A classification scheme for ternary structures with infinite antiprism and octahedron columns used to predict the structure of Sc₃Re₂Si₄

Abstract

A classification of temary transition-metal silicides (and germanides) containing infinite parallel columns of Si(Ge)-centered square antiprisms and infinite parallel columns of transition-metal-centered octahedra is given which is based on the composition of the antiprisms and on the linkage of the octahedra. This scheme allows one to classify the following structure types: Zr4foaGe7, Nb4Cr2Sis, Nb2CraSis, Hf2Ru3Si4, and also ZrFeSi2, ZrMnSi2 and LuMnGe2. The previously reported Sc3Re2Si3 structure has structural features which could be classified in the scheme if extra Si atoms are present. It is shown that Sc3Re2Si3 is in fact in error, the true composition being Sc3Re2Si4 and its structure represents the eighth structure type of this structure family. Sc3Re2Si4: Mr=619"61, IntroductionIn two recent systematic studies of the structures of ternary rare-earth -transition-metal silicides and homologues (Gladyshevskii & Bodak, 1982; Parth6 & Chabot, 1984) it has been possible to correlate a great number of different structure types from geometric considerations. One of the aims of such an undertaking is to understand and interpret the 0108-7681/85/040213-07501.50 sometimes complicated chemical formulas in relation to the structural features. In the case of ternary structures with centered trigonal prisms it was, for example, possible to formulate the so-called waistcontact-restriction rule. This rule permits the calculation of the correct composition for complete atom ordering at the prism centers for structures which were previously reported as partially ordered (Parth6, Chabot & Hovestreydt, 1983; Parth6 & Hovestreydt, 1985).In this paper we draw attention to particular ternary structures of general composition RxTrMz where R = very late rare-earth element, Sc or a transition element of the fourth group (also sometimes Nb or Ta); T = smaller transition element of Cr, Mn, Fe or Co group (also V); and M = Si or Ge. The structures of interest here are characterized by two kinds of infinite columns, both of which are parallel to the shortest cell axis (of about 5 to 6/~). One is formed of faceshared square antiprisms of R atoms or a mixture of R and T atoms, each antiprism being centered by an M atom. The second kind of infinite column consists of face-shared octahedra of M atoms, each octahedron being centered by a T atom. The centered antiprisms and centered octahedra may occasionally be deformed, but any distance between the central atom and an atom forming the polyhedron is always equal to or smaller than the sum of the metallic radii (Teatum, Gschneidner & Waber, 1960 Table 1. Drawings of the structure types, in a projection along the column axes, can be found in Fig. 1. The structures can be conveniently classified according to:-the nature of the atoms forming the square antiprism columns and -the linkage of the octahedron columns. Nature of the atoms forming the antiprism columnsExperimentally, it is found that the M-centered antiprisms can be formed either of R atoms only (RsM), of R and T atom...

Bridgman crystal growth of Yb2Ru3Ge4—A ternary germanide with a three-dimensional network of condensed distorted RuGe5 and RuGe6 units

“…Yb 2 Ru 3 Ge 4 is isotypic with Hf 2 Ru 3 Si 4 [14,15]. So far, only Zr 2 Ru 3 Si 4 [15] crystallizes with this peculiar monoclinic structure type, and Sc 3 Re 2 Si 4 can be considered as a site occupancy variant of Hf 2 Ru 3 Si 4 [14]. The Sc 3 Re 2 Si 4 and Hf 2 Ru 3 Si 4 structures belong to a larger family of intermetallic structure types that can be constructed from infinite antiprism and octahedron columns.…”

“…Yb 2 Ru 3 Ge 4 is isotypic with Hf 2 Ru 3 Si 4 [14,15]. So far, only Zr 2 Ru 3 Si 4 [15] crystallizes with this peculiar monoclinic structure type, and Sc 3 Re 2 Si 4 can be considered as a site occupancy variant of Hf 2 Ru 3 Si 4 [14].…”

“…The Sc 3 Re 2 Si 4 and Hf 2 Ru 3 Si 4 structures belong to a larger family of intermetallic structure types that can be constructed from infinite antiprism and octahedron columns. Chabot and Partheé ffectively used this classification scheme to predict the structure of Sc 3 Re 2 Si 4 [14].…”

“…Pearson code mC72 then readily revealed isotypism with Hf 2 Ru 3 Si 4 [14,15]. Consequently, in the final cycles, the Yb 2 Ru 3 Ge 4 structure was refined with the setting of Hf 2 Ru 3 Si 4 .…”

“…Intermetallic Yb x T y X z compounds (T ¼ late transition metal; X ¼ element of the 3rd, 4th, or 5th main group) are interesting candidates when searching for intermediate valence materials, since ytterbium can occur in the diamagnetic divalent ([Xe]4f 14 ) or paramagnetic trivalent ([Xe]4f 13 ) oxidation state. Especially the trivalent ytterbium compounds are interesting for comparison with related cerium intermetallics, since they exhibit the f-hole analogue of [Xe]4f 1 cerium.…”