Quaternary rare-earth arsenides REAg1−xZnyAs2 (RE=La–Nd, Sm, Gd–Dy) with tetragonal SrZnBi2- and HfCuSi2-type structures

• Ag and Zn atoms are disordered within quaternary arsenides REAg1−xZnyAs2.
• In Zn-richer phases, Zn deficiencies develop to counteract electron excess.
• Distortions of square As net appear to be suppressed.

Reactions of the elements at 800 °C with the nominal compositions REAg1−xZnxAs2 resulted in quaternary arsenides REAg1−xZnyAs2 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 REZn0.67As2. 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 LaAg0.5Zn0.5As2, PrAg0.5Zn0.5As2, and NdAg0.5Zn0.5As2 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. PrAg0.5Zn0.5As2 and NdAg0.5Zn0.5As2 are paramagnetic with effective magnetic moments consistent with trivalent RE species.

On proceeding from fully stoichiometric REAgAs2 to substoichiometric REZn0.67As2, deficiencies in Zn content become increasingly prominent in quaternary arsenides REAg1−xZnyAs2.Figure optionsDownload as PowerPoint slide