Publication Date:
2012-04-05
Description:
We have systematically examined the thermoelectric properties of the perovskite-related layered strontium-niobates Sr n Nb n O 3 n +2 ( n = 4, 4.33, 4.5, and 5) and Sr 2− x La x Nb 2 O 7 , 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 O 3 n +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 Sr 2− x La x Nb 2 O 7 , thermally activated behaviors were displayed even in heavily La -doped materials. Strong electron lattice interactions due to low symmetric NbO 6 octahedra appeared to be present over the whole doping range, with Sr 2− x La x Nb 2 O 7 showing a lower electrical conductivity than metallic Sr n Nb n O 3 n +2 . However, the ZT of Sr 2− x La x Nb 2 O 7 is one order of magnitude larger than for Sr n Nb n O 3 n +2 due to the much larger Seebeck coefficient, and increased up to 0.048 at room temperature on increasing the La dopant level.
Print ISSN:
0002-7820
Electronic ISSN:
1551-2916
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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