  A novel Ti3+-based thiospinel ZnTi2S4 is successfully synthesized via a
low-temperature ion-exchange reaction. ZnTi2S4 shows 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 MgTi2O4
exhibiting the metal-insulator transition associated with a molecular orbital
crystallization (MOC). Furthermore, the magnetic susceptibility of ZnTi2S4
shows 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 MgTi2O4 and ZnTi2S4 would
be due to the different magnitude of overlap between Ti 3d and p orbitals (O:
2p and 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.

Strongly Correlated Electrons;Materials Science