Berlin 2015 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 22: Functional Materials IV: Thermoelectric and Multiferroic Materials

MM 22.1: Vortrag

Dienstag, 17. März 2015, 10:15–10:30, TC 010

Thermoelectric properties of the layered rhodates K_xRhO₂ and Na_xRhO₂ — •Udo Schwingenschlögl, Yasir Saeed, and Nirpendra Singh — KAUST, Thuwal 23955-6900, Saudi Arabia

The thermoelectric properties of the layered oxides K_xRhO₂ (x = 1/2 and 7/8) are investigated by means of the electronic structure, as determined by ab inito calculations and Boltzmann transport theory. In general, the electronic structure of K_xRhO₂ is similar to Na_xCoO₂, but with strongly enhanced transport. K_7/8RhO₂ exceeds the ultrahigh power factor of Na_0.88CoO₂ reported previously by more than 50%. The roles of the cation concentration and the lattice parameters in the transport properties in this class of compounds are explained. In addition, we study the 3R phases of Na_xRhO₂ for different Na vacancy configurations and concentrations. As compared to the analogous 2H phases, the modified stacking of the atomic layers in the 3R phases reduces the interlayer coupling. As a consequence, the 3R phases are found to be superior in the technologically relevant temperature range. The Rh d_3z²−r² orbitals still govern the valence band maxima and therefore determine the transport properties. A high figure of merit of 0.35 is achieved in hydrated Na_0.83RhO₂ at 580 K by water intercalation, which is 34% higher than in the non-hydrated phase. References: Adv. Funct. Mater. 22, 2792 (2012); Sci. Rep. 4, 4390 (2014).