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Start Over Author "Stock, Chris" Topic neutrons
3 results on '"Stock, Chris"'

1. Alignment facility and software for single‐crystal time‐of‐flight neutron spectroscopy.

Author

Liu, Zihao, Lane, Harry, Frost, Christopher D., Ewings, Russell A., Attfield, J. Paul, and Stock, Chris

Subjects
TIME-of-flight spectroscopy, NEUTRON spectroscopy, SINGLE crystals, INTEGRATED software, COMPUTER software, NEUTRON sources
Abstract

An instrument and software algorithm are described for the purpose of characterization of large single crystals at the Alignment Facility of the ISIS spallation neutron source. A method for both characterizing the quality of the sample and aligning it in a particular scattering plane is introduced. A software package written for this instrument is presented, and its utility is demonstrated by way of an example of the structural characterization of large single crystals of Pb(Mg1/3Nb2/3)O3. Extensions and modifications of characterization instruments for future improved beamlines are suggested. It is hoped that this software will be used by the neutron community for pre‐characterizing large single crystals for spectroscopy experiments and that in the future such a facility will be included as part of the spectroscopy suite at other spallation neutron sources. [ABSTRACT FROM AUTHOR]

Published
2021
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2. Physical Review B

Author

Stock, Chris, Ellis, D., Swainson, I. P., Xu, Guangyong, Hiraka, Haruhiro, Zhong, Z., Luo, Hongjie, Zhao, X., Viehland, Dwight D., Birgeneau, R. J., Shirane, Gen, Materials Science and Engineering (MSE), and Virginia Tech

Subjects
Neutrons, Behavior, Titanate, Ferroelectricity, Phase transitions, Physics, Temperature, Single crystals, Model
Abstract

Using neutron elastic and inelastic scattering and high-energy x-ray diffraction, we present a comparison of 40% Pb(Mg1/3Nb2/3)O-3-60% PbTiO3 (PMN-60PT) with pure Pb(Mg1/3Nb2/3)O-3 (PMN) and PbTiO3 (PT). We measure the structural properties of PMN-60PT to be identical to pure PT, however, the lattice dynamics are exactly that previously found in relaxors PMN and Pb(Zn1/3Nb2/3)O-3 (PZN). PMN-60PT displays a well-defined macroscopic structural transition from a cubic to tetragonal unit cell at 550 K. The diffuse scattering is shown to be weak indicating that the structural distortion is long-range in PMN-60PT and short-range polar correlations (polar nanoregions) are not present. Even though polar nanoregions are absent, the soft optic mode is short-lived for wave vectors near the zone center. Therefore PMN-60PT displays the same waterfall effect as prototypical relaxors PMN and PZN. We conclude that it is random fields resulting from the intrinsic chemical disorder which is the reason for the broad transverse optic mode observed in PMN and PMN-60PT near the zone center and not due to the formation of short-ranged polar correlations. Through our comparison of PMN, PMN-60PT, and pure PT, we interpret the dynamic and static properties of the PMN-xPT system in terms of a random field model in which the cubic anisotropy term dominates with increasing doping of PbTiO3.

Published
2006

3. Coupled Commensurate Cation and Charge Modulation in the Tunneled Structure, Na0.40(2)MnO2.

Author

Kruk, Izabela, Zajdel, Pawel, Beek, Wouter van, Bakaimi, loanna, Lappas, Alexandros, Stock, Chris, and Green, Mark A.

Subjects
*MANGANESE oxides, *NEUTRONS, *SYNCHROTRON radiation, *CATIONS, *MAGNETORESISTANCE
Abstract

Na0.40(2)MnO2 belongs to a family of mixed Mn3+ and Mn4+ porous oxides that contains both octahedral and square pyramidal Mn—O units. Neutron and synchrotron radiation studies identify the presence of both sodium ordering (TNa ≈ 310 K) and Mn charge and orbital ordering. Below TNa, the centrosymmetric Pbam structure adopts an (ab 4c) supercell of Pnnm symmetry that accommodates a coupled commensurate modulation down the c-axis channels of both Na position and occupancy with Mn valence. [ABSTRACT FROM AUTHOR]

Published
2011
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