Tuning the Thermoelectric Properties of Transition Metal Oxide Thin Films and Superlattices on the Quantum Scale

Combining advanced growth and characterization techniques with state-of-the-art first-principles simulations in the frameworks of density functional theory and Boltzmann transport theory, recent advances in the field of transition metal oxide films and superlattices (SLs) as thermoelectric materials are discussed, with particular focus on a selection of quantum-scale approaches to tune their thermoelectric performance. Specifically, PdCoO 2 films grown on regular and miscut substrates have enabled experimental confirmation of the large predicted out-of-plane Seebeck coefficient of this anisotropic material and also reveal the necessity of a Hubbard-U parameter on the Co 3 d states. Furthermore, oxygen diffusion and incorporation from the SrTiO 3 ( 001 ) substrate lead to a significant enhancement of the high-temperature Seebeck coefficient in LaNiO 3 / LaAlO 3 ( 001 ) SLs. Next, it is shown how n- and p-type materials can be achieved either by exploiting interface polarity in a LaNiO 3 / SrTiO 3 ( 001 ) SL or using epitaxial strain to shift orbital-dependent transport resonances across the Fermi level in ( LaNiO 3 ) 3 / ( LaAlO 3 ) 1 ( 001 ) SLs. Moreover, confinement- and strain-induced metal-to-insulator transitions induce high Seebeck coefficients and power factors in short-period ( LaNiO 3 ) 1 / ( LaAlO 3 ) 1 ( 001 ) and ( Sr X O 3 ) 1 / ( SrTiO 3 ) 1 ( 001 ) SLs ( X = V, Cr, Mn). Finally, a relation between the topologically nontrivial Chern insulating behavior and enhanced thermoelectric response in ( EuO) 1 / ( MgO) 3 ( 001 ) SLs is established. The article concludes with a discussion of challenges and future topics of research in oxide thermoelectrics.