اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدOxygen vacancy induced electric polarization changes in Fe,Co-substituted SrTiO$_{3-delta}$
77
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We use density functional theory (DFT) calculations to show that oxygen vacancies ($v_mathrm{O}$) induce noncentrosymmetric polar structures in SrTi$_{0.75}$Fe$_{0.125}$Co$_{0.125}$O$_{3-delta}$ (STFC) with $delta = {0.125, 0.25}$, enhance the magnetic moment and give rise to large changes in the electric polarization $vertDelta Pvert$. Variations of $delta$ or oxygen vacancy migration for a given deficiency are shown to be effective mechanisms to tune the ferroic order parameters, with the former yielding $vertDelta Pvert$ values up to $sim{8mu}$C/c$m^{2}$ while the latter yields $vertDelta Pvert$ up to $sim{23mu}$C/c$m^{2}$. The underlying mechanism is the differentiated self-regulatory-like ferroic response of Fe and Co through the (Fe/Co)-$v_mathrm{O}$ and Fe-$v_mathrm{O}$-Co interactions, which drive B-site off-centering, bending of O$_{4,5}$ incomplete octahedra and B-$v_mathrm{O}$ aligned distortions, all with characteristic charge redistributions. Our results capture characteristics observed in the end-members of the series SrTi(Co,Fe)O$_{3}$, and predict multiferroic behavior that could also be present in other ABO$_{3-delta}$ magnetic oxides.
قيم البحث
اقرأ أيضاً
We use density functional theory to calculate the structure, band-gap and magnetic properties of oxygen-deficient SrTi$_{1-x-y}$Fe$_x$Co$_y$O$_{3-delta}$ with x = y = 0.125 and ${delta}$ = (0,0.125,0.25). The valence and the high or low spin-states o
f the Co and Fe ions, as well as the lattice distortion and the band-gap, depend on the oxygen deficiency, the locations of the vacancies, and on the direction of the Fe-Co axis. A charge redistribution that resembles a self-regulatory response lies behind the valence spin-state changes. Ferromagnetism dominates, and both the magnetization and the band gap are greatest at ${delta}$ = 0.125. This qualitatively mimics the previously reported magnetization measured for SrTiFeO$_{3-delta}$, which was maximum at an intermediate deposition pressure of oxygen.
The conductive characteristics of Bi0.9La0.1Fe0.96Mg0.04O3(BLFM) thin film are investigated at various temperatures and a negative differential resistance (NDR) is observed in the thin film, where a leakage current peak occurs upon application of a d
ownward electric field above 80 oC. The origin of the NDR behavior is shown to be related to the ionic defect of oxygen vacancies (VO..) present in the film. On the basis of analyzing the leakage mechanism and surface potential behavior, the NDR behavior can be understood by considering the competition between the polarized distribution and neutralization of VO...
In contrast to bulk materials, nanoscale crystal growth is critically influenced by size- and shape-dependent properties. However, it is challenging to decipher how stoichiometry, in the realm of mixed-valence elements, can act to control physical pr
operties, especially when complex bonding is implicated by short and long-range ordering of structural defects. Here, solution-grown iron-oxide nanocrystals (NCs) of the pilot wustite system are found to convert into iron-deficient rock-salt and ferro-spinel sub-domains, but attain a surprising tetragonally distorted local structure. Cationic vacancies within chemically uniform NCs are portrayed as the parameter to tweak the underlying properties. These lattice imperfections are shown to produce local exchange-anisotropy fields that reinforce the nanoparticles magnetization and overcome the influence of finite-size effects. The concept of atomic-scale defect control in subcritical size NCs, aspires to become a pathway to tailor-made properties with improved performance for hyperthermia heating over defect-free NCs.
Epitaxial interfaces and superlattices comprised of polar and non-polar perovskite oxides have generated considerable interest because they possess a range of desirable properties for functional devices. In this work, emergent polarization in superla
ttices of SrTiO$_3$ (STO) and LaCrO$_3$ (LCO) is demonstrated. By controlling the interfaces between polar LCO and non-polar STO, polarization is induced throughout the STO layers of the superlattice. Using x-ray absorption near-edge spectroscopy and aberration-corrected scanning transmission electron microscopy displacements of the Ti cations off-center within TiO6 octahedra along the superlattice growth direction are measured. This distortion gives rise to built-in potential gradients within the STO and LCO layers, as measured by in situ x-ray photoelectron spectroscopy. Density functional theory models explain the mechanisms underlying this behavior, revealing the existence of both an intrinsic polar distortion and a built-in electric field, which are due to alternately positively and negatively charged interfaces in the superlattice. This study paves the way for controllable polarization for carrier separation in multilayer materials and highlights the crucial role that interface structure plays in governing such behavior.
Reversible topotactic transitions between oxygen-vacancy-ordered structures in transition metal oxides provide a promising strategy for active manipulation of material properties. While transformations between various oxygen-deficient phases have bee
n attained in bulk ABO$_{3-delta}$ perovskites, substrate clamping restricts the formation of distinct ordering patterns in epitaxial films. Using in-situ scanning transmission electron microscopy (STEM), we image a thermally driven reversible transition in La$_{0.5}$Sr$_{0.5}$CoO$_{3-delta}$ films on SrTiO$_3$ from a multidomain brownmillerite (BM) structure to a uniform phase wherein oxygen vacancies order in every third CoO$_x$ plane. Because temperature cycling is performed over a limited temperature range (25 {deg}C - 385 {deg}C), the oxygen deficiency parameter $delta$ does not vary measurably. Under constant $delta$, the topotactic transition proceeds via local reordering of oxygen vacancies driven by thermal strain. Atomic-resolution imaging reveals a two-step process whereby alternating vertically and horizontally oriented BM domains first scale in size to accommodate the strain induced by different thermal expansions of La$_{0.5}$Sr$_{0.5}$CoO$_{3-delta}$ and SrTiO$_3$, before the new phase nucleates and quickly grows above 360 {deg}C. Upon cooling, the film transform back to the mixed BM phase. As the structural transition is fully reversible and $delta$ does not change upon temperature cycling, we rule out electron-beam irradiation during STEM as the driving mechanism. Instead, our findings demonstrate that thermal strain can solely drive topotactic phase transitions in perovskite oxide films, presenting opportunities for switchable ionic devices.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
