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Hcp Structure (hcp + structure)

Distribution by Scientific Domains

Physics and Astronomy	50%

Selected Abstracts

Phase Transformations During High-Pressure Torsion of Pure Zr and of a Zr-2.5%Nb Alloy,

ADVANCED ENGINEERING MATERIALS, Issue 8 2010
Alexander P. Zhilyaev
Zirconium at normal conditions (room temperature and atmospheric pressure) has an HCP structure with lattice parameters a,=,3.2313,Å and c,=,5.1477,Å (,-phase). During loading under hydrostatic conditions in diamond anvil cells, a transition from the , -phase to an , -phase occurs at a pressure between 2 and 6 GPa and from , to , (bcc) at 30 GPa. It has been recently reported that the , to ,,+,, transformation might be induced by HPT processing. The resulting microstructures are stable at room temperature and atmospheric pressure. This paper explores the influence of previous processing steps and of composition in the feasibility of the HPT induced , to ,,+,, transformation. It will be shown that neither previous quenching nor high temperature HPT processing prevents the transformation from occurring during subsequent room temperature HPT. The addition of elements such as Nb also seems to favor the transformation. Understanding well the potential of HPT to stabilize high-pressure phases at normal conditions might be critical, as it will open a whole new range of applications for already existing materials. [source]

TEM Analysis of Hcp-Co Films Deposited by Gas Flow Sputtering

IEEJ TRANSACTIONS ON ELECTRICAL AND ELECTRONIC ENGINEERING, Issue 4 2008
Hiroshi Sakuma Member
Abstract In this study, the crystal structure of Co thin films deposited by a low-energy sputtering, gas flow sputtering (GFS) and conventional RF magnetron sputtering (MS) is investigated. The emphasis is on whether fcc-like regions are present in a hcp-Co film. X-ray diffraction (XRD) shows no fcc peak for both films deposited by GFS and MS. Electron diffraction reveals that fcc structure is present in the film deposited by MS. Lattice images are observed by using transmission electron microscopy. Every other line in the lattice image of the film deposited by GFS is bright or dark, which is suggestive of the ABAB stacking of the hcp structure. In addition, stacking faults are observed. Copyright © 2008 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [source]

Highly crystalline cobalt nanowires with high coercivity prepared by soft chemistry

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 4 2009
G. Viau
Abstract Cobalt nanorods and wires were prepared by reduction of a cobalt salt in a liquid polyol. These particles crystallize with the hcp structure and the growth axis is parallel to the crystallographic c -axis. The kinetic control of the growth allows to vary the mean diameter of the rods and their aspect ratio. Dumbbell like shape particles consisting of a central rod with two conical tips were also obtained. Magnetization curves of oriented wires present very high coercivity (up to 9 kOe) resulting from both a high shape anisotropy and the high magnetocrystalline anisotropy of the hcp cobalt. Micromagnetic simulations showed that the magnetization reversal is shape dependent. The conical tips of the dumbbell particles strongly contribute to the coercivity decrease and must be precluded for permanent magnet applications. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

First-principles study of phase transition of tin and lead under high pressure

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2008
Shouxin Cui
Abstract The phase transitions of Sn and Pb under high pressure are investigated theoretically using the first-principles pseudopotential method. The calculated results show that for Sn the sequence of phase transitions is ,-Sn , ,-Sn , bct , bcc under high pressure while hcp-Sn is not observed up to 200 GPa, which is in good agreement with experiments. In addition, for Pb the calculated results indicate that Pb can un- dergo two phase transitions under high pressure: one is the phase transition from fcc to the hcp structure at a pressure of 16 GPa and the other is the phase transition from hcp to the bcc structure at a pressure of 109 GPa. Furthermore, all the transition pressure and volume changes during the phase transformation are consistent with the experimental values. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]