AA′2Rh6O12: A New Family of Rhodium Oxides Exhibiting High Thermopower Coupled with High Electrical Conductivity

A new family of rhodium oxides with the SrCa 2 Sc 6 O 12 structure has been discovered. The new compounds prepared are SrMg 2 Rh 6 O 12 , La 1-x Mg 2-y Rh 6 O 12 , Bi 0.8 Li 2 Rh 6 O 12 , Pb 0.78 Li 2 Rh 6 O 12 , Bi 0.75 Sc 1.10 -(Rh 4.92 Sc 1.08 )O 12 , SrBe 2 RhO 12 , and Bi 0.68 Be 2 RhO 12 . All compounds can be considered Rh 3+ /Rh 4+ mixed-valence compounds with the highest average oxidation being +3.4. Structural analyses based on single-crystal X-ray diffraction data were performed for four of the compounds, and triangular coordination for Be was found in the case of Bi 0.68 Be 2 Rh 6 O 12 . All the compounds are good electrical conductors, and a Seebeck coefficient of 200μV/K was found for Bi 0.88 Li 2 RhO 12 and SrMg 2 RhO 12 . The magnetic properties of Pb 0.78 Li 2 Rh 6 O 12 , Bi 0.78 Li 2 Rh 6 O 12 and Bi 0.68 Be 2 Rh 6 O 12 are discussed.