Volume 119, Issue 5-6

Concerning the final stage of the crystal growth of electrolytic nickel, copper and gold films it can be shown that a certain preferred orientation is always connected with a special characteristic crystal shape at the surface of the electrolytic films. Using electron-microscope replicas it is seen that in the case of (211) and (110) orientation twinned crystals are predominant and probably responsible for the development of the special one-degree-orientation. The twinning can be deduced from the extra reflections found in the reflection electron diffraction diagram. These extra reflections do not belong to an hexagonal phase as reported in the literature. In addition the existence of twins is demonstrated by means of electron-microscope dark-field image and small-area diffraction technique. These techniques also prove the presence of “crystals” with a “five-fold” rotational symmetry explained by a double twinning mechanism. The correlation of preferred orientation and a typical characteristic crystal shape existing in spite of quite different production conditions and different face-centered cubic metals is explained by the assumption of a common growth mechanism for electrolytic deposition and condensation from vapor.

An x-ray analysis of the crystal structure of barium hydroxide octahydrate has been carried out by two-dimensional Fourier methods. The monoclinic crystals belong to the space group P 2 1 / n and have four formula units in a cell of dimensions a = 9.35 Å, b = 9.28 Å, c = 11.87 Å with β = 99°. The R factor for 1020 visually observed reflections in eight zones is 0.124. The barium ion in this structure is found to be coordinated by eight water oxygens in the form of a slightly distorted Archimedean antiprism at distances between 2,69 Å and 2.77 Å. Based on the interatomic distances hydrogen bonds have been proposed, which link the oxygen atoms with one another utilising all the hydrogen atoms in the unit cell.

The crystal structure of zinc metaborate has been determined by single crystal x-ray methods. The crystals have cubic symmetry with a = 7.48±0.01 Å, space group I [unk]3 m , and two molecules in the unit cell. A complete set of atomic parameters has been determined by Patterson and electron-density projections and the final parameters have been refined by ( F o – F c ) syntheses. The structure has all boron atoms in four-fold coordination. All these tetrahedra are linked to each other forming a three-dimensional framework. The zinc ion lies inside of a tetrahedron whose corners are occupied by three oxygen atoms of the metaborate ion and a free oxygen atom.

Streaked reflections have been observed in photographs of some twinned crystals of the compound [Zn(N 2 H 4 ) 2 ]Cl 2 . Systematic absences of streaks are explained by finding geometrical relations at the boundary layer between lattices of two individuals of the twin. By referring both individuals to the same axial system, matrices for vector transformation in direct space from one individual to the other have been found in all the three twin laws observed. The treatment has been extended to polysynthetic twins. Rules are given for finding vectors common to all the individuals. Existence of common vectors is conditioned by the geometry (obliquity) of the unit cell and by the displacement of the individuals. From relations between direct lattices, vectors in reciprocal space are derived and reflections corresponding to sharp spots easily recognized. Geometrical relations between unit-cell constants, which had been indicated as causes of twinning, have been shown to be very important in determining diffraction effects of x-rays in twinned crystals.

An electron-diffraction study was made of the structure of deposits of NaF condensed in vacuum on to polished stainless steel and on fresh NaCl cleavage faces. The structure of co-deposits of Nacl and NaF on polished stainless steel was also studied. The observed stages of development of the NaF deposits were similar to those found in the case of NaCl under the same conditions, by R amos and W ilman and which were described in a previous paper. The effect of the atmospheric moisture was not so marked as in the NaCl deposits. Epitaxial growth of NaF deposits condensed in vacuum on to fresh cleavage faces of NaCl was found even in deposition on substrates virtually at room temperature, as well as when this was initially at 200°C. The experiments made with simultaneous condensation of NaCl and NaF in vacuum on stainless steel show that the cell dimensions of both materials in the co-deposits agree closely with those of the materials when they were deposited individually, and moreover the “reflection” patterns show that the crystals in the co-deposit have the same orientation as in the separate deposits. However the cell dimensions obtained for the NaF is slightly larger than that found by Swanson and Tatge with x-rays. It appears, therefore, that there was little or no formation of solid solutions of NaF and NaCl, each kind of crystal growing in the same manner as when the other material was absent.

The structure of an authigenic maximum microcline from the Pontiskalk limestone, Switzerland, has been refined to an R value of 8.5% by a full-matrix least-squares program using 797 observed and 207 unobserved reflections. The ordering of tetrahedral Si,Al atoms is nearly complete and there is no significant structural difference from an igneous maximum microcline. The crystal is considered to have grown very slowly at a low temperature within the stability field of the fully ordered phase.

Tetrahedrite, Cu 12 Sb 4 S 13 , has a curious superstructure based on the sphalerite arrangement. This structure was proposed by P auling and N euman in 1934 on the basis of a limited number of measured intensities. Least-squares refinement in this study reduced an initial disagreement index of 27.9% to 3.9% and thus confirmed the correctness of the structure. The absolute configuration of the structure was established. Tetrahedrite contains two sorts of copper atoms. A first type is coordinated by four sulfur atoms at 2.342 Å which form a nearly regular tetrahedron. The second type of copper atom is in an unusual triangular coordination, being bonded only to one sulfur atom at 2.234 Å and two at 2.272 Å. This group is planar, and the copper atom has a highly anisotropic thermal motion. The antimony atom is bonded to three sulfur atoms at 2.446 Å, which form bond angles of 95° 8′, but has six additional sulfur neighbors at the van der Waals distance of 4.033 Å. The polyhedra are linked in a complex manner which is discussed in detail.

The six complex hexagonal and rhombohedral layer structures known as hexagonal ferrites can be derived by stacking three building-block types, S , R , and T , having 2, 3, and 4 anion layers, respectively. The anion framework of R and T contains stacking reversals after each layer; the stacking sequence of R is 1·1·1, T is 1·1·1·1. S has a spinel-like configuration; its stacking is designated 2. Larger structural units, RS and TS , have sequences of 1·1·3 and 1·1·1·3, respectively. The six known hexagonal ferrites consist of one or two of the stacking sequences 1·1·3, 1·1·1·3, and 1·1·5. The family is thus similar to a polytypic system; it involves, however, the stacking of chemically different layers. Single-crystal x-ray studies have disclosed four new structures which, together with three of the original phases, form a series of mixed-layer structures, RS…TS . The new structures are derived from the so-called Z phase, ( RS TS ) 2 or (113 1113) 2 , by adding TS (1113) units, giving ( RS TS ) 2 ( TS ) n or (113 1113) 2 (1113) n . Weissenberg patterns have shown many syntactically intergrown crystals with n = 1, 2, 3, or 4, corresponding to the structures 84 R , 102 R , 40 H , and 138 R , respectively. Dimensions along c reach 331 Å. One-dimensional structure-factor and electron-density calculations confirmed the stacking model. Permutation of structural units within a given stacking sequence gives rise to additional phases, one of which has been observed. The remaining three original hexagonal ferrites comprise a second series, RS…S . Other series, combinations, and permutations may exist, giving a vast number of possible structures.

NiSeO 4 · 6H 2 O is tetragonal, probable space group D 4 4 – P 4 1 2 1 2, with a = 6.914, c = 18.420 Å. MgSeO 4 · 6H 2 O is monoclinic, space group C 2 h 6 – C 2/ c , with a = 10.21, b = 7.35, c = 24.8 Å and β = 98°26′.

B-trimethyl N-triphenyl borazole crystallizes in the monoclinic system with a tetramolecular unit cell of dimensions a = 13.092, b = 15.001, c = 10.642 Å (± .015 Å), β = 98°30′. The density is 1.09 g/cm 3 and the principal refractive indices are α = 1.619, β = 1.630, γ = 1.638 (± .001). The most probable space group is Ic .

Crystal system and lattice constants of dicyclohexyl thiophosphinic acid and tetracyclohexyl diphosphine disulphide have been determined. The lattice structure of the investigated crystals is built up from structural units, which are smaller than the unit cell and connected by σ -operations.