Band Jahn-Teller Instability and Formation of Valence Bond Solid in a   Mixed-Valent Spinel Oxide LiRh2O4
  We have synthesized a new spinel oxide LiRh2O4 with a mixed-valent configuration of Rh3+ and Rh4+. At room temperature it is a paramagnetic metal, but on cooling, a metal-insulator transition occurs and a valence bond solid state is formed below 170 K. We argue that the formation of valence bond solid is promoted by a band Jahn-Teller transition at 230 K and the resultant confinement of t2g holes within the xy band. The band Jahn-Teller instability is also responsible for the observed enhanced thermoelectric power in the orbital disordered phase above 230 K. 
Yoshihiko Okamoto, Seiji Niitaka, Masaya Uchida, Takeshi Waki, Masashi   Takigawa, Yoshitaka Nakatsu, Akira Sekiyama, Shigem...