The AFLOW Fleet for Materials Discovery

The traditional paradigm for materials discovery has been recently expanded to incorporate substantial data driven research. With the intent to accelerate the development and the deployment of new technologies, the AFLOW Fleet for computational materials design automates high-throughput first principles calculations, and provides tools for data verification and dissemination for a broad community of users. AFLOW incorporates different computational modules to robustly determine thermodynamic stability, electronic band structures, vibrational dispersions, thermo-mechanical properties and more. The AFLOW data repository is publicly accessible online at aflow.org, with more than 1.7 million materials entries and a panoply of queryable computed properties. Tools to programmatically search and process the data, as well as to perform online machine learning predictions, are also available.Comment: 14 pages, 8 figure

Fracture mechanics of mollusc shells

The shape and structure of the shells of molluscs has attracted considerable attention. One aspect of interest is the comparatively high resistance to fracture of these shells. It is known that they are composite structures of aragonite, other calcereous materials, and up to 5% by volume of protein 'glue'. A large component of their toughening derives from crack tip blunting, deflection and closure, concepts well-known from the field of fracture mechanics. However, the possibility that they might also derive a measure of toughening from a residual stress distribution has been generally overlooked, although Illert first raised this over a decade ago. The optimum situation would be when the inner surface of the shell is maintained in a state of tensile stress, while the outer layers are in the necessarily counter-balancing compressive state. We have examined this hypothesis using a combination of neutron diffraction and scanning electron microscopy and find that it is certainly feasible. However, a definitive proof will require a diffraction study at higher resolution. © 2006 Elsevier B.V. All rights reserved

Microstrain in hydroxyapatite carbon nanotube composites.

Synchrotron radiation diffraction data were collected from hydroxyapatite–carbon nanotube bioceramic composites to determine the crystallite size and to measure changes in non-uniform strain. Estimates of crystallite size and strain were determined by line-profile fitting of discrete peaks and these were compared with a Rietveld whole-pattern analysis. Overall the two analysis methods produced very similar numbers. In the commercial hydroxyapatite material, one reflection in particular, (0 2 3), has higher crystallite size and lower strain values in comparison with laboratory-synthesized material. This could indicate preferential crystal growth in the [0 2 3] direction in the commercial material. From the measured strains in the pure material and the composite, there was a degree of bonding between the matrix and strengthening fibres. However, increasing the amount of carbon nanotubes in the composite has increased the strain in the material, which is undesirable for biomedical implant applications. © 2008, Wiley-Blackwel

Composition- and temperature-dependent phase transitions in 1:3 ordered perovskites Ba4-xSrxNaSb3O12.

A series of 25 members of the 1:3 ordered perovskite family of the type Ba4-xSrxNaSb3O12 has been synthesized and their structures determined using synchrotron X-ray and neutron powder diffraction techniques. At room temperature the sample Ba4NaSb3O12 has a cubic structure in space group Im (3) over barm with a = 8.2821(1) angstrom, where the Na and Sb cations are ordered in the octahedral sites but there is no tilting of the (Na/Sb)O-6 octahedra. As the average size of the A-site cation decreases, through the progressive replacement of Ba by Sr, tilting of the octahedra is introduced firstly lowering the symmetry to tetragonal in P4/mnc then to orthorhombic in Cmca and ultimately a monoclinic structure in P2(1)/n as seen for Sr4NaSb3O12 with a = 8.0960(2) angstrom, b = 8.0926(2) angstrom, c = 8.1003(1) angstrom and β = 90.016(2)degrees. The powder neutron diffraction studies show that the orthorhombic and tetragonal phases in Cmca and P4/mnc co-exist at room temperature for samples with x between 1.5 and 2. © 2007, Elsevier Ltd

Programs for the management and processing of neutron diffraction data.

This report describes the programs developed over about five years at Lucas Heights for the processing of crystallographic data from manual and computer-controlled diffractometers. The description, theory, and input and output formats are given, but not the program listings. Sections 2 and 3 describe the programs for handling, editing and reducing the 5-hole tape produced by manually-operated machines. Section 4 describes the revised versions of the programs associated with the computer-controlled diffractometers. It replaces the previous report AAEC-E-191 as an operating manual for these instruments. Section 5 describes the programs for sorting, absorption-correcting and evaluating standard deviations. Section 6 describes the Job-Control procedures

Coexistence of ferroelectricity and magnetism in transition-metal-doped n = 3 Aurivillius phases.

Magnetic-cation-doped three-layer Aurivillius phases Bi2-xSr2+x(Nb/Ta)(2+x)M1-xO12, x approximate to 0.5 and M = Ru4+, Ir4+ or Mn4+, are shown to have the same orthorhombic space group symmetry and similar dielectric and ferroelectric properties as their (non-magnetic) ferroelectric parent compounds Bi2-xSr2+xNb2+xTi1-xO12, x = 0, 0.5. The magnetic-cation-doped phases also show evidence for short-range ferromagnetic (M = Mn) and antiferromagnetic (M = Ru and Ir) exchange, demonstrating the potential of these naturally layered phases as templates for multiferroic (magnetoelectric) materials. © 2008, Institute of Physic

New neutron powder diffractometers at Australia's OPAL reactor will boost materials science.

Two new powder diffractometers, ECHIDNA [1] and WOMBAT, [2] aiming for high angular resolution and high intensity, respectively, are being commissioned within the Neutron Beam Instrumentation Project at the new Australian Neutron Source OPAL near Sydney.Australian Ceramic Societ

Coupled Li1+/Nb5+ and O2-/F- ordering on the Na and Cl sites of the average NaCl structure of Li4NbO4F.

The average, as well as the cation and anion 'disordered', crystal Structure of Li4NbO4F has been carefully investigated via coupled neutron and X-ray powder diffraction studies as well as via electron diffraction studies. The existence of a spectacular highly structured diffuse intensity distribution in the latter provides strong evidence for coupled Li1+/Nb5+ and O2-/F- ordering on the Na and Cl sites of the average NaCl structure of Li4NbO4F. Bond valence sum calculations have been used to investigate local crystal chemistry as well as to Suggest plausible local crystal chemical constraints while ab initio DFT based theoretical calculations of a 2 x 2 x 2 supercell have been carried Out in order to provide additional insight into the local crystal chemistry of this compound. © 2009, Elsevier Ltd