title: Structure determination of KScS₂, RbScS₂ and KLnS₂ (Ln = Nd, Sm, Tb, Dy, Ho, Er, Tm and Yb) and crystal-chemical discussion.
abstract: The title structures of KScS2 (potassium scandium sulfide), RbScS2 (rubidium scandium sulfide) and KLnS2 [Ln = Nd (potassium neodymium sufide), Sm (potassium samarium sulfide), Tb (potassium terbium sulfide), Dy (potassium dysprosium sulfide), Ho (potassium holmium sulfide), Er (potassium erbium sulfide), Tm (potassium thulium sulfide) and Yb (potassium ytterbium sulfide)] are either newly determined (KScS2, RbScS2 and KTbS2) or redetermined. All of them belong to the α-NaFeO2 structure type in agreement with the ratio of the ionic radii r(3+)/r(+). KScS2, the member of this structural family with the smallest trivalent cation, is an extreme representative of these structures with rare earth trivalent cations. The title structures are compared with isostructural alkali rare earth sulfides in plots showing the dependence of several relevant parameters on the trivalent cation crystal radius; the parameters thus compared are c, a and c/a, the thicknesses of the S-S layers which contain the respective constituent cations, the sulfur fractional coordinates z(S(2-)) and the bond-valence sums.
authors.affiliation: Institute of Physics of the Czech Academy of Sciences, Na Slovance 2, 182 21 Praha 8, Czech Republic.
authors.forename: Lubomír
authors.initials: L
authors.lastname: Havlák
authors.affiliation: Institute of Physics of the Czech Academy of Sciences, Na Slovance 2, 182 21 Praha 8, Czech Republic.
authors.forename: Jan
authors.initials: J
authors.lastname: Fábry
authors.affiliation: Institute of Physics of the Czech Academy of Sciences, Na Slovance 2, 182 21 Praha 8, Czech Republic.
authors.forename: Margarida
authors.initials: M
authors.lastname: Henriques
authors.affiliation: Institute of Physics of the Czech Academy of Sciences, Cukrovarnická 10, 162 00 Praha 6, Czech Republic.
authors.forename: Michal
authors.initials: M
authors.lastname: Dušek
keywords: X-ray single-crystal structure determination; alkali rare earth sulfides; crystal chemistry