Chemical Bond Engineering in Charge-Balanced Layered TiSe<sub>2</sub> Derivatives: 3D Charge Transport and Lattice Anharmonicity for Exceptional Thermoelectric Performance
Weibin Xu, Weiping Guo, Lin Liao, Chenghao Xie, Jingjing Cui, Qicai Mei, Songlin Li, Jinsong Wu, Zhong‐Zhen Luo, Qingjie Zhang, Xinfeng Tang, Gangjian Tan
Abstract
Layered transition metal dichalcogenides (TMDs) have emerged as a paradigm for investigating emergent quantum phenomena, particularly through their unique charge density wave (CDW) transitions and electron correlation effects. However, the inherent semimetallic characteristics of prototypical compounds such as TiSe 2 fundamentally constrain their thermoelectric performance. Herein, we unveil a breakthrough in thermoelectric TMDs through dual chemical control of both intralayer bonding and interlayer charge dynamics under valence compensation. Through partial substitution of 1/3 Ti 4+ ions with Cr 3+ in the intralayer TiSe 6 octahedral framework, we effectively suppress antibonding orbital interactions, thereby widening the bandgap from −0.46 to 0.53 eV. Simultaneously, controlled Cu + intercalation into interlayer selenium-coordinated void octahedra (i.e., van der Waals gaps) establishes three-dimensional charge transport pathways, resulting in a remarkable 50% enhancement in carrier mobility. Meanwhile, the vibrationally anharmonic Cu–Se bonding configuration dramatically reduces the lattice thermal conductivity to one-fourth that of pristine TiSe 2 . This concerted optimization culminates in a record-breaking dimensionless figure of merit ( ZT = 0.82) at 673 K in Cu-deficient composition of Cu 0.8 CrTi 2 Se 6, representing a 40-fold enhancement over undoped TiSe 2 and setting a new benchmark for single-phase bulk TMD thermoelectrics. Our work demonstrates how atomic-scale coordination engineering can unlock superior thermoelectric performance in traditionally “non-ideal” material systems.