Contribution to the crystal chemistry of rare earth chalcogenides. III. The crystal structure and twinning of SmS_1.9

Abstract

The structure of samarium disulfide SmS 1.9, space group P4 2 /n; lattice constants a 19.717(2) A; c 15.928(1) A has been determined and refined by LS method to R 0.0345; R w 0.0419. The structure is a tenfold superstructure from the structure type ZrSSi.[S 2 ] 2± ± dumbbells with interatomic distances 2.146(1) A between S atoms were observed in the structure. Fully ordered vacancies and orientation of the [S 2 ] 2± ± dumbbells are responsible for the formation of the superstructure. The investigated sample was twinned by the reticular merohedral law, the twin symmetry is 4/mm H m H , the twinning symmetry elements are (310) and (120) mirror planes and the twin index is n 5.

LaSe1.85, CeSe1.83, NdSe1.83 and SmSe1.84 – four new rare earth metal polyselenides with incommensurate site occupancy and displacive modulation

“…Figure 9 displays an extended approximately 10a  10b section of the modulated Se2 layer of CeSe 1.83 574 C. Graf and T. Doert Brought to you by | New York University Bobst Library Technical Services Authenticated Download Date | 6/9/15 3:29 PM at z % 0. If the interatomic distances of known rare earth polyselenides are taken into account [1][2][3][4][5][6][7], three ranges of selenium -selenium distances can roughly be recognized in the modulated Se layer. The shortest Se--Se distances of 2.35 until about 2.6 A, illustrated as straight lines in Fig.…”

“…Both patterns are characteristic for the CeSe 1.9 type and have been found to be the energetically favored solution for these defect layers [23]. The chalcogen deficient planar layers in this tenfold superstructure of the ZrSSi type consist of an ordered array of these two patterns only [4][5][6]. In the Gd 8 Se 15 type, a disordered arrangement of these patterns occurs [7].…”

“…[1][2][3][4][5][6][7], e.g.). The structures consist of an alternating stacking of puckered [LnX] double layers and planar X layers and can be regarded as superstructures of the ZrSSi type [8].…”

Microwave‐Assisted Synthesis, Characterization, and Thermal Decomposition of Rare‐Earth Metal Disulfides RES2 (RE = La, Pr, Nd)

“…Two commensurate superstructures of the aristotype are known for sulfur deficient rare‐earth metal polysulfides RE S 2– δ : the CeS 1.9 type, a tenfold superstructure with δ = 0.1 (i.e. ten percent chalcogen defects in the planar layers)1,11 and the Gd 8 Se 15 type, a 24‐fold superstructure ideally with δ = 0.125 (12.5 % chalcogen defects in the planar layers) 6…”

Gd8Se15—A 24-Fold Superstructure of the ZrSSi Type

“…[4] A closely related monoclinic 24-fold supercell (space group A2 1 /m11) describes DyS 1.76 and Dy 6 S 11 , both with substantial disorder. [5,6] A related 24-fold supercell was suggested for YSe 1.83 but without a structural solution. [7] Finally, the structure of Dy 11 Se 20 has been refined in a model which is based on a 66-fold supercell.…”