Are niobium oxide dihalide materials good thermoelectrics: the study case of NbOI₂

Thermoelectric materials offer the possibility to transform heat waste directly into electrical energy. Finding such materials is challenging since they should have simultaneously a large electrical conductivity and a low lattice thermal conductivity. These almost mutually exclusive conditions are usually encountered in materials containing Pb, making them not sustainable. Therefore, we study oxide dihalide materials as a sustainable alternate option.

We propose here to evaluate the potential for thermoelectric applications of the niobium oxide dihalide materials. Our study is motivated by the chemical abundance and ease of fabrication of oxyhalides, and the wide range of properties offered by the presence of mixed anions. We consider the case of NbOI₂ and find that this material has a relatively large electron affinity, making it likely to be a good n-type semiconductor. We calculate the electronic transport properties and lattice thermal conductivity through the third-order force constants and discuss its potential for thermoelectricity as well as the different conditions required (e.g. thickness, temperature) to achieve good efficiency.