J.H.N. van Vucht

Martensitic transformations in gold-titanium, palladium-titanium and platinum-titanium alloys near the equiatomic composition

Abstract Alloys of compositions near AuTi, PdTi, and PtTi are B19-type orthorhombic at room temperature and, at higher temperatures, have an ordered CsCl-type structure (B2-type). The martensitic transformations involved were studied by X-ray diffraction. The composition dependence of the martensitic-transformation characteristics, such as Ms, Mf, As and Af-temperatures, were determined. Lattice constants of the high-temperature phases are given.

Note on the crystal structure of the ternary rare earth-3d transition metal compounds of the type RT4Al8

Abstract The occurrence and crystal structures of ternary compounds of the composition RT 4 Al 8 (T = V, Cr, Mn, Fe, Co, Ni or Cu, R = rare earth, Y or Th) have been investigated. The various effects of the atomic sizes are discussed.

THE STRUCTURES OF THE RARE-EARTH TRIALUMINIDES

Abstract An extensive study has been made of the trialuminides of the rare-earth metals. In addition to showing the existence of several Ni3Sn-type trialuminides hitherto unknown (those of Ce, La, Pr and Nd) the detailed structures are given of a number of rhombohedral trialuminides (those of Y and Tb which are isotypic with BaPb3, and those of HoAl3 and DyAl3 which both have the HoAl3 type of structure). These structures, together with the Ni3Ti type, encountered with the ternary trialuminides (Gdx, Er1−x)Al3 and (Yx, Er1−x)Al3, and also the PuAl3 type form a family of transition structures between the Ni3Sn and the Cu3Au types. As the rare-earth/Al radius ratio decreases the trialuminides adopt structures passing from predominantly hexagonal to predominantly cubic, subject to the two rules that the layer repeat period of the lattice tends to be a minimum and that the alternation of hexagonal and cubic stacking is a maximum.

Atomic-environment classification of the cubic “intermetallic” structure types

Abstract In this paper we give a complete description of the geometrical atomic environments found in the structure types of the cubic intermetallic compounds. Our analysis of 172 structure types which have been reported in the literature showed that 128 are geometrically possible, while the remaining 44 structure types have improbable interatomic distances. We have classified all point sets of these structure types in terms of the realized geometrical atomic environments and give rules for the analysis as well as the classification. In our systematic and comprehensive analysis of the cubic structure types we have verified all known relationships between these structure types, but the analysis also revealed new non-trivial relationships. In addition, we observed that 21 atomic environment types are strongly preferred. Out of 13 917 point sets investigated, 12 790 (92%) belong to one of those 21 atomic environment types. Of the 5521 compounds crystallizing into one of the 128 structure types, 46% belong to a single-environment group (structures in which all atoms have the same type of environment), 37% combine two environment types, 9% have three environments and the rest (8%) have four or more environments.

On the crystal structures of some compounds of gallium with potassium, rubidium and caesium

Abstract The atomic structures of CsGa 7 and CsGa 3 are given together with some raw data for two more Cs-Ga phases. A better structure description for RbGa 7 , analogous to that of CsGa 7 , is proposed. A region of existence for KGa 3 is reported.

Phase equilibria and superconductivity in the molybdenum-platinum system

Abstract The phase diagram of the Mo-Pt system was determined by X-ray diffraction methods, metallographic techniques and the direct observation of melting phenomena. Seven single-phase regions were observed: terminal b.c.c. Mo solid solution, A15 (β-W)-type Mo6Pt, disordered h.c.p. Mg type, ordered Mg3Cd — type Mo3Pt2, ortho-rhombic MgCd-type MoPt, orthorhombic MoPt2 and a terminal f.c.c. pt solid solution. Particular attention was paid to the nature of formation of the A15 phase.

The crystal structure of La2Ni3

Abstract The crystal structure of the compound La2Ni3 has been determined from X-ray powder diffraction data. La2Ni3 is orthorhombic, space group Cmca (no. 64). The lattice constants are a = 5.113 8 A , b = 9.731 6 A and c = 7.907 5 A . The unit cell contains four formula units La2Ni3. Atomic position parameters were obtained by a refinement procedure. La2Co3 has the same type of structure.

The crystal structures of Eu3Ag2, EuAg and EuCu

Abstract The crystal structures of the compounds Eu3Ag2, EuAg and EuCu were determined by means of X-ray diffraction on powder samples. The compound Eu3Ag2 crystallizes in the tetragonal U3Si2 structure. The lattice constants are a = 8.461 A and c = 4.515 A . The compound EuAg crystallizes in the orthorhombic FeB structure. The lattice constants are a = 8.037 A , b = 4.764 A and c = 6.259 A . The crystal structure of the compound EuCu was found to be isotypic with that of EuAg. For EuCu the lattice constants are a = 7.980 A , b = 4.424 A and c = 6.049 A .

Superconductivity of NbSn2

In the course of investigations on the Nb/sub 3/Sn phase diagram, a new superconductive intermetallic compound was found with the composition NbSn/sub 2/ and having a critical temperature of 2.60 deg K. A short description is given of the preparation of NbSn/sub 2/, and the results of measurements of the resistance transition and critica1 field are preserted. (H.D.R.)

The Ceto getter—its chemical structure and hydrogen gettering properties

Abstract Ceto, which is an alloy of thorium, mischmetall and aluminium is used as a non-evaporating getter. In the course of an elaborate investigation of the ternary system Th-Ce-Al, it has been proved that its crystallographic structure is of the CuAl 2 type, just like the closely related binary compound Th 2 Al. The properties of the Th 2 Al, Ceto and intermediate compounds with regard to hydrogen were studied. X-ray and neutron diffraction, supplemented by nuclear magnetic resonance measurements, each at liquid nitrogen temperature, and room temperature, gave information about the structure of the reaction products. Hydrogen equilibrium-pressure measurements at temperatures from 250°C up to 700°C gave thermodynamic information and enebled to calculate the equilibrium pressures at lower temperatures. A kinetic study, based on a simple model, of an autocatalytic sorption is reported.