The effect of grain size on the thermoelectric properties of n-type nanocrystalline bismuth-telluridebased thin films is investigated. We prepare the nanocrystalline thin films with average grain sizesof 10, 27, and 60 nm by a flash-evaporation method followed by a hydrogen annealing process. Thethermoelectric properties, in terms of the thermal conductivity by a differential 3 method, theelectrical conductivity, and the Seebeck coefficient are measured at room temperature and used toevaluate the figure of merit. The minimum thermal conductivity is 0.61 W m−1 K−1 at the averagegrain size of 10 nm. We also estimate the lattice thermal conductivity of the nanocrystalline thinfilms and compare it with a simplified theory of phonon scattering on grain boundaries. Fornanosized grains, the lattice thermal conductivity of nanocrystalline thin films decreases rapidly forsmaller grains, corresponding to the theoretical calculation. The figure of merit is also decreased asthe grain size decreases, which is attributed to the increased number of defects at the grainboundaries.
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机译：研究了晶粒尺寸对n型纳米晶碲化铋基薄膜热电性能的影响。我们通过闪蒸法和氢退火工艺制备了平均晶粒尺寸为10、27和60 nm的纳米晶体薄膜。就通过微分3法的导热率，热导率和塞贝克系数而言的热电性质在室温下测量，并用于评价品质因数。在10 nm的平均晶粒尺寸下，最小热导率为0.61 W m-1 K-1。我们还估计了纳米晶薄膜的晶格热导率，并将其与晶界上声子散射的简化理论进行了比较。对于纳米尺寸的晶粒，纳米晶粒薄膜的晶格热导率对于较小的晶粒会迅速降低，这与理论计算相对应。品质因数也随着晶粒尺寸的减小而减小，这归因于晶界处缺陷数量的增加。
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