Kraemer D, Chen G
Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Rev Sci Instrum. 2014 Apr;85(4):045107. doi: 10.1063/1.4870278.
Advances in thermoelectric materials in recent years have led to significant improvements in thermoelectric device performance and thus, give rise to many new potential applications. In order to optimize a thermoelectric device for specific applications and to accurately predict its performance ideally the material's figure of merit ZT as well as the individual intrinsic properties (Seebeck coefficient, electrical resistivity, and thermal conductivity) should be known with high accuracy. For that matter, we developed two experimental methods in which the first directly obtains the ZT and the second directly measures the individual intrinsic leg properties of the same p/n-type thermoelectric couple device. This has the advantage that all material properties are measured in the same sample direction after the thermoelectric legs have been mounted in the final device. Therefore, possible effects from crystal anisotropy and from the device fabrication process are accounted for. The Seebeck coefficients, electrical resistivities, and thermal conductivities are measured with differential methods to minimize measurement uncertainties to below 3%. The thermoelectric couple ZT is directly measured with a differential Harman method which is in excellent agreement with the calculated ZT from the individual leg properties. The errors in both the directly measured and calculated thermoelectric couple ZT are below 5% which is significantly lower than typical uncertainties using commercial methods. Thus, the developed technique is ideal for characterizing assembled couple devices and individual thermoelectric materials and enables accurate device optimization and performance predictions. We demonstrate the methods by measuring a p/n-type thermoelectric couple device assembled from commercial bulk thermoelectric Bi2Te3 elements in the temperature range of 30 °C-150 °C and discuss the performance of the couple thermoelectric generator in terms of its efficiency and materials' self-compatibility.
近年来，热电材料的进展使热电装置性能得到显著提升，进而催生了许多新的潜在应用。为了针对特定应用优化热电装置，并理想地准确预测其性能，理想情况下应高精度地知晓材料的优值ZT以及各个本征特性（塞贝克系数、电阻率和热导率）。为此，我们开发了两种实验方法，第一种直接获取ZT，第二种直接测量同一p/n型热电耦合器件的各个本征腿特性。这样做的优点是，在将热电腿安装到最终器件中后，所有材料特性都在相同的样品方向上进行测量。因此，考虑到了晶体各向异性和器件制造过程可能产生的影响。采用差分法测量塞贝克系数、电阻率和热导率，以将测量不确定度降至3%以下。用差分哈曼法直接测量热电耦合ZT，其与根据各腿特性计算出的ZT高度吻合。直接测量和计算得到的热电耦合ZT的误差均低于5%，这明显低于使用商业方法时的典型不确定度。因此，所开发的技术非常适合表征组装好的耦合器件和单个热电材料，并能实现精确的器件优化和性能预测。我们通过测量由商用块状热电Bi2Te3元件组装而成的p/n型热电耦合器件在30°C至150°C温度范围内的性能来演示这些方法，并从效率和材料自兼容性方面讨论耦合热电发电机的性能。
