Structure and physical properties of K0.63RhO2 single crystals

S H Yao,Z B Gu,B B Zhang,S T Zhang,J Zhou,Y F Chen,Y B Chen,S T Dong

doi:10.1063/1.4767464

Abstract

K0.63RhO2 single crystals were successfully grown by the flux method. Rietveld refinement of power X-ray diffraction patterns suggests that K0.63RhO2 belongs to the monoclinic P63mmc space group. Transport measurements on K0.63RhO2 revealed metallic behavior. The temperature-dependent resistance is well fitted by a different power law in two different temperature ranges. Antiferromagnetic ordering is observed in the ab-plane of K0.63RhO2 below 50 K. The most attractive feature of K0.63RhO2 is its significant Seebeck coefficient at room temperature (46 μV/cm), which is much greater than that of normal metals. Considered all together, the metallic conductivity, the significant Seebeck effect, and the non-hygroscopic properties of K0.63RhO2 make it a promising candidate material for thermoelectric applications.

Highlights

Compounds of the form AxBO2 (A = alkali metal, B = transition metal), with a bronze-type crystal structure, have attracted much attention among physicists and materials scientists
To understand the physical properties of KxRhO2, we investigated its electronic structure from first principles
The hexagonal symmetry along the c-axis of K0.63RhO2 is evident from the selected-area electron diffraction (SAED) pattern

Summary

INTRODUCTION

The giant Seebeck effect (with a Seebeck coefficient ∼100 μV/K at 300 K) is displayed when x = 0.75 (i.e., Na0.75CoO2),[1,2] and superconductivity is observed when x = 0.35 in Na0.35CoO2 · 1.3H2O with a Tc of approximately 5 K.3 These novel physical properties have two main origins. Terasaki et al find that the thermopower of La1-xSrxRhO3 is approximately 100 μV/K up to 500 ◦C, comparable to the value in Na0.75CoO2.2 Another rhodium oxide, K0.49RhO2, displays a large Seebeck coefficient (∼40 μV/K at 300 K), which is much greater than in many normal metals.[6] A giant thermoelectric effect was predicted in K7/8RhO2 by the first principles calculations.[7] many important problems remain unresolved with regard to the KxRhO2 system.

EXPERIMENTAL

RESULTS AND DISCUSSIONS

CONCLUSIONS