Google Search
A6: Characterization
After the oracle of Hicks and Dresselhaus, many low-dimensional conductors are transvalued as new thermoelectric (TE) materials. [1] Among them, transition-metal trichalcogenides MX3 (M=Ti, Zr, Nb, Ta; X=S, Se) are well-known inorganic quasi-one-dimensional conductors. The whisker-shape crystal consists of very long triangular columns of M-X unit extended in the b-axis direction of the crystal. They demonstrate high anisotropic electronic conduction, because the conduction carriers can move in the triangular column.
We know well that information of thermal conduction is an extremely promising lead to the understanding of the thermoelectric properties of these materials. In the present work, we have measured the b-axis thermal conductivity of NbSe3 using four-probe 3ω method. [2]
Single crystals measured were synthesized by chemical vapor transport technique. Typical sample size was 0.1 μm in the thickness, 10 μm in the width, and 4 mm in the length. The whisker crystal was mounted on a sample holder adiabatically. We applied ac current (0.1 Hz to 1 kHz) to the sample, and detected the 3ω voltage V3ω at room-temperature. We could detect sufficient large V3ω component from several samples.
We have obtained the room-temperature thermal conductivity κ from the low frequency limit of V3ω. The mean value of the κ of NbSe3 is 2.0±0.3 WK-1m-1. This value is smaller than the reported value [3] and is the same order of typical thermoelectric materials, such as Bi2Te3.
[1] L. D. Hicks and M. S. Dresselhaus, Phys. Rev., B47, 12727 (1993).
[2] L. Lu, W. Yi, and D. L. Zhang, Review of Sci. Instrum., 72, 2996 (2001).
[3] J. W. Brill, C. P. Tzou, G. Verma and N. P. Ong, Solid State Commun. 39, 233 (1981).