Handbook of Crystallographic Data for Intermetallic Phases

Abstract

Present-day microcomputers offer a wealth of computing power at very liBited costs. In fact, it is now well possible, as we showed some years ago, to have a simple least-squares structure refinement progran running on a $ lOOO.-computer.Another, and possibly more important, field in which microcomputers can be applied is teaching. As a rule, crystallographic methods depend heavily on computing, and the associated programs are nearly always black boxes which do not elucidate anything of uhat is g0ing on. To explain these methods to students, simulations can be used. As an example, a direct ~ethod teaching

Hexagonal-Diamond-like Gold Lattices, Ba and (Au,T)3 Interstitials, and Delocalized Bonding in a Family of Intermetallic Phases Ba2Au6(Au,T)3 (T = Zn, Cd, Ga, In, or Sn)

“…The Pearson symbol for this structure is hR66. Although there are other isopointal phases with Pearson symbol hR66 that utilize the same set of Wyckoff positions, 27 these exhibit different coordinates and bonding patterns, which render them as different structural types. There is no precedent whatsoever for any part of this particular structure, composition range, or bonding details; the results once again represent more of the new and unanticipated ways in which these particular elements can express a new chemistry associated with an unexplored region of phase space.…”

“…In fact, the hexagonal-diamond-like Au lattice in the present 2−6−3 structure resembles more the In 2 2− anionic lattices in CaIn 2 -type structures (P6 3 /mmc), 30 regardless of the Au lattice puckering along the (001) direction allowed by the R3̅ c symmetry. In addition, both CaAu 2 and SrAu 2 form CeCu 2 -type structures, 27 in which the Au lattice also resembles that of the In 2 2− lattice in CaIn 2 except that "ladders" are formed in these. These facts encouraged us to check the structural relationship with BaAu 2 .…”

Gold Network Structures in Rhombohedral and Monoclinic Sr2Au6(Au,T)3 (T = Zn, Ga). A Transition via Relaxation

“…It is of great interest to examine how the structure and bonding evolve when the Ba is replaced by smaller Sr atoms and how electronic factors matter when Zn is replaced by trivalent Ga. One germane fact here is that the corresponding binary aurides containing the smaller alkaline-earth metals Sr and Ca have CeCu 2 -type structures (Imma), in contrast to the AlB 2 -type BaAu 2 (P6/mmm). 15 Here, we report the systemic investigation of the corresponding phases in the Sr−Au−T (T = Zn, Ga) systems. The syntheses and structures for both the isotypic rhombohedral phases and the new monoclinic C2/c versions in the Sr 2 Au 6 (Au,T) 3 (T = Zn, Ga) systems result with the smaller Sr substituent and a higher Au contents.…”

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

“…also play pronounced roles in structural stabilization, for example, for CaAu 2 Si 2 (12), CaAuAl 3 (12), RAl 2 Ga 2 (R = rare-earth metal) (15), and SrAl 2 Pb 2 (16). 34 Zheng and Hoffmann 12 have demonstrated by means of EHTB bonding analyses that the CeMg 2 Si 2 type structure is predicted to be more stable than the BaAl 4 type for typical analogues with large vec values (≥15); vice versa, BaAl 4 structures are more stable than CeMg 2 Si 2 at vec ≤ 15. Yet, no simple 1:4 phase has hitherto been reported in the lower vec region (<12).…”