Ternary rare-earth zinc arsenides REZn2As3 (RE=La–Pr) containing defect fluorite-type slabs

The ternary rare-earth zinc arsenides REZn2As3 (RE=La–Pr) have been prepared by reactions of the elements at 800 °C. They adopt new tetragonal structure types, with the La member (space group I4/mmm, Z=4, a=4.1133(2) Å, c=32.1246(14) Å) differing from the Ce and Pr members (space group P4/nmm, Z=2, a=4.0804(6)–4.0534(12) Å, c=16.089(5)–16.059(10) Å, respectively) in the disposition of RE-centred square antiprisms on opposite sides of square As nets. The structures contain thick anionic slabs, built from edge-sharing ZnAs4 tetrahedra, that can be considered either as stackings of three PbO-type layers or as fragments of the fluorite-type structure. These slabs are deficient in Zn and are reminiscent of the same features in binary arsenide Zn3As2. LaZn2As3 exhibits temperature-independent paramagnetism whereas CeZn2As3 follows modified Curie–Weiss behavior consistent with Ce3+ species but with no occurrence of long-range ordering.