Thermoelectric materials: an introduction

Welcome to the themed issue of Dalton Transactions on Thermoelectric Materials! Thermoelectric materials are solid-state semiconductors that transform heat into electric power or produce cold from an applied voltage. The pioneering work of Ioffe in the 1950s led to the introduction of the first thermoelectric coolers and power generators based on doped bismuth telluride. Since then thermoelectric materials have secured several niche applications, such as spot cooling and deep-space power generation, but even today most devices rely upon bismuth telluride and similar chemical compounds with only moderate thermoelectric performance.

Thermoelectric materials with better efficiency will play an important role as energy materials, namely, as materials for energy storage, conversion, recovery, and transfer. In a global drive for clean energy sources to replace carbon-based fossil fuels, new thermoelectric materials are now receiving appropriate attention and will find many new applications in the future. The emerging and prospective areas of application of thermoelectric materials include: automotive waste heat power generation, direct solar thermal energy conversion, and superconducting electronics. All these areas require new and advanced thermoelectric materials displaying better performance and chemical and thermal stability at the appropriate operating temperatures and environmental safety levels.

There is no theoretical limit for the thermoelectric figure-of-merit, which describes the performance of a thermoelectric material. The problem of developing new thermoelectric materials is linked with chemical design which involves property tuning based on knowledge of the structure–property relationships of semiconductors and semimetals of different natures and also of the concepts of solid state chemistry and condensed matter physics. Indeed, the development of better thermoelectric materials had long been hampered by the necessity of finding compounds possessing high electrical conductivity, high thermopower and, at the same time, low thermal conductivity properties that do not coexist in the majority of compounds. After several decades of looking for better recipes for improving bismuth telluride’s thermoelectric performance by doping and alloying, interest in the field of thermoelectric materials has grown enthusiastically following two important discoveries. In the mid-1990s, Slack developed a concept of solids behaving as both a phonon glass and an electron crystal due to a structural separation of entities, thus rendering possible simultaneous optimisation of the charge carrier and heat transport. Almost ten years later, Dresselhouse introduced nanostructured thermoelectric materials where the quantum confinement amplifies the thermopower while numerous grain boundaries ensure low thermal conductivity. The current research into thermoelectric materials embraces compounds of different chemical compositions and structure types. They include cage compounds, such as filled skutterudites and clathrates, various intermetallics and Zintl phases, complex transition metal oxides, nanostructured tellurides and selenides, as well as other types of semiconductors and semimetals.

The development of thermoelectric materials is surveyed in the selection of papers written by experts in the field for this themed issue of Dalton Transactions. A compilation of two Perspectives and 17 articles represents a temporal slice of the activity in this area, including both achievements thus far and prospects for future development. Also, this issue serves to illustrate that focus on an important type of materials, in this case thermoelectric materials, gives rise to new ideas and discoveries in manifold aspects of inorganic, solid state, and materials chemistry, and nanosciences. I hope you enjoy reading it!

Professor Andrei V. Shevelkov

Moscow State University, Russia

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