We report the synthesis and characterization of polycrystalline ${\mathrm{Na}}_2{\mathrm{RuO}}_3$, a layered material in which the ${\mathrm{Ru}}^{4+}$ ($4d^4$ configuration) form a honeycomb lattice. The optimal synthesis condition was found to produce a nearly ordered ${\mathrm{Na}}_2{\mathrm{RuO}}_3$ ($C2/c$ phase), as assessed from the refinement of the time-of-flight neutron powder diffraction. Magnetic susceptibility measurements reveal a large temperature-independent Pauli paramagnetism $[{\chi }_0\sim 1.42\left(2\right)\times {10}^{-3}$ emu/mol Oe] with no evidence of magnetic ordering down to 1.5 K, and with an absence of dynamic magnetic correlations, as evidenced by neutron scattering spectroscopy. The intrinsic susceptibility (${\chi }_0$) together with the Sommerfeld coefficient of $\gamma =11.7\left(2\right)$ mJ/Ru mol ${\mathrm{K}}^2$ estimated from heat capacity measurements gives an enhanced Wilson ratio of $R_W\approx 8.9\left(1\right)$, suggesting that magnetic correlations may be present in this material. While transport measurements on pressed pellets show nonmetallic behavior, photoemission spectroscopy indicates a small but finite density of states at the Fermi energy, suggesting that the bulk material is metallic. Except for resistivity measurements, which may have been compromised by near-surface and interface effects, all other probes indicate that ${\mathrm{Na}}_2{\mathrm{RuO}}_3$ is a moderately correlated electron metal. Our results thus stand in contrast to earlier reports that ${\mathrm{Na}}_2{\mathrm{RuO}}_3$ is an antiferromagnetic insulator at low temperatures.

• Received 23 April 2020
• Revised 16 July 2020
• Accepted 20 August 2020

DOI:https://doi.org/10.1103/PhysRevMaterials.4.094202