Optical response, lithiation and charge transfer in Sn-based 211 MAX phases with electron localization function

Abstract

In this study, optical response, lithiation and charge transfer in existing M2SnC MAX phases with electron localization function (ELF) were investigated for the first time using the density functional theory (DFT). Calculations show that the non-zero value of ε1(0) is an indication of the large availability of free charge carriers in these metallic systems. High reflection of light at the low frequencies indicates the high conductivity and low absorption power of the studied materials. In the visible light region, the average reflectivity of M2SnC is more than 40%, making them potential coating materials for reducing solar heating with greater possibility for Nb2SnC. M2SnC phases are optically anisotropic. The static absorption coefficient represents the universal non-zero value for the hexagonal M2SnC phases. The Plasma frequency is found to be slightly larger for ⟨001⟩ polarization. Lithium (Li) incorporation into M2SnC show that the formation energy required for Li incorporation into Lu2SnC is low, and therefore, it should be suitable for use as an anode in battery. The chemical bonds (M–X) between transition metal ions and carbon are expected to be strong localized bonds as predicted from the ELF maps. The bonds (M–Sn) between transition metal M and A-group element Sn are less localized and more spread out, possibly pointing to a weaker bond. The magnitude of the Bader charges is significantly larger compared to the Mulliken and Hirshfeld charges. According to Bader analysis, maximum charge transfer occurs in Hf2SnC and minimum charge transfer occurs in V2SnC.

Keywords

• MAX phases
• Optical response
• Lithiation
• Charge transfer
• Electron localization function