Thermoelectric Properties And Mechanism Of P-type SiGe-based Alloy Material Optimized By Nano-second-phase Composite

Thermoelectric materials have the advantage of directly converting thermal energy into electrical energy,and have extensive application prospects in fields such as space exploration and wearable self-powered devices.Among them,Si Ge-based thermoelectric materials have been applied in deep space exploration due to their excellent mechanical properties and thermal stability.However,current research on Si Ge materials often focuses on the high-temperature range,and the performance control in the middle and low-temperature range is rarely reported.In addition,due to the coupling of electrical and thermal properties,the thermoelectric performance of Si Ge alloys is often unable to be synergistically regulated.Based on the above problems,this paper focuses on the synergistic optimization strategy of Si Ge-based thermoelectric materials in the middle and low-temperature range.First,during the sintering process,the electrical and thermal properties of Si Ge often increase synergistically,so it is necessary to adjust the sintering process to balance the porosity and crystallinity.In addition,the excessively high carrier concentration and thermal conductivity of p-type Si Ge severely restricts the optimization of thermoelectric performance.To decouple the thermoelectric parameters of Si Ge-based thermoelectric materials,Ti₂C is introduced to synergistically optimize the thermoelectric performance.Finally,to overcome the limitations of Ti₂C,Ta C is used as a nanoscale second-phase composite to further optimize the thermoelectric performance of Si Ge alloys.The main research conclusions of this paper are as follows:（1）This paper investigates the effects of spark plasma sintering（SPS）process on the microstructure and thermoelectric properties of Si Ge alloys,and obtains the optimal sintering process（1423 K for 3 minutes）.The study shows that finely tuning the sintering temperature and holding time of Si Ge alloys can significantly increase their crystallinity and reduce the pore size,which plays an important role in optimizing their electrical properties and suppressing acoustic transport.Ultimately,the Si₈₀Ge₂₀B_0.8sample achieves excellent power factor(3.9 W m^-1K^-1).This results in a maximum ZT value（～0.54 at673 K）and lays the foundation for research on nanoscale second-phase composites.（2）Due to Ti₂C low-dimensional characteristics,it can simultaneously reduce thermal conductivity without deteriorating electrical performance.In this study,Ti₂C nanolayered structures were introduced into Si Ge alloys,and the resulting two-dimensional Ti₂C layers were able to enhance phonon scattering and suppress thermal conductivity(reduced to～2.42 W m^-1K^-1)after high-temperature sintering.Ultimately,with optimized thermal transport performance,the maximum ZT of（Ti₂C）_0.9-Si₈₀Ge₂₀B_0.8reached～1.04 at 873K,and the average ZT_avgwas～0.51（323-873 K）.This relatively a high level among current Si Ge materials.However,due to certain limitations in carrier tuning mechanisms,there is still room for further optimization of electrical performance.（3）To further decouple the thermoelectric parameters,Ta C particles with a work function matching Si Ge were introduced to enhance phonon scattering while regulating carrier concentration,achieving performance improvement of thermoelectric materials.The characteristic of work function matching enables Ta C to release electrons into Si Ge valence band and achieve the purpose of regulating carrier concentration.At room temperature,the carrier concentration of（Ta C）₁-Si₈₀Ge₂₀B_0.8was optimized from～3×10²⁰cm^-3(Si₈₀Ge₂₀B_0.8)to～1.17×10²⁰cm^-3.In addition,Ta C doping also caused new phonon scattering centers（nanoscale second phase scattering,dislocations,defects,etc.）.Under the synergistic effect of carrier engineering and scattering mechanisms,the power factor of（Ta C）₁-Si₈₀Ge₂₀B_0.8reached～2943.42μW m^-1K^-2at 873 K,and the lowest thermal conductivity was reduced to 2.36W m^-1K^-1.Ultimately,the maximum ZT value of composite 1mol%Ta C reached～1.06,and the average ZT_avgvalue in the temperature range of 323-873 K was～0.59.The highest output power was approximately～9.8%(calculated using engineering ZT_eng),which provides new ideas for optimizing the thermoelectric performance of Si Ge.This study decoupled the thermoelectric parameters and optimized the carrier concentration while enhancing phonon scattering,which resulted in a significant improvement in the thermoelectric performance of Si Ge alloys.This provides new optimization strategies for related materials.