Diffusion Enhancement by Frenkel Defects in NaCl-Type High Entropy Materials

High entropy materials (HEMs) have attracted attention as materials with excellent mechanical properties, irradiation resistance, ionic conductivity, and thermoelectric performance.<br/>For instance, materials with high lithium-ion permeability and melting temperatures are desirable for use as separators in lithium-ion batteries to improve their safety. Consequently, developing HEMs with high diffusion coefficients for specific ions is of great interest. Although the macroscopic strength and crystal stability in HEMs are closely linked to the diffusion of atoms, there is a lack of understanding of the diffusion mechanism due to the complexity of the atomic interactions.<br/>In this study, we focus on the high-entropy superconductor AgInSnPbBiTe5 whose superconductivity is robust against external pressure. The Coulomb potential is dominant in this material, which exhibits the NaCl structure at room temperature and pressure. We have investigated the superconductivity and structure experimentally, as well as the vibrational properties by molecular dynamics (MD) simulations. The simplicity and clarity of the Coulomb potential in these systems facilitate an in-depth investigation of diffusion over extended periods and large system sizes. We therefore considered that investigating the diffusion properties using MD simulations of this system would elucidate the diffusion mechanism of HEMs.<br/>Here, we reveal that In+ spontaneously forms Frenkel defect and enhancing diffusion not only of In+ but also other cations. The charge plays a more crucial role than the size of the cation in the formation of Frenkel defects. Furthermore, as a result of enhanced diffusion, short-range order is formed by structural relaxation. This insight not only enhances comprehension of HEMs diffusion mechanisms but also develops HEMs with properties such as self-healing from damage and high ion permeability, advancing the field of material science.