Charge transfer on the metallic atom-pair bond, and the crystal structures adopted by intermetallic compounds

Abstract

It has been argued in our recent papers that the heat of formation of intermetallic compounds is mostly concentrated in the nearest neighbor unlike atom-pair bonds, and that the positive term in Miedema's equation is associated with charge transfer on the bond to maintain electroneutrality. In this paper, taking examples of some well populated crystal-structure types such as MgCu(2), AsNa(3), AuCu(3), MoSi(2) and SiCr(3) types, the effect of such charge transfer on the crystal structures adopted by intermetallic compounds is examined. It is shown that the correlation between the observed size changes of atoms on alloying and their electronegativity differences is supportive of the idea of charge transfer between atoms. It is argued that the electronegativity and valence differences need to be of the required magnitude and direction to alter, through charge transfer, the elemental radius ratios R(A)/R(B) to the internal radius ratios r(A)/r(B) allowed by the structure types. Since the size change of atoms on alloying is highly correlated to how different R(A)/R(B) is from the ideal radius ratio for a structure type, the lattice parameters of intermetallic compounds can be predicted with excellent accuracy knowing R(A)/R(B). A practical application of the approach developed in our recent papers to superalloy design is presented.

Structural, Chemical Bonding, Electronic and Magnetic Properties of XY3(X = Al, Ga and Y = V, Nb, Cr, Mo) Compounds

“…Since the hardness depends on the bulk modulus, which is a function of both strength of intermetallic bonding and the rigidity of the frame work of lattice [19]. The calculated bulk modulus values listed in Tables III and IV clearly show that the compounds in conguration II have high bulk moduli as compared to conguration I.…”

“…4.93 * * Ref. [19] The bulk modulus for material can be dened as the change in pressure to the fractional volume of compression which can be written as…”

Core–Shell-Structured Low-Platinum Electrocatalysts for Fuel Cell Applications

“…Furthermore, from the reports [117,284,285,287,330,429,430], it can be seen that in cases Another outstanding advantage of AuPt bimetallic nanoparticles with alloy or core-shell structures is the significantly higher catalytic activities for CO oxidation relative to pure Pt and Au nanoparticles, suggesting that AuPt bimetallic nanoparticles are an excellent candidate for low-temperature anode electrocatalysts [110,283,432]. As stated previously, Au possesses higher electronegativity than Pt and this contact between Pt and Au atoms results in subtle net charge transfers from Pt to Au [433,434]. This subtle net charge transfer can increase the d-band vacancy of Pt sites, subsequently weakening the binding of CO on Pt sites, facilitating the removal of intermediate CO-like species and promote the anti-poisoning abilities of Pt catalysts in MORs [435,436].…”

Metallic nanoparticles for catalysis applications

“…Note pure Au NPs are not active for this reaction, there is no apparent indication of size and shape effect (Miller et al, 2006), and no change in Au-Au and Pt-Pt bond lengths (Kang et al, 2006;Mukarjee et al, 1995;Chou et al, 1976). Because of the difference in their electronegativity, mixing of Pt and Au atoms results in small but not negligible Pt-toAu net charge transfer (Rajasekharan and Seshubai, 2012;Tedsree et al, 2011;Berg et al, 1998). Such charge transfer will occur throughout the alloy NPs, modifying the electron density distribution of all atoms involved (Mott et al, 2007b,c;Ge et al, 2006;Galvagno and Parravano, 1979;Selvarani et al, 2009;Dai and Balasubramanian, 1994;Tian et al, 2006;Pedersen et al, 1999;Skulason et al, 2010).…”