Experimental and Computational Insight into the Chemical Bonding and Electronic Structure of Clathrate Compounds in the Sn–In–As–I System

Inorganic clathrate materials are of great fundamental interest and potential practical use for application as thermoelectric materials in freon-free refrigerators, waste-heat converters, direct solar thermal energy converters, and many others. Experimental studies of their electronic structure and bonding have been, however, strongly restricted by (i) the crystal size and (ii) essential difficulties linked with the clean surface preparation. Overcoming these handicaps, we present for the first time a comprehensive picture of the electronic band structure and the chemical bonding for the Sn_{24–<i>x</i>–δ}In_<i>x</i>As_{22–<i>y</i>}I₈ clathrates obtained by means of photoelectron spectroscopy and complementary quantum modeling

Rapid Surface Oxidation of Sb₂Te₃ as Indication for a Universal Trend in the Chemical Reactivity of Tetradymite Topological Insulators

Within the past few years, topological insulators (TIs) have attracted a lot of interest due to their unique electronic structure with spin-polarized topological surface states (TSSs), which may pave the way for these materials to have a great potential in multiple applications. However, to enable consideration of TIs as building blocks for novel devices, stability of TSSs toward oxidation should be tested. Among the family of TIs with a tetradymite structure, Sb₂Te₃ is of <i>p</i>-type and appears to be the least explored material since its TSS is unoccupied in the ground state, a property that allows the use of optical excitations to generate spin currents relevant for spintronics. Here, we report relatively fast surface oxidation of Sb₂Te₃ under ambient conditions. We show that the clean surface reacts rapidly with molecular oxygen and slowly with water, and that humidity plays an important role during oxide layer growth. In humid air, we show that Sb₂Te₃ oxidizes on a time scale of minutes to hours, and much faster than other tetradymite TIs. The high surface reactivity revealed by our experiments is of critical importance and must be taken into account for the production and exploitation of novel TI-based devices using Sb₂Te₃ as a working material. Our results contribute to the comprehensive understanding of the universal trend underlying the chemical reactivity of tetradymite TIs

Reactivity of Carbon in Lithium–Oxygen Battery Positive Electrodes

Unfortunately, the practical applications of Li–O₂ batteries are impeded by poor rechargeability. Here, for the first time we show that superoxide radicals generated at the cathode during discharge react with carbon that contains activated double bonds or aromatics to form epoxy groups and carbonates, which limits the rechargeability of Li–O₂ cells. Carbon materials with a low amount of functional groups and defects demonstrate better stability thus keeping the carbon will-o’-the-wisp lit for lithium–air batteries