Colossal Thermoelectric Power Factor in K_7/8RhO₂

Abstract

We discuss the thermoelectric and optical properties of layered KxRhO2 (x = 1/2 and 7/8) in terms of the electronic structure determined by first principles calculations as well as Boltzmann transport theory. Our optimized lattice constants differ significantly from the experiment, but result in optical and transport properties close to the experiment. The main contribution to the optical spectra are due to intra and inter-band transitions between the Rh 4d and O 2p states. We find a similar power factor for pristine KxRhO2 at low and high cation concentartions. Our transport results of hydrated KxRhO2 at room temperature show highest value of the power factor among the hole-type materials. Specially at 100 K, we obtain a value of 3×10 −3 K −1 for K 7/8 RhO2, which is larger than that of Na0.88CoO2 [M. Lee et al., Nat. Mater. 5, 537 (2006)]. In general, the electronic and optical properties of KxRhO2 are similar to NaxCoO2 with enhanced transport properties in the hydrated phase.

Large thermopower from dressed quasiparticles in the layered cobaltates and rhodates

“…In K x RhO 2 , similar e g pockets are also predicted [ Fig. 4(b)] [27]. However, our data reveal that the topmost e g dispersion is essentially flat near K at 0.25 eV below E F .…”

“…However, our data reveal that the topmost e g dispersion is essentially flat near K at 0.25 eV below E F . Interestingly, the total occupied bandwidth of the t 2g complex is only renormalized by a factor of 1.15 from the DFT value [27], suggesting a weak electron correlation. Therefore, in K x RhO 2 , the sinking of the e g pockets without strong electron correlation provides new opportunities to test the existing theories.…”

“…respectively. According to the density functional theory (DFT) calculation [27], we attribute the features between 0 and 2 eV to the rhodium 4d t 2g orbitals, and those between 2 and 7 eV to the oxygen 2p orbitals. Similar electronic structure has been reported in Na x CoO 2 , where the cobalt 3d t 2g bands disperse within 1 eV from E F , and the oxygen 2p bands reside between 2 and 6 eV [19,21,22].…”

Structure and physical properties of K0.63RhO2 single crystals

“…6 A giant thermoelectric effect was predicted in K 7/8 RhO 2 by the first principles calculations. 7 However, many important problems remain unresolved with regard to the K x RhO 2 system. For example, how does the thermopower of K Can there be superconductivity in the water-intercalated K x RhO 2 ?…”

Lattice dynamics of KxRhO2 single crystals

“…4 The K content also affects strongly the crystal structure which in turn modifies the thermoelectric, electrical, and magnetic transport properties. Saeed et al 5 calculated the electronic structure of K x RhO 2 (x = 0.5 and x = 7/8) showing that K x RhO 2 is a potential thermoelectric material. Further studies confirmed that K x RhO 2 (x = 0.49 and 0.63) single crystals exhibits a moderate Seebeck coefficient at room temperature.…”