M.L. Fornasini

Rare-earth intermediate phases with zinc

Abstract The existence and the structure of the rare earth-zinc intermediate phases in the range 75–88 at.% Zn has been investigated: the compositions MZn3, M3Zn11, MZn4, M13Zn58, MZn5, M3Zn17 and M3Zn22 were examined. A part of the Er-Zn system has been studied by differential thermal analysis. The different types of structure occurring in these intermetallic phases were correlated through the coordination number of the component atoms. The trend of the rare-earth coordination number appears to be related to the existence of ranges of the different phases. In the series of isomorphous compounds, the known, linear dependence of the lattice dimensions upon the rare-earth trivalent ionic radii is confirmed.

CrB-type equiatomic compounds of europium, ytterbium and alkaline-earth metals with Si, Ge, Sn, Pb

Abstract Some MX compounds of Eu and Yb with Si, Ge, Sn, and Pb have been prepared together with the corresponding compounds of the alkaline-earth elements. The crystal structures of YbSi, EuSi, BaSi, EuGe, SrGe, BaGe, EuSn, SrSn, BaSn, and SrPb have been determined. These compounds crystallize with the CrB structure type and their lattice constants, atomic parameters and interatomic distances are reported.

Rare-earth intermediate phases with cadmium.

Abstract The behaviour of all rare-earth metals with cadmium has been studied for the following compositions: MCd 3 , MCd 4 , M 2 Cd 9~ , MCd 6 and M 2 Cd 17 . The crystal structure of these phases has been determined together with that of ThCd 11 . A survey of all R.E.-Cd intermetallic compounds is given. Structural and geometrical relations among the types of structure occurring are examined.

The gadolinium-cadmium system

Abstract The gadolinium-cadmium equilibrium phase diagram has been established by differential thermal-, chemical-, metallographic- and X-ray analyses. Besides the already known intermediate phases (GdCd, GdCd 2 , GdCd 6 ), three other compounds were found: GdCd 3 (Ni 3 Sn-type), GdCd 4~ (γ-brass type) and Gd 2 Cd 9~ (Gd 13 Zn 58 or Pu 2 Zn 9~ -type). No solid solubility range was observed around the intermediate phases. Only GdCd melts congruently (1170 °C). Cd forms a solid solution with Gd, lowering the α-β transformation of the rare-earth metal from 1238 ° to 725 °C (at ~ 15 at.% Cd). Microhardness, density and magnetic susceptibility were also measured on single phase specimens.

Re-examination of the CaGa system and crystal structure of CaGa4, a monoclinic distortion of the BaAl4 type

Abstract The gallium-rich region of the CaGa system (64.9 – 84.6 at.% Ga) was re-examined by X-ray methods. In addition to the CaGa 2 phase with the CaIn 2 structure type, another phase, CaGa 2 + x , was found in a limited homogeneity range, being 0.1 ⩽ x ⩽ 0.4, with crystal structure derived from the AlB 2 type. The mechanism of solid solubility formation was clarified by single crystal refinement. The new phase Ca 3 Ga 8 was identified by powder diffraction data as isotypic with Eu 3 Ga 8 . The structure of CaGa 4 , determined by single crystal methods, can be described as a new monoclinic distortion of the BaAl 4 type, related to the low temperature form of CaAl 4 . Crystal data of the nine intermediate phases present in the CaGa system are given and a revised form of the phase diagram is proposed.

Crystal structure of the ternary R.E.Mo2Al4 phases (R.E. = Gd, Er, Yb)

Abstract The crystal structure of the ternary phase YbMo 2 Al 4 , space group I 4 mmm ,a = 6.717 and c= 5.312 A , Z = 2 , has been determined. GdMo 2 Al 4 and ErMo 2 Al 4 have been found to be isomorphous. The close structural relationship between these phases and the ternary MT 4 Al 8 ( M = Ce , Y ; T = Cr , Mn , Fe , Cu ), crystallizing in a superstructure of the ThMn 12 type, is pointed out.

Crystal structure of the so-called R.E.5Pd2 compounds

The crystal structure of Dy5Pd2 has been determined using single-crystal photographic data. The compound is cubic, a = 13.529 A, space group Fd3m, and the elementary cell contains 68 Dy and 28 Pd atoms with three crystallographic sets partially filled. The R.E.5Pd2 compounds, where R.E. = Tb, Ho, Er, Tm, LuandY, are isotypic with Dy5Pd2, and their lattice constant values are reported.

The crystal structure of the Ba7AL13 phase

Abstract The crystal structure of the intermediate phase known as BaAl2 has been determined and its composition established; this corresponds to Ba7Al13 and the phase crystallizes in the trigonal space group P 3 m1 with the lattice constants: a = 6.099 ± 0.002, c = 17.269 ± 0.006 A . The atomic arrangement appears to be closely related to that of the Laves phase polytype, MgNi2. The influence of the electron concentration on the stability of the Ba7Al13 phase has been examined by partial or total substitution of Al atoms, but evidence of the AlB2-type of structure was found in every case (BaAl1.5-Si0.5, a = 4.37, c = 5.14 A ; BaZnSi, α = 4.388, c = 4.841 A ).