Spin-orbit-enhanced correlation sensitivity and anomalous magnetic response in non-dimerized 4d 4 ilmenite CdRuO 3

We report the synthesis and physical properties of CdRuO 3 , a nominal Ru 4+ 4d 4 ilmenite with edge-sharing RuO 6 honeycomb layers. Powder x-ray diffraction establishes a crystallographically non-dimerized R -3 structure with equivalent Ru–Ru bonds and a strongly distorted RuO 6 environment. The compacted-pellet resistivity is nonmetallic but non-Arrhenius, while the heat capacity contains a finite residual linear term. Matched nonmagnetic calculations show that PBE+ U without spin–orbit coupling remains metallic or semimetallic up to U eff = 3 eV, whereas PBE+SOC+ U exhibits a strong U eff dependence and opens a direct gap of approximately 55 meV at Γ for U eff = 2.5 eV. Spin–orbit coupling therefore markedly enhances the correlation sensitivity of the non-cubic Ru t 2g manifold. After subtraction of a dilute Curie–Weiss defect contribution, the susceptibility remains weakly nonmonotonic and is inconsistent with both an ordinary Pauli response and independent spin-only S = 1 moments. CdRuO 3 thus realizes the non-dimerized structural branch predicted for ruthenium ilmenites, but not a simple robust multiorbital metal.