We have prepared the oxyhydrate Na0.3RhO2·0. 6H2O by extracting Na+ cations from NaRhO2 and intercalating water molecules using an aqueous solution of Na2S 2O8. Rietveld refinement, thermogravimetric analysis (TGA), and energy-dispersive X-ray analysis (EDX) reveal that a non-stoichiometric Na0.3(H2O)0.6 network separates layers of edge-sharing RhO6 octahedra containing Rh 3+(4d6, S=0) and Rh4+ (4d5, S=1/2). The resistivities of NaRhO2 and Na0.3RhO 2·0.6H2O (T<300) reveal insulating and semi-conducting behavior with activation gaps of 134 and 7.8 meV, respectively. Both Na0.3RhO2·0.6H2O and NaRhO 2 show paramagnetism at room temperature, however, the sodium-deficient sample exhibits simultaneously a weak but experimentally reproducible ferromagnetic component. Both samples exhibit a temperature-independent Pauli paramagnetism, for NaRhO2 at T>50 K and for Na0.3RhO2·0.6H2O at T>25 K. The relative magnitudes of the temperature-independent magnetic susceptibilities, that of the oxide sample being half that of the oxyhydrate, is consistent with a higher density of thermally accessible electron states at the Fermi level in the hydrated sample. At low temperatures the magnetic moments rise sharply, providing evidence of localized and weakly-ordered electronic spins with effective moment per formula unit values of 2.0×10-1 μB for NaRhO2 and 0.8×10-1 μB for Na0.3RhO2·0.6H2O.
Bibliographical noteFunding Information:
Research at Brookhaven National Laboratory is supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Materials Science and the Division of Chemical Sciences under contract DE-AC02-98CH10886. Research carried out in part at the NSLS at BNL is supported by the US DOE (DE-Ac02-98CH10886 for beam line X7A).
All Science Journal Classification (ASJC) codes
- Condensed Matter Physics
- Materials Chemistry