اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدTowards Ultra Low Cobalt Cathodes: A High Fidelity Computational Phase Search of Layered Li-Ni-Mn-Co Oxides
99
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
Layered Li(Ni,Mn,Co,)O$_2$ (NMC) presents an intriguing ternary alloy design space for optimization as a cathode material in Li-ion batteries. Recently, the high cost and resource limitations of Co have added a new design constraint and high Ni-containing NMC alloys have gained enormous attention despite possible performance trade-offs. It is not fully understood if this material space is a disordered solid solution at room temperature and any arbitrary combination can be used or if there exist distinct transition metal orderings to which meta-stable solid solutions will decay during cycling and affect performance. Here, we present a high fidelity computational search of the ternary phase diagram with an emphasis on high-Ni, and thus low Co, containing compositional phases to understand the room temperature stability of the ordered and disordered solid solution phases. This is done through the use of density functional theory training data fed into a reduced order model Hamiltonian that accounts for effective electronic and spin interactions of neighboring transition metal atoms at various lengths in a background of fixed composition and position lithium and oxygen atoms. This model can then be solved to include finite temperature thermodynamics into a convex hull analysis to understand the regions of ordered and disordered solid solution as well the transition metal orderings within the ordered region of the phase diagram. We find that for the majority of transition metal compositions of the layered material, specifically medium to high-Ni content, prefer transition metal ordering and predict the collection of preferred compositions in the ordered region.
قيم البحث
اقرأ أيضاً
Substantial amounts of the transition metals Mn, Fe, Co, and Ni can be substituted for Li in single crystalline Li$_2$(Li$_{1-x}T_x$)N. Isothermal and temperature-dependent magnetization measurements reveal local magnetic moments with magnitudes sign
ificantly exceeding the spin-only value. The additional contributions stem from unquenched orbital moments that lead to rare-earth-like behavior of the magnetic properties. Accordingly, extremely large magnetic anisotropies have been found. Most notably, the magnetic anisotropy alternates as easy-plane $rightarrow$ easy-axis $rightarrow$ easy-plane $rightarrow$ easy-axis when progressing from $T$ = Mn $rightarrow$ Fe $rightarrow$ Co $rightarrow$ Ni. This behavior can be understood based on a perturbation approach in an analytical, single-ion model. The calculated magnetic anisotropies show a surprisingly good agreement with the experiment and capture the basic features observed for the different transition metals.
Transition metal nitrides have attracted much interest of the scientific community for their intriguing properties and technological applications. Here we focus on yttrium dinitride (YN$_{2}$) and its formation and structural transition under pressur
e. We employed a fixed composition USPEX search to find the most stable polymorphs. We choose yttrium as a proxy for the lanthanide series because it has only $+3$ oxidation state, contrary to most transition metals. We then computed thermodynamic and dynamical stability of these structures compared to the decomposition reactions and we found that the compound undergoes two structural transitions, the latter showing the formation N$_{4}$ chains. A closer look into the nature of the nitrogen bonding showed that in the first two structures, where nitrogen forms dimers, the bond length is intermediate between that of a single bond and that of a double bond, making it hard to rationalize the proper oxidation state configuration for YN$_{2}$. In the latter structure where there is the formation of N$_{4}$ chains, the bond lengths increase significantly, up to a value that can be justified as a single bond. Finally, we also studied the electronic structure and the dynamical stability of the structures we found.
The discovery of intrinsic magnetic topological order in $rm MnBi_2Te_4$ has invigorated the search for materials with coexisting magnetic and topological phases. These multi-order quantum materials are expected to exhibit new topological phases that
can be tuned with magnetic fields, but the search for such materials is stymied by difficulties in predicting magnetic structure and stability. Here, we compute over 27,000 unique magnetic orderings for over 3,000 transition metal oxides in the Materials Project database to determine their magnetic ground states and estimate their effective exchange parameters and critical temperatures. We perform a high-throughput band topology analysis of centrosymmetric magnetic materials, calculate topological invariants, and identify 18 new candidate ferromagnetic topological semimetals, axion insulators, and antiferromagnetic topological insulators. To accelerate future efforts, machine learning classifiers are trained to predict both magnetic ground states and magnetic topological order without requiring first-principles calculations.
Misfit-layered (ML) cobalt oxides of the general formula of [MmA2Om+2]qCoO2 have been proven to be efficient thermoelectric materials as the structure is capable in accommodating the two seemingly contradictory characteristics of high electrical cond
uctivity and large thermo-electric power. They are also potential hosts for other oxymoron-like functions. The known phases all contain one or two square-planar MO (M = Co, Bi, Pb, Tl, etc.) layers sandwiched together with AO (A = Ca, Sr, Ba, etc.) planes of square symmetry and CoO2 layers of hexagonal symmetry. Here we report realization of the simplest (m = 0) ML phase forming in the Sr-Co-O system with the cation ratio, Sr/Co = 1. Atomic-resolution TEM imaging confirms for the new phase the parent three-layer crystal structure, SrO-SrO-CoO2, which is compatible with the formula of [Sr2O2]qCoO2. Electron diffraction reveals that the phase is rather commensurate, i.e. the misfit parameter q is 0.5. Nevertheless, in terms of the transport-property characteristics the new ML parent is comparable to its earlier-established and more complex derivatives.
We present results of kinetic Monte Carlo simulations of a modified Ziff-Gulari-Barshad model for the reaction CO+O --> CO_2 on a catalytic surface. Our model includes impurities in the gas phase, CO desorption, and a modification known to eliminate
the unphysical O poisoned phase. The impurities can adsorb and desorb on the surface, but otherwise remain inert. In a previous work that did not include CO desorption [G. M. Buendia and P. A. Rikvold, Phys. Rev. E, 85 031143 (2012)], we found that the impurities have very distinctive effects on the phase diagram and greatly diminish the reactivity of the system. If the impurities do not desorb, once the system reaches a stationary state, the CO_2 production disappears. When the impurities are allowed to desorb, there are regions where the CO_2 reaction window reappears, although greatly reduced. Following experimental evidence that indicates that temperature effects are crucial in many catalytic processes, here we further analyze these effects by including a CO desorption rate. We find that the CO desorption has the effect to smooth the transition between the reactive and the CO rich phase, and most importantly it can counteract the negative effects of the presence of impurities by widening the reactive window such that now the system remains catalytically active in the whole range of CO pressures.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
