Crystal structure and band structure calculations of and

Autor: C. Haas, R.A. de Groot, Changming Fang, Ga Wiegers, Auke Meetsma
Rok vydání: 1996
Předmět:
Zdroj: Physica B: Condensed Matter. 226:259-267
ISSN: 0921-4526
DOI: 10.1016/0921-4526(96)00271-2
Popis: The crystal structures of Pb 1 3 TaS 2 and Sn 1 3 NbS 2 were determined using single-crystal X-ray diffraction. The space group is P6322 and the unit cell dimensions are: a = 5.759(1), c = 14.813(1) A and a = 5.778(1), c = 14.394(1) A , for the Pb and Sn compounds, respectively. The post-transition metal atoms occupy one-third of the trigonal-antiprismatic holes between sandwiches NbS2 and TaS2. The Nb and Ta atoms are in trigonal-prismatic coordination by sulfur atoms. The stacking of sandwiches is the same as in 2H disulfides. The arrangement of the post-transition metal atoms is different for the two compounds. A bond valence calculation showed Sn and Pb to be divalent. Ab initio band structure calculations were performed for Sn 1 3 NbS 2 using the localized spherical wave method, and for Pb 1 3 TaS 2 with the augmented spherical wave method with spin-orbital interactions included. The calculations show that the rigid band model is approximately valid for the electronic structures; the main difference with those of 2HNbS2 and 2HTaS2 being the presence of Sn 5s and 5p (Pb 6s and 6p) bands and a larger S 3p/Nb(Ta) 4d (5d) gap in the intercalates (1.0 eV for Sn 1 3 NbS 2 , 1.3 eV for Pb 1 3 TaS 2 . The Sn 5s (Pb 6s) bands are at the bottom (bonding) and top (antibonding) of the valence bands which range from about −7 to about 0 eV. The conduction bands are composed of Nb 4dz2 or Ta 5dz2 orbitals hybridized with S 3p. These bands are filled to about 0.3 holes per Nb (Ta), corresponding to a donation of two electrons per Sn (Pb).
Databáze: OpenAIRE
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