We demonstrate a first-principles method to compute all factors entering the vacancy-mediated self-diffusion coefficient. Using density functional theory calculations of fcc Al as an illustrative case, we determine the energetic and entropic contributions to vacancy formation and atomic migration. These results yield a quantitative description of the migration energy and vibrational prefactor via transition state theory. The calculated diffusion parameters and coefficients show remarkably good agreement with experiments. We provide a simple physical picture for the positive entropic contributions.
Abstract Ca‐ion batteries (CIBs) show promise to achieve the high energy density required by emerging applications like electric vehicles because of their potentially improved capacities and high operating voltages. The development of CIBs is hindered by the failure of traditional graphite and calcium metal anodes due to the intercalation difficulty and the lack of efficient electrolytes. Recently, a high voltage (4.45 V) CIB cell using Sn as the anode has been reported to achieve a remarkable cyclability (>300 cycles). The calciation of Sn is observed to end at Ca 7 Sn 6 , which is surprising, since higher Ca‐content compounds are known (e.g., Ca 2 Sn). Here, the Sn electrochemical calciation reaction process is investigated computationally and the reaction driving force as a function of Ca content is explored using density functional theory (DFT) calculations. This exploration allows the identification of threshold voltages which govern the limits of the calciation process. This information is then used to design a four‐step screening strategy and high‐throughput DFT is utilized to search for anode materials with higher properties. Many metalloids (Si, Sb, Ge), (post‐)transition metals (Al, Pb, Cu, Cd, CdCu 2 ) are predicted to be promising inexpensive anode candidates and warrant further experimental investigations.
Low-dimensional materials with charge density waves (CDW) are attractive for their potential to exhibit superconductivity and nontrivial topological electronic features. Here we report the two-dimensional (2D) chalcogenide, BaSbTe2S which acts as a new platform hosting these phenomena. The crystal structure of BaSbTe2S is composed of alternating atomically thin Te square-net layers and double rock-salt type [(SbTeS)2]2- slabs separated with Ba2+ atoms. Due to the electronic instability of the Te square net, an incommensurately modulated structure is triggered and confirmed by both single-crystal X-ray diffraction, electron diffraction, and the presence of an energy bandgap in this compound. Our first-principles electronic structure analysis and investigation of structural dynamical instability suggest that the Te network plays a dominant role in its origin. The incommensurate structure is refined with a modulation vector of q = 0.351(1)b* using an orthorhombic cell of a = 4.4696(5) Å, b = 4.4680(5) Å, and c = 15.999(2) Å under superspace group Pmm2(0β0)000 at 293 K. The modulation vector q varies as a function of both occupancy of Te in the square net and temperature, indicating the CDW order can be modulated by local distortions. The CDW can be suppressed by pressure, leading to the emergence of superconductivity with a Tc up to 7.5 K at 13.6 GPa, suggesting a competition between the CDW order and superconductivity. Furthermore, electrical transport under the magnetic field reveals the existence of compensated high mobility electron- and hole-bands near the Fermi surface (μ ∼600-3500 cm2V-1s-1), suggesting Dirac-like band dispersion.
In situ transmission electron microscopy is a powerful tool to capture spatiotemporal evolution of dynamic phenomena. In article number 1804925, Vinayak P. Dravid, Kai He, and co-workers implement this method to uncover atomic structural evolution of electrochemically reversible phase transformations during lithiation and delithiation of SnSe2, which is promising for lithium-ion batteries.
The authors computed bandgaps and formation energy values of more than 1100 crystalline materials using Density Functional Theory (DFT) with HSE and PBE approximations of the pseudopotentials. They analyzed accuracies of HSE and PBE approximations among different classes of materials. They also built a multi-fidelity machine learning model to predict the bandgap at HSE accuracy when a material's PBE bandgap is known. The new high-throughput DFT (HSE, PBE) data of more than 1100 materials and the predicted HSE bandgap data of more than 21,000 materials are available publicly via a dedicated web app.
An entry from the Inorganic Crystal Structure Database, the world’s repository for inorganic crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the joint CCDC and FIZ Karlsruhe Access Structures service and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
This material is based upon work supported as part of the
Revolutionary Materials for Solid State Energy Conversion, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC00010543.
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