Research On Bi₂Te₃and Zr-Ni-Sn Thermoelectric Thin Films Prepared By Magnetron Sputtering

Thermoelectric (TE) thin film is a class of material that can realize highdensity mutual conversion between heat and electricity. The Bi2Te3is the bestTE material at near room temperature, and the half-Heusler (HH) alloy is lowcost material which also has excellent TE performance. Many attentions havebeen focused on the improvement of the TE properties of their thin films.Magnetron sputtering is an extensively adopted method for the preparation ofthin films in industry. The techniques to improve the TE properties of Bi2Te3thinfilms prepared by magnetron sputtering need further exploitation，and few peoplehave tried to prepare thin films of HH alloys by magnetron sputtering. In thisdissertation，the nanocrystalline Bi2Te3thin films and amorphous Zr-Ni-Sn thinfilms were prepared by magnetron sputtering. The influence of Pb doping,annealing and nanocrystalline structure on the TE properties of Bi2Te3thin films,and the influence of amorphous structure on the TE properties of ZrNiSn thinfilms, were investigated.Fast and accurate measurement of Seebeck coefficient (S) is not onlysignificant for the study of TE materials, but also for the real-time detection andcontrol on a production line of TE materials. The dissertation first described acustomized Seebeck coefficient measurement setup based on dynamic method.This setup achieved a measurement speed of14~23K min-1. At the same time, itcan record data in a high density, which can provide the dependence of the S tothe temperature precisely. Compared with the datas given by ZEM-2, thedeviations of the S measured by the customized setup are within8.4%.The nanocrystalline Bi2Te3thin films were prepared by magnetron sputtering.The effects of Pb doping, annealing and nanocrystalline structure on the TEproperties of Bi2Te3were investigated. Pb doping can effectively tune the carrierconcentration (n), and the sample doped with0.38at.%Pb achieved a powerfactor (S2σ) of2.50×10-3W·K-2·m-1at473K. After annealing the n values ofBi2Te3thin films were reduced, which contributed to the increase of S anddecrease of electrical conductivity (σ). This phenomenon was more obvious inthe sample doped with0.38at.%Pb. The thermal conductivities (λ) of the Bi2Te3 thin films were estimated conservatively according to their grain sizes and σvalues. It is found that the sample doped with0.38at.%Pb achieved a ZT valueof0.94at473K. It is concluded that Pb doping and annealing can tune the n toan optimal level, and the nanocrystalline structure can suppress the latticethermal conductivity, and their co-effects lead to the enhancement of TEproperties of the Bi2Te3thin films.The amorphous structured Zr-Ni-Sn thin films were prepared by magnetronsputtering. It is found that the concentrations of Zr and Ni of the thin filmsincrease and decrease with the increase of sputtering power, respectively. Thevariation of concentration affect the TE properties of Zr-Ni-Sn thin films, andthe sample deposited with a sputtering power of80W achieved a S and S2σ of114.3μV·K-1and2.77mW·K-2·m-1, respectively. The amorphous structuresignificantly reduced the λ of the Zr-Ni-Sn thin films. The λ values of the thinfilms prepared with different sputtering powers ranged from1.4to2.2W·m-1·K-1at room temperature, which is much lower than the common λ value of10W·m-1·K-1of half-Heusler alloys. The amorphous structure is helpful for the enhancementof TE properties of half-Heusler thin films.