Lattice Distortion Effect in High Entropy Thermoelectric Materials: Mechanisms and Optimization Strategies
The global energy crisis and environmental pollution necessitate efficient recovery and utilization of thermal energy resources such as industrial waste heat. Thermoelectric materials, enabling direct conversion between thermal and electrical energy, offer broad application prospects in waste heat power generation and chip cooling. The energy conversion efficiency is determined by the dimensionless figure of merit, ZT = (S^2σ/κ)T, where S is the Seebeck coefficient, σ is the electrical conductivity, κ is the thermal conductivity, and T is the absolute temperature. Ideal thermoelectric materials require both a high power factor (PF = S^2σ) and low thermal conductivity. However, the strong coupling between electrical and thermal transport parameters makes synergistic optimization challenging. Over the past two decades, strategies such as band engineering, nanostructuring, liquid-like ions, interstitial atoms, phonon softening, and defect engineering have been explored. Among these, entropy engineering has emerged as a novel strategy that achieves synergistic optimization by introducing multiple components to increase configurational entropy. High entropy materials, originating from alloys, are defined as multi-principal element systems with five or more elements in near-equiatomic ratios forming single-phase solid solutions. The molar configurational entropy ΔS_conf = R∑x_i ln x_i, with materials classified as high entropy (ΔS_conf > 1.5R), medium entropy (1R < ΔS_conf < 1.5R), or low entropy (ΔS_conf < 1R). Four core effects are summarized: high entropy effect, lattice distortion effect, sluggish diffusion effect, and cocktail effect. Research has expanded from alloys to oxides, chalcogenides, and half-Heusler compounds. This review systematically summarizes the mechanisms by which lattice distortion in high entropy materials affects electrical and thermal transport, and discusses optimization strategies for thermoelectric performance.