Porter C E, Crawford C M, Toberer E S
Materials Science, Colorado School of Mines, Golden, Colorado 80401, USA.
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91011, USA.
Rev Sci Instrum. 2024 Aug 1;95(8). doi: 10.1063/5.0222406.
Nernst coefficient measurements are a classic approach to investigate charge carrier scattering in both metals and semiconductors. However, such measurements are not commonly performed, despite the potential to inform material design strategies in applications such as thermoelectricity. As dedicated instruments are extremely scarce, we present here a room temperature apparatus to measure the low field Nernst coefficient (and magneto-Seebeck coefficient) in bulk polycrystalline samples. This apparatus is specifically designed to promote accurate and facile use, with the expectation that such an instrument will make Nernst measurements de rigueur. In this apparatus, sample loading and electrical contacts are all pressure-based and alignment is automatic. Extremely stable thermal control (10 mK of fluctuation when ΔT = 1 K) is achieved from actively cooled thermoelectric modules that operate as heaters or Peltier coolers. Magneto-Seebeck measurements are integrated into the system to correct for residual probe offsets. Data from the apparatus are provided on bulk polycrystalline samples of bismuth, InSb, and SnTe, including raw data to illustrate the process of calculating the Nernst coefficient. Finally, we review how Nernst measurements, in concert with Seebeck, Hall, and electrical resistivity, can be analyzed via the Boltzmann equation in the relaxation time approximation to self-consistently predict the Fermi level, effective mass, and energy-dependent relaxation time.
能斯特系数测量是研究金属和半导体中载流子散射的经典方法。然而，尽管这种测量有可能为热电等应用中的材料设计策略提供信息，但通常并不进行。由于专用仪器极为稀少，我们在此展示一种室温装置，用于测量块状多晶样品中的低场能斯特系数（以及磁塞贝克系数）。该装置经过专门设计，以促进准确且便捷的使用，期望这样的仪器能使能斯特测量成为常规操作。在该装置中，样品加载和电接触均基于压力，且对准是自动的。通过作为加热器或珀尔帖冷却器运行的主动冷却热电模块，实现了极其稳定的热控制（当ΔT = 1 K时波动为10 mK）。磁塞贝克测量集成到系统中，以校正残余的探头偏移。提供了来自铋、锑化铟和碲化锡块状多晶样品的该装置数据，包括原始数据以说明能斯特系数的计算过程。最后，我们回顾了如何通过弛豫时间近似下的玻尔兹曼方程，结合塞贝克、霍尔和电阻率测量来分析能斯特测量，从而自洽地预测费米能级、有效质量和能量相关的弛豫时间。
