Thermoelectric materials directly convert thermal energy into electrical energy, offering a promising solid-state solution for waste heat recovery. For thermoelectric devices to make a significant impact on energy and the environment the major impediments are the efficiency, availability and toxicity of current thermoelectric materials. Typically, efficient thermoelectric materials contain heavy elements such as lead and tellurium that are toxic and not earth abundant. Many materials with unusual structures containing abundant and benign elements are known, but remain unexplored for thermoelectric applications. In this paper we demonstrate, with the discovery of high thermoelectric efficiency in Ca 3 AlSb 3 , the use of elementary solid-state chemistry and physics to guide the search and optimization of such materials.

Visit the Dalton Transactions website for more cutting-edge inorganic and organometallic research www.rsc.org/dalton The AZn 2 Sb 2 (P3m1, A = Ca, Sr, Eu, Yb) class of Zintl compounds has shown high thermoelectric efficiency (zT~1) and is an appealing system for the development of Zintl structure-property relationships. High temperature transport measurements have previously been conducted for all known compositions except for SrZn 2 Sb 2 ; here we characterize polycrystalline SrZn 2 Sb 2 to 723 K and review the transport behavior of the other compounds in this class. Consistent with the known AZn 2 Sb 2 compounds, SrZn 2 Sb 2 is found to be a hole-doped semiconductor with a thermal band gap0 .27 eV. The Seebeck coefficients of the AZn 2 Sb 2 compounds are found to be described by similar effective mass (m*~0.6 m e ). Electronic structure calculations reveal similar m* is due to antimony p states at the valence band edge which are largely unaffected by the choice of A-site species. However, the choice of A-site element has a dramatic effect on the hole mobility, with the room temperature mobility of the rare earth-based compositions approximately double that found for Ca and Sr on the A site. This difference in mobility is examined in the context of electronic structure calculations.

The magnitude of the renormalization of the band gaps due to zero-point motions of the lattice is calculated for 18 semiconductors, including diamond and silicon. This particular collection of semiconductors constitute a wide range of band gaps and atomic masses. The renormalized electronic structures are obtained using stochastic methods to sample the displacement related to the vibrations in the lattice. Specifically, a recently developed one-shot method is utilized where only a single calculation is needed to get similar results as the one obtained by standard Monte-Carlo sampling. In addition, a fast real-space GW method is employed and the effects of G 0 W 0 corrections on the renormalization are also investigated. We find that the band-gap renormalizations inversely depend on the mass of the constituting ions, and that for the majority of investigated compounds the G 0 W 0 corrections to the renormalization are very small and thus not significant.

We address the metal–organic frameworks UiO-6x (x = 6, 7, 8), their band gaps, and the changes in the band gaps upon perturbations in the metal–organic framework structures. Computational studies were performed with complementary experimental band gap measurements. Band gap modulations upon hydrogen substitutions by NH2 and NO2 on the organic linker, hydroxylation and dehydroxylation of the metal center, different linker lengths (x = 6, 7, 8), and Ti and Hf substitutions for Zr were analyzed in detail. The origin of the band gap changes was thoroughly investigated, and this work confirmed a reduction in the band gap upon NH2 and NO2 substitutions. Furthermore, this work explicitly illustrated that changes in the band gap were also observed by changing the coordination around the Zr atom, whereas isovalent substitutions on the metal center did not yield significant perturbations of the band gap.