Decoupling The Electron And Phonon Transport In P-Type GeTe-Based Thermoelectric Materials By Implanting Low Dimensional Cabon Materials

As global energy consumption continues to increase,more than half of all energy is wasted in waste heat.Applying thermoelectric materials has become a focus of attention to energy use efficiency.However,most thermoelectric materials currently need to be more efficient,mainly because thermoelectric properties are coupled with each other.Therefore,increasing negatively affects the other,which is one of the main factors hindering their market adoption.Recently,researchers have introduced nanotechnology into bulk thermoelectric materials and have achieved exciting results,successfully improving the performance of thermoelectric materials.The introduction of nanomaterials holds new promise for improved performance of thermoelectric materials,with decoupling of thermoelectric properties becoming possible.Thermoelectric materials have been researched and developed over many years,and some outstanding results have been achieved,including materials such as Pb Te and GeTe,which have maximum zT values above the boundary of 2.Despite the excellent thermoelectric properties of Pb Te as a representative of type IV–VI halides,the toxicity of Pb limits its potential applications.Consequently,GeTe has attracted considerable interest due to its similar band structure,chemical bonding,and environmental friendliness.The presence of many germanium vacancies in intrinsic GeTe materials leads to a high carrier concentration in this material,exhibiting extremely high electrical and thermal conductivity.However,this phenomenon also suppresses the Seebeck coefficient,which severely limits the material’s thermoelectric properties.Therefore,how to enhance the thermoelectric properties of intrinsic GeTe materials and how to achieve decoupling optimization in GeTe-based thermoelectric materials have become key scientific issues in the study of GeTe-based thermoelectric materials,and the following research has been carried out in this topic to address the key scientific issues:（1）GeTe-based thermoelectric materials were successfully prepared by high-temperature melting and vacuum hot-pressure sintering methods.By replacing Bi doping at the Gesite,the carrier concentration of the materials can be effectively reduced.The Seebeck coefficient and electronic thermal conductivity of the materials can be improved,and the Seebeck coefficient and electronic thermal conductivity of Ge_0.95Bi_0.05Te at room temperature are ～ 119.6 μV K-1 and ～ 1.55 W m^-1K^-1,respectively.The Bi-doped samples contain many microstructural defects,which can scatter carriers well and reduce the lattice thermal conductivity of the material,further optimizing the thermal conductivity and improving the material’s thermoelectric properties.It was found that the best overall performance of the samples was achieved when the doped Bi element content was 5%,and the maximum zT value and the average zT value of Ge_0.95Bi_0.05Te were ～ 2.03（723 K）and～ 1.22（323–773 K）,respectively.（2）For the first time,an excellent phase interface layer was successfully constructed by implanting MWCNTs into Bi-doped GeTe.The phase interface between MWCNTs and the matrix Ge_0.95Bi_0.05Te acts as a phonon scattering center,reducing the lattice thermal conductivity without affecting electron transport.Effectively increasing the power factor to～ 4482 μW^-1m^-1K^-2 and reducing the thermal conductivity to ～ 1.27 W m^-1K^-1 at 723 K,the maximum zT ～ 2.3 and zTavg ～ 1.43 were obtained over the temperature range 323-773 K,making it highly competitive among lead-free GeTe based thermoelectric materials.This study guides decoupling electron and phonon transport by implanting one-dimensional carbon materials in thermoelectric materials.（3）Through process modification,multilayer graphene nanosheets were successfully introduced into a matrix of Ge_0.95Bi_0.05Te,which enhanced the electrical conductivity of the material and increase the power factor to ～ 4729 μW^-1m^-1K^-2;and simultaneously decreases the thermal conductivity of the material to ～ 1.36 W m^-1K^-1 and achieves the maximum zT ～ 2.34 and zTavg ～ 1.27 at 323 – 773 K.This study guides decoupling electron and phonon transport by implanting two-dimensional carbon materials in thermoelectric materials.