First-Principles Determination of the K-Conductivity Pathways in KAlO₂

Abstract

Investigation of novel fast ion-conducting materials requires an accurate description of the ionic diffusion. The tiling method proposed by Blatov and coworkers, based on geometric characteristics, is a viable alternative to molecular dynamics simulations, allowing us to build models of the pathway system in crystal structures; however, the reliability is limited. Using first-principles simulations, we calculate the potential barriers of the ionic migration between voids in the structure of KAlO2 with local framework distortions and compare the results with those of the tiling method. We estimate the potential barriers for complex ion-conducting channels including several hopping distances. The effect of Coulomb interaction between charge carriers located in adjacent pathways on the potential barriers is discussed, and the effects of the framework flexibility are analyzed. Quantitative results on the potential barriers of ionic diffusion in a crystal structure and its dependence on the shape of the channels are important for assessing the potential of a specific compound.

Ionic Conductivity in Ti-Doped KFeO2: Experiment and Mathematical Modeling

“…These five paths form a three-dimensional migration map and represent all possible hopping channels between two crystallographically nonequivalent positions of potassium (K1 and K2, Figures , ). Similar channels were recently found for cationic migration in the KAlO 2 structure . The migration energy values were derived from the NEB calculations and are listed in Table .…”

“…Similar channels were recently found for cationic migration in the KAlO 2 structure. 24 The migration energy values were derived from the NEB calculations and are listed in Table 1. Interestingly, paths 5 form one-periodic [100] diffusion channels only between K1 positions with extremely low migration barrier, less than 0.1 eV/ion.…”

“…Recently, the conductivity of the undoped KAlO 2 was investigated by DFT methods. 24 The authors showed that the activation energies for all channels are rather high (0.7 eV/ion) compared to the typical values for the Li-ion electrolytes (0.2−0.5 eV/ ion). 25 For K 1−x Fe 1−x Ti x O 2 contradictory data were reported elsewhere.…”

“…Besides, the authors did not study the doped samples with increase of temperature and, therefore, did not estimate the contribution of the dynamic structure disordering. Recently, the conductivity of the undoped KAlO 2 was investigated by DFT methods . The authors showed that the activation energies for all channels are rather high (0.7 eV/ion) compared to the typical values for the Li-ion electrolytes (0.2–0.5 eV/ion) .…”

Local Coordination versus Overall Topology in Crystal Structures: Deriving Knowledge from Crystallographic Databases

“…Traditionally, the geometrical descriptors (interatomic distances, angles, packings, point and space symmetries, etc.) composed the main part of this set because the mathematical base (Euclidean geometry and space group theory) was developed primarily for them. ,, When experimental technique became rather precise, physical descriptors such as electron density distribution and other derived parameters were being explored more often. − A significant progress in DFT methods attracted even stronger attention to this group of descriptors. − At the same time, topological descriptors such as atomic net topology, tiling parameters, and entanglement class remained less developed or even unknown until the end of the 1990s. However, in the past 15–20 years, we saw a great progress in the so-called topological crystal chemistry or reticular chemistry. − The number of topological descriptors was essentially increased, − and special software , and databases − have been developed, which has already resulted in the appearance of the first topological knowledge storages…”