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Thermoelectric Responses in Layered Strontium‐Niobates Via Two Ways of Charge Carrier Control Techniques

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Abstract:

We have systematically examined the thermoelectric properties of the perovskite‐related layered strontium‐niobates Sr n Nb n O3n+2 (n = 4, 4.33, 4.5, and 5) and Sr2−x La x Nb2O7, prepared using two charge carrier control techniques. Both have a similar anisotropic crystal structure that gives all the samples prepared a relatively low thermal conductivity. However, the two systems show very different behaviors with respect to Seebeck coefficient and resistivity. In Sr n Nb n O3n+2, an n‐driven semiconductor‐metal transition occurs between n = 4.33 and 4.5, with highly metallic properties observed in their magnitudes and temperature dependence at higher values of n. We also observed the microstructures to gain a further understanding of their properties, and elucidated the unconventional charge distribution in the intermediate n = 4.5 material. By contrast, in Sr2−x La x Nb2O7, thermally activated behaviors were displayed even in heavily La‐doped materials. Strong electron lattice interactions due to low symmetric NbO6 octahedra appeared to be present over the whole doping range, with Sr2−x La x Nb2O7 showing a lower electrical conductivity than metallic Sr n Nb n O3n+2. However, the ZT of Sr2−x La x Nb2O7 is one order of magnitude larger than for Sr n Nb n O3n+2 due to the much larger Seebeck coefficient, and increased up to 0.048 at room temperature on increasing the La dopant level.

Document Type: Research Article

DOI: https://doi.org/10.1111/j.1551-2916.2012.05169.x

Publication date: 2012-05-01

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