Gallium and indium under high pressure

Ga and In crystallize in unusual open ground-state crystal structures. Recent experiments have discovered that Ga under high pressure transforms into a close-packed structure, while this has so far not been observed for In. Results from first principles calculations explain in a simple way this difference in behavior. We predict a so far undiscovered transition of In to a close-packed structure at extreme pressures and show that the structure determining mechanism originates from the degree of s-p mixing of the valence orbitals. Group-III elements are shown to strongly disobey the standard corresponding-state rule.

Superstructure Ordering of Intermetallics: B8 Structures in the Pseudo-Cubic Regime

The structural chemistry of the intermetallic B8-type compounds is reviewed.

The Phase Co(1)(-)(x)()Ni(x)()Sn(2): Structural Variations Based on the Stacking of Two Different Planar Nets

The investigation of the tin-rich part of the ternary system Co/Ni/Sn yielded the phase Co(1)(-)(x)()Ni(x)()Sn(2) with the range of composition 0.23(3) < x < 0.59(3). When using a large excess of tin, Co(1)(-)(x)()Ni(x)()Sn(2) crystallizes at 500 degrees C in a structure isotypic to that of tetragonal PdSn(2) whereas a modification with the orthorhombic CoGe(2) structure type always forms from a stoichiometric mixture of the elemental components or from a tin melt at temperatures above 550 degrees C. The structures of Co(0.625)Ni(0.375)Sn(2) were determined by single-crystal X-ray diffraction methods (PdSn(2)-type space group I4(1)/acd, a = 6.2360(5) Å, c = 23.588(2) Å, Z = 16; CoGe(2)-type space group Aba2, a = 6.2439(4) Å, b = 6.2493(4) Å, c = 11.778(1) Å, Z = 8). Both structures have the same building unit consisting of three consecutive planar nets 4(4), 3(2)434, 4(4) formed by tin atoms. The condensation of the building blocks in the c direction gives rise to different stacking sequences. In the PdSn(2)-type, a ABCD sequence is realized and the c axis is doubled compared to the ideal CoGe(2)-type with AB stacking. Electron diffraction and high-resolution electron microscopy studies revealed the existence of other, complex, stacking variants as well as stacking faults in the Co(1)(-)(x)()Ni(x)()Sn(2) system.

Structure of Mn8Sn5

The title compound crystallizes as a slightly incommensurate modulation of the B8-type structure. In a basic NiAs structure, ∼60% of the trigonal pyramidal interstices are filled with Mn atoms in an ordered manner. The highest corresponding commensurate space group is Pbnm (Pnma, No. 62) with the cell parameters a = 21.9114 (4), b: 7.6003 (5), c = 5.5247  (5) Å. The four-dimensional superspace group of the incommensurate structure is Cmcm(α00)0s0 (No. 63.8), with the conventional setting Amam(00γ)0s0. The cell parameters for this incommensurate cell are a = 382 (1), b = 7.600 (2), c = 5.525 (2) Å, q = [0.616 (5), 0, 0]. The structural refinements were carried out on a multiply twinned specimen. The R-factors were 0.037 for the incommensurate refinement and 0.046 for one commensurate approximation. The refinements unambiguously show that the modulation is caused by the step-like modulation of one Mn site, which is accompanied by small displacive modulations of the basic lattice. The incommensurate nature of the modulation is manifested in a slight splitting of fifth-order satellites, visible in electron diffraction.

Bone graft proteins influence osteoconduction. A titanium chamber study in rats

Although it is often emphasized that the matrix of bone grafts contains several growth factors, it is not known if these factors become activated and play a role in bone grafting. We therefore compared ground defatted bone which had or had not been deproteinized by heating with water to 270 degrees C at an autogenic pressure of 55 bar. This is a careful ceramic procedure which leaves the mineral unchanged. Deproteinized and non-deproteinized bone granulae derived from cortical rat bone were placed in titanium bone conduction chambers implanted bilaterally in rat tibiae. Ingrowing bone could enter the cylindrical interior of the chamber only at one end. It then penetrated the material in the chamber, but due to the length of the cylinder, it never reached the other end. The mean distance which the ingrown bone had reached in the material was then measured on histological slides. The bone formation activity was measured by TcMDP scintimetry. With the protein-containing granulae, the mean bone ingrowth distance and the scintimetric activity were increased by 41% and 31%, respectively (p < 0.01). We conclude that there is a limited favourable effect of proteins in a graft. Our grounded material had a large fracture surface area with no osteoid lining. The leakage of growth factors from such areas may explain the extraordinarily good clinical incorporation of morselized compacted allografts.