Electronic Properties of Surface Terminations in Metal Hexaborides from Density Functional Theory


Metal hexaborides (MB6) are refractory ionic crystals with unique thermophysical properties including low work functions, chemical inertness, and high hardness values among other. Also, they have a broad variety of potential applications such as thermionic emitters, corrosion-resistant coatings, sensors, and catalysis among many other. Many of the electrochemical properties of MB6 materials can be controlled through careful tuning of the cation profile. However, the majority of studies have focused on exploiting the physico-chemical properties at extreme conditions to better understand the mechanism of electron emission, leaving a significant portion of the low-temperature characteristics unexplored. In an effort to bridge this gap, we study the effect of terminal cation placement on the surface on the electronic properties of stoichiometric metal hexaborides formed with Ba, Ca, La, and Sr using density functional theory (DFT). Electronic structure calculations for various surface termination geometries have recently given evidence in support of low-lying complex surface layouts stabilized by large migration barriers. These surface configurations are also found to produce a number of features relevant to dynamics. A combination of band-bending, charge fluctuations, and inversion layers act together to form a localized surface state for a particular cation termination geometry. In this presentation, these effects are discussed in terms of the wide range of properties reported in the literature, including conductivity, ferromagnetism, and De Haas-van Alphen effects.

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