Competing anisotropic microstructures of Bi2(Te0.95Se0.05)3 thermoelectric materials by Bridgman technique

• Anisotropic thermoelectric properties due to microstructures were investigated.
• OIM results showed orientations of grain boundaries and unit cells.
• Enhanced power factor was obtained when a-axes and grain boundaries are aligned.
• An optimum pulling rate resulted in columnar infinitely long vertical grains.
• Grain boundary effect can be avoided in Bridgman grown Bi2(Te0.95Se0.05)3.

In this study, Bridgman technique was used to grow Bi2(Te0.95Se0.05)3 thermoelectric materials. Pulling rates were varied at 0, 2, 4 and 8 mm/h. Anisotropic thermoelectric properties were investigated by measuring Seebeck coefficients, resistivities and power factors and microstructures by Orientation Imaging Microscopy (OIM) and X-ray diffraction, in the directions perpendicular and parallel to the pulling direction. An enhanced power factor of 2.01 mW/mK2 in the direction parallel to the pulling direction was obtained for the pulling rate of 2 mm/h. The OIM result showed that infinitely long grains, with grain boundaries and crystal a-axis parallel to the pulling direction were responsible for the enhanced power factor. Competing effects of orientations of unit cells and grain boundaries were observed in all other samples.

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