Importance Of Phase Separation Research Articles

Tuning the Phase Separation, Charge Ordering, and Electronic Transport in Electron‐Doped Manganite Films by Piezo‐Strain and Magnetic Field

AbstractThe macroscopic physical properties and functionalities of strongly correlated complex oxides usually originate from and depend sensitively on microscopic interactions, which can be controlled by an external stimulus. Here, in electron‐doped La0.85Hf0.15MnO3/Pb(Mg1/3Nb2/3)O3‐PbTiO3 multiferroic heterostructure, the role of phase separation in manipulating charge ordering and electronic transport by piezo‐strain and magnetic field is determined. The electric‐field‐induced lateral compressive piezo‐strain suppresses the charge‐ordering transition temperature and decreases the film resistance with a giant gauge factor of 27 368, due to the enhancement of the double‐exchange interaction between the Mn3+–Mn2+ ions and the suppression of the electron‐phonon coupling stemming from the Jahn‐Teller deformation. Moreover, the magnetic field can weaken the piezo‐resistance effect by 342 times. This result, together with elastically controlled magnetoresistance effect, demonstrates intimate correlation between the piezo‐strain‐induced and magnetic‐field‐induced effects by adjusting phase separation tendency. The findings indicate the importance of phase separation in multi‐field quantum control of electron‐doped perovskite manganites.

Ion-assisted phase separation in compound films: An alternate route to ordered nanostructures

In recent years, observations of highly ordered, hexagonal arrays of self-organized nanostructures on binary or impurity-laced targets under normal-incidence ion irradiation have excited interest in this phenomenon as a potential route to high-throughput, low-cost manufacture of nanoscale devices or nanostructured coatings. The currently prominent explanation for these structures is a morphological instability driven by ion erosion discovered by Bradley and Shipman; however, recent parameter estimates via molecular dynamics simulations suggest that this erosive instability may not be active for the representative GaSb system in which hexagonal structures were first observed. Motivated by recent experimental and numerical evidence suggesting the likely importance of phase separation during thin-film processing, we here generalize the Bradley-Shipman theory to include the effect of ion-assisted phase separation. The resulting system admits a chemically driven finite-wavelength instability that can explain the order of observed patterns even when the erosive Bradley-Shipman instability is inactive. In a relevant simplifying limit, it also provides an intuitive instability criterion similar to results in thin-film deposition, as well as predictions on pattern wavelengths that agree qualitatively with experimental observations. Finally, we identify a characteristic experimental signature that distinguishes the chemical and morphological instabilities and highlights the need for specific additional experimental data on the GaSb system.

A Comparison Between Round Turbulent Jets and Particle-Laden Jets in Crossflow by Using Time-Resolved Stereoscopic Particle Image Velocimetry

Time-resolved stereoscopic particle image velocimetry (TR-ST-PIV) measurements were performed to compare the velocity and vorticity field, and the three-dimensional high intensity vorticity structures between a round turbulent single-phase jet and a particle-laden jet in crossflow. The experiments involved steady fresh water jet sources with a particle mass loading of ∼2.0% injected into steady fresh water crossflows. The TR-ST-PIV system was combined with a phase discrimination method that separates two-phase stereo PIV images into dispersed phase images and continuous phase images that are analyzed by using particle tracking velocimetry and stereo-PIV algorithms, respectively. The analysis shows the importance of phase separation for accurate velocity results. It provides instantaneous velocity fields where the dispersed phase preferentially concentrated in regions of low vorticity with the velocity not matching the continuous phase. The jet and the particle-laden jets trajectories are compared to each other and with results in the literature. Similarly, a comparison of mean velocity and vorticity fields between both flows suggest enhanced mixing in the particle-laden jet due to the effects of the dispersed phased which lowered the centerline velocities and enhanced the penetration in the cross-stream direction of the continuous phase. The Taylor’s frozen flow hypothesis is applied to reconstruct the 3D high intensity vorticity structures in a volume. The visualization of the three-dimensional structures corresponding to the intermediate scales of the flow shows slightly elongated structures preferentially aligned with the jet centerline axis.

THE PHYSICS OF CRYSTALLIZATION FROM GLOBULAR CLUSTER WHITE DWARF STARS IN NGC 6397

We explore the physics of crystallization in the deep interiors of white dwarf (WD) stars using the color-magnitude diagram and luminosity function constructed from proper-motion cleaned Hubble Space Telescope photometry of the globular cluster NGC 6397. We demonstrate that the data are consistent with the theory of crystallization of the ions in the interior of WD stars and provide the first empirical evidence that the phase transition is first order: latent heat is released in the process of crystallization as predicted by van Horn. We outline how these data can be used to observationally constrain the value of Γ ≡ E Coulomb/E thermal near the onset of crystallization, the central carbon/oxygen abundance, and the importance of phase separation.

Nonmagnetic Insulator State inNa1CoO2and Phase Separation of Na Vacancies

Crystallographic, magnetic, and NMR properties of a Na1CoO2 single crystal with x approximately = 1 are presented. We identify the stoichiometric Na1CoO2 phase, which is shown to be a nonmagnetic insulator, as expected for homogeneous planes of Co3+ ions with S = 0. In addition, we present evidence that, because of slight average Na deficiency, chemical and electronic phase separation leads to a segregation of Na vacancies into the well-defined, magnetic, Na0.8CoO2 phase. The importance of phase separation is discussed in the context of magnetic order for x approximately = 0.8 and the occurrence of a metal-insulator transition for x --> 1.