Ternary CaCu4P2-type pnictides AAg4 Pn 2 (A=Sr, Eu; Pn=As, Sb)

Abstract: Four ternary pnictides AAg4 Pn 2 (A=Sr, Eu; Pn=As, Sb) were prepared by reactions of the elements at 850°C and their crystal structures were determined from single-crystal X-ray diffraction studies. These silver-containing pnictides AAg4 Pn 2 adopt the trigonal CaCu4P2-type structure (Pearson symbol hR21, space group R3̄m, Z=3; a=4.5555(6)Å, c=24.041(3)Å for SrAg4As2; a=4.5352(2)Å, c=23.7221(11)Å for EuAg4As2; a=4.7404(4)Å, c=25.029(2)Å for SrAg4Sb2; a=4.7239(3)Å, c=24.689(2)Å for EuAg4Sb2), which can be derived from the trigonal CaAl2Si2-type structure of the isoelectronic zinc-containing pnictides AZn2 Pn 2 by insertion of additional Ag atoms into trigonal planar sites within [M 2 Pn 2]2− slabs built up of edge-sharing tetrahedra. Band structure calculations on SrAg4As2 and SrAg4Sb2 revealed that these charge-balanced Zintl phases actually exhibit no gap at the Fermi level and are predicted to be semimetals. [Copyright &y& Elsevier]