Crystal structures and new perspectives on Y_3Au_4 and Y_14Au_51

摘要

Y_3Au_4 (triyttrium tetragold) and Y_14Au_51 (tetradecayttrium henpentaconta-gold), two binary representatives of Au-rich rare earth (R) systems crystallize with the space groups R3 and P6/m, adopting the Pu_3Pd_4 and Gd_14Ag_51 structure types, respectively (Pearson symbols hR42 and hP65). A variety of binary R-Au compounds have been reported, although only a few have been investigated thoroughly. Many reports lack information or misinterpret known compounds reported elsewhere. The Pu_3Pd_4 type is fairly common for group 10 elements Ni, Pd, and Pt, while Au representatives are restricted to just five examples, i.e. Ca_3Au_4, Pr_3Au_4, Nd_3Au_4, Gd_3Au_4, and Th_3Au_4. Sm_6Au_7 is suspected to be Sm_3Au_4 due to identical symmetry and close unit-cell parameters. The Pu_3Pd_4 structure type allows for full substitution of the position of the rare earth atom by more electronegative and smaller elements, i.e. Ti and Zr. The Gd_14Ag_51 type instead is more common for the group 11 metals, while rare representatives of group 12 are known. Y_3Au_4 can be represented as a tunnel structure with encapsulated cations and anionic chains. Though tunnels are present in Y_14Au_51, this structure is more complex and is best described in terms of polyhedral 'pinwheels' around the tunnel forming polyhedra along the c axis.