Hydrogen in Polar Intermetallics.Binary Pnictides of Divalent Metals with Mn_5Si_3-type Structures and Their Isotypic Ternary Hydride Solutions

摘要

Studies of the hydrogen-free binary A_5Pn_3 systems for A = Ca,Sr,Ba,Sm,Eu,Yb and Pn (pnictogen) = As,Sb,Bi,reveal four new examples,(Ca,Yb)_5Bi_3 and Eu_5(Sb,Bi)_3,among the 16 that form with a hexagonal (P6_3/mcm) Mn_5Si_3-type structure.Most of the previous literature on unit cell dimensions for these correspond to those of smaller ternary hydrides (or other materials).Previously reported Ba_5As_3 and cubic SmAs could not be reproduced.New cubic anti-Th_3P_4 phases are also found in the Sm- As and Ba- Sb- F systems.Crystal structures have been refined from single-crystal X-ray data for hexagonal Sr_5As_3H_(approx 1),Ca_5Sb_3,Ba_5Sb_3H_(approx 0.7),Sm_5Sb_3H_(approx 1),Eu_5Sb_3,Yb_5Sb_3,and Eu_5Bi_3.The widths of H solubility regions in the hexagonal parent structures in terms of cell constant changes have been determined for 12 examples,eight of which with more hydrogen further convert into known orthorhombic Ca_5Sb_3F-type phases.The Sm_5Sb_3 and Sm_5Bi_3 members contain trivalent cations according to several criteria.Magnetic susceptibility data are reported for Eu_5Sb_3 and Eu_5Bi_3,which contain normal Eu~(11) states.