稀有金属 2013,37(05),757-761
Na和Al双掺杂P型Bi0.5Sb1.5Te3热电材料的制备及性能研究
段兴凯 胡孔刚 满达虎 丁时锋 江跃珍 郭书超
九江学院机械与材料工程学院新能源材料研究中心
九江学院电子工程学院
摘 要：
采用真空熔炼及热压烧结技术制备了Na和Al双掺杂P型Bi0.5Sb1.5Te3热电材料。利用X射线衍射 (XRD) 、扫描电子显微镜 (SEM) 对样品的物相结构和表面形貌进行了表征。XRD分析结果表明, Na0.04Bi0.5Sb1.46-x Al x Te3块体材料的XRD图谱与块体材料Bi0.5Sb1.5Te3的图谱完全对应, 所有块体材料的衍射峰均与衍射卡JCPDS 49-1713对应, 这表明Na和Al元素已经完全固溶到Bi0.5Sb1.5Te3晶体结构中, 形成了单相固溶体合金。SEM形貌表明材料组织致密且有层状结构特征。Na和Al双掺杂提高了Bi0.5Sb1.5Te3在室温附近的Seebeck系数。在Na掺杂量为0.04时, 同时Al掺杂量由x=0.04增加至0.12, 电导率逐渐降低, 在实验掺杂浓度范围内, Na和Al双掺杂会使P型Bi0.5Sb1.5Te3材料的电导率受到较大的损失。在300500 K时, 通过Na和Al部分替代Sb, Na0.04Bi0.5Sb1.42Al0.04Te3和Na0.04Bi0.5Sb1.38Al0.08Te3样品的热导率均有不同程度地减小, 在300K时双掺杂样品Na0.04Bi0.5Sb1.42Al0.04Te3的最大ZT值达到1.45。
关键词：
双掺杂;热压;微结构;热电性能;
中图分类号： TB34
作者简介：段兴凯 (1972-) , 男, 江西九江人, 博士, 副教授;研究方向:纳米复合热电材料 E-mail:duanxingkai@163.com;
收稿日期：2013-05-06
基金：国家自然科学基金项目 (51161009);江西省教育厅科技项目 (GJJ13722) 资助;
Preparation and Thermoelectric Properties of Na and Al Dual Doped P-Type Bi0.5Sb1.5Te3
Duan Xingkai Hu Konggang Man Dahu Ding Shifeng Jiang Yuezhen Guo Shuchao
Center for New Energy Materials Research, School of Mechanical and Materials Engineering, Jiujiang University
School of Electronic Engineering, Jiujiang University
Abstract：
Na and Al dual doped P-type Bi0. 5Sb1. 5Te3thermoelectric materials were synthesized by vacuum melting and hot pressing method. Phase structure and surface morphology were analyzed by X-ray diffraction ( XRD) , scanning electron microscope ( SEM) .XRD results indicated that all the characteristic peaks of the bulk Na0. 04Bi0. 5Sb1. 46- x Al x Te3could be indexed into bulk Bi0. 5Sb1. 5Te3.All diffraction peaks of the bulk materials were consistent with the diffraction cards JCPDS 49-1713. This indicated that Na and Al elements were completely dissolved into the crystal structure of Bi0. 5Sb1. 5Te3. The single-phase solid solution alloy was formed. SEM results showed that the bulk samples were compact with the laminated structure. Na and Al dual doping improved the Seebeck coefficient of Bi0. 5Sb1. 5Te3near the room temperature. While the concentration of Na was 0. 04, the concentrations of Al increased from x = 0. 04to 0. 12, the electrical conductivity decreased gradually in the experimental concentration range. Na and Al dual doping could make the electrical conductivity of P-type Bi0. 5Sb1. 5Te3material a great loss. The thermal conductivity of Na0. 04Bi0. 5Sb1. 42Al0. 04Te3and Na0. 04Bi0. 5Sb1. 38Al0. 08Te3samples were decreased through Na and Al partial substitution of Sb in 300 ~ 500 K. The maximum ZT value reached 1. 45 at 300 K for Na0. 04Bi0. 5Sb1. 42Al0. 04Te3sample.
Keyword：
dual doping; hot pressing; microstructure; thermoelectric properties;
Received： 2013-05-06
热电转换技术是利用半导体材料的Seebeck效应与Peltier效应直接实现热能与电能之间的相互转换, 它具有尺寸小、可靠性高、无传动部件、无噪音、无污染等优点, 在各种余热废热的回收利用以及空间特殊电源等领域具有广阔的应用前景[1,2]。在当今世界范围的化石能源短缺、温室气体排放、环境污染加剧的背景下, 开发高性能热电材料备受人们的广泛关注。热电材料的性能优值ZT是表征热电材料转换效率优劣的重要指标, ZT=S2σΤ/κ, 其中S是Seebeck系数, σ是电导率, T是绝对温度, κ是热导率。高效热电材料需要大的Seebeck系数, 高的电导率和低的热导率。近年来, 利用热压[3,4,5,6,7], 放电等离子烧结 (SPS) [8,9,10,11], 高压烧结 (HPS) [12], 热挤压[13]、纳米复合[14,15], 纳米结构化[16,17]以及低维化[18]等方法已经成功地制备了较高性能的Bi2Te3基热电材料。
材料热电性能的3个重要参数Seebeck系数、电导率和热导率之间是相互关联的, Seebeck系数增加会使电导率减小、电导率升高可使Seebeck系数降低以及热导率增大, 如何实现这些参数的独立调控或协同调控是提高材料热电性能的核心。众所周知, 适当地掺杂可以在一定程度上改善材料的热电性能, 基于掺杂提高Bi2Te3基材料热电性能的研究目前已经取得了一定进展[19,20,21,22]。利用3个价电子数的Al代替5个价电子数的Sb, 有利于进一步提高P型Bi0.5Sb1.5Te3热电材料在室温附近的Seebeck系数。另一方面, 碱金属原子的特殊声子模式, 可以降低Bi2Te3基材料的热导率[23], 碱金属掺杂也可以有效地提高Seebeck系数[24]。本文采用真空熔炼并结合热压烧结方法制备了Na0.04Bi0.5Sb1.46-xAlxTe3和Bi0.5Sb1.5Te3块体热电材料, 并研究了Na和Al双掺杂对P型Bi0.5Sb1.5Te3材料热电性能的影响。
1 实验
Bi (99.99%) , Sb (99.99%) , Te (99.99%) , Na (99.5%) 和Al (99.99%) 元素粉末分别依据Na0.04Bi0.5Sb1.46-xAlxTe3 (x=0.04, 0.08, 0.12) 和Bi0.5Sb1.5Te3的原子分数称重, 依次装入石英管并真空封装, 在1073 K的温度下熔炼8 h, 在熔炼过程中保持石英管均匀缓慢转动, 随炉冷却到室温, 将熔炼得到的合金用玛瑙研钵研磨, 筛选采用300目的分样筛。将筛选后的粉末装入石墨模具中进行热压, 热压温度703 K、压力60 MPa、热压时间1 h、真空度为1×10-3Pa。热压后获得Φ19.4 mm×4 mm的块体样品, 然后按照性能测试的尺寸要求对块体样品进行线切割。
采用德国布鲁克AXS有限公司的D8Advance型X射线衍射仪 (XRD) 分析样品的物相结构。样品的形貌表征使用捷克TESCAN公司的Vega II LSU型扫描电子显微镜 (SEM) 。样品的Seebeck系数 (S) 和电导率 (σ) 采用热电性能综合测试仪 (HGTE-Ⅱ型) 在300~500 K范围内进行测量。用LFA 457激光导热系数测量仪测试热扩散系数 (λ) , 并用实验所测的样品密度 (D) 、比热容 (CP) 和热扩散系数, 根据公式λ=κ/ (DCP) 计算出材料的热导率, 测量温度范围为300~500 K。
2 结果与讨论
2.1 微观结构
图1为Bi0.5Sb1.5Te3和Na0.04Bi0.5Sb1.46-xAlxTe3块体材料的XRD图谱, 双掺杂样品的衍射峰 (006) , (015) , (10 10) , (00 15) , (00 18) 特征峰均与Bi0.5Sb1.5Te3的吻合, 图中各样品的峰位与斜方六面体结构的Bi0.5Sb1.5Te3衍射峰 (JCPDS 49-1713) 完全对应, 表明Na和Al元素已经完全固溶到Bi0.5Sb1.5Te3晶体结构中, 形成了单相固溶体合金。
图1 Bi0.5Sb1.5Te3和Na0.04Bi0.5Sb1.46-xAlxTe3块体材料的XRD图谱Fig.1XRD patterns of bulk Bi0.5Sb1.5Te3sample and Na0.04Bi0.5Sb1.5-xAlxTe3samples
图2是Bi0.5Sb1.5Te3和Na0.04Bi0.5Sb1.42Al0.04Te3块体材料平行于热压方向的SEM照片。如图2 (a) 所示, Bi0.5Sb1.5Te3的SEM形貌表明材料组织较致密, 具有明显的层状结构特征。Na0.04Bi0.5Sb1.42Al0.04Te3的SEM形貌如图2 (b) 所示, SEM图表明材料组织致密, 材料结晶较好, 也具有一定的层状结构特征, 但层状结构特征不是很明显。
2.2 热电性能
图3是Bi0.5Sb1.5Te3和Na0.04Bi0.5Sb1.46-xAlxTe3的电性能与温度的关系曲线。由图3 (a) 可知, Na和Al部分替代Sb后, Seebeck系数仍为正值, 所有样品均表现出P型半导体传导特性。在300~350 K测量温度范围内, 所有双掺杂样品的Seebeck系数均高于Bi0.5Sb1.5Te3, 在Na掺杂量为0.04时, Al掺杂量由x=0.04增加至0.12, Seebeck系数逐渐降低。在350~500 K的高温区, 双掺杂样品的Seebeck系数均低于Bi0.5Sb1.5Te3的值。由图3 (b) 可知, 除了Na0.04Bi0.5Sb1.42Al0.04Te3样品的高温区之外, 在整个测量温度范围内, 双掺杂样品的电导率都低于Bi0.5Sb1.5Te3的值, 这主要与双掺杂之后导致材料的空穴浓度和迁移率减少有关。在Na掺杂量为0.04时, Al掺杂量由x=0.04增加至0.12, 电导率逐渐降低。因此, 在实验掺杂量范围内, Na和Al双掺杂会使P型Bi0.5Sb1.5Te3材料的电导率受到较大的损失。
图2 Bi0.5Sb1.5Te3和Na0.04Bi0.5Sb1.42Al0.04Te3块体材料的SEM照片Fig.2 SEM images of bulk Bi0.5Sb1.5Te3 (a) and Na0.04Bi0.5Sb1.42Al0.04 (b) samples
图3 Bi0.5Sb1.5Te3和Na0.04Bi0.5Sb1.46-xAlxTe3的电性能与温度的关系Fig.3 Temperature dependence of electrical properties of Bi0.5Sb1.5Te and Na0.04Bi0.5Sb1.46-xAlxTe3
图4 Bi0.5Sb1.5Te3和Na0.04Bi0.5Sb1.46-xAlxTe3的热导率及ZT值与温度的关系Fig.4 Temperature dependence of thermal conductivity (a) and ZT (b) of Bi0.5Sb1.5Te3and Na0.04Bi0.5Sb1.46-xAlxTe3
图4是Bi0.5Sb1.5Te3和Na0.04Bi0.5Sb1.46-xAlxTe3的热导率和热电优值与温度的关系曲线。图4 (a) 表明了在整个测量温度范围内, Na0.04Bi0.5Sb1.42Al0.04Te3和Na0.04Bi0.5Sb1.38Al0.08Te3样品的热导率都小于Bi0.5Sb1.5Te3的热导率, 而在Na掺杂量为0.04时, Al掺杂量由x=0.04增加至0.12, 热导率逐渐增加。可见, 热导率的减小是源于碱金属掺杂, 因为碱金属原子的特殊声子模式, 可以有效降低Bi2Te3基材料的热导率[23]。从图4 (b) 可以看出在300~350 K温度范围内, Na0.04Bi0.5Sb1.42Al0.04Te3样品的热电优值较Bi0.5Sb1.5Te3有较大幅度地提高, 300 K时的最大ZT值达到1.45。在Na掺杂量为0.04时, Al掺杂量由x=0.04增加至0.12, 热电优值在整个测量温度范围内逐渐减小, 这主要是因为样品的电导率逐步减小和热导率逐步增加相关联。
3 结论
采用真空熔炼结合热压烧结制备了Na0.04Bi0.5Sb1.46-xAlxTe3半导体热电材料, Na和Al双掺杂可以有效提高Bi0.5Sb1.5Te3在室温附近的Seebeck系数, 在Na掺杂浓度为0.04时, Al掺杂浓度由x=0.04增加至0.12, 电导率逐渐降低, 在实验掺杂浓度范围内, Na和Al双掺杂会使P型Bi0.5Sb1.5Te3材料的电导率受到较大的损失。通过Na和Al部分替代Sb, Na0.04Bi0.5Sb1.42Al0.04Te3和Na0.04Bi0.5Sb1.38Al0.08Te3样品的热导率均有不同程度地减小, Na0.04Bi0.5Sb1.42Al0.04Te3在300 K时的最大ZT值达到1.45, 因此, Na和Al共掺杂可以有效提高P型Bi0.5Sb1.5Te3在室温附近的热电性能优值。
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