【作者】 王婷婷；

【导师】 宋英；

【作者基本信息】 哈尔滨工业大学 ， 化学工程与技术， 2017， 硕士

【摘要】 钙钛矿型Sr Ti O3基材料是目前报道的性能最好的n型氧化物热电材料之一。对于Sr Ti O3基热电材料来说,La元素的研究已经比较成熟,但单掺La的Sr Ti O3基陶瓷仍然具有电导率随温度升高而降低,热导率偏高的不足,导致其热电性能仍然较低。因此本论文拟通过Bi和La共掺杂以及Sr缺失的设计来提高Sr Ti O3基陶瓷材料的热电性能。本论文采用改进的固相法制备Bi和La共掺杂Sr Ti O3基粉体,之后在1500℃,5%H2/95%N2还原气氛下烧结制备相应陶瓷材料。通过对材料的物相组成、显微形貌、电导率、Seebeck系数以及热导率等分析,研究不同Bi掺杂浓度及不同Sr缺失量对Sr Ti O3基陶瓷的组成、微观形貌及热电性能的影响。首先,对La0.1Bix Sr1-x Ti O3(x=0,0.05,0.075,0.1)陶瓷的烧结工艺、组成、显微结构和热电性能进行研究。研究发现,1500℃保温6h可以使低Bi掺杂浓度的试样(x=0~0.05)获得更好的烧结效果,但保温4h可以使材料获得更小的晶粒从而降低热导率,提高材料性能。同时,保温4h制备的试样在Bi掺杂量x=0.075时获得了最佳的热电性能,其功率因子在500℃时最大,为692μW·m-1·K-2,ZT值在500℃时为0.172,比未掺杂Bi的La0.1Sr0.9Ti O3提高了130%。其次,分别制备名义组成为La0.1Bix Sr0.9-1.25x Ti O3、La0.1Bix Sr0.9-1.5x Ti O3、La0.1Bix Sr1-1.25(0.1+x)Ti O3和La0.1Bix Sr1-1.5(0.1+x)Ti O3(x=0,0.05,0.075,0.1@4h;x=0,0.025,0.05,0.065@6h)四种类型两个系列的Sr缺失的Bi和La共掺Sr Ti O3基陶瓷试样,研究Sr缺失对Bi和La共掺Sr Ti O3基陶瓷的物相组成及显微形貌的影响。结果表明,两批试样均在Bi掺杂量超过0.05时检测到Bi2O3,但Sr缺失可以增加Bi的最大掺入量;同时,Sr缺失还有提高陶瓷烧结效果,细化晶粒的作用。最后,对上述四种类型两个系列的Sr缺失的Bi和La共掺Sr Ti O3基陶瓷试样进行热电性能的分析。结果表明,保温4h和6h制备试样的电导率和Seebeck系数虽有所不同,但都在y=1-1.25(0.1+x),x=0.05时获得最佳性能,其最佳功率因子分别为保温4h试样的1213μW·m-1·K-2(300℃)和保温6h试样的1034μW·m-1·K-2(500℃),分别比La0.1Sr0.9Ti O3和La0.1Bix Sr1-x Ti O3提高420%、340%和75%、49%。另外,二者的ZT值在500℃时分别为0.235和0.227,分别比La0.1Sr0.9Ti O3和La0.1Bix Sr1-x Ti O3提高260%、250%和37%和32%,说明Bi-La双掺及Sr缺失的协同作用可有效提高Sr Ti O3基陶瓷的热电性能。同时,相同组成不同保温时间制备的La0.1Bi0.05Sr0.8125Ti O3试样的ZT值相近,在测试误差范围内,也说明了本论文研究材料性能的稳定性和可重复性。更多还原

【Abstract】 Perovskite-type Sr Ti O3 is reported to be one of the best performance of n-type oxide thermoelectric materials.For Sr Ti O3-based thermoelectric materials,the study of La element doping is relatively mature,but its conductivity decreases with increasing temperature and thermal conductivity is very high,resulting in the thermoelectric properties still low.So in this paper,we designed La and Bi co-doped and Sr vacancy to improve the thermoelectric properties of Sr Ti O3-based ceramics.In this paper,Sr Ti O3 powder was prepared by an improved solid phase method.Then,the corresponding ceramic materials were sintered at 1500℃ and5%H2/95%N2 reduction atmosphere.Besides,through the analysis of phase composition,microstructure,electrical conductivity,Seebeck coefficient and thermal conductivity of the materials,the effect of La and Bi co-doped and Sr vacancies on the structure and thermoelectric properties of ceramics was investigated.Firstly,the La0.1Bix Sr1-x Ti O3(x=0,0.05,0.075,0.1)ceramic’s sintering process,composition,structure and thermoelectric properties were studied.The result indicated that the longer holding time can make the samples with low doping concentration(x=0~0.05)obtain better sintering effect,while shorter holding time can get smaller grain size so as to reduce the thermal conductivity and improve material performance.Moreover,the best thermoelectric properties were obtained in the sample with 4 hours holding time and 0.075 Bi doping content.The maximum power factor is 692μW·m-1·K-2 at 500℃,and highest ZT value is 0.172 at 500 ℃,which is 130% higher than La0.1Sr0.9Ti O3 ceramics without Bi.Secondly,four types and two series of ceramics with Sr vacancies and La,Bi co-doped which nominal composition was La0.1Bix Sr0.9-1.25 x Ti O3,La0.1Bix Sr0.9-1.5x Ti O3,La0.1Bix Sr1-1.25(0.1+x)Ti O3 and La0.1Bix Sr1-1.5(0.1+x)Ti O3(x=0,0.05,0.075,0.1 @4h;x=0,0.025,0.05,0.065 @6h)were prepared.The results showed that the impurity phase Bi2O3 was detected when Bi doping content was exceeded 0.05 and the presence of Sr vacancies can increase the maximum amount of Bi addition.At the same time,the Sr vacancies also enhance the sintering effect and refine the grain.Finally,the thermoelectric properties of the four types and two series of samples were tested.The results showed that the conductivity and Seebeckcoefficient of the samples prepared under two different conditions were slightly different,but they all get the best performance at y=1-1.25(0.1+x)and x=0.05,and the best power factor is 1213μW·m-1·K-2(300℃)when holding time is 4h and1034μW·m-1·K-2(500℃)when holding is 6h,which is 420% and 340% higher than La0.1Sr0.9Ti O3 and 75%and 49% higher than La0.1Bix Sr1-x Ti O3.The ZT values of the two are 0.235 and 0.227 at 500℃,which are 260% and 250% higher than La0.1Sr0.9Ti O3 and 37% and 32% higher than La0.1Bix Sr1-x Ti O3 respectively.Thus indicated that the synergistic effect of Bi-La co-doped and Sr vacancies can effectively improve the thermoelectric properties of Sr Ti O3 based ceramics.Since the values La0.1Bi0.05Sr0.8125 Ti O3 samples prepared with the same composition and different holding time are very close,and within the test error range,the stability and repeatability of the material properties studied in this thesis are demonstrated.更多还原