Ternary rare-earth zinc arsenides REZn1–xAs2 (RE=La–Nd, Sm)

The ternary rare-earth zinc arsenides REZn1−xAs2 (RE=La–Nd, Sm) were prepared by reaction of the elements at 800 °C. Single-crystal and powder X-ray diffraction analysis revealed a defect SrZnBi2-type average structure for the La member (Pearson symbol tI16, space group I4/mmm, Z=4; a=4.0770(9) Å, c=20.533(5) Å), in contrast to defect HfCuSi2-type average structures for the remaining RE members (Pearson symbol tP8, space group P4/nmm, Z=2; a=4.0298(5)–3.9520(4) Å, c=10.222(1)–10.099(1) Å in the progression from Ce to Sm). The homogeneity range is not appreciable (estimated to be narrower than 0.6<1−x<0.7 in SmZn1−xAs2) and the formula REZn0.67As2 likely represents the Zn-rich phase boundary. The Ce–Nd members are Curie–Weiss paramagnets. LaZn0.67As2 shows activated behavior in its electrical resistivity, whereas SmZn0.67As2 exhibits anomalies in its temperature dependence of the electrical resistivity.

LaZn1−xAs2 adopts a SrZnBi2-type structure whereas the remaining members of the REZn1−xAs2 series (RE=Ce–Nd, Sm) adopt a HfCuSi2-type structure.Figure optionsDownload as PowerPoint slideHighlights
► REZn1–xAs2 adopts SrZnBi2-type (RE=La) or HfCuSi2-type (RE=Ce–Nd, Sm) structures.
► Trends in RE substitution and local distortion around Zn-centered tetrahedra can be rationalized by geometrical factors.
► Zn vacancies occur to reduce Zn–As and As–As antibonding interactions.