Modulating Interlayer Chemical Bonding Heterogeneity for Electron-Phonon Decoupling: Unlocking High Thermoelectric Performance in Layered CuCrTi₂Se₆

Layered CuCrTi₂Se₆, a structurally tailored transition-metal dichalcogenide (TMD) derivative, exhibits intrinsically low lattice thermal conductivity but is limited by inferior carrier mobility arising from weak interlayer electronic coupling. Here, we modulate interlayer bonding heterogeneity via a charge-balanced “one Cr replaces three Cu” strategy to form (Cu_1-3xCr_x)CrTi₂Se₆, achieving electron–phonon decoupling. Structural characterizations and density functional theory calculations confirm Cr incorporation into interlayer octahedral sites, inducing two synergistic effects: (i) Replacing ionic interlayer Cu─Se bonds with more covalent Cr─Se bonds facilitates rapid interlayer charge transfer and enhances carrier mobility by ∼60% without altering the electronic band structure; (ii) The reduced interlayer atomic density induced by non-equiatomic Cr/Cu substitution weakens interlayer mechanical coupling, as evidenced by a suppressed shear modulus and transverse sound velocity. When combined with phonon scattering from Cr/Cu point defects, this synergistic effect reduces the room-temperature lattice thermal conductivity by 22%. The optimized (Cu_0.79Cr_0.07)CrTi₂Se₆ achieves a peak thermoelectric figure of merit ZT ≈ 1.0 at 673 K (a record for TiSe₂-based TMDs), and its single-leg device reaches ∼6.1% efficiency at ΔT = 500 K. This work establishes interlayer chemical bonding modulation as a paradigm for high-performance layered thermoelectric materials via electron-phonon decoupling.