Ab initio study of local lattice distortion of hexagonal closed-packed high-entropy (Mo0.25Nb0.25Ta0.25V0.25) (Al0.5Si0.5)2 and the influence on thermodynamic property

Abstract

High-entropy ceramics have been increasingly attracting great attention due to their novel properties and widespread applications. In this paper, the local lattice distortion (LLD) of hexagonal closed-packed high-entropy (MoNbTaV) (AlSi)2 and the influence on thermodynamic properties are studied using density functional theory and special quasi-random structure for modelling the chemical disorder. The comparative study between pristine and distorted structures shows that LLD improves the stability and ductility of (MoNbTaV) (AlSi)2, in spite of the little effect on lattice constants. Then LLD is quantified in terms of the standard deviation of statistical distribution of bond lengths. The results show that in (MoNbTaV) (AlSi)2, the LLD in the intra-layer is obviously stronger. Moreover, the influence of LLD on electronic structure is further studied, showing that the larger DOS at EF may be correlated with the larger LLD. The Fermi level of distorted structure is closer to the bottom of pseudogap, and the TDOS at Fermi level decreases significantly, so the LLD stabilizes the structure. Especially, the effect of LLD on thermodynamic properties is deeply investigated. Stemming from the normal high-temperature softening of vibration of LLD, thermodynamic entropy is larger, the thermal expansion is stronger, and the heat capacity is enhanced particularly at low temperature. The present study shows that the stability, ductility and thermodynamic properties can be adjusted by LLD, so is valuable for the understanding and designing of the multi-anionic high-entropy ceramics.