Ternary BaAl₄-type derivative structures

Abstract

Ternary BaAl4-type derivative stluctures are frequently found with rare-earth-transition-metal silicides and germanides with the rare-earth atoms occupying the Ba sites and the two other kinds of atoms distributed in ordered fashion on the A1 sites. The possible ternary BaA14-type derivative structures with the same unit cell as BaA14 are investigated. If it is assumed that transition-metal-transition-metal contacts are to be excluded only seven hypothetical BaAl4-type derivative structures are possible. Three of these are already known as ThCr2Si2, CaBe2Ge 2 and BaNiSn 3 types. Segments of these three structures and of other BaAl4-type derivative structures are found in various intergrowth structures. The BaA14-type derivative structures can be classified according to the type of coordination polyhedron around the transition metal, which can be a tetrahedron or a square pyramid. The tendency of the transition metal to have one or the other coordination polyhedron determines which BaAl4-type derivative structure is formed and explains also the occurrence of the HfFe2Si 2 and U2C03Si 5 types -BaAla-type derivative structures with larger unit cells.

An Unusual Electron Count and Electron-Deficient Multi-Center Bonding in One Class of Intermetallics: The BaAl4, CaAl2Zn2, CeMg2Si2 and FCC Al Structures

“…Since then chemists, in their industrious search for new structures, trying to 1 understand the abundance given to us in the micro scopic arrangem ents of atoms in the solid state, have found to their amazement that over 400 compounds crystallize in this prototype [2]. And this does not count the variants on this structural type or close relatives to it [3], structures such as C aBe2G e2 [4], T1Cu4S3 [5], BaPtSn3 [6], SrZnBi2, SrZnSb2 and SrCuSn2 [7], Physicists joined the march recently, the vast collections of com pounds, especially the Let us describe the resulting structure in term s of sublattices. There are in the BaAl4 structure obvious Ba layers, and two kinds of Al.…”

Formation of Nets of Corner-Shared Bicapped Gold Squares in SrAu3Ge: How a BaAl4-Type Derivative Reconciles Fewer Valence Electrons and the Origin of Its Uniaxial Negative Thermal Expansion

“…9 Presented here are the synthesis, structure, and bonding of SrAu 3 Ge, which shows close relationships with its parents CeMg 2 Si 2 and, further, BaAl 4 (and other ordered variants). 11 From the valence electron counts (vec) viewpoint, the contrasting CeMg 2 Si 2 structure has been well explained as a preferred model for electron-rich BaAl 4 -related derivatives (vec ≥ 16). 12 However, La 3 Al 11 type structures and its variants have usually been the preferred options for products with 12 or fewer electrons.…”

Antiferromagnetism inEuCu2As2andEuCu1.82Sb2single crystals

“…The two crystal structures are shown in Fig. 2, and are both ternary derivatives of the binary BaAl 4 -type structure, 46 consisting of layers of Eu, Cu and As/Sb atoms stacked along the tetragonal c axis. From Fig.…”