Metallic state in the vicinity of molecular orbital crystallization in the d$^1$ thiospinel ZnTi$_2$S$_4$ prepared via a reductive ion-exchange reaction

TL;DR

This study reports the synthesis of a Ti3+-based thiospinel ZnTi2S4 that exhibits metallic behavior near a molecular orbital crystallization transition, highlighting the role of orbital overlap and electron itinerancy.

Contribution

It introduces a novel ZnTi2S4 compound synthesized via ion-exchange, demonstrating metallic ground state behavior contrasting with similar spinels undergoing metal-insulator transitions.

Findings

ZnTi2S4 shows metallic ground state features.

Magnetic susceptibility indicates MOC fluctuations.

Difference from MgTi2O4 linked to orbital overlap.

Abstract

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.