AuCu, type

Remarks on the alloy crystal chemistry of the 4th group metals. Selected groups of isostructural phases, pertaining to simple common structural types have been collected in Table 5.25. A number of them (for instance CsCl, AuCu types, Laves phases, AuCu3 type) correspond to more or less extended solid solution... 

Several 1 1 compounds with CsCl, AuCu-type structures are formed especially with metals close to the end of the transition series and with semi-metals and non-metals of the 15th and 16th groups. 

Rh and Ir alloys. A choice of formulae, composition ranges and structure types observed in selected intermediate phases of the Rh and Ir alloys is shown in Table 5.48b. Notice in the Rh (Ir) regions of the systems, several CaCu5-, AuCu3-, Cu2Mg-type phases and, in the central parts of the diagrams, CsCl-type (andNiAs-and AuCu-type) solid solutions phases. 

Nucleobases, including 9-methyl-, 9-ethyl-, 1,9-dimethyl-guanine and 2-amino-6-methoxy-9-methylpurine, form complexes of the type Au(N)Cl3 when reacted with [AuCU] in water at pH 3—4. Binding of a AuCh unit to the N (7) position of the purine ring was confirmed by X-ray crystallography [26]. 

Even when complete miscibility is possible in the solid state, ordered structures will be favored at suitable compositions if the atoms have different sizes. For example copper atoms are smaller than gold atoms (radii 127.8 and 144.2 pm) copper and gold form mixed crystals of any composition, but ordered alloys are formed with the compositions AuCu and AuCu3 (Fig. 15.1). The degree of order is temperature dependent with increasing temperatures the order decreases continuously. Therefore, there is no phase transition with a well-defined transition temperature. This can be seen in the temperature dependence of the specific heat (Fig. 15.2). Because of the form of the curve, this kind of order-disorder transformation is also called a A type transformation it is observed in many solid-state transformations. 

Because strings of the same atoms come to be adjacent when these layers are stacked, alternating layers of atoms of one kind each are formed. These layers are planar in AuCu they are inclined relative to the plane of the paper in the unit cell (Fig. 15.1) they are parallel to the base plane. The layers of equal atoms are undulated in the other two structure types. 

A first group of superstructures, described in several paragraphs of this chapter and of Chapter 7, must be mentioned these include the types tP2-AuCu(I), cP4-AuCu3 and tP4-Ti3Cu which can be considered face-centred cubic-based substitutional ordered superstructures. 

This structure can be considered a superstructure of the AuCu(I) type with 1N atom inserted in an octahedral interstice. This structure, as the previously described cP5-Fe4N type, can be considered an interstitial ordered phase. 

A special case of long-period structure to be considered is the oI40-AuCu(II) type structure which has ID substitutional and displacive modulations (Fig. 3.41). We must first mention that ordering of the Au-Cu face-centred cubic (cF4-Cu type) solid solution, having a 50-50 atomic composition, re-distributes Cu and Au atoms... 

Figure 7.26. Section sequence parallel to the base plane of the tP2-AuCu (I) type structure. A tP4 pseudo-cell is outlined by dotted lines.

A special type of modulated superstructure (long-period superstructure) is known for AuCu (AuCul) and results in the oI40-AuCu (II) type. This antiphase-domain structure has been discussed in 3.11.1 (Fig. 3.41). 

This structure can be described as a tetragonal distortion of the AuCu3-type structure. It may also be considered a variant of the previously described AuCu( I) type (compare with its tP4 pseudo-cell). 

Figure 7 The unit cells of alloy phases of interest as high-temperature structural intermetallics their structure types are (a) NiA.1 CsCl (cP2, B2) type (b) TisAl NijSn (hP8, DO 19) type (c) NisAl CusAu (cP4, LI2) type (d) TiAls TiAls (tI8, DO22) type (e) TiAl AuCu (tP4, LIq)) type...

The thioether complexes of the type [AuCl(SR2)] are useful synthetic intermediates and prepared by the reaction of [AuCU] with the corresponding diaUcylsulfide according to equation (5). 

Tetrakis(acetylacetonato) complexes of zirconium and hafiiium were reported in 1904 and 1926, respectively, and a large number of j3-diketonate derivatives have been described subsequently (Table 10). These compounds are of the type [M(dik)4], [M(dik)3X], [M(dik)2X2], M(dik)X3 and [M(dik)3]Y (dik = -diketonate anion X = C1, Br, I, NO3, or alkoxide Y = [FeCU], [AuCU], [PtCU] or 2[Zr(S04)3]). Additional j3-diketonate compounds include the anionic complex [NEt4][Zr(bzbz)F4] (bzbz = dibenzoylmethanate) and the 1 1 ZrCU-diketone adducts [ZrCl4(MeCOCR2COMe)] (R = H or Me). " Early work on zirconium and hafnium jS-diketonates has been reviewed by Larsen, Bradley and Thornton, Fackler and Mehrotra et al. ... 

The Ca-Pb phase diagram has been determined by thermal and X-ray methods. It contains four compounds, of which two melt congruently [CajPb (m.pt. 1476 K) and CaPbs (m.pt. 939 K)], the others decomposing peritectically [CajPba (d., 1400 K) and CaPb (d, 1241K)]. The crystal structures of CajPb, CajPbs, and CaPbg were confirmed and CaPb was found to crystallize with the AuCu-I type structure unit-cell parameters are collected in Table 1. The two eutectics occur at 90.5 mol % Ca (1023 K) and 36.5 mol % Ca (911 K). ... 

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