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Empirical bond length–bond valence (BV) relations provide insight into the link between structure of and ion transport in solid electrolytes and mixed conductors. Building on our earlier systematic adjustment of BV parameters to the bond softness, here we discuss how the squared BV mismatch is linked to the absolute energy scale and used as a general Morse‐type interaction potential for analyzing low‐energy ion migration paths in ion conducting solids or mixed conductors by either an energy landscape approach or molecular dynamics (MD) simulations. For a wide range of lithium oxides we could thus model ion transport revealing significant differences to an earlier geometric approach. This novel BV‐based force‐field has then been applied to investigate a range of mixed conductors, focusing on cathode materials for lithium ion battery (LIB) applications to promote a systematic design of LIB cathodes that combine high energy density with high power density. To demonstrate the versatility of the new BV‐based force field it is applied in exploring various strategies to enhance the power performance of safe low cost LIB materials including LiFePO4, LiVPO4F, LiFeSO4F, etc.

Herein, preparation of Ag2ZnSnSe4(AZTSe) thin films using physical vapor deposition followed by selenization in a quartz tube with rapid thermal process (RTP) is reported. The precursor stacks, [Sn/Se/ZnSe/Se/Ag/Se] × 4, are deposited onto the glass substrate at 100 °C using the combination of thermal and e‐beam evaporation methods. The post selenization of precursors is conducted at different temperatures (300–425 °C). The X‐ray diffraction and Raman spectra of the precursor films selenized at 400 °C reveal the formation of single‐phase AZTSe, exhibiting a kesterite structure with a preferred orientation along the (112) plane. These films show larger grains of ≈230 nm with the homogeneous distribution of Ag, Zn, Sn, and Se across the film thickness. The precursor films selenized at temperatures ≤400 °C show the fundamental absorption edge of AZTSe (Eg= 1.36–1.44 eV) as well as an additional adsorption edge (Eadd= 1.31–1.32 eV) corresponding to ZnSn+ SnZndefect complex. The Hall effect measurement indicates n‐type conductivity irrespective of selenization temperature. For films selenized at 400 °C, the carrier concentration is decreased to 2.83 × 1011cm−3and results in a high mobility of 73.9 cm2(V s)−1, which is attributed to the reduction of SnZndefects. A systematic study is conducted to prepare Ag2ZnSnSe4(AZTSe) thin films using the two‐step process and precisely manifests the impact of selenization temperature on the growth mechanism for obtaining single phase, and the role of the antisite defect complex (ZnSn+ SnZn) on the optical and electrical properties of AZTSe thin films is discussed in detail.

Empirical bond length – bond valence relations provide insight into the link between structure of and ion transport in solid electrolytes and mixed conductors. Building on their earlier systematic adjustment of bond‐valence (BV) parameters to the bond softness, Adams and Rao (pp. 1746–1753) discuss how the squared BV mismatch is linked to the absolute energy scale and is used as a general Morse‐type interaction potential for analyzing the low‐energy ion migration paths in ion conducting solids or mixed conductors by either an energy landscape approach or molecular dynamics (MD) simulations. The cover image shows in the background examples from the wide range of lithium oxides for which ion transport pathways have been studied in this work, revealing significant differences to an earlier geometric approach. The novel BV‐based force‐field has then been applied to investigate a range of mixed conductors, focusing on cathode materials for lithium ion battery (LIB) applications to promote a systematic design of LIB cathodes. As an example the cover image shows on the left hand side the Li ion effect of a FeLi/LiFeantisite defect on the Li ion trajectory for a MD simulation of LiFePO4(red and blue indicate two layers). Here as in many cases the MD simulation will yield a trajectory only for unphysically high temperatures (here 1000 K) or extremely long simulation times, while a BV‐based analysis shows the energy landscape for the mobile Li and the relevant paths from snapshots of the room temperature simulation (right image).

Li1.4N1.6M0.4(PO4)3 with M = Al, Ga, N = Ti, Ge were prepared by annealing of the mixtures at 800°C. X-ray diffraction showed the formation of NASICON phase with space group R-3c along with a minor impurity second phase. Rietveld refinement of the X-ray data was performed to identify the structural variation. The compound with N = Ti and M = Al exhibited lattice parameters a = 8.5015 Aå and c = 20.820 Aå, slightly lower than for the undoped Ti compound (N = M = Ti). Measurements of σionic were carried out on sintered pellets by impedance spectroscopy at 30°C, highest ionic conductivity 2.57 x 10-4 S/cm among the prepared samples was observed when N = Al and M = Ti, two orders of magnitude higher than for the undoped case. Bond valence approach was applied to visualize the migration pathways of Li+ ion and barrier energies were estimated. Obtained Li site energy landscapes indicate the continuous Li transport pathway accessible with activation energy of 0.45eV for undoped Li1Ti2(PO4)3 and 0.42 eV for N = Al and M = Ti doped compound.