Controllable Preparation And Electrical Properties Of Lead And Antimony Chalcogenides Nanomaterials With Different Morphologies

Thermoelectric materials is a kind of special functional material which canconvert the heat source into electricity directly. By means of thermoelectric devices,the waste heat coming from the combustion of fossil fuel can be recycled, and thenthe utilization can be enhanced. However, due to the low thermoelectric figure ofmerit, the thermoelectric materials are still far way from practical application. Thus,the enhancement of the thermoelectric figure of merit is the key point in the field ofthermoelectric materials. Theoretical simulations and experimental results indicatethat the thermoelectric performance will be remarkbly enhanced in low dimensionalsystem. Lead and antimony chalcogenides have been attracted much attentionbecause of their high thermoelectric performances. In this paper, the lead andantimony chalcogenides were selected as the research objects, and the lead andantimony chalcogenides nanomaterials with different morphologies were fabricatedand the formation mechanisms and electrical properties were studied by X-raydiffraction, scaning electron microscope, Transmission electron microscope andelectrical property testing system.Without using any template and surfactant, lead sulfide nanorod was preparedthe formation mechanism was investigated in detail. And we discovered that thenanorods were composed of nanocubes through an oriented attachment process. Byusing tellurium and sodium hydroxide as precursors, the core-shell structuralPbS/PbTe nanorods were fabricated via a hydrothermal route. The electricalproperties of the obtained samples were investigated by a self-desinedthermoelectric test system, and the results indicated that the core-shell structuralPbS/PbTe nanorods have the higher power factors compared with that of pure phasePbS. Meanwhile, the thermoelectric properties of PbS/PbTe nanorods can be tunedby changing the molar ratio of PbS and Te.By using thioglycollic acid as a surfactant and sulfur source, binary phasedPbS/PbSe hollow spheres were fabricated and the reaction parameters influencingthe morphology were discussed systematically. The experimental results presentedthat these PbS and PbSe nanoparticles can aggregate together to form PbS/PbSehollow spheres with the assistance of thioglycollic acid, which can be named asclassical self assembly process accompanied by Ostwald ripening process. Moreover,electrical properties measurements demonstrated that the obtained PbS/PbSe hollowspheres had the higher electrical conductivity and Seebeck coefficient than that ofPbSe nanoparticles in the temperature range of300-600K. The maximum powerfactor of205.4μW/（K²·m） can be achieved at500K for PbS/PbSe hollow spheres, which is two times higher than that of PbSe nanoparticles.By using glucose as a surfactant, the flower-like PbTe crystals were synsthsizedand the different reaction factors influencing the morphology were systematicallyinvestigated. Based on the experimental results, a possible formation mechanism ofOstwald ripening accompanied by anisotropic growth mechanism was proposed.When sodium selenite was added into reaction system instead of part of sodimtellurite, the flower-like PbSe/PbTe nanocrystals were fabricated by a solvothermalmethod. The experimental results displayed that the nanopaltes were composed ofPbSe and PbTe nanocrystals with the size less than30nm, simultaneously, thesubstitution of Se and Te elements could be observed. The electrical properties testsdemonstrated that the electrical conductivity of40S/m can be achieved, which isone and three times higher than than that of100nm PbTe nanoparticles and6nmPbTe film, respectively.The hierachical Sb₂Se₃and Sb₂Te₃crystlas were fabricated with the help ofglucose or citric acid. Experimental results described that the glucose and citric acidmolecules played a crucial role in the formation of hierachical Sb₂Se₃and Sb₂Te₃crystlas. Glucose and citric acid molecules used as surfactants can be absorbed ontothe surface of Sb₂Se₃and Sb₂Te₃nuclei, which promoted the aggregation the thenanoparticles due to their hydrogen bonds and electrostatic effects. Meanwhile, themolecules can also be adsorbed onto some crystal surfaces of materials, whichprohibited the growth rate of these surfaces, thus, hierachical Sb₂Se₃and Sb₂Te₃crystlas can be obtained. The electrical properties measurements indicated that thethe morphology of Sb₂Se₃samples had much impact on the Seecek coefficients. Theworm-like Sb₂Se₃has the maximum Seecek coefficient, which can reach to1400μV/K at350K. The Seecek coefficients and the electrical conductivites are relatedto the size of Sb₂Te₃crystals, the sample with bigger size has the higher electricalconductivity and lower Seecek coefficient.