Structures of the ternary iron germanium pnictides FeGe(1-x)Pn(x) (Pn=P, As, Sb)

The pseudo-binary FeGe-FePn (Pn=P, As, Sb) systems have been investigated b y X-ray diffraction methods. The phosphide and arsenide systems form ternar y solid solutions FeGe1-xPx (0.4 less than or equal to x less than or equal to 1.0) and FeGe1-xAsx (0.3 less than or equal to x less than or equal to 1.0) crystallizing in MnP-type structures. The antimonide system is more co mplex, forming intermetallic compounds that display incipient ordering of S b-2 pairs as they are stuffed into the FeGe (x=0) structure while Ge atoms are gradually removed. The structures of on intermediate member FeGe0.80Sb0 .20 (x = 0.20) and of the Limiting member FeGe0.67Sb0.33 (x = 0.33) in this progression were determined by single-crystal X-ray diffraction. Both comp ounds crystallize in hexagonal space groups: P6(3)/mmc, a = 8.796(2), c = 8 .004(2) Angstrom, Z = 6 for Fe3Ge2.4Sb0.6 (or FeGe0.80Sb0.20), and P6/mmm, a = 8.9885(5), c = 7.9043(6) Angstrom, Z = 6 for Fe3Ge2Sb (or FeGe0.67Sb0.3 3). Beyond this point, ternary solid solutions FeGe1-xSbx (0.4 less than or equal to x less than or equal to 1.0) are formed, crystallizing in NiAs-ty pe structures. (C) 2000 Elsevier Science S.A. All rights reserved.