Synthesis, Crystal Structures and Properties of the Zintl Phases Sr2ZnP2, Sr2ZnAs2, A2ZnSb2 and A2ZnBi2 (A = Sr and Eu)

The new intermetallic compounds Sr2ZnP2, Sr2ZnAs2, A(2)ZnSb(2) and A(2)ZnBi(2) (A = Sr, Eu) have been synthesized from the corresponding elements through high-temperature reactions using the flux-growth method. Their structures have been established by single-crystal and powder X-ray diffraction. In all cases, the X-ray diffraction patterns can be successfully indexed based on hexagonal cells in the space group P6(3)/mmc (no. 194) with lattice parameters in the range a = 4.31-4.73 angstrom and c = 7.9-8.55 angstrom. The average structure can be described in the ZrBeSi type (Pearson symbol hP6; 3 unique positions) with defects on the zinc site - structure refinements indicate that every second zinc position is vacant, i.e., their formula unit is AZn(1-x)Pn with x = 0.5 (A = Sr, Eu; Pn = P, As, Sb, Bi). No stoichiometry breadth was observed, which could imply that a super-structure with a long-range order of the zinc vacancies is plausible and evidence for such was sought using electron diffraction. The results from these experiments, as well as magnetic susceptibility measurements and band structure calculations using the LMTO code are also discussed.