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Search Publications by: Eric J. Cockayne (Fed)

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Displaying 51 - 73 of 73

Energetics of Li Atom Displacements in K1-xLixTa03: First-Principles Calculations

July 1, 2003
Author(s)
S A. Prosandeev, Eric J. Cockayne, Benjamin P. Burton
K 1-xLi xTaO 3 (KLT) solid solutions exhibit a variety of interesting physical phenomena related to large local displacements of Li-ions from ideal perovskite A-site positions. First-principles calculations for KLT supercells were used to investigate these

First Principles Studies of KnbO 3 , KtaO 3 and LiTaO 3 Solid Solutions

August 1, 2002
Author(s)
S A. Prosandeev, Eric J. Cockayne, Benjamin P. Burton
KTaO3-based solid solutions exhibit a variety of interesting physical phenomena. To better understand these phenomena, we performed first-principles calculations on [K1-x,Lix]TaO3 (KLT) and K[Ta1-xNbx]O3 (KTN) supercells. Our results show Li displacements

Total-Energy-Based Structure Prediction for Decagonal Al-Ni-Co

February 11, 2002
Author(s)
M Mihalkovic, I Al-Lehyani, Eric J. Cockayne, C L. Henley, N Moghadam, J A. Moriarty, Yijun Wang, M Widom
Quasicrystals are metal alloys whose noncrystallographic symmetry and lack of structural periodicity challenge methods of both experimental structure determination and theoretical structural prediction. Here we employ total energy calculations and Monte

Effective Hamiltonian Study of PZT 95/5

January 21, 2002
Author(s)
K Leung, Eric J. Cockayne, A F. Wright
An effective Hamiltonian is constructed for PbZr0.95Ti0.05O3. It is parameterized using ab initio results computed in the virtual crystal approximation. The phase diagram depends sensitively on the energetic competition between the stable orthorhombic

Unexpected Ground State Structures in Relaxor Ferroelectrics

January 1, 2002
Author(s)
Benjamin P. Burton, Eric J. Cockayne
Cluster expansion Hamiltonians derived from pseudopotential total energies were used to predict ground-state (GS) cation configurations for some A(B^{3+}1⁄2B'^{5+}1⁄2)O3, A(B^{2+}{1/3}B'^{5+}{2/3})O3 , and [A^{1+}1⁄2A'^{3+}1⁄2]BO3 perovskites. Predicted GS

Temperature-Dependent Behavior of PbSc 1/2 Nb 1/2 O 3 From First Principles

July 1, 2001
Author(s)
Eric J. Cockayne, Benjamin P. Burton, L Bellaiche
We study the ferroelectric phase transition in PbSc1/2Nb1/2O3 (PSN) using a first-principles effective Hamiltonian approach. Results for PSN with NaCl-type ordering of Sc and Nb on the B sites shows that a Pb-centered effective Hamiltonian is appropriate

Prediction of the [Na 1/2 Bi 1/2 ] TiO 3 Ground State

February 1, 2001
Author(s)
Benjamin P. Burton, Eric J. Cockayne
The Vienna Ab-initio Simulation Package (VASP) was used to perform fully relaced, planeware psudopotential calculations of formation energies (δE V ASP) for a large number of ordered supercells in the perovskite based system NaTiO 3 - BiTiO 3, including 36

Abstracts for the MSEL Assessment Panel, March 2001

January 26, 2001
Author(s)
Leslie E. Smith, Alamgir Karim, Leonid A. Bendersky, C Lu, J J. Scott, Ichiro Takeuchi, Kathleen M. Flynn, Vinod K. Tewary, Davor Balzar, G A. Alers, Stephen E. Russek, Charles C. Han, Haonan Wang, William E. Wallace, Daniel A. Fischer, K Efimenko, Wen-Li Wu, Jan Genzer, Joseph C. Woicik, Thomas H. Gnaeupel-Herold, Henry J. Prask, Charles F. Majkrzak, Norman F. Berk, John G. Barker, Charles J. Glinka, Eric K. Lin, Ward L. Johnson, Paul R. Heyliger, David T. Read, R R. Keller, J Blendell, Grady S. White, Lin-Sien H. Lum, Eric J. Cockayne, Igor Levin, C E. Johnson, Maureen E. Williams, Gery R. Stafford, William J. Boettinger, Kil-Won Moon, Daniel Josell, Daniel Wheeler, Thomas P. Moffat, W H. Huber, Lee J. Richter, Clayton S. Yang, Robert D. Shull, R A. Fry, Robert D. McMichael, William F. Egelhoff Jr., Ursula R. Kattner, James A. Warren, Jonathan E. Guyer, Steven P. Mates, Stephen D. Ridder, Frank S. Biancaniello, D Basak, Jon C. Geist, Kalman D. Migler
Abstracts relating to research and development in the NIST Materials Science and Engineering Laboratory (MSEL) are presented for a poster session to be presented to the 2001 MSEL Assessment Panel.

Phonons and Static Dielectric Constant in CaTiO 3 From First Principles

August 1, 2000
Author(s)
Eric J. Cockayne, Benjamin P. Burton
CaTiO 3 has a static dielectric constant that extrapolates to a value greater than 300 at zero temperature. We investigate the origin of this large dielectric response on a microscopic level, using first-principles plane-wave pseudopotential density

Ab-Initio Energetics of Transition Metal Ordering in Decagonal Al-Co-Cu

January 21, 2000
Author(s)
M Widom, I Al-Lehyani, Yijun Wang, Eric J. Cockayne
We perform ab-initio total energy calculations for approximants to a model of decagonal A1CoCu. These calculations support previously proposed chemical ordering of Co and Cu atoms along tile edges. Preferred arrow orientations are identified and shown to

Generation of Quasicrystals Via a Single Cluster

January 21, 2000
Author(s)
Eric J. Cockayne
We present a columnar cluster with 46 atoms per repeat distance which forces a quasicrystal when space is filled by interpenetrating copies of itself. The atomic positions in the resultant quasicrystal are remarkably similar to those in models for real

Pressure Dependence of Instabilities in Perovskite PbZrO 3

January 21, 2000
Author(s)
Eric J. Cockayne, K M. Rabe
We have computed the frequencies of selected normal modes in perovskite PbZrO 3 (PZ) as a function of lattice parameter using local density functional theory variational linear response. The most significant instabilities that freeze in to give the

Combined EXAFS and First-Principles Theory Study of Pb 1-x Ge x Te

December 1, 1999
Author(s)
Bruce D. Ravel, Eric J. Cockayne, E Newville, K M. Rabe
The narrow band-gap semiconductor Pb 1-xGe xTe has a low-temperature ferroelectric rhombohedral phase whose average structure is a distorted rocksalt structure. We have measured the Extended X-Ray-Absorption Fine-Structure (EXAFS) spectra of Pb 1-xGe xTe

The Local Structure of Ferroelectric Pb 1-x Ge x Te

May 1, 1999
Author(s)
Bruce D. Ravel, Eric J. Cockayne, K M. Rabe
The narrow band-gap semiconductor Pb_{1-x}Ge_xTe has a low-temperature ferroelectric rhombohedral phase whose average structure is a distorted rock salt structure. We have measured the Extended X-ray-Absorption Fine-Structure spectra of Pb_{1-x}Ge_xTe with

Stable Quasicrystalline Sphere Packing

March 1, 1999
Author(s)
Eric J. Cockayne, M Mihalkovic
Wills (1990, J. Phys., Paris 51, 1061), found a method relating certain decagonal disk packings to decagonal sphere packings with high packing fractions. Applying this technique to the decagonal rectangle-triangle tiling generated by inflation, we obtain a