Estimating Energy Conversion Efficiency of Thermoelectric Materials: Constant Property Versus Average Property Models

Abstract

Maximum thermoelectric energy conversion efficiencies are calculated using the conventional ''constant property'' model and the recently proposed ''cumulative/average property'' model (Kim et al. in Proc Natl Acad Sci USA 112:8205, 2015) for 18 high-performance thermoelectric materials. We find that the constant property model generally predicts higher energy conversion efficiency for nearly all materials and temperature differences studied. Although significant deviations are observed in some cases, on average the constant property model predicts an efficiency that is a factor of 1.16 larger than that predicted by the average property model, with even lower deviations for temperature differences typical of energy harvesting applications. Based on our analysis, we conclude that the conventional dimensionless figure of merit ZT obtained from the constant property model, while not applicable for some materials with strongly temperature-dependent thermoelectric properties, remains a simple yet useful metric for initial evaluation and/or comparison of thermoelectric materials, provided the ZT at the average temperature of projected operation, not the peak ZT, is used.

Heat flow measurement as a key to standardization of thermoelectric generator module metrology: A comparison of reference and absolute techniques

“…Alternatively a cumulative property model can be used to conclude on, which was proposed by Kim et al [21] and which accounts for the temperature dependency of material properties by means of a different expression for the maximum efficiency with the use of a so called engineering figure of merit. A recent analysis for 18 high-performance thermoelectric materials by Armstrong et al [22] revealed an overestimated prediction of  by the constant property model compared to the cumulative model, which equalled a factor of 1.16 on the average. Regardless of the chosen model for TEM efficiency a pure analytic or simulation-based determination of TEM properties on the base of experimentally determined material properties is subjected to significant errors too, due to necessitated assumptions on elusive electric and thermal coupling conditions and inherent uncertainties of the applied characterization methods.…”

Enhancing NASA's Multi-Mission Radioisotope Thermoelectric Generator Using Highly Efficient Thermoelectric Materials

“…where , TH, and TC are the Carnot efficiency ( − ), hot junction temperature, and cold junction temperature values, respectively. (Armstrong et al, 2017). The quantity Z is a dimensionless TE figure of merit used to evaluate the performance of a TE material, where ZTavg is the Z value (often written as ZT) at the average temperature of a projected operating range (Armstrong et al, 2017).…”

“…(Armstrong et al, 2017). The quantity Z is a dimensionless TE figure of merit used to evaluate the performance of a TE material, where ZTavg is the Z value (often written as ZT) at the average temperature of a projected operating range (Armstrong et al, 2017). The TE figure of merit can be described by:…”

“…Where S is the material's Seebeck coefficient, a constant relating the produced voltage of a material in response to a temperature difference, is its electrical resistivity (sometimes described as electrical conductivity, which is the inverse of resistivity), and is the material's thermal conductivity (Armstrong et al, 2017).…”

Ab initio investigation of electronic and magnetic properties of antiferromagnetic/ferroelectric LaMnO3/BaTiO3 interface

“…Theoretical studies of magnetoelectric coupling involve such heterostructures as Fe/BaTiO 3 [19], Co 2 MnSi/BaTiO 3 [20], [21], Fe(Ni,Co,CrO 2 )/BaTiO 3 /normal metal [22] etc. Recent paper considered a supercell of ferromagnetic perovskite Sr-doped LaMnO 3 and ferroelectric BaTiO 3 [23]. The spontaneous electrical polarization of BaTiO 3 causes the accumulation of spin-polarized electrons in the ferromagnetic half-metallic La 1−x A x MnO 3 layer at the interface perpendicular to the direction of polarization.…”