Systematic Study on Crystal Structures in Tetragonal RB₂C₂ (R=Rare Earth) Compounds

Detailed crystal structures of the tetragonal RB₂C₂ (R=La, Ce, Pr, Nd, Tb, Dy, Ho, Er, Tm and Lu) compounds which include the antiferroquadrupolar ordering materials, DyB₂C₂ and HoB₂C₂, have been investigated by neutron powder diffraction technique. RB₂C₂ are crystallised in the same LaB₂C₂ type crystal structure with P4/mbm symmetry. The structure of the B C network which consists of non-regular squares and octagons are nearly the same in the system except slight rotation as rare earth atoms become heavier.