High-pressure synthesis, crystal structure determination, and a Ca   substitution study of the metallic rhodium oxide NaRh2O4
  The sodium rhodate NaRh2O4 was synthesized for the first time and characterized by neutron and x-ray diffraction studies, measurements of magnetic susceptibility, specific heat, electrical resistivity, and the Seebeck coefficient. NaRh2O4 crystallizes in the CaFe2O4-type structure, which is comprised of a characteristic RhO6 octahedra network. The compound is metallic in nature, probably reflecting the 1 to 1 mixed valence character of Rh(III) and Rh(IV) in the network. For further studies of the compound, the Rh valence was varied significantly by means of an aliovalent substitution: the full range solid solution between NaRh2O4 and CaRh2O4 was achieved and characterized as well. The metallic state was dramatically altered, and a peculiar magnetism developed in the low Na concentration range. 
K. Yamaura (1), Q. Huang (2), M. Moldovan (3), D.P. Young (3), A. Sato   (1), Y. Baba (1), Y. Matsui (1), and E. Takayama-Mu...