【作者】 杨磊；

【导师】 张旦；

【作者基本信息】 河北大学 ， 凝聚态物理， 2023， 硕士

【摘要】 热电材料可以使热能和电能相互转换,在缓解能源危机方面发挥着重要作用。Pb Te基热电材料性能优良而受到广泛的关注,但其含有Te而价格比较昂贵,这使得Pb Te基热电器件的成本增加,因而寻求价格低廉且高性能的替代材料成为了研究重点。与Pb Te相比,PbSe具有组元廉价的同时兼有更高的机械强度和更强的化学稳定性,因而在热电应用方面具有发展前景。本论文在PbSe材料的基础上,通过掺杂稀土元素来调控PbSe材料的热电性能并得到了明显的改善效果,具体研究如下:首先,系统地研究了稀土元素La掺杂对PbSe电热输运性能的影响。研究发现:La是调节n型PbSe载流子浓度的有效掺杂剂;La掺杂可以使PbSe的导带边缘平坦而增加能带有效质量,从而有利于提高Seebeck系数。得益于载流子浓度和能带结构的同步调控,0.125%La掺杂PbSe的功率因子在873 K达到了1129μWm^-1K^-2,相比本征PbSe的67μWm^-1K^-2提升了近16倍,改善效果显著;同时,由于La掺杂导致的额外点缺陷散射和双极热导的抑制,使得晶格热导率在测试温度范围内都有所降低,在873 K掺杂含量为0.125%La的样品中最低可达0.78 Wm^-1K^-1。在热和电输运性能的双重优化下,所有La掺杂样品中0.125%La掺杂PbSe具有最高的平均功率因子和最低的热导率,最终在300-873 K之间实现了0.71的高平均ZT,在773 K获得了0.96的峰值ZT。其次,系统地研究了稀土元素Gd掺杂对PbSe电热输运性能的影响。研究表明:Gd掺杂可以调节n型PbSe载流子浓度并抑制本征激发;同时也可以使PbSe的导带边缘更平坦而显著增加能带有效质量,从而有利于提高Seebeck系数。相比于La掺杂的样品,Gd掺杂样品有效质量更大且维持较高的迁移率,进而有利于获得更高的电输运性能。此外得益于Gd掺杂带来的额外点缺陷散射导致的晶格热导率降低,在载流子浓度和能带结构的联合调节下,在300-873 K之间掺杂Gd含量为0.15%的PbSe中获得了1325μWm^-1K^-2的高平均功率因子,在873 K掺杂含量为0.15%Gd的样品中热导率降至1.14 Wm^-1K^-1,最终在300-873 K之间掺杂含量为0.15%Gd下实现了0.52的高平均ZT,在823 K获得了0.72的峰值ZT。最后,由于Gd掺杂PbSe样品相比于La掺杂具有更大的有效质量且维持较高的迁移率,同时Gd没有La活泼而方便称量,因此我们在Gd掺杂的基础上通过引入过量Cu进一步优化PbSe的热电性能。研究表明:在添加过量Cu之后不仅提高了样品(Pb_0.9985Gd_0.0015-x Cu;x=0.15%-0.25%)的迁移率同时还维持了其原有的有效质量,这使得其电学性能得到明显改善,从而获得了较高的功率因子。在873 K时x=0.2%样品的功率因子由939μWm^-1K^-2（x=0）提高到1668μWm^-1K^-2,提高效果显著。过量Cu的引入导致样品出现高密度位错,从而增强声子的散射而降低材料的晶格热导率,在温度为873 K相比于未引入Cu的0.89 Wm^-1K^-1晶格热导率降至0.58 Wm^-1K^-1（x=0.2%）,最终在电热输运性能的协同调节下Pb_0.9985Gd_0.0015Se-0.2%Cu样品在773 K取得了1.4的最高ZT值,并在300-873 K之间获得了0.97的高平均ZT值。更多还原

【Abstract】 Thermoelectric materials,featured by the mutual heat and electricity interconversion,play an important role in alleviating the energy crisis.Pb Te-based thermoelectric materials have attracted widespread attention because they have excellent properties,but the expensive Te element increases the cost of Pb Te-based thermoelectric devices,therefore searching for the low-cost and high-performance alternative materials has become the focus of thermoelectric field.Compared to Pb Te,PbSe is much cheaper and possesses a higher mechanical strength and a stronger chemical stability,showing prospect for thermoelectric applications.In this thesis,we comprehensively investigate the effect of rare earth element（La and Gd）substitutions on the thermoelectric performance of PbSeand the detailed results are as follows:Firstly,the effect of La-doping on the electrical and thermal transport properties of PbSe was studied systematically.The results showed that La was an effective dopant for regulating the concentration of PbSe carriers,La-doping could flatten the conduction band of PbSe to increase the effective mass,thereby improving the Seebeck coefficient.Under the combined regulation of carrier concentration and band structure,the power factor of 0.125%La-doped PbSe reached 1129μWm^-1K^-2 at 873 K,which is nearly 16 times higher than that of the pristine PbSe.The lattice thermal conductivity decreased in the measured temperature range due to the additional point defect scattering caused by La-doping and the suppression of bipolar thermal conductivity,and the 0.125%La-doping PbSe obtained a low thermal conductivity of 0.78 Wm^-1K^-1at 873 K.Under the simultaneous optimization of thermal and electrical transport properties,0.125%La-doping PbSe owned the highest average power factor and a decreased lattice thermal conductivity.Consequently,a high average ZT value of 0.71between 300-873 K and a peak ZT value of 0.96 at 773 K were achieved in 0.125%La-doping PbSe.Secondly,the effect of Gd-doping on the electrical and thermal transport properties of PbSe was studied systematically.The results showed that Gd-doping could effectively regulate the carrier concentration of PbSe and inhibited intrinsic excitation.Moreover,Gd-doping also made the conduction band edge of PbSe become more flattening,which was beneficial to improve the Seebeck coefficient.Compared with La-doping PbSe,Gd-doping PbSe has a higher DOS effective mass and maintains a high mobility which were conducive to obtaining higher electrical transport properties.A high average power factor of 1325μWm^-1K^-2 was obtained in the 0.15%Gd-doping PbSe between 300-873 K.Moreover,the lattice thermal conductivity decreased because of the intensified point defect scattering caused by Gd-doping and the thermal conductivity was decreased to 1.14 Wm^-1K^-1 at 873 K for the 0.15%Gd-doping PbSe.Finally,a peak ZT value of 0.72 at 823 K and a high average ZT value of 0.52 were achieved in the 0.15%Gd-doping PbSe.Thirdlly,Gd-doping PbSe has a greater effective mass than La-doping PbSe and maintains a high mobility.In addition,Gd metal is not as active as La which is convenient to weigh in lab.Therefore,we further regulated the electrical and thermal transport properties of Gd-doping PbSe by introducing excess Cu(Pb_0.9985Gd_0.0015-x Cu;x=0.15%-0.25%)for higher thermoelectric performance.The results showed that the mobility was improved substantially after the addition of excess Cu and its effective mass was maintained,resulting in a higher power factor.When x=0.2%,the power factor significantly increased from 939μWm^-1K^-2（x=0）to 1668μWm^-1K^-2.The introduction of interstitical Cu led to high-density dislocation,thereby enhancing the scattering of phonons for a low lattice thermal conductivity.The lattice thermal conductivity was reduced from 0.89 Wm^-1K^-1 of Cu-free sample to 0.58 Wm^-1K^-1（x=0.2%）at 873 K.Finally,the highest ZT value of 1.4 at 773 Kand a high average ZT value of 0.97 between 300-873 K were obtained in the Pb_0.9985Gd_0.0015Se-0.2%Cu sample due to the co-regulation of electrical and thermal transport properties.更多还原