Fabrication And Properties Of P-type Telluride Thermoelectric Materials In Medium Temperature Range

Thermoelectric material is a kind of semiconductor which can be used to convertdirectly heat energy to electricity, and have important application values and prospectsin waste heat of industry recycling and using. Mesothermal thermoelectric materialshave become the research hotspot in recent years because they are ideal choices toindustrial waste heat recycling. In this paper through the solid solution alloying,efficient doping and nano-composite technology, P-type GeTe and PbTe as theresearch object were prepared by hot pressing and spark plasma sintering (SPS). ByXRD, SEM, EDS and test of thermoelectric performance, mechanical strength andhigh temperature creep behavior, the influence mechanism of components, doping andpreparation technology on the properties of materials were systematic studied..The Quasi-ternary (GeTe)x(Mn0.6Sn0.4Te)1-xwas formed by introducingMnTe-SnTe into GeTe. By adjusting the proportion of solid solution, the performanceand phase transition temperature of materials has been optimized. The maximum ZT1.57was received in the temperature range720K~750K with x=0.85. Ge Substitutedby Mn and Sn which are with relatively large atomic radius, lattice distortion degreecould be effectively reduced and bending strength of quasi-ternary GeTe-basedmaterial was increased. Adding Nb as a diffuse phase into quasi-ternary GeTe-basedthermoelectric material could effectively control the dislocation climbing speed andthe grain boundary sliding, enhance resistance of high temperature creep. Whenadding ratio of Nb reaches3wt%, the deformation rate of GeTe-based material wasless than0.4%under the experimental conditions of100N load at600℃for100h.Electrically neutral nano-Bi2Te3was doped into (GeTe)0.85(Mn0.6Sn0.4Te)0.15material. Adding nanometer particle has an obvious effect on reducing lattice thermalconductivity of materials. The maximum ZT of the prepared materials was1.54,attained in the temperature around700K with0.03at%nano-Bi2Te3. During sinteringprocess, part of the nano-particles grew up which was likely to affect the performanceof GeTe-based material samples. After adding electrically neutral Bi2Te3, phasetransition temperature of the materials were decreased obviously, the lowest of whichwas519k for x=0.015. The Pb0.5Sn0.5Te+0.25wt%Te materials added homogeneous and heterogeneousnano-phase were prepared by SPS. Optimization of carrier concentration andreduction of lattice thermal conductivity by adjusting sintering temperature andadding nano-phase were main contribution to the improvement of ZT. Nano phase asthe second phase effectively improved the mechanical strength of PbTe-basedmaterials. The adding ratio of Nano-phase was not the bigger the better. For thehomogeneous or heterogeneous nano-composite PbTe materials, the maximum ZTwas1.31and1.05respectively when x=0.03, each of which was larger than themaximum ZT0.84of homogeneous PbTe-based materials.The research of samples of Pb1-xSnxTe+yat%Ag doped with Ag shows that alarge number of holes would be introduced and alloy scattering would be improvedwith x increasing. Under the condition of y=0, the sample for x=0.25obtained themaximum ZT1.08. With Ag doped into quasi-binary solid solution, the carrierconcentration increased rapidly, and the electrical conductivity improved significantly.when doping amount increasing to0.02at%, doping effect would disappear because ofthe saturation of hole concentration and no intrinsic excitation. The electricalconductivity would multiplied with the increase of y no longer. Pb0.75Sn0.25Te materialgained maximum ZT value1.43in650k for y=0.01. Appropriate heat treatmenttemperature can optimize integrated thermoelectric properties of materials. Comparedwith the maximum ZT and bending strength of Pb0.75Sn0.25Te+0.01wt%Ag beforeheat treatment, which were increased by8%and nearly13%respectively after treatedat500℃for20hours.