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In a solid-state Li ion battery, the solid-state electrolyte exists principally in regions of high externally applied potentials, and this varies rapidly at the interfaces with electrodes because of the formation of electrochemical double layers. We investigate the implications of these for a model solid-state Li ion Li|Li3OCl|C battery, where C is simply a metallic intercalation cathode. We use density functional theory to calculate the potential dependence of the formation energies of the Li+ charge carriers in superionic Li3OCl. We find that Li+ vacancies are the dominant species at the cathode while Li+ interstitials dominate at the anode. With typical Mg aliovalent doping of Li3OCl, Li+ vacancies dominate the bulk of the electrolyte, as well, with freely mobile vacancies that are only ∼10–4 of the Mg doping density at room temperature. We study the repulsive interaction between Li+ vacancies and find that this is extremely short-range, typically only one lattice constant because of local structural r...

SrZn 2 Sn 2 and Ca 2 Zn 3 Sn 6 , two closely related new polar intermetallic compounds, were obtained by high temperature reactions of the elements. Their crystal structures were determined with single crystal XRD methods, and their electronic structures were analyzed by means of DFT calculations. The Zn–Sn structure part of SrZn 2 Sn 2 comprises (anti-)PbO-like {ZnSn 4/4 } and {SnZn 4/4 } layers. Ca 2 Zn 3 Sn 6 shows similar {ZnSn 4/4 } layers and {Sn 4 Zn} slabs constructed of a covalently bonded Sn scaffold capped by Zn atoms. For both phases, the two types of layers are alternatingly stacked and interconnected via Zn–Sn bonds. SrZn 2 Sn 2 adopts the SrPd 2 Bi 2 structure type, and Ca 2 Zn 3 Sn 6 is isotypic to the R 2 Zn 3 Ge 6 compounds ( R =La, Ce, Pr, Nd). Band structure calculations indicate that both SrZn 2 Sn 2 and Ca 2 Zn 3 Sn 6 are metallic. Analyses of the chemical bonding with the electron localization function (ELF) show lone pair like basins at Sn atoms and Zn–Sn bonding interactions between the layers for both title phases, and covalent Sn–Sn bonding within the {Sn 4 Zn} layers of Ca 2 Zn 3 Sn 6 .

Silicon is the most important material for solar cells. However, its low conversion rate/quantum efficiency requires a rather high material consumption. Thus, researchers undertake enormous experimental and theoretical efforts to find alternative Si allotropes with a better efficiency and in the ideal case a direct electronic band gap. In recent years and months many new allotropic Si structures have been reported; however, they are often described incoherently and without context to existing structures. Our approach allows a classification of many of these allotropes and a relation of their structures to substructures of, for example, known Zintl phases. For this so-called "chemi-inspired" search for promising Si structures we present a "construction kit" as a guide to introducing a large number of tetrahedral Si allotropes, all derived by a modification of the pristine cubic diamond structure. In addition, this approach allows us to realize structural (topological) relationships between experimentally accessible Zintl phases of different composition, such as open tetrahedral frameworks, to a yet unknown extent, including even known phase transitions of specific Zintl phases. In topological, structural, and computational analyses (on a DFT-PBE0/SVP level of theory) we show the close relationship of ten low-energy Si structures derived from the cubic diamond modification; five of them are new, and some show quasi-direct band gaps. A simple deviation of this approach enables the construction of many more tetrahedral structures.