Crystal structures of the compounds Yb5.5AgSe8, YbAgSe2 and YxYb1−xCuYbSe3 (x = 0.11)

The crystal structure of the Yb5.5AgSe8 compound (space group Fd3¯m, Pearson symbol cF58, a = 1.1530(1) nm, R1 = 0.0388) was determined by means of X-ray single crystal diffraction. The Se atoms in the structure of the Yb5.5AgSe8 compound are stacked in a close-packed arrangement with layers in the sequence ABC. The Yb1 and Yb2 atoms are located in octahedral interstices, whereas the Ag atoms are located in tetrahedral interstices. The crystal structures of the compounds YbAgSe2 (space group P212121, Pearson symbol oP16, a = 0.68168(2) nm, b = 1.35842(5) nm, c = 0.41302(1) nm, RI = 0.0804) and YxYb1−xCuYbSe3 (x = 0.11) (space group Pnma, Pearson symbol oP24, a = 1.04114(5) nm, b = 0.39777(2) nm, c = 1.31088(6) nm, RI = 0.0884) were determined using X-ray powder diffraction. The Se atoms in the structure of the YbAgSe2 compound are stacked in a close-packed arrangement with layers in the sequence AB. Half of the octahedral interstices are occupied by Yb atoms. Remaining octahedral interstices are occupied by Ag atoms. Octahedral surrounding of the atoms of the statistical mixture M (Y + Yb), trigonal prismatic of the Yb atoms and tetrahedral of the Cu atoms exist in the crystal structure of the YxYb1−xCuYbSe3 (x = 0.11) compound.