Quaternary rare-earth arsenides REAg_1−xZn_yAs₂ (RE=La–Nd, Sm, Gd–Dy) with tetragonal SrZnBi₂- and HfCuSi₂-type structures

Reactions of the elements at 800 °C with the nominal compositions REAg_1−xZn_xAs₂ resulted in quaternary arsenides REAg_1−xZn_yAs₂ in which the combined Ag and Zn content deviates increasingly from unity in the Zn-richer phases, reflecting the transition from the fully stoichiometric ternary silver-containing arsenides REAgAs₂ to the substoichiometric zinc-containing ones REZn_0.67As₂. Powder X-ray diffraction analysis indicated SrZnBi₂-type (space group I4/mmm, Z=4; RE=La, Ce) and HfCuSi₂-type structures (space group P4/nmm, Z=2; RE=Pr, Nd, Sm, Gd, Tb, Dy). Single-crystal X-ray diffraction analysis performed on LaAg_0.5Zn_0.5As₂, PrAg_0.5Zn_0.5As₂, and NdAg_0.5Zn_0.5As₂ indicated that the Ag and Zn atoms are disordered within metal-centred tetrahedra and provided no evidence for distortion of the square As nets. The small electron excess tolerated in these quaternary arsenides and the absence of distortion in the square nets can be traced to the occurrence of As–As states that are only weakly antibonding near the Fermi level. PrAg_0.5Zn_0.5As₂ and NdAg_0.5Zn_0.5As₂ are paramagnetic with effective magnetic moments consistent with trivalent RE species. - Graphical abstract: On proceeding from fully stoichiometric REAgAs₂ to substoichiometric REZn_0.67As₂, deficiencies in Zn content become increasingly prominent in quaternary arsenides REAg_1−xZn_yAs₂. - Highlights: • Ag and Zn atoms are disordered within quaternary arsenides REAg_1−xZn_yAs₂. • In Zn-richer phases, Zn deficiencies develop to counteract electron excess. • Distortions of square As net appear to be suppressed.