Reliable measurements of the Seebeck coefficient on a commercial system
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The Seebeck coefficient is an important parameter of thermoelectric materials, which is routinely measured by commercial or home-made equipment based on different methods. However, due to various temperature offsets in the measurement, the determination of temperature gradient can be inaccurate, leading to a large uncertainty in Seebeck coefficient. To elucidate the influence of the inaccurate temperature gradient on the determination of Seebeck coefficient, an error analysis has been performed on a commercial system. Several potential factors that may affect the establishment of temperature gradient were discussed in detail. A comparison between the single point method and the slope method was made to verify which is more accurate to calculate the Seebeck coefficient from the raw measurement data. It is suggested that the slope method is more preferable and the single point method can also be accurate enough when a relatively large temperature gradient is adopted.
I. INTRODUCTION
Thermoelectric (TE) materials, which can generate electricity from waste heat or be used as solid-state Peltier coolers, have attracted renewed attention because of their potential role in a global sustainable energy solution. The efficiency of a TE material is represented by the dimensionless figure of merit zT 5 a2rT/j, which is usually obtained from the separate measurement of temperature T dependent Seebeck coefficient a, electrical conductivity r, and thermal conductivity j.1,2 Given the fact that a 20% improvement in the zT value of the stateof-the-art TE materials would make significant commercial impact, measurement accuracy is of critical importance. For example, compared to the values obtained today, a 30% overestimation of the high temperature thermal conductivity of the lead chalcogenides is found in the early steady-state method, leading to an underestimation of zT.3,4 Similarly, due to the various challenges in the measurements, a combined uncertainty of the power factor a2r can readily reach up to 27%.5 Such discrepancies are to be expected even today as absolute accuracy in TE measurements is still not possible. Thus, sufficient care on the TE measurement should be taken, even if carried on commercial systems.6 The Seebeck coefficient is an important parameter of TE materials, which is routinely measured by different commercial or home-made instruments.7–10 However,
due to various techniques applied in the measurement and the absence of standardized criteria, the measured Seebeck coefficient is often subject to irreproducibility and inconsistency in results, making it difficult for interlaboratory comparison. Fortunately, a recent review gave a systemic comparison of a variety of metrologies applied on the Seebeck coefficient measurements, which provides convenience to the researchers in this field.11 While it is not geometry dependent for isotropic materials, the Seebeck coefficient is highly sensitive to the electronic structure and thus can be a useful tool in the studies of transport properties of charge carriers. Recent progresses i
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