Incommensurately modulated lanthanide coinagemetal diarsenides. II. GdCuAs2, GdAu1dAs2 and TbAu1dAs2 – new distortion variants of the HfCuSi2 type with irregularly stacked zigzag chains of arsenic atoms

摘要

GdCuAs2, GdAu1-As2 and TbAu1-As2 crystallize as incommensurately modulated variants of the HfCuSi2 type. Structure models have been developed in the monoclinic superspace group P121/m1(0)00 (No. 11.1). The components of the modulation wavevectors q = a* + 0b* + c* are = 0.04 (1) and = 0.48 (1) for GdCuAs2, = 0.03 (1) and = 0.48 (1) for GdAu1=As2 and = 0.02 (1) and = 0.46 (1) for TbAu1-As2. The predominant effect of the positional modulation is the distortion of a square net of arsenic atoms, which results in planar zigzag chains. Rod groups and layer groups of the respective structure motifs are identified and discussed.