Metal–insulator transition in Na-doped post-spinel CdRh2O4

Na doping of post-spinel CdRh2O4 was achieved over the full composition range to NaRh2O4 using high-pressure and high-temperature synthesis conditions. X-ray diffraction analysis confirmed that Na occupies the Cd site and that the host structure is retained, in sharp contrast to what was observed for spinel CdRh2O4, where Na was not accommodated at all. As the Na content was increased, the electrically insulating state changed to a conducting state at a critical composition close to x = 0.75 in Cd1−xNaxRh2O4. The specific heat data confirm that the density of electronic states at the Fermi level was enhanced around this composition, suggesting that the metal–insulator transition is likely induced by band filling. In addition, unusual antiferromagnetism was observed in several compounds with intermediate Na concentrations, and this phenomenon was seemingly independent of the metal–insulator transition.

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► Full-range substitution of Na for Cd was achieved in post-spinel CdRh2O4.
► The host structure was retained for all Na concentrations.
► In contrast Spinel CdRh2O4 does not accommodate Na under similar conditions.
► The Na substitution caused a metal–insulator transition.