New thermoelectric materials based on thin films of chromium nitride (CrN)
Although thermoelectric materials (TE) are well known and have been used for many years, even in the field of space engineering, the problem is that even they are reliable, their performance is quite small and they are expensive. The most common materials used in commercial TE devices are based on lead (Pb), bismuth (Bi), tellurium (Te) and selenium (Se), which have several problems, as instability, toxicity or scarcity. So, the design of efficient TE materials to produce electricity from heat from industrial processes in a cleaner and more competitive way is one of the current challenges in materials science. In this work, published in Advanced Materials ('Epitaxial CrN Thin Films with High Thermoelectric Figure of Merit'), CiQUS researchers have demonstrated that rock salt chromium nitride (CrN) shows intrinsic lattice instabilities that suppress its thermal conductivity. Furthermore, through the fabrication of high-quality epitaxial CrN thin films, an enhancement up to 250 % of the thermoelectric figure of merit (a measure of the conversion efficiency) was reported in single-crystalline films of CrN at room temperature compared to bulk CrN. The conclusions of this work show that well established chemical ideas like resonant bonding can be also applied to tune thermal transport functionalities in transition metal nitrides and oxides. These results, along with its high thermal stability, resistance to corrosion, and exceptional mechanical properties, make CrN a promising material for high-temperature thermoelectric applications. This research was led by Prof. Francisco Rivadulla (ERC-Starting Grant at CiQUS, University of Santiago de Compostela) and has been carried out in collaboration with research groups at the Universities of Wisconsin–Madison, MIT-Boston, Lincoln-Nebraska and Boise-Idaho.
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