Fabrication and superconductivity of NaxTaS2 crystals -: art. no. 014534

In this paper we report the growth and superconductivity of NaxTaS2 crystals. The structural data deduced from x-ray diffraction pattern shows that the sample has the same structure as 2H-TaS2. A series of crystals with different superconducting transition temperatures (T-c) ranging from 2.5 K to 4.4 K were obtained. It is found that the T-c rises with the increase of Na content determined by energy-dispersive x-ray microanalysis(EDX) of scanning electron microscope (SEM) on these crystals. Compared with the resistivity curve of un-intercalated sample 2H-TaS2 (T-c=0.8 K, T-CDW approximate to 70 K), no signal of charge density wave (CDW) was observed in samples Na0.1TaS2 and Na0.05TaS2. However, in some samples with lower T-c, the CDW appears again at about 65 K. Comparison between the anisotropic resistivity indicates that the anisotropy becomes smaller in samples with more Na intercalation (albeit a weak semiconducting behavior along c-axis) and thus higher T-c. It is thus concluded that there is a competition between the superconductivity and the CDW. With the increase of sodium content, the rise of T-c in NaxTaS2 is caused mainly by the suppression to the CDW in 2H-TaS2, and the conventional rigid band model for layered dichalcogenide may be inadequate to explain the changes induced by the slight intercalation of sodium in 2H-TaS2.