Polar intermetallics

Polar Intermetallics and ZintI Phases along the ZintI Border... 

The validity (or lack thereof) of the classical Zind formahsm as applied to less polar intermetallics, involving metals along the Zind border, is nicely probed by electron-poof trelides. Seminal work by Corbett [44] and Belin [48] recognized the proclivity of trelides (Ga, In, H) to form cluster-based anion structures. The apparent electron deficiency in the chemical bonding of these cluster com-... 

Polar Intermetallics and Zint Phases along the ZIntI Border... 

Our work described in this section clearly illustrates the importance of the nature of the cations (size, charges, electronegativities), electronegativity differences, electronic factors, and matrix effects in the structural preferences of polar intermetallics. Interplay of these crucial factors lead to important structural adaptations and deformations. We anticipate exploratory synthesis studies along the ZintI border will further result in the discovery of novel crystal structures and unique chemical bonding descriptions. 

Protons are not the sole species that can be incorporated into the lattices of different host materials. At the beginning of the 1960s, Boris N. Kabanov showed that during cathodic polarization of different metals in alkaline solutions, intercalation of atoms of the corresponding alkali metal is possible. As a result of such an electrochemical intercalation, either homogeneous alloys are formed (solid solutions) or heterogeneous polyphase systems, or even intermetallic compounds, are formed. 

Polar intermetallics are loosely referred to as electron-poorer relatives of Zintl phases in which the active metals do not contribute all of their valence electrons, rather they bond with the more electronegative components to some degree. The structures cannot be simply accounted for by octet rules because of substantial delocalized bonding among the atoms. 

The components of polar intermetallics generally include an active metal from the group 1 or 2 or the rare-earth series plus, sometimes, a late-transition metal, and a metal from the p-block. Because of the presence of an electron-poorer late transition metal, polar intermetallics generally have lower e/a values (about 2.0-4.0) than classic Zintl phases (>4.0) [45], Note these values are traditionally calculated over only electronegative atoms [45], in contrast to those of Hume-Rothery phases (<2.0) [45] and QC/ACs (2.0 0.3) [25], for which electron counts are considered to be distributed over all atoms. The former two higher values are decreased to about 1.5-2.5 and >2.5, respectively, when counted over all atoms (but with omission of any dw shells). For comparison purposes, Fig. 3 sketches the distribution of all these intermetallic phases according to e/a counted over all atoms, as we will use hereafter. 

Since all known QC systems, with e/a of about 1.75-2.20 [25], lie close to the approximate border between the Hume-Rothery and polar intermetallic phase regions, a reasonable starting place for development of new QC/AC systems is to study selected polar intermetallic systems with nearby e/a values. Synthetic explorations of such polar intermetallics have been significant only in the past few decades [42,45], Knowledge and insights developed about the diverse interplays between composition-structure-electronic structure-physical properties for these phases were expected to be a considerable aid to the discovery of novel QC/ACs. 

Toward Quasicrystals and Their Approximants 3.1 Polar Intermetallics Containing the Triels... 

Active metal. The selection of active metal is also a critical factor. For polar intermetallics and Zintl phases, alkali, alkaline-earth, and rare-earth elements have... 

Some intermetallic compounds have the same structures as those of simple polar compounds. Quite a few AM type intermetallic compounds have the NaCl (3 2PO, Section 5.1.1) structure, but usually for those differing significantly in electronegativities. Table 5.1 includes many compounds of the types MP, MAs, MSb, and MBi. The NiAs structure (2-2PO, Section 5.2.1) is found for a few MAs and MSb compounds (Table 5.5), the MSn compounds of Fe, Ni, Cu, Pd, Pt, Rh, and Au, and MnBi, NiBi, PtBi, and RhBi. The ZnS structures (CN 4) are not usually encountered for intermetallic compounds. The compounds of Al, Ga, and In with P, As, and Sb have the zinc blende (ZnS, 3 2PT, Section 6.1.1) structure. These are semiconductors or insulators. Because the bcc structure is common for metals, it is not surprising that many 1 1 intermetallic compounds have the CsCl structure (3 2PTOT, Section 7.2.1). A few of these intermetallic compounds are included in Table 7.1 a more extensive list is given in Table 9.1. 

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