Origin of large thermopower in LiRh_2O_4: Calculation of the Seebeck coefficient by the combination of local density approximation and dynamical mean-field theory

摘要

Motivated by the newly synthesized mixed-valent spinel. LiRh_2O_4 for which a large thermopower is observed in the metallic cubic phase above 230 K [Y. Okamoto et al, Phys. Rev. Lett. 101, 086404 (2008)], we calculate the Seebeck coefficient by the combination of local density approximation and dynamical mean-field theory (LDA+DMFT). The experimental values are well reproduced not only by LDA+DMFT but also by the less involved Boltzmann equation approach. A careful analysis of the latter shows unexpectedly that the origin of the large thermopower shares a common root with a very different oxide: Na_xCoO_2. We also discuss how it is possible to further increase the power factor of LiRh_2O_4 through doping, which makes the material even more promising for technological applications.