercial applications. Although large-scale atomistic models of vitreous-SiO$_2$ (v-SiO$_2$) having medium-range order (MRO) have been successfully developed by melt-quench through classical molecular dynamics, the MRO is not well studied for the smaller-scale models developed by melt-quench using ab-initio molecular dynamics (AIMD). In this study, we obtain atomistic models of v-SiO$_2$ by performing melt-quench simulation using AIMD. The final structure is compared with the experimental data and some recent atomistic models, on the basis of the structural properties. Since AIMD allows for the estimation of electronic structure, a detailed study of electronic properties is also done. It shows the presence of defect states mainly due to dangling bonds in the band-gap region of electronic density of states, whereas the edge-shared type of defective structures in the glassy models are found to contribute mainly in the valence band. In addition, Oxygen and Silicon vacancies as well as bridging Oxygen type of defects were created and their contributions to the band-gap were studied.

Abstract: Grain boundaries can dissociate into facets if that reduces their excess energy. This, however, introduces line defects at the facet junctions, which present a driving force to grow the facets in order to reduce the total number of junctions and thus the system's energy. Often, micrometer-sized facet lengths are observed and facet growth only arrests for kinetic reasons. So far, energetically stable, finite-sized facets have not been observed, even though theoretical stability conditions have already been proposed. Here, we show a case where nanometer-sized facets are indeed stable compared to longer facets in [111] tilt grain boundaries in Cu by atomistic simulation and transmission electron microscopy. The facet junctions lack a Burgers vector component, which is unusual, but which leads to attractive interactions via line forces. Atomistic simulations predict that the same phenomenon also occurs in at least Al and Ag.

Abstract: Sliding ferroelectricity is widely existed in van der Waals (vdW) two-dimensional (2D) multilayers, exhibiting great potential on low-dissipation non-volatile memories. However, in a vdW heterostructure, interlayer sliding usually fails to reverse or distinctly change the electric polarization, which makes the electrical control difficult in practice. Here we propose that in a vdW magnetic system, the interlayer spin interaction could provide an extra degree-of-freedom to remarkably tune the electric polarization. Combining tight-binding model analysis and first-principles calculations, we show that in the CrI3/MnSe2 and other vdW magnetic heterobilayers, the switching of the interlayer magnetic order can greatly change, even reverse the off-plane electronic polarization. Furthermore, interlayer sliding causes a non-volatile switching of the magnetic order and, thus, reverses the electric polarization, suggesting a non-volatile magnetoelectric coupling effect. These findings will significantly advances the development of 2D ferroelectrics and multiferroics for spintronic applications.

Abstract: Chemical doping efficiently optimizes the physical properties of Heusler compounds, especially their anomalous transport properties, including anomalous Hall conductivity (AHC) and anomalous Nernst conductivity (ANC). This study systematically investigates the effect of chemical doping on AHC and ANC in 1493 magnetic cubic Heusler compounds using high-throughput first-principles calculations. Notable trends emerge in Co- and Rh-based compounds, where chemical doping effectively enhances the AHC and ANC. Intriguingly, certain doped candidates exhibit outstanding enhancement in AHCs and ANCs, such as (Co$_{0.8}$Ni$_{0.2}$)$_2$FeSn with considerable AHC and ANC values of $-2567.78$~S\,cm$^{-1}$ and $8.27$~A\,m$^{-1}$K$^{-1}$, respectively, and (Rh$_{0.8}$Ru$_{0.2}$)$_2$MnIn with an AHC of $1950.49$~S\,cm$^{-1}$. In particular, an extraordinary ANC of $8.57$~A\,m$^{-1}$K$^{-1}$ is identified exclusively in Rh$_2$Co$_{0.7}$Fe$_{0.3}$In, nearly double the maximum value of $4.36$~A\,m$^{-1}$K$^{-1}$ observed in the stoichiometric Rh$_2$CoIn. A comprehensive band structure analysis underscores that the notable enhancement in ANC arises from the creation and modification of the energy-dependent nodal lines through chemical doping. This mechanism generates a robust Berry curvature, resulting in significant ANCs. These findings emphasize the pivotal role of chemical doping in engineering high-performance materials, thereby expanding the horizons of transport property optimization within Heusler compounds.

Abstract: Through its capability for 3D mapping of Li at the nanoscale, atom probe tomography (APT) is poised to play a key role in understanding the microstructural degradation of lithium-ion batteries (LIB) during successive charge and discharge cycles. However, APT application to materials for LIB is plagued by the field induced delithiation (deintercalation) of Li-ions during the analysis itself that prevents the precise assessment of the Li distribution. Here, we showcase how a thin Cr-coating, in-situ formed on APT specimens of NMC811 in the focused-ion beam (FIB), preserves the sample's integrity and circumvent this deleterious delithiation. Cr-coated specimens demonstrated remarkable improvements in data quality and virtually eliminated premature specimen failures, allowing for more precise measurements via. improved statistics. Through improved data analysis, we reveal substantial cation fluctuations in commercial grade NMC811, including complete grains of LiMnO. The current methodology stands out for its simplicity and cost-effectiveness and is a viable approach to prepare battery cathodes and anodes for systematic APT studies.