铌掺杂二氧化钛的热电性能研究

发布时间：2018-02-11 03:08

  本文关键词： 热电性能 掺杂 Ti_(1-x)Nb_xO_2-d Magnéli相 TinO_2n-1　出处：《河北师范大学》2017年硕士论文　论文类型：学位论文

【摘要】：随着人类社会的发展,煤、石油、天然气等不可再生能源逐渐枯竭,这些能源的使用导致了全球变暖,进而导致沙漠化区域逐渐增大以及海平面的上升,这使得新能源的探索和开发工作变得越来越重要,而要真正地使用新能源则必须借助于新能源材料。热电材料属于一种新能源材料,它可以直接将废热转化为电能而不会造成环境污染,是一种绿色可持续能源材料。热电转换作为传统发电技术的有效补充,得到人们越来越多的关注。热电材料目前面临的最大挑战是其能量转换效率在很大程度上尚未达到实际应用的需要。为了使热电材料得到更加广泛的应用,科研工作者尝试通过掺杂等方式来提高材料的热电性能。本论文选取氧化物半导体热电材料TiO_2作为研究对象,对其进行Nb元素掺杂,并进行了不同还原条件的热处理,然后研究了Nb元素掺杂和不同的还原条件处理对系列样品的热电性能的影响。本文的具体工作如下:1、使用传统的固相反应法,通过在1473 K,H2/Ar混合气氛中进行还原处理,制备了不同Nb含量的Ti_(1-x)Nb_xO_2-d系列陶瓷样品。XRD图谱显示,x=0.0,0.005,0.01样品表现为混合的三斜相TinO_2n-1结构(8≤n≤10),而x=0.04,0.08样品表现为单一的金红石型TiO_2结构,这表明较高的Nb掺入量可以稳定TiO_2的金红石结构。在最高测试温度380 K,x=0.01样品给出该系列样品的最大ZT值0.023,这一数值大约是x=0.0未掺杂样品ZT值(0.009)的2.6倍。在室温到380 K范围,该系列样品的输运行为满足小极化子导电机制。2、使用固相反应法在高温(1573 K)还原性气氛(H2)中制备了不同Nb掺杂量的Ti_(1-x)Nb_x O_2-d系列陶瓷样品。粉末XRD结果显示:x=0.0,0.01,0.02和0.04样品表现为混合的三斜相TinO_2n-1结构(4≤n≤6),在x=0.08,0.20样品中出现了四方相金红石型TiO_2的衍射峰,而x=0.40,0.60样品表现为单一的金红石型结构,这表明较高浓度的Nb掺杂,可以使TiO_2的金红石型结构稳定存在。在100-380K的温度范围,测试了该系列样品的热电性能。测试结果表明,样品的电阻率和塞贝克系数随温度的变化都表现为半导体行为。通过分析证明了样品在室温到380 K温区的输运行为满足小极化子导电机制。在最高测试温度380 K,x=0.20样品给出该系列样品的最大ZT值0.016。3、使用PLD方法在衬底温度为550℃,激光能量密度为5 J/cm2,沉积频率为2 Hz,氧压为1.0×10-2 Pa的条件下,在(0001)取向的单晶Al2O3衬底上外延生长了119 nm厚度的TiO_2薄膜。由XRD图谱可看出,制备的薄膜为(l00)取向的金红石型TiO_2薄膜,(200)和(400)晶面衍射峰分别出现在39.13°和84.25°。在室温下,测量了金红石TiO_2薄膜的电阻率和塞贝克系数,四探针法测试结果给出该薄膜的室温电阻率为130 mΩ·cm,其塞贝克系数为-55μV/K,计算得到金红石TiO_2薄膜样品室温时的功率因子为0.0023 mW/(m·K2)。
[Abstract]:With the development of human society, non-renewable energy sources, such as coal, oil and natural gas, are gradually exhausted. The use of these sources of energy leads to global warming, which in turn leads to the gradual enlargement of desertification areas and the rise of sea level. This makes the exploration and development of new energy more and more important, and the real use of new energy has to rely on new energy materials. Thermoelectric materials are a kind of new energy materials. It can directly convert waste heat into electric energy without environmental pollution. It is a green and sustainable energy material. Thermoelectric conversion is an effective supplement to traditional power generation technology. The biggest challenge of thermoelectric materials is that their energy conversion efficiency has not met the needs of practical application to a great extent. In order to make thermoelectric materials more widely used, In this paper, the oxide semiconductor thermoelectric material (TiO_2) is chosen as the research object, which is doped with NB element and heat treated under different reduction conditions. Then the effects of NB doping and different reduction conditions on the thermoelectric properties of the series samples were studied. The specific work of this paper is as follows: 1, using the traditional solid state reaction method, the reduction treatment is carried out in the mixed atmosphere of 1473 Ku H2 / ar. The samples of Ti_(1-x)Nb_xO_2-d series with different NB contents were prepared. The results showed that the samples showed mixed triclinic phase TinO_2n-1 structure (8 鈮，

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