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Materials

Ceramics

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Displaying 901 - 925 of 1323

A New Octahedral Tilt System in the Perovskite Phase Ca 3 Nb 2 O 8

April 1, 2003
Author(s)
L M. Cranswick, W G. Mumme, I E. Grey, Robert S. Roth, P Bordet
The perovskite-related phase Ca 3Nb 2O 8, when grown as single crystals from a calcium vanadate flux, incorporates a smallamount of vanadium from the flux to form the composition Ca 3Nb 2-xV xO 8 with x = 0.025 . The crystals have pseudo-cubicsymmetry with

Flux Pinning and Properties of Solid-Solution (Y,Nd) 1+x Ba 2-x Cu 3 O 7-d Superconductors

April 1, 2003
Author(s)
T J. Haugan, M E. Fowler, J C. Tolliver, Paul N. Barnes, Winnie K. Wong-Ng, Lawrence P. Cook
The effect of chemical composition variations on the flux pinning and physical properties of (Y,Nd)1+xBa2-xCu3O7-d superconductors was studied in powders processed by solid-state reaction and equilibrated in air at 910 C. An extended region of single-phase

High-Accuracy Determination of the Dependence of the PhotoluminescenceEmission Energy on Alloy Composition in Al x Ga 1-x As Films

April 1, 2003
Author(s)
Lawrence H. Robins, J T. Armstrong, Ryna B. Marinenko, Albert J. Paul, J G. Pellegrino, Kristine A. Bertness
In an effort to improve the accuracy of photoluminescence (PL)spectroscopy as a composition (Al mole fraction) measurement method forthe Al xGa 1-xAs alloy system, the PL peak emission energy,E PL,peak, was measured at room temperature for a set of MBE

Singular Grain Boundaries in Alumina and Their Roughening Transition

April 1, 2003
Author(s)
C W. Park, D C. Yoon, J Blendell, C A. Handwerker
The shapes and structures of grain boundaries formed between the basal (0001) surface of large alumina grains and randomly oriented small alumina grains are shown to depend on the additions of SiO 2, CaO, and MgO. If a sapphire crystal is sintered at 1620

Asymptotic Behavior of a Strain Percolation Model for a Deforming Metal

March 1, 2003
Author(s)
Y Shim, Lyle E. Levine, R M. Thomson, D E. Kramer
In this paper, we present a recent advance in theoretical understanding of a deforming metal, using a strain percolation model which possibly explains spasmodic, fine slip line burst events occurring in the metal. The model addresses how the additional

Cracking and the Indentation Size Effect for Knoop Hardness of Glasses

March 1, 2003
Author(s)
George D. Quinn, P Green, K Xu
The Knoop Hardness of five glasses as measured over a wide range of indentation loads. Hardness decreased with increasing load in accordance with the classic indentation size effect (ISE). At moderate loads, cracking dramatically altered the indentation

Small-Angle Neutron Scattering Study of the Role of Feedstock Particle Size on the Microstructural Behavior of Plasma-Sprayed Yttria-Stabilized Zirconia Deposits

March 1, 2003
Author(s)
H Boukari, Andrew J. Allen, Gabrielle G. Long, J Ilavsky, Jay S. Wallace, C C. Berndt, H Herman
The microstructures of thick plasma-sprayed yttria-stabilized (8% mass) zirconia deposits have been studied in a series of Porod small-angle neutron scattering (SANS) and multiple small-angle neutron scattering (MSANS) experiments. Three main void

Model for Estimating Wear Transition Loads in Ceramics

February 19, 2003
Author(s)
S Jahanmir
The wear behavior of advanced ceramics (alumina, silicon nitride, and silcon carbide) changes as the load or the coefficient of friction is increased. This change is associated with a drastic increase in wear rate at a critical load that depends on the

Agglomerate Formation During Drying

February 1, 2003
Author(s)
A Vertanessian, Andrew J. Allen, M J. Mayo
The evolution of agglomerate structure during drying of particles from suspension has been studied for a nanocrystalline Y2O3 (8 mol %)-stabilized ZrO2 powder. Agglomerates in drying and dried suspensions were examined at the smallest size scales (100 nm

Crack Growth Threshold in Soda Lime Silicate Glass: Role of Hold-Time

February 1, 2003
Author(s)
J -. Guin, Sheldon M. Wiederhorn
Atomic force microscopy was used to examine the shapes of cracks and residual features left behind on the fracture surface after holding cracks at a stress intensity factor below the fatigue threshold for soda lime silicate glass. After propagating a crack

Electron Energy Loss Spectroscopy of CeO 2 -x Nanoparticles

January 7, 2003
Author(s)
W Lijun, H J. Wiesmann, A R. Moodenbaugh, Daniel A. Fischer, Y Zhu, M Suenaga
ria has been widely studied due to its applications, such as a catalyst in vehicle emissions system and an electrolyte material in solid oxide fuel cells. Recently, it has been reported that CeO2-x nanoparticles exhibit lattice expansion and valence

An Alternative Method of Solving Multilayer Bending Problem

January 1, 2003
Author(s)
C H. Hsueh, S K. Lee, Tze J. Chuang
Stress distributions in multilayers subjected to both residual stresses and external bending are analyzed to derive closed-form analytical solutions. There are always three unknowns to be solved and three equilibrium conditions to be satisfied in the

Biaxial Stress Dependence of the GaAs-Like and AlAs-Like Raman Lines in Al x Ga 1-x As

January 1, 2003
Author(s)
Grady S. White, Albert J. Paul, Kristine A. Bertness, Alexana Roshko
Raman peak shifts of Al xGa 1-xAs have been measured as a function of both x and applied biaxial stress in a backscatter geometry. Within the precision of the Raman measurements, the stress-induced peak shifts of the Raman singlet GaAs-like and AlAs-like

Machining Damage Cracks: How to Find and Characterize Them by Fractography

January 1, 2003
Author(s)
George D. Quinn, L K. Ives, S Jahanmir
Subsurface machining cracks may control strength and performance of finished ceramics. Previously, machining cracks had been though to be difficult or impossible to detect and characterize, especially in toughened ceramics with interlocking grain
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