Synthesis and characterization of Na0.3RhO2·0.6H2O—a semiconductor with a weak ferromagnetic component

Abstract

We have prepared the oxyhydrate Na 0.3 RhO 2 ⋅0.6H 2 O by extracting Na + cations from NaRhO 2 and intercalating water molecules using an aqueous solution of Na 2 S 2 O 8 . Rietveld refinement, thermogravimetric analysis (TGA), and energy-dispersive x-ray analysis (EDX) reveal that a non-stoichiometric Na 0.3 (H 2 O) 0.6 network separates layers of edge-sharing RhO 6 octahedra containing Rh 3+ (4d 6 , S=0) and Rh 4+ (4d 5 , S=1/2). The resistivities of NaRhO 2 and Na 0.3 RhO 2 ·0.6H 2 O (T < 300) reveal insulating and semi-conducting behavior with activation gaps of 134 meV and 7.8 meV, respectively. Both Na 0.3 RhO 2 ⋅0.6H 2 O 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 NaRhO 2 at T > 50 K and for Na 0.

Superconductivity of cobalt oxide hydrate, Na (H3O) CoO2· yH2O

“…This exhibits superconductivity at approximately 4.6 K. Li x CoO 2 Á yH 2 O and K x CoO 2 Á yH 2 O, which may also include H 3 O ions, were reported soon after the discovery of the superconductor with Na [23][24][25] and do not exhibit superconductivity. Many oxides with different transition metal ions but similar crystal structures to BLH or MLH exist [26][27][28][29][30], which also do not exhibit superconductivity. On the other hand, superconductivity is induced by similar hydration in niobium and tantalum sulfates [31,32], although the NbS 2 /TaS 2 layer is largely different from the CoO 2 layer in BLH or MLH; the niobium or tantalum ions are coordinated in trigonal prisms of sulfur ions [33].…”

Widely spaced planes of magnetic dimers in theBa6Y2Rh2Ti2O17−δNguyen1, Straus2, Zhang3 et al. 2021Phys. Rev. Materials3000View full textAdd to dashboardCite

“…The material is a semiconductor with transport and optical band gaps of about 0.16 eV, effective magnetic moment of about 1.5 µB per formula unit, a Curie Weiss theta of about -2.8 K, no magnetic ordering observed down to 0.35 K, and an anomalous heat capacity is seen at low temperatures. The magnetic moment, which is low but present, makes this a rare but not unique example of a magnetic rhodium oxide 4,16,26,27 . The heat capacity at low temperatures (~0.35 K) follows a power law with an exponent of 0.57, much smaller than the expected value of 3, and shows an upturn under zero applied magnetic field that is suppressed by applied fields larger than 2 Tesla.…”

“…After the discovery of superconductivity in Na0.35CoO2.1.6H2O 1,2 , the search for structurally and chemically related superconductors became of significant interest [3][4][5] . A metalinsulator transition was found in NaxRhO2 at x = 0.67, for example, but superconductivity was not observed 3 .…”

“…A metalinsulator transition was found in NaxRhO2 at x = 0.67, for example, but superconductivity was not observed 3 . This was attributed by some researchers to the strong spin-orbit coupling present for the 4d transition metal Rh, which defeats the superconductivity 3,4,6,7 . Rhodium-based compounds exhibit a variety of other interesting properties, however, from photocatalyst and photoelectrolytic electrodes (e.g.…”

Superior thermoelectric response in the 3R phases of hydrated NaxRhO2

“…For Na x RhO 2 it has been shown that the water intercalation and the elongated unit cell result in a decrease of the resistivity18. Accordingly, in Ref.…”