Study On Pb-Bi-Sb-Te Thermoelectric Composite Materials

Thermoelectric materials can directly convert heat into electricity used by solid carrier transportation energy.The high performance of thermolelectric materials is benefit to solve the problem of energy crisis.There are the three thermoelectric properties:Seebeck coefficient,electric conductivity and thermal conductivity.Those decided by the transport process of the electron and the phonon,which PN junction can decouple in a certain degree.It is easy to arrange the ordered structure for the PbTe Nanocubes(NCs)at surface of micro-size Bi0.5Sb1.5Te3 powder flake,what is named by PN junction.The studies focus on the size,morphology,surface oxidation and dispersion of PbTe cubic nanocrystal,which also influence the work function of PN junction,which the thermoelectric performance of embedded structure PN junction thermoelectric nanocomposite materials PbTe/Bi0.5Sb1.5Te3 were studied in detail.The morphology of PN junction embedded structure in thermoelectric nanocomposite materials was firstly characterized by scanning electron microscope(SEM),high resolution transmission electron microscope(HRTEM),electron probe microanalysis(EPMA),Raman spectroscopy(Raman)and time-of-flight secondary ion mass spectrometry(TOF-SIMS).At the same time,it is interesting to how to restrain the surface oxidization of PbTe and to maintain the embedded structure in the sintering process of thermoelectric composites.What optimize the ZT is divided into the following three parts in this paper.Firstly,fast and easy performing method based on the widely used hot injection method,which is introduced to fabricate PbTe NCs with high purity.The rapid injection reduced excessive oxidation of the surface of the solution.Results show that the size of the PbTe nanocrystals is 17±20nm,the morphology is uniform,the square shape is close to 90° angle,and the perfect dispersion in toluene solvent.This approach can prevent the PbTe NCs surface oxidization.The way to solve the problem of the excessive oxidization surface,high purity of PbTe remained stable.In addition,device was consisted that PbTe nanocrystals array into a gold-plated silicon template,which the resistivity is measured by a four-probe method,indicating a low resistance of the high-purity PbTe NCs.Secondly,The PN junction was formed by the assembled technology,whose component were N-type PbTe array into the surface of P-type.Bio.5Sb1.5Te3.Work function of PN junction is measured by ultraviolet photoelectron spectroscopy(UPS).This results show that the work function of orderly arrayed PbTe deposition(3.5eV)is much lower than the disordered assemblies(4.5eV).The rapid extraction of toluene solvent was used by vacuum pump in a short time.In oder to be lead to the less surface roughness,which was benefit to reduce the work function by keeping the ordered PbTe cubic nanocrystals.Reduction of work function shows that the electron escaping energy becomes smaller.It provides theoretical support for PN junction enhancing better thermoelectric properties.Lastly,the embedded PN junction thermoelectric nanocomposite material was formed successfully with the assembled film-cold press-spark plasma sintering(SPS)for the first time.N-type PbTe arrayed at the surface of P-type by the cold pressure,what becomes PN junction.And then,a number of PN junction flakes loaded into the self-made graphite jig.The bulk thermoelectric materials were finished by SPS.The high ZT(1.69)of embedded PN junction thermoelectric nanocomposite materials at 348K causes by the high Seebeck coefficient and low thermal conductivity.The major factor of increasing the ZT is determined by N-type PbTe(0.05%)concentration,The TE materials contained PN junction has a common characterization that the higher Seebeck coefficient(S)and the lower total thermal conductivity(?total)were tested by the instrument.The Seebeck coefficient becomes stronger due to the increasing carrier mobility and the lower carrier concentration at the same time.The lower lattice thermal conductivity(?lat)derived from size effect enhanced the scattering of phonons dramatically.It is a kind of neutralization effect between the hole and electron in the carrier depletion.It is benefit to reduce the electron thermal conductivity(?ele).The PN junction has the influence on the phonons and carriers at the same time.In conclusion,the perfect PbTe was formatted by the modified hot-injected method with the toluene solvent,whose characterization is the controllable size,cubic morphology,the low surface oxidation,single dispersion and high purity.Work function of PN junction can influence the thermoelectric performance.The embedded structure PN junction thermoelectric nanocomposite materials had a higher ZT value.