Chemical Bond Engineering in Charge-Balanced Layered TiSe₂ Derivatives: 3D Charge Transport and Lattice Anharmonicity...

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 TiSe₂ 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 Ti⁴⁺ ions with Cr³⁺ in the intralayer TiSe₆ 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 TiSe₂. This concerted optimization culminates in a record-breaking dimensionless figure of merit (ZT = 0.82) at 673 K in Cu-deficient composition of Cu_0.8CrTi₂Se₆, representing a 40-fold enhancement over undoped TiSe₂ 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.