Die Kristallstruktur von LaCrS₃

Electron diffraction observations from some so-called 'LnMS3' layer compounds isostructural with '~LaCrS3' and from cannizzarite, ~Pb46Bi54S127

“…3, its zone axis is [310] t = [li0]r. The diffraction spots (Fig. 3b) are streaked, and reveal twinning [by reflection in (001), as previously reported by Kato et al (1977)], with a preponderance of one twin. The corresponding image (Fig.…”

“…1 for '~LaCrS3'). Also, (iv) the stacking unit is in this case just one pair of layers [instead of the six pairs reported for '~LaCrS 3' (Kato et al, 1977)]. Notice also the undulations (in the e* direction) of the layers in cannizzarite (Fig.…”

“…The style '~LaCrS3' reflects the fact that there has been some argument about the exact stoichiometry of this compound: the non-commensurability between the two layer types suggested an ideal composition La6CrsSl6 since, for the subcells, a r = ao, e* = e*, but b r ~ b o x 5/3 and, for full occupancy of sites, the subceU contents are T = 2LaS, O = CrS 2. We believe that any doubt has now been resolved in favour of the more complicated formula (Otero-Diaz et al, 1985), so that there is no need to invoke disorder on the La sites of the structure as was previously done (Kato et al, 1977) in order to accommodate the simpler (but incorrect) stoichiometry 'LaCrS3'.…”

“…Fig. 1 shows the monoclinic structure of',-,LaCrS 3' as reported by Kato, Kawada & Takahashi (1977) which has a= 5.936, b =5.752, c= 11.036 A, a--90.39, fl= 95.30 and y= 90.02 ° for T, a = 5.936, b = 3.435, c = 11.053 A, ~t = 93.29, fl = 95.29 and y = 90.03 ° for O and, for the true unit cell, a=5.94, b=17.2, c=66.2A and ~t=90.3, fl= 95.3, y= 90.0 °. The style '~LaCrS3' reflects the fact that there has been some argument about the exact stoichiometry of this compound: the non-commensurability between the two layer types suggested an ideal composition La6CrsSl6 since, for the subcells, a r = ao, e* = e*, but b r ~ b o x 5/3 and, for full occupancy of sites, the subceU contents are T = 2LaS, O = CrS 2.…”

“…1. The structure of 'LaCrS 3' according to Kato et al (1977) projected along a. Four pseudo-tetragonal T layers and five pseudo-orthohexagonal O layers are drawn; the outline of half the unit cell, i.e.…”