Contribution to the crystal chemistry of rare-earth chalcogenides. II. Thecrystal structure and twinning of rare-earth disulfide PrS2

The structure of the presodyme disulfide PrS2 has been determined and refin ed by the LS method in space group P2(1)/b11 (14) with a = 4.054(1) Angstro m b = 8.058(1) Angstrom; c = 8.079(1) Angstrom and alpha = 90.08(2)degrees to the final values of discrepancy factors R = 0.0188; R-w = 0.0204. The st ructure is a derivative structure of the ZrSSi (or PbFCl) structure type. A heringbone pattern of S-2(2-) dumbbells with interatomic distance 2.135(1) Angstrom is observed in the planes parallel to (001). The investigated cry stal has been twinned by pseudomerohedral law, the twin symmetry is mm'm' a nd the twinning symmetry elements are (010) and (001) mirror planes.