T hompson e t al 57 f ound the lattice parameters of

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Unformatted text preview: up each sandwich layer are predominantly covalently bonded. allow T iS 2 The relatively weak interlayer forces ( like several other layered compounds) to a ccomodate extra atoms in this Van der Waals "region" (between the layers of T iS ) w ithout altering the original 2 structure of the host layers. Symmetry and energy considerations indicate that there are two possible types of preferred sites within the Van der Waals "region" where the intercalated atoms are most - likely t o reside. The two types of sites are generally labelled "octahedral" and "tetrahedral" sites where the designations refer to the coordination of sulfur atoms around each site. There is one octahedral site and two tetrahedral sites for each T iS u nit. 2 The larger octahedral sites ( F i g . 5) are located midway between two T i S 2 l ayers directly above the Ti atoms (at the fractional coordinate 0 , 0 , 1 /2), w hile the tetrahedral sites (Fig. 5 ) a re located above the S a toms in planes just above and below the plane of octahedral sites within the Van der Waals layer (at the fractional coordinates 1 / 3 , 2 / 3 , z a nd 2 / 3 , 1 / 3 , -2 w here z=5/8). 2 -2 (b) Titanium Disulphide - P reparation T iS2 d oes not occur naturally but has been produced b y a t least four methods: P age - 1 1 - H eating titanium trisulfide to 600 C to d isp.roportionate t itanium trisulfide to form titanium disulfide and sulfur ( 38). T he process is difficult to control however and usually results in substantial crystal imperfections. ii) R eacting titanium tetrachloride with hydrogen sulfide t o form titanium disulfide and hydrogen chloride ( 3 8 ) , b ut substantial amounts of chlorine (up to 2 p ercent) have been found to contaminate the crystal. iii) R eacting elemental titanium and sulfur directly at temperatures greater than 500 C t o form titanium disulfide ( 3 8 , 4 1 ) , w hich can be well controlled for producing high quality powder samples. iv) Chemical vapor transport techniques ( 4 1 ) , w hich is the preferred method for growing high quality single crystals. P...
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