Substitution by strontium induces significant oxygen deficiency in the crystal lattice of K₂NiF₄-type Nd_2−xSr_xNiO_4−δ at elevated temperatures which, in combination with significant electronic conductivity, implies enhanced mixed ionic–electronic transport.

Zinc oxide (ZnO) has a very broad and versatile range of applications provided by its high abundance and optical and electrical properties, which can be further tuned by donor substitution. Al-doped ZnO is probably the most thoroughly investigated material with regard to thermoelectric properties. Fairly reasonable electrical properties of donor-doped zinc oxide are usually combined with high thermal conductivity limiting potential applications. Here we report a new self-forming nanocomposite concept for ZnO-based thermoelectrics, where a controllable interplay between the exsolution of the nanophases and modification of the host matrix suppresses the thermal transport while imparting enhanced electrical performance. The thermoelectric performance of the best-obtained composite, described by the dimensionless figure-of-merit ZT, at 920–1200 K is almost twice that of the pure matrix composition and reaches up to 0.11. The proposed approach invokes controlled interactions between composite components as a novel tool for decoupling the electrical and thermal transport parameters and shows clear prospects for an implementation in other thermoelectric oxide systems. The results indicate that the proposed concept may also constitute a promising pathway to achieve stable electrical performance at high temperatures, which currently represents one of the major challenges towards achieving ZnO-based thermoelectrics.