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Reactions of the elements at 800 °C with the nominal compositions RE Ag 1 − x Zn x As 2 resulted in quaternary arsenides RE Ag 1 − x Zn y As 2 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 RE AgAs 2 to the substoichiometric zinc-containing ones RE Zn 0.67 As 2 . Powder X-ray diffraction analysis indicated SrZnBi 2 -type (space group I 4/ mmm , Z =4; RE =La, Ce) and HfCuSi 2 -type structures (space group P 4/ nmm , Z =2; RE =Pr, Nd, Sm, Gd, Tb, Dy). Single-crystal X-ray diffraction analysis performed on LaAg 0.5 Zn 0.5 As 2 , PrAg 0.5 Zn 0.5 As 2 , and NdAg 0.5 Zn 0.5 As 2 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 0.5 Zn 0.5 As 2 and NdAg 0.5 Zn 0.5 As 2 are paramagnetic with effective magnetic moments consistent with trivalent RE species.

The title compounds are prepared from the elements (800 °C, 10 d) and characterized by powder and single crystal XRD, electrical resistivity measurements, and TB-LMTO-ASA band structure calculations.

Three series of quaternary pnictides, LnCuZnAs2 (Ln: Y, La—Nd, Sm, Gd—Lu), LnAgZnP2 (Ln: La—Nd, Sm, Gd—Dy), and LnAgZnAs2 (Ln: La—Nd, Sm, Gd—Dy) are prepared by solid reaction of the elements (evacuated silica tubes, 1.

The pnictides Ln2Mn3Cu9P7 (Ln: La—Nd, Sm, Gd—Dy) and Ln2Mn3Cu9As7 (Ln: La—Nd) are prepared from stoichiometric mixtures of the elements (800 °C, 14 d).