Metallic state in the vicinity of molecular orbital crystallization in thed1thiospinel ZnTi2S4prepared via a reductive ion-exchange reaction.

A novel Ti3+-based thiospinel ZnTi2S4is successfully synthesized via a low-temperature ion-exchange reaction. ZnTi2S4shows a signature of metallic ground state evidenced by a contribution of conduction electrons in the heat capacity and Pauli-like paramagnetic susceptibility. These observations contrast to the electronic state of similar Ti3+-based spinel MgTi2O4exhibiting the metal-insulator transition associated with a molecular orbital crystallization (MOC). Furthermore, the magnetic susceptibility of ZnTi2S4shows a pseudogap-like behavior indicated by a vast peak in the magnetic susceptibility around 110 K, likely originating from the MOC fluctuation. The origin of the difference in the electronic states of MgTi2O4and ZnTi2S4would be due to the different magnitude of overlap between Ti 3dandporbitals (O: 2pand S: 3p). The presence of a MOC state in the close vicinity of insulator-metal transition may suggest the importance of itinerancy in a MOC.