| Thermoelectric materials can realize conversion between thermal and electrical energy directly,it is a kind of extremely potential new energy material,it's advantages include no pollution,no noise,small size,simple structure,high reliability,long life and other characteristics.Currently Pb Te thermoelectric material has been demonstrated to be a kind of high thermoelectric performance materials,but due to its' high cost and environmental pollution problems,it can't be a wide range of applications.Sn Te,which is perceived to be more environmentally friendly than Pb Te has same rock salt structure as Pb Te.It is thought to be clean and free from contamination thermoelectric materials which can replace Pb Te,give rise to thermoelectric researchers' attention.In this thesis,We are doping modification on Sn Te in allusion to the two disadvantages of Sn Te as thermoelectric materials: one is the eigen too high hole concentration and the small band gap lead to serious bipolar diffusion shows low Seebeck coefficient.Another is too high thermal conductivity.Experiment with high temperature vacuum melting,quenching and spark plasma sintering(SPS)process was prepared(Sn0.8Ge0.2)1-x Mnx Te,(Sn0.8Ge0.2)1-x Inx Te,(Sn0.9Mn0.11)1-x Inx Te three series alloy samples,respectively to study the phase composition,microstructure and thermoelectric performance,and finally we gain good thermoelectric performance Sn Te base materials.For Ge/Mn codoping(Sn0.8Ge0.2)1-x Mnx Te(x=0,0.03,0.06,0.09,0.12,0.15,0.18,0.20)series alloy research shows that: Ge/Mn codoping can widen the band gap of Sn Te alloys and convergence its band structure,Ge doping increased Mn's solid solubility of Sn Te alloy.In this system the solid solubility of Mn is more than 20 mol %,all alloys keep p type semiconductor properties.Ge/Mn codoping can effectively improve the electrical performance of Sn Te alloy,getting high power factor,reduce the thermal conductivity of the alloy at the same time.When Mn doping amount is 15 mol %,the sample get ZT value up to1.22 in 873 K,is 3.81 times that of the pure Sn Te in ZT value with the same temperature.For Ge/In codoping(Sn0.8Ge0.2)1-x Inx Te(x=0,0.002,0.005,0.01,0.015,0.02)series alloy research shows that: On the base of Sn0.8Ge0.2Te alloy's high power factor,In doping can produce resonance level effect to the band structure of the alloys,this effect can increase alloy state density so as to improve the Seebeck coefficient.Because the Seebeck coefficient had been improved in the entire test temperature regions,power factor of the alloys in this system have been improved in the entire test temperature zone,and the alloy thermal conductivity is reduced with the increase of doping amount.The sample with 1mol% In doping gets maximum ZT 1.18(873 K),calculate its average ZT values in 298 ~ 873 K temperature region,the available components is up to 0.61 by(Sn0.8Ge0.2)0.99In0.01 Te alloy,it's 4.32 times compare with pure Sn Te.For Mn/In codoping(Sn0.9Mn0.11)1-x Inx Te(x=0,0.002,0.005,0.01,0.015,0.02)series alloy research shows that: through the introduction of Mn and In elements can expand Sn Te's band gap,its band structure become convergence and introduced the effect of resonance level at the same time,thus the Seebeck coefficient has been improved more efficiency.While doping amount of In as 1mol%,the Seebeck coefficient is 101 ?V/K at room temperature,3.46 times that of the pure Sn Te,but because the resistivity of alloy also increases with increased with the amount of doping,eventually lead to not so much power factor ascense;Because elements doping lead to alloy's thermal conductivity greatly reduce,the optimal composition(Sn0.9Mn0.11)0.99In0.01Te's ZT value is up to 1.21 under 873 K. |
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