Clara Brink Shoemaker

A ternary alloy with PbCl2-type structure: TiNiSi(E)

Abstract : Beck and coworkers have found E phases in several ternary systems of transition elements with either silicon or germanium at the composition 1:1:1. The crystal structure of TiNiSi(E) has been determined and refined by least squares with (limited) three-dimensional single-crystal data to a final R value of 0.086 (excluding 002 due to apparent extinction, and all nonobserved reflexions). The lattice parameters for the primitive orthorhombic cell are: a sub 0 = 6.1484=0.0012, b sub 0 = 7.0173=0.0014, c sub 0 = 3.6698=0.0007 A. The E phase is isotypic with PbCl2(C23), space group Pnam. All near-neighbor distances are within 0.06 A of the following average values: Ti-Ti 3.18, Ti-Ni 2.83, Ti-Si 2.61, Ni-Ni 2.67, Ni-Si 2.33 A. The numbers of nearneighbors are compared with those in Co2Si, theta Ni2Si and U3Si2. (Author)

Concerning atomic sites and capacities for hydrogen absorption in the AB2 Friauf-Laves phases

Abstract There is considerable confusion in the literature concerning the maximum number of hydrogen atoms per AB2 that can be absorbed by the C15 and C14 Friauf-Laves phases (variously reported as 5.125 and 7). If all the tetrahedral sites are independently available to hydrogen, the number could approach 17; since, in practice, it rarely exceeds five, we assume that one or more limiting principles operate. The one that we discuss here is assumed to be mainly electrostatic and to be due to electron transfer resulting from electronegativity differences between the hydrogen and metal atoms. Assuming the operation of an exclusion rule which states that two tetrahedra with a face in common may not both contain hydrogen atoms at their centers, after an exhaustive model study we find a maximum occupancy of six hydrogen atoms per AB2 in C15 and of 6 1 3 in C14. Two attractive models accommodating six hydrogen atoms (one for C15, the other for C14) are examined in some detail and the possible implications of these and related models with respect to the step-function absorption model of Jacob, Shaltiel and coworkers is discussed. The possible occupation of triangle sites is discussed briefly.

Neutron diffraction studies of the cubic ZrCr2Dx and ZrV2Dx (Hx) PHASES

Abstract Deutendes of ZrCr 2 and both hydrides and deutendes of ZrV 2 were studied by neutron diffraction in order to determine the relative occupancies of the different types of tetrahedral sites existing in the C15 Friauf-Laves phases. In ZrV 2 , within the range of stoichiometry used, both Zr 2 V 2 and ZrV 3 sites are occupied by deuterium with the relative occupancies depending on the total absorption. In ZrCr 2 only the Zr 2 Cr 2 site is progressively filled until the formula approaches ZrCr 2 D 3.5 , near the experimental limit of absorption, at which point a minor amount of deuterium may enter ZrCr 3 sites.

The crystal structure of NbCoB

(i) two strong water-thiosulphate oxygen hydrogen bonds, O(4)-H(1) . . .0(3) (2.73 A) and O(5)-H(3) . . .0(3) (2.77 ,~), (ii) two weak water-thiosulphate oxygen hydrogen bonds, O(4)-H(2) . . .0(2) (2.94 A) and O(5)-H(4) . . .0(3*) (2.81 A) , (iii) two water-water oxygen hydrogen bonds O(6)-H(5) . . .0(4*) (2.73 A) and O(7)-H(8) . . .0(8*) (2.79 A) , (iv) three water-sulphur hydrogen bonds, O(6)-H(6). . .S(I*) (3.30 A) O(7)-H(7): . . S(I*) (3.13 A) and O(8)-H(10).. .S(1) (3.40 A) .

On the relationship between μ-MnAl4.12 and the decagonal Mn–Al phase

Abstract The structure of μ-MnAl4.12 is presented in layers perpendicular to a pseudo fivefold axis. Similarities with 2D Penrose tiling and structures proposed for decagonal Mn–Al are described. Modifications of existing models for the decagonal Mn–Al phase are proposed which take into account the distances between the atoms and the packing principles as displayed in the μ phase.

Neutron Diffraction Studies of the Order of the Atoms in the P Phase and the R Phase

Abstract : The ordering of the atoms in two ternary alloys, P phase (Mo-Ni-Cr) and R phase (Mo-Fe-Mn), both structurally related to the sigma phase, has been studied by powder neutron diffraction. The at.% Mo on each site was taken to be approximately that determined in previous X-ray single-crystal studies, which showed that Mo preferentially occupies CN16 and CN15 sites. From the best fit between observed and calculated neutron diffraction diagrams it is apparent that, in the P phase, Ni preferentially occupies CN12 positions. In the R phase, Mn shows only a slight preference for CN14 and CN15 positions over CN12 positions when competing with Fe. The results are consistent with those of ordering studies of related transition element intermetallic compounds. (Author)