Noncentrosymmetric rare-earth copper gallium chalcogenides RE 3CuGaCh 7 (RE=La–Nd; Ch=S, Se): An unexpected combination

The quaternary rare-earth chalcogenides RE 3CuGaS7 and RE 3CuGaSe7 (RE=La–Nd) have been prepared by reactions of the elements at 1050°C and 900°C, respectively. They crystallize in the noncentrosymmetric La3CuSiS7-type structure (hexagonal, space group P63, Z=2) in which the a-parameter is largely controlled by the RE component (a=10.0–10.3Å for the sulfides and 10.3–10.6Å for the selenides) whereas the c-parameter is essentially fixed by the …