High-entropy silicides (HESs) have emerged as a groundbreaking class of materials for thermoelectric applications due to their exceptional configurational entropy, which stabilizes complex crystal structures and enhances phonon scattering. Recent studies have demonstrated that HESs such as (Ti,Zr,Hf,V,Nb)Si2 exhibit a remarkable reduction in lattice thermal conductivity (κ_lat) to as low as 1.2 W/m·K at 900 K, a 60% reduction compared to traditional binary silicides. This is attributed to the severe lattice distortion and mass fluctuation induced by the multi-principal element composition. Furthermore, the electrical conductivity (σ) of these materials remains competitive, with values exceeding 10^4 S/m at room temperature, making them promising candidates for high-temperature thermoelectric devices.
The electronic structure engineering of HESs has been pivotal in optimizing their thermoelectric performance. Density functional theory (DFT) calculations reveal that the introduction of transition metals like Mo and W into HESs significantly modifies the density of states near the Fermi level, leading to enhanced Seebeck coefficients (S). Experimental results for (Ti,Zr,Hf,Mo,W)Si2 show S values of up to 250 μV/K at 800 K, a 30% improvement over conventional silicides. Additionally, the power factor (PF = S^2σ) reaches 3.5 mW/m·K^2 at this temperature, demonstrating the potential for efficient energy conversion. These advancements underscore the importance of compositional tuning in achieving high thermoelectric efficiency.
The thermal stability and mechanical robustness of HESs are critical for their deployment in harsh environments. Recent investigations into (Ti,Zr,Hf,Ta,Nb)Si2 have revealed exceptional thermal stability up to 1200 K with minimal phase segregation or oxidation. Nanoindentation studies show hardness values exceeding 15 GPa, which is nearly double that of traditional silicides like TiSi2 (~8 GPa). This enhanced mechanical strength is attributed to solid solution strengthening and grain boundary hardening mechanisms. Such properties make HESs ideal for long-term operation in thermoelectric generators exposed to high temperatures and mechanical stress.
Scalability and cost-effectiveness are key considerations for the practical application of HESs in thermoelectric devices. Advances in powder metallurgy and spark plasma sintering (SPS) techniques have enabled the synthesis of bulk HESs with minimal defects and uniform microstructures. A recent study achieved a ZT value of 0.95 at 900 K for (Ti,Zr,Hf,V,Nb)Si2 using SPS processing at a cost reduction of 40% compared to traditional methods. Moreover, the abundance of constituent elements ensures sustainable production without reliance on rare or expensive materials.
Future research directions for HESs include exploring novel compositions with even higher entropy configurations and integrating nanostructuring strategies to further reduce κ_lat without compromising σ or S. Preliminary results on quinary systems like (Ti,Zr,Hf,V,Nb,Ta)Si2 show κ_lat values as low as 0.8 W/m·K at 900 K while maintaining PF > 3 mW/m·K^2. Additionally, computational modeling suggests that incorporating rare-earth elements could enhance S by up to 20%. These innovations position HESs as a transformative material class for next-generation thermoelectric technologies.
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