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Enhanced Thermoelectric Properties of Selenium-Deficient Layered TiSe2–x: A Charge-Density-Wave Material

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journal contribution
posted on 12.11.2014, 00:00 by Ranu Bhatt, Shovit Bhattacharya, Ranita Basu, Sajid Ahmad, A. K. Chauhan, G. S. Okram, Pramod Bhatt, Mainak Roy, M. Navaneethan, Y. Hayakawa, A. K. Debnath, Ajay Singh, D. K. Aswal, S. K. Gupta
In the present work, we report on the investigation of low-temperature (300–5 K) thermoelectric properties of hot-pressed TiSe2, a charge-density-wave (CDW) material. We demonstrate that, with increasing hot-pressing temperature, the density of TiSe2 increases and becomes nonstoichiometric owing to the loss of selenium. X-ray diffraction, scanning electron microscopy, and transimission electron microscopy results show that the material consists of a layered microstructure with several defects. Increasing the hot-press temperature in nonstoichiometric TiSe2 leads to a reduction of the resistivity and enhancement of the Seebeck coefficient in concomitent with suppression of CDW. Samples hot-pressed at 850 °C exhibited a minimum thermal conductivity (κ) of 1.5 W/m·K at 300 K that, in turn, resulted in a figure-of-merit (ZT) value of 0.14. This value is higher by 6 orders of magnitude compared to 1.49 × 10–7 obtained for cold-pressed samples annealed at 850 °C. The enhancement of ZT in hot-pressed samples is attributed to (i) a reduced thermal conductivity owing to enhanced phonon scattering and (ii) improved power factor (α2σ).