Homologous Series of Rare-Earth Zinc Arsenides REZn_2–xAs₂·n(REAs) (RE = La–Nd, Sm; n = 3, 4, 5, 6)

Four series of ternary rare-earth zinc arsenides have been prepared by reaction of the elements at 750 °C: RE₄Zn_2–xAs₅ forming for RE = La–Nd, Sm; and RE₅Zn_2–xAs₆, RE₆Zn_2–xAs₇, RE₇Zn_2–xAs₈ forming for RE = Ce, Pr, Nd, Sm. They crystallize in trigonal structure types in space group P3̅m1 with Z = 1 for RE₄Zn_2–xAs₅ and RE₇Zn_2–xAs₈, or space group R3̅m1 with Z = 3 for RE₅Zn_2–xAs₆ and RE₆Zn_2–xAs₇. Through the structural principle of intergrowing rocksalt-type [REAs] slabs of variable thickness within a parent CaAl₂Si₂-type structure containing Zn-deficient [Zn_2–xAs₂] slabs built from edge-sharing Zn-centered tetrahedra, these ternary arsenides belong to a homologous series with the formulation REZn_2–xAs₂·n(REAs) (n = 3, 4, 5, 6). Quaternary derivatives Ce₄(Mn,Zn)_2–xAs₅ and Ce₆(Mn,Zn)_2–xAs₇ were also obtained in which Mn partially substitutes for Zn. Band structure calculations predict that the electronic properties can be gradually modified from semiconducting to semimetallic behavior as more [REAs] slabs are introduced.