Homologous Series of Rare-Earth Zinc Arsenides <i>RE</i>Zn<sub>2–<i>x</i></sub>As<sub>2</sub>·<i>n</i>(<i>RE</i>As) (<i>RE</i> = La–Nd, Sm; <i>n</i> = 3, 4, 5, 6)
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Four series of ternary rare-earth zinc arsenides have been prepared by reaction of the elements at 750 °C: RE4Zn2–xAs5 forming for RE = La–Nd, Sm; and RE5Zn2–xAs6, RE6Zn2–xAs7, RE7Zn2–xAs8 forming for RE = Ce, Pr, Nd, Sm. They crystallize in trigonal structure types in space group P3̅m1 with Z = 1 for RE4Zn2–xAs5 and RE7Zn2–xAs8, or space group R3̅m1 with Z = 3 for RE5Zn2–xAs6 and RE6Zn2–xAs7. Through the structural principle of intergrowing rocksalt-type [REAs] slabs of variable thickness within a parent CaAl2Si2-type structure containing Zn-deficient [Zn2–xAs2] slabs built from edge-sharing Zn-centered tetrahedra, these ternary arsenides belong to a homologous series with the formulation REZn2–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.
