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Ternary samples with the composition Yb(Cu,Ag,Au,Pd,Pt) x Ga 4 - x have been synthesized from the elements by high frequency melting followed by heat treatment at 600 °C. The crystal structure of all compounds was investigated using X-ray single-crystal or powder techniques and belongs to the BaAl 4 type of structure. The homogeneity regions of the Yb(Cu,Ag,Au,Pd,Pt) x Ga 4 - x phases have been established from X-ray powder diffraction analyses and lie in the range x = 0.30 –0.95 for Cu, 0.25 –0.43 for Ag, 0.22 –1.45 for Au, 0.23 –0.65 for Pt and near x = 0.25 for Pd. The unit cell dimensions vs. composition reveal a significant deviation from Vegard's rule for Cu and Au and a slight deviation for Ag and Pt. A partially ordered occupation of the 4 d and 4 e sites in the BaAl 4 structure type has been found depending on the M/Ga ratio in the homogeneity range. The weak temperature-dependent paramagnetism of these compounds is due to the non-magnetic ground state of ytterbium (Yb 2+ ). However, for YbPt 0.5 Ga 3.5 a rather intermediate valence behaviour (Yb 2+ → Yb 3+ ) is encountered.

The crystal structure of Co4Al13 has been investigated using metallography, X-ray single crystal and powder diffraction methods. A sample with the composition Co24Al76 has been synthesized in a high frequency furnace and heat treated at 850 °C to achieve homogenization. The crystal structure of Co4Al13 belongs to a new structure type: Pearson's symbol, oP102; space group, Pmn2 1 ; a = 8.158(1) A , b = 12.342 (1) A , c = 14.452(2) A ; V = 1455.1(5) A ; Z = 6 . The final value of the reliability factor is 0.0618 for 839 symmetry-independent reflections ( &|;F&|; > 4σ(F) ) with isotropic extinction and anisotropic thermal displacement coefficients. The shortest interatomic distances are those of CoCo (2.86 A), CoAl (2.24 A) and AlAl (2.24 A). The coordination numbers of the atoms are 8–11 for Co and 9–13 for Al. The structure of Co4Al13 is built from the same structure segments as Fe4Al13 but differs from that of Fe4Al13 by the stacking sequence (numeric symbol 12 for Co4Al13 and ∝ for Fe4Al13). In both structures, pentagonal “channels” occur. The atoms with pentagonal-prismatic or icosahedral environment are located on the axes of these channels.

Unit cell parameters and macroscopic densities were measured for gadolinium-rich (xH 2/3) of the dihydride GdH2+x (defect CaF2 type). The experimentally determined values of the number of atoms in the unit cell are consistent with the results of earlier work on some dihydrides REH2+x isotypical with CaF2. It was concluded that for the hydrogen-rich compositions, the excess hydrogen atoms occupy the Wyckoff (octahedral) position (b) of the space group Fm3m, whereas for the gadolinium-rich compositions vacancies occur on the hydrogen sites (c). The gadolinium sites (a) remain occupied fully by gadolinium atoms in the homogeneity range of the gadolinium dihydride. A set of powder diffraction data was obtained for GdH2.

The structure of the ternary phase Co 3 Al 8 Ga, Pearson symbol oI 96, space group Immm , a =12.0081(7) A, b =7.5701(6) A, c =15.394(1) A is isotypic with Co 2 NiAl 9 . Powder diffraction data are reported for this ternary intermetallic compound. Using liquid quenching, the metastable pseudoternary decagonal phase d -Co(Al, Ga) 3 ( m ) was obtained in the aluminium-rich portion of the ternary system Co–Al–Ga. Gallium substitutes for aluminium atoms in the d -Co(Al, Ga) 3 ( m ) phase up to a mol fraction x Ga =0.10. In the phase of the binary system Co–Al richest in aluminium, Co 2 Al 9 , the aluminium atomic positions can be occupied by gallium up to a gallium content of x Ga =0.05.

Two different types of lattice distortion are observed in the platinum-rich phases with aluminium, gallium and indium. While in the binary phases Pt 3 Al(l) and Pt 3 Ga(l) (homeotypic with the Ir 3 Si structure), the tetragonal substructure lattice distortion shows the values c / a >1, the ternary platinum-based representatives of the CuAu type significantly show the values of the axial ratio c / a ≪1. This tetragonal lattice distortion increases with increasing valence electron concentration. No continuous solid solution between the homologous isostructural phases Ni 3 Al and Pt 3 Al(h) was found either by means of rapid liquid quenching or by heat treatment of the alloys Ni 0.75− x Pt x Al 0.25 . The ternary phase NiPt 2 Al (CuAu type) occurs in the composition range 0.37≤ x Pt ≤0.50. Structural and powder diffraction data are presented for the ternary phases NiPt 2 Al, Pt 2 CuAl and Pt 2 CuGa (CuAu type).

X-ray high-temperature powder diffraction investigations were made in situ on the aluminide TiAl 2 (Pearson symbol tI 24, space group I 4 1 / amd , HfGa 2 type) in the temperature range 20–763°C. The unit cell parameters and the unit cell volume increase linearly with temperature, whereas the axial ratio c / a hardly changes with temperature. Metallographical and X-ray powder diffraction investigations on the heat-treated and subsequently quenched alloys show that TiAl 2 is stable up to 1200°C. In the as-cast alloy TiAl 2 , a metastable orthorhombic modification TiAl 2 (m) has been observed ( oC 12, Cmmm , ZrGa 2 type). X-ray powder diffraction data for the stable TiAl 2 modification are presented.

The unit cell parameters of the trihydride GdH3 (Pearson symbol hP24, space group P3c1, HoH3 type) were determined employing Guinier powder diffraction patterns. The structure of the interstitial compound GdH3 is formed by departing from a hexagonal close-packed substructure of gadolinium and by filling its tetrahedral and triangular atomic positions with hydrogen atoms. The occupation of interstitial atomic positions in the hexagonal close-packed structure causes lattice dilatation associated with a significant change of the axial ratio c/a. In the intermediate phases of the binary system Gd–H, the interatomic distance between gadolinium and hydrogen atoms, dGd–H, decreases with increasing hydrogen content; the shortest dGd–H distance was observed to occur in GdH3. A set of powder diffraction data was obtained for GdH3.

Ni3Al4 is a representative of the Ni3Ga4 type structure, an ordered variant of the defect CsCl type structure. X-ray powder diffraction data are given. The phase transformation NiAl → Ni3Al4 was studied by means of X-ray diffraction, metallography and scanning electron microscopy. The phase diagram for the concentration range Ni50Al50-Ni20Al80 is shown. The relationship between the homeotypic structures NiAl, Ni3Al4 and Ni2Al3 in addition to some other brass-like structures is discussed from the point of view of the validity of Norbury's rule.