Improved thermoelectric properties of gadolinium intercalated compounds Gd ux TiS u2 at the temperaturesfrom 5 to 310 K
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The thermoelectric properties of Gd intercalated compounds GdxTiS2 have been investigated at the temperatures from 5 to 310 K. The results indicate that Gd intercalation into TiS2 leads to substantial decrease of both its electrical resistivity and its lattice thermal conductivity L (L is lowered by 20% and 46% at 300 K for x ⳱ 0.025 and 0.05, respectively). Specially, as compared to the pristine TiS2 the figure of merit ZT of the intercalated compound GdxTiS2 has been improved at all temperatures investigated, and specifically, the ZT value of Gd0.05TiS2 at 300 K is about three times as large as that of TiS2.
I. INTRODUCTION
Thermoelectric materials have attracted much attention in recent years for possible applications to “environmentally friendly” electric-power generators and highly reliable, small-scale refrigerators used for electronic devices.1 The efficiency of a thermoelectric material is determined by the dimensionless figure of merit, ZT (ZT ⳱ S2T/, here S, , , and T are the thermopower, electrical resistivity, thermal conductivity, and temperature, respectively). Hence, a good thermoelectric material should have high S, low and . TiS2 has an anisotropic structure with a trigonal space group P3¯m. In the S–Ti–S sandwich layers, TiS6 octahedrons are combined with each other tightly through strong covalent bonds, with each layer stacking together under weak van der Waals force. Due to this quasi-twodimensional structure, TiS2 was reported to have large thermopower and power factor (S2/) at room temperature,2 indicating that TiS2 is a potential candidate for thermoelectric applications. However, because of its large lattice thermal conductivity, its ZT value is too small for practical application.2 Therefore, reduction of its conductivity is of great significance in raising its thermoelectric properties. As to reduction of thermal conductivity, Slack3 proposed that a crystal structure containing weakly bound atoms or molecules that “rattle” within atomic cages could reduce lattice thermal conductivity, and latter
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0055 480
http://journals.cambridge.org
J. Mater. Res., Vol. 21, No. 2, Feb 2006 Downloaded: 13 Apr 2015
experiments proved his idea.4 Layered-structured TiS2 is well known for its capability for intercalation of a wide range of elements into its van der Waals gap.5 Intercalation of heavy element into TiS2 may reduce its thermal conductivity by atomic “rattling” and raise its thermoelectric properties. Nevertheless, to our knowledge little work aimed at improving thermoelectric properties of TiS2 by means of intercalation of heavy elements has been reported. In the present work, thermoelectric properties of Gd intercalated compounds GdxTiS2 (x ⳱ 0.025, 0.05) are investigated, and the results indicate that proper Gd intercalation into TiS2 can improve its thermoelectric properties effectively. II. EXPERIMENTAL METHODS
Polycrystals of gadolinium intercalated compounds GdxTiS2 (x ⳱ 0.025, 0.05)
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