Structure Of Intermetallic Compounds Research Articles

Nanocrystalline intermetallic compounds—structure and mechanical properties

Nanocrystalline intermetallic compounds (Ni 3Al, NiAl, TiAl) with crystallite sizes in the range 5–20 nm were prepared by means of an inert gas condensation technique. As-prepared nanocrystalline Ni 3Al samples (24 at.% Al) exhibited no superlattice reflection in X-ray diffraction (XRD) and transmission electron microscopy. Ordering occurred during annealing starting at 400 °C. In contrast, as-prepared nanocrystalline NiAl samples (50 at.% Al) were at least partially ordered. XRD spectra of as-prepared nanocrystalline TiAl samples (54 at.% Al) suggested that these samples consisted of a mixture of α 2-Ti 3Al and γ-TiAl. Vickers hardness measurements showed that nanocrystalline samples were substantially harder than polycrystalline indicating that grain refinement caused strengthening. Hot pressing at temperatures up to 650 °C under high vacuum conditions results in retarded grain growth compared with annealing.

Ground state structures of intermetallic compounds: A first-principles Ising model

Predictions of the equilibrium crystal structure of simple compounds, e.g., within first-principles total energy methods are usually carried out by searching for the lowest energy among a small number, O(10), of intuitively selected candidate structures. We show how calculations of the total energies of O(10) structures can be used instead to define a first-principles, multi-spin Ising Hamiltonian, whose ground state structures on a fixed lattice can be systematically searched using lattice theory methods. This is illustrated for the intermetallic compounds CuAu, CuPd, CuPt, and CuRh, for which the correct ground states are identified out of more than 65,000 possible structures.

Effect of ternary additions on the structural stability and electronic structure of intermetallic compounds: Al3Ti + Cu

The effects of substituting Cu for either Ti or Al in Al3Ti were studied by the first-principles local density self-consistent linear muffin tin orbital method. The Cu atoms are found to strongly favor Al sites and to promote the stability of the L12 phase, in agreement with experiment. Surprisingly, the rigid band model is closely followed when Cu substitutes for Al. However, the structure of the density of states undergoes remarkable changes if Cu substitutes for Ti; a much weaker hybridization occurs in both L12- and DO22-like structures, giving rise to weaker binding effects. The modification of bond directionality upon Cu addition is determined by comparing the charge density for the structures calculated with those of pure Al3Ti. The effect of tetragonal distortion is also examined. By comparing with the bonding characteristics of pure Al3Ti in the L12 and DO22 structures, the addition of Cu to Al3Ti is found to be equivalent to the tetragonal distortion in DO22 Al3Ti as far as bonding is concerned, resulting in the stabilized L12-like structure for (AlCu)3Ti. The semi-empirical inverse relation between the structural stability and the density of states at Fermi energy is well established.

Examples of linear structures of intermetallic compounds described as intergrowth of segments of simple basic structures

Examples of linear structures of intermetallic compounds described as intergrowth of segments of simple basic structures

Examples of linear structures of intermetallic compounds described as intergrowth of segments of simple basic structures

Dans le mecanisme d'intercroissance des composes intermetalliques binaires et ternaires de lanthanides ou de metaux alcalinoferreux, on a utilise pour decrire leur structure, des segments de la structure de base BaAl 4 , AlB 2 , W, Po, Cu 3 Au, CaI 2 ou des hybrides obtenus par la combinaison des deux segments de ces types. Ceci permet de representer la connexite a travers les structures. Tous les composes etudies, a une exception pres, contiennent des fragments AlB 2 , c'est-a-dire que les faces communes des prismes rhomboedriques comportant les lanthanides ou les metaux alcalinoterreux sont centrees autour des petits atomes

Magnetic anisotropy and crystal structure of intermetallic compounds of the ThMn12 structure

Intermetallic compounds of the type RE(TM1−xMx)12 with RE=Y, Er; TM=Fe, Co; M=Si, Ti, V of the ThMn12 tetragonal crystal structure have been studied by the singular point detection technique and high-resolution neutron powder diffraction in order to (a) evaluate both the rare-earth and transition-metal sublattice contributions to the magnetocrystalline anisotropy, (b) compare the Fe and Co anisotropies in the ThMn12 structure, and (c) to verify the existence of any preferential entrance in the transition metal sublattice for various stabilizing ions. The transition metal anisotropy is of the same type (Fe axial, Co planar) and magnitude as in RE2Fe14B compounds. However, there is no anomalous temperature behavior of the anisotropy field Ha. With decreasing temperature, the value of Ha increases from 21 kOe at 293 K to 37 kOe at 78 K in YFe11Ti. Similar values are obtained for other Fe-based compounds. The contribution of Er to the anisotropy is found to be surprisingly low. The anisotropy field of ErFe11Ti varies from 24 kOe at 293 K to 63 kOe at 100 K. The observed low values of the Curie temperatures in these compounds appears once again to limit their use in possible applications. Neutron powder diffraction shows that the 8j and 8f sites of the ThMn12 structure are virtually fully occupied by Fe, while the 8i site is partially occupied by Fe and V in YFe10V2.

ChemInform Abstract: Cage Structures of Intermetallic Compounds. On LaRuSn3, CeRuSn3, PrRuSn3, and NdRuSn3.

AbstractThe new title compounds have been prepared by annealing stoichiometric mixtures of the elements (argon atmosphere, 5 h to 1200 °C, 5 h to 900 °C).

Einführung in eine anorganische Strukturchemie

Abstract A systematic description and classification of inorganic structure types is proposed on the basis of homogeneous or heterogeneous point configurations (Bauverbände) described by invariant lattice complexes and coordination polyhedra; subscripts or matrices explain the transformation of the complexes in respect (M) to their standard setting; the value of the determinant of the transformation matrix defines the order of the complex. The Bauverbände (frameworks) may be described by three-dimensional networks or two-dimensional nets explicitely shown with structures types of the I- and F-family. Examples of structure types of different orders are listed for the homogeneous or pseudohomogeneous I-, P-, F-, Y**-, S-, + Y-, Q- and C-families and for the heterogeneous [I + W]-, [D + T]- and [Y(31) + Dx]-families. Homeotypic are those structure types, which replace their points of the configurations by polyhedra like dumb-bell (21), triangle (31), tetrahedron (4t), octahedron (6o), cuboctahedron (12co), icosahedron (12i) etc. forming the I[polyhedra]- P[polyhedra]- etc. families. Furthermore, layer descriptions are applied with two-dimensional nets of H, G, N, N[43243] and N[6434] with different stacking sequences and in combination with other nets. The system is proposed after the study of the cubic inorganic structure types and the structures of intermetallic compounds with tetragonal symmetry.

L'analogie des modes d'insertion et d'empilement dans les phases Nd 2Fe 14B, Mn 5SiC, et Fe 5SiB 2

The tetrahedrally close-packed (tcp) structures of intermetallic compounds are characterized by exclusively tetrahedral voids and cannot accommodate “interstitial atoms” like carbon or boron. In many transition metal compounds, boron and carbon are in trigonal prisms. As a consequence, the formation of ternary phases like Nd2Fe14B or Mn5SiC requires a deformation of close-packed structures from which these structures may be derived. The hexagonal or pentagonal antiprisms surrounded by tetrahedral interstices which characterize these complex metallic structures are systematizxcally transformed to hexagonal or pentagonal prisms surrounded by trigonal prisms. Similarly Fe5SiB2 may be derived from a hypothetical structure “Fe2Si” of type Fe2B in which the squared antiprisms surrounded by tetrahedral interstices are transformed to squared prisms surrounded by trigonal prisms.

Factors which influence the structure of intermetallic compounds

Factors which influence the structure of intermetallic compounds

Information on the structures of intermetallic compounds from Miedema's theory

We show that, notwithstanding the isotropic nature of Miedema's semiempirical theory for the heat ΔH of formation of intermetallic phases and contrary to the present view in the literature, the parameters φ ∗ and n ws used to predict the signs of ΔH can contribute quantitatively to our understanding of structural phenomena. On a ( Δφ ∗ , Δn ws 1 3 ) map considerable resolution is obtained among the binary systems in which different structure types occur, showing the importance of the energy of formation of an intermetallic compound in deciding the crystal structure that it adopts. This is demonstrated for binary systems where AsNa 3, TiNi 3 and CeCu 2 structure types exist.

The Th-Pb system and the alloying behaviour of thorium with the group IVb elements

The Th-Pb system was investigated using differential thermal, X-ray and metallographic analyses. As for the Th-Sn system, four intermediate phases were found, two of which (Th 5Pb 3 and Th 5Pb 4) were not previously known. The existence of the two compounds ThPb 2 and ThPb 3, was confirmed but no evidence was found for the formation of ThPb and ThPb 4 which have been reported in the literature. One eutectic point at about 1.0 at.% Th with a melting temperature of 310°C was determined. ThPb 3 and ThPb 2 were formed by peritectic reactions at 1100°C and 1230°C respectively. The diagram for compositions with a thorium content greater than that of ThPb 2 was proposed on the basis of a survey of other known R-Pb diagrams. A brief analysis of the existence and crystal structures of intermetallic compounds of thorium with group IVb elements is also reported.

Electronic structure of intermetallic compounds by interpolation schemes

AbstractThe applicability is studied of a d‐band LCAO interpolation scheme and of the recursion method to intermetallic compounds with CsCl structure of two transition metals. Input data are APW energy eigenvalues, needed for this purpose at only a few points of high symmetry in the Brillouin zone. The interpolation scheme works with an accuracy that is sufficient for calculating densities of states, but works much faster than the APW calculation. From the LCAO hopping parameters local densities of states are obtained with the recursion method.

Relationships between intermetallic compound structure and hydride formation

The structures of four families of intermetallic compounds are analyzed in terms of the number, sizes, positions and symmetry properties of tetrahedral interstitial holes. The structure types considered are hexagonal AB 5 (D2 d), cubic AB 2 (C15), hexagonal AB 2 (C14) and orthorhombic AB (B f). Holes and clusters of holes are considered in terms of their suitability for hydrogen occupancy in the formation of intermetallic compound hydrides. In the cases of the hydrides LaNi 5H 6 and LaCo 5H 4, the parent hexagonal structure P6/ mmm is changed on hydriding to trigonal P31 m in the former case and to orthorhombic Cmmm in the latter case. The symmetry changes that correspond to these transformations are shown to be directly related to the amount of hydrogen absorbed; i.e. some potential sites in the parent compound are retained and others are not, depending on the structural change. In those cases where structural data for the hydride phases are not available or where the parent structure does not change on hydriding, it is shown that reasonable estimates of the extent of hydrogen absorption can be made based on the number and the sizes of available holes or hole clusters in the parent compound.

Calculations of bandstructure of intermetallic compounds using the multiple scattering Xα cluster method and k dependent boundary conditions

The spherical Wigner-Seitz boundary condition (1933, 1934) for approximately treating electronic states in solids by atomic calculations can be readily extended to include molecular clusters. If, in addition, matching conditions for cluster wavefunctions at the outer sphere radius R are taken to be wavevector dependent, some approximate representation of the energy bands En(k) is obtained. The self-consistent multiple scattering (SCMS) X alpha method with modified boundary conditions has been applied to calculations of the electronic structure of Cu metal and Al2Au and Al2Cu alloys. The results for Cu agree well with SC X alpha bandstructures, as to bandwidths and positions, giving quite reasonable density of states (DOS) curves. The cluster DOS are compared with X-ray emission and photoelectron (ESCA) spectra of the alloys. The results show that the model can describe the main features of electronic structure of intermetallic compounds, with very little computational effort.

Relationships between intermetallic compound structure and hydride formation

Relationships between intermetallic compound structure and hydride formation

Electronic structure of intermetallic compounds with CsCl structure: NMR relaxation times

NMR relaxation times T1 and T2 at the Sc and La sites have been measured in a series of intermetallic compounds ScB (B=Cu, Ag, Pd, Rh, Ir, Ru) and LaAg. The product (T1T) is constant for temperatures between 30K and 300K. Below 30K an influence of magnetic impurities on the susceptibility and spin-lattice relaxation time measurements has been found. The analysis for the electronic structure is given in terms of local susceptibilities based on these T1 measurements and in terms of a two-band model.

Electronic structure of intermetallic compounds with CsCl structure

Susceptibility, specific heat and Knight shift measurements as well as bandstructure calculations have been made for intermetallic compounds of the CsCl structure, ScB (where B is Ag, Cu, Pd, Rh, Ir, Ru), YRh and LaAg, to study the influence of filling the d shell of atom B. An analysis is given which yields quantitative results for the local susceptibilities, as characterized for the different angular momenta and sites of origin.

Influence of repulsive energy on structural parameters of close-packed metal structures

Observed values of the c a ratios and of the atomic parameters of closepacked structures of intermetallic compounds having a composition XZ 3 and T-type order in the layers, are accounted for fairly accurately with the aid of a simple model involving short-range repulsive energy between nearest-neighbour atoms exclusively. The influence of the radius ratio of the constituent atoms on the stacking sequence of the layers in the compounds is also discussed with the aid of the model. In the Appendix, crystal structure data are given for the trialuminides XAl 3 ( X = La, Gd, Th, Y and Ho), and for Ce 3Al. The data were obtained by a least-squares refinement of powder X-ray diffraction data.

Crystal and Magnetic Structure of Intermetallic Compounds of the Type Th(CoxFe1−x)5

The series Th(CoxFe1−x)5 was investigated by means of neutron diffraction. All compounds investigated (x = 0, 0.2, 0.4, 0.6, and 1.0) were found to crystallize in the hexagonal CaCu5 type of structure. Their lattice constants were determined at 4.2 K as well as at room temperature. It is shown that only part of these compounds are true ferromagnets. For the compounds with x = 0 and x = 0.2 antiferromagnetic cimponents are also present, leading to a doubling of the magnetic unit cell. For all compounds investigated the magnetic structure is given in detail. Die Th(CoxFe1−x)5-Serie wurde mit Neutronenbeugung untersucht. Alle untersuchten Verbindungen (x = 0; 0,2; 0,4; 0,6 und 1,0) kristallisieren in der hexagonalen CaCu5-Sturktur. Ihre Gitterkonstanten wurden sowohl bei 4,2 K als auch bei Raumtemperatur bestimmt. Es wird gezeig, das nur ein Teil dieser Verbindungen echte Ferromagnete sind. Fur die Verbindungen mit x = 0 und x = 0,2 sind antiferromagnetische Komponenten anwesend, die zu einer Verdopplung der magnetischen Elementarzelle fuhren. Fur alle untersuchten Verbindungen wird die magnetische Struktur ausfuhrlich angegeben.