Density of states for MgSc 2 S 4 , MgSc 2 Se 4 , MgY 2 S 4 , and MgY 2 Se 4 from top to bottom. The total DOS is given in gray. The projected DOS are shown in red for S and Se, in green for t 2g and yellow for e g d-orbitals. The energy zero is set to the top of the valence band.

Density of states for MgSc 2 S 4 , MgSc 2 Se 4 , MgY 2 S 4 , and MgY 2 Se 4 from top to bottom. The total DOS is given in gray. The projected DOS are shown in red for S and Se, in green for t 2g and yellow for e g d-orbitals. The energy zero is set to the top of the valence band.

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In the area of sustainable energy storage, batteries based on multivalent ions such as magnesium have been attracting considerable attention due to their potential for high energy densities. Furthermore, they are typically also more abundant than, e.g., lithium. However, as a challenge their low ion mobility in electrode materials remains. This stu...

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... order to elucidate the influence of the electronic structure on the properties of the spinels, we have plotted in Fig. 4 the density of states (DOS) of MgB 2 X 4 spinels with B =Sc and Y, and X = S and Se that can be realized experimentally. 59,60 Note that these spinel structures also exhibit trigonal distortions, but they are smaller than those for the spinels with later d-band metals, as shown in Fig. 2b. In Sc and Y, the d-orbitals are empty which ...
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... energy range from −4 eV to 0 eV. For both systems, the DOS of the t 2g and e g states is rather broad and overlaps with each other. The main effect of replacing S ions by Se ions is a reduction of the band gap by about 0.5 eV and a smaller ligand field splitting between anti-bonding e g and non-bonding t 2g states. In the valence band depicted in Fig. 4, d-derived 64 and calculated charge density differences 65 for MgSc 2 S 4 . Details of this charge analysis can be found in the Supplementary Information. Specifically, we considered the insertion of Mg into an octahedral site of the host Sc 2 S 4 lattice at a low concentration resulting in a Mg 0.125 Sc 2 S 4 structure. We find that this ...
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... important role of covalent contributions in the interaction within the spinels is also reflected in the significant width in the density of states of the chalgonide-derived states shown in Fig. 4. For covalent and metallic interactions, the strengths of single bonds typically decreases with increasing coordination 15 based on bond-order conservation arguments, so that the single bond becomes weaker for higher coordination. Furthermore, these interactions scale with the overlap between atomic orbitals which falls off ...
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... Calculated Mg migration barriers for several transition metal ions in the sul de-spinels. Figure 4 Density of states for MgSc2S4, MgSc2Se4, MgY2S4, and MgY2Se4 from top to bottom. The total DOS is given in gray. ...

Citations

... 29 However, we could recently show that the stability of ions in chalcogenide spinels can only be understood if deviations from a purely ionic interaction are taken into account. 48 It is essential to realize that the considered binary materials span the whole range of interaction characteristics between metallic and ionic bonding. Such bonding characteristics can in fact been classified in so-called Van Arkel-Ketelaar triangles 49 in which compounds are placed according to the mean electronegativity χ mean (x-axis) and the electronegativity difference ∆χ (y-axis) of the constituting elements. ...
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Ion mobility is a critical performance parameter in electrochemical energy storage and conversion, but also in other electrochemical devices. Based on first-principles electronic structure calculations, we have derived a descriptor for the ion mobility in battery electrodes and solid electrolytes. This descriptor is entirely composed of observables that are easily accessible: ionic radii, oxidation states and the Pauling electronegativities of the involved species. Within a particular class of materials, the migration barriers are connected to this descriptor through linear scaling relations upon the variation of either the cation chemistry of the charge carriers or the anion chemistry of the host lattice. The validity of these scaling relations indicates that a purely ionic view falls short of capturing all factors influencing ion mobility in solids.The identification of these scaling relations has the potential to significantly accelerate the discovery of materials with desired mobility properties.