Synthesis and characterization of Na03RhO206H2O - a semiconductor with a weak ferromagnetic component

TL;DR

This study synthesizes and characterizes Na3RhO6·H2O, revealing its semi-conducting properties and weak ferromagnetism, with structural analysis showing layered RhO6 octahedra and differing magnetic behaviors between hydrated and non-hydrated samples.

Contribution

It introduces a new oxyhydrate compound with unique magnetic and electronic properties, combining synthesis, structural, and magnetic characterization.

Findings

Na3RhO6·H2O is semi-conducting with a small activation gap.

The hydrated sample exhibits a weak ferromagnetic component.

Both samples show temperature-independent Pauli paramagnetism.

Abstract

We have prepared the oxyhydrate Na03RhO206H2O by extracting Na+ cations from NaRhO2 and intercalating water molecules using an aqueous solution of Na2S2O8. Synchrotron X-ray powder diffraction, thermogravimetric analysis (TGA), and energy-dispersive x-ray analysis (EDX) reveal that a non-stoichiometric Na03(H2O)06 network separates layers of edge-sharing RhO6 octahedra containing Rh3+(4d6, S=0) and Rh4+ (4d5, S=1/2). The resistivities of NaRhO2 and Na03RhO206H2O (T < 300) reveal insulating and semi-conducting behavior with activation gaps of 134 meV and 7.8 meV, respectively. Both Na03RhO206H2O and NaRhO2 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 Na03RhO206H2O 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 weakl -ordered electronic spins.