Powder diffractometry and DANSE: powDANSE

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Powder diffractometry and DANSE powDANSE

• S.J.L. Billinge
• Dept. Physics and Astronomy and Center for
  Fundamental Materials Research
• Michigan State University.

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Outline

• PowDANSE objectives
• Scientific frontiers
• Project plan PowDANSE objectives revisited

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PowDANSE objectives

• Baseline objectives (basic engineering)
• Advanced objectives (enabling new science)

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PowDANSE objectives

• Baseline objectives (basic engineering)
• On day 1 allow POWGEN3 to give real-time
  Rietveldable data to users
• On day 1 allow POWGEN3 to give real-time
  total-scattering S(Q) data (including an
  extensive overhaul of existing total-scattering/PD
  F data analysis codes)
• On day 1 give the user an intuitive graphical
  data manipulation toolkit for basic real-time
  data interrogations
• On day 1 give the instrument scientist a powerful
  suite of data interrogation tools for painless
  user support
• Work towards day 1 support of future SNS powder
  diffractometers (disordered materials
  diffractometer etc.)
• As a legacy, support all the worlds powder
  diffractometers with the same data analysis
  capabilities within the same software framework

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PowDANSE objectives

• Advanced Objectives (enabling new science)
• Prototype and test new codes that radically
  depart from existing data analysis methods
• Optimize the use of precious neutron beam-time by
  simulating experiments before and during
  data-collection as well as after
• Investigate ways in which access to TeraGrid type
  cyberinfrastructure will allow qualitatively new
  scientific problems to be addressed with powder
  diffraction
• Extend scope of the codes to single-crystal
  diffraction and single-crystal total-scattering
  studies

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Powder diffraction brief tour

• Basic work-horse of materials science/ chemistry/
  physics (from full-profile fitting methods)
• Accurate atomic positions
• Sample quality characterization (usually from
  in-house x-ray)
• Sample phase analysis
• Phase diagram determination
• Higher level information strain distributions,
  inhomogeneous strains, textures in polycrystals
• Powder diffractometers are among the most heavily
  oversubscribed instruments at facilities despite
  high throughput
• Large and diverse user base

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Powder diffraction brief tour

• (not strictly powders but) Structural analysis
  of glasses and liquids
• Progress being made on enormously complex but
  fundamental issues such as solvation structures
  and hydrophobic interactions
• Higher level information now wanted from glasses
  such as strain distributions
• New horizons structure solution from powder data
• New horizons nanocrystallography
• Solving structures from materials with nano-scale
  structural motifs
• Over the horizon Cooperative refinement and
  Total determination

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powDANSE main contributors

• Main contributors
• me
• Jason Hodges (powgen3)
• Thomas Proffen (npdf)
• Jim Richardson (gppd)
• Chris Benmore (glad)
• SNS disordered materials diffractometer IS
• Tightly coupled consultative roles (?)
• Brian Toby (nist)
• Angus Wilkinson (g tech)
• Paolo Radaelli (isis)
• Alan Soper/Spencer Howells/Robert McGreevy (isis)
• More loosely coupled consultative roles (?)
• Takeshi Egami (jins)
• Jim Jorgensen (anl)
• Single crystal people Si Moss/Lee Robertson/Ray
  Osborn/Richard Wellberry

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Science

• Some Physics

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Local vs. long-range structure semiconductor
alloy In1-xGaxAs
Average arsenic atomic probability distribution
at different indium concentrations
Petkov et al., PRL. 83, 4089 (1999) Jeong et
al., PRB (2001)
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What does the polaron look like?
S.J.L. Billinge et al, Phys. Rev. Lett. 77, 715
(1996) S. J. L. Billinge, et al., Phys. Rev. B
62, 1203 (2000)
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Charge-stripes in correlated-electron oxides

• Long Cu-O bonds
• Short Cu-O bonds
• Strain will build up here
• Qualitatively we see that lattice strain will
  tend to break up the stripes into short segments!

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Evidence for Charge inhomogeneities La2-xAxCuO4
(ASr,Ba)

• In-plane Cu-O PDF peak width broadens with doping
  (then sharpens)

Bozin et al. Cond-mat/9907017
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Affect of misfit strain on stripe microstructure

• Collaboration with Phil Duxbury at MSU
• Model lattice gas with strain

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Science

• Some Chemistry

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Diffuse scattering Underneath the Bragg-peaks
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Nanocrystallography Beyond Crystallography

• Crystallography fails in nanocrystalline
  materials

Nanocrystalline V2O5.nH2O xerogel
Crystalline V2O5
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Structure of xerogel

• Xerogel has bilayers of edge-shared VO6 octahedra
  separated by water molecules
• Notice loss in peak amplitude above 11.5 Å gt
  turbostratic disorder

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Crystals and nanocrystals

• In crystals, the oscillation amplitude in G(r) is
  independent of r
• In Nanocrystals, the amplitude falls off with
  increasing r
• Thanks to Valentin Levashov and MFT for the plot.

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Nanostructure in the xerogel
V. Petkov, et. al., J. Am. Chem. Soc. 121, 10157
(2002).

• Turbostratic disorder seen in the PDF consistent
  with bent and tangle fibres

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Atomic order in disordered carbon
High temperature processing
Low temperature processing
V. Petkov et al., Philos. Mag. B 79, 1519 (1999).

• Pyrolize Polyfurfuryl alcohol at high temperature
  in an inert atmosphere
• The resulting carbon is nanoporous and
  disordered. PDF reveals atomic order evolving
  with process T

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Total scattering then and now

• 1950
• 1999

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Alumino-silicates

• (Si,Al)O4 tetrahedral networks
• Important catalysts zeolites, microporous
  materials
• Cannot study AlO4 and SiO4 separately (Si and Al
  have similar x-ray and neutron scattering
  lengths)
• RSi 1.61A, RAl 1.75A, DR 0.14A
• x-ray data from Advanced Photon Source

V. Petkov et al., Phys. Rev. Lett., 85, 3436
(2000).
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Chemical specificity

• Using anomalous scattering we can get a chemical
  specific PDF - in this case it is the In-DDF
• High resolution total-PDF is compared with (low
  resolution) chemically resolved differential
• Both data-sets can be co-refined using PDFFIT
• This is the PDF equivalent of XAFS but higher
  neighbor information is present

Petkov et al. J. Appl. Phys. 88, 665 (2000).
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Structure of intercalants inorganic electride

• Cs forms Cs in zig-zag pattern
• Electrons are counter-ions

• Zeolite ITQ-4 has 1D channels of 7Å diameter
• Cs is intercalated
• X-ray data from NSLS-X7A

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Ferrocene Fe(C5H5)2
Model data for a rigid molecule
Fe-C
C-C
ring-ring
Experimental data APS 1-ID, 80 keV
Fe
C
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Rapid Acquisition PDFs

• Fast neutron PDFs (powGEN3)
• Fast x-ray PDFs
• Four orders of magnitude decrease in data
  collection time!
• Nickel data, 1s collection time, Qmax 28 Å-1

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RAPDF
BiVO

• Low-Z materials possible AlF3 Good
  reproducibility

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Summary

• Frantic overview of current scientific questions
  in the Billinge-group as an unrepresentative
  taste of what can be done
• Strawman proposal for powDANSE objectives

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Acknowledgements

• Valeri Petkov (former post-doc, now at CMU)
• Xiangyun Qiu (MSU student)
• Thomas Proffen (former post-doc, now staff at
  LANL0
• Il-Kyoung Jeong (former MSU student now postdoc
  at LANL)
• Emil Bozin (post-doc and former student)
• Group of Mercouri Kanatzidis
• Group of Jim Dye
• Pete Chupas and group of Clare Grey
• Other Billinge group members involved
• Matthias Gutmann
• Pete Peterson
• Facilities
• IPNS, MLNSC, ISIS and people therein
• Funding NSF-DMR 0075149, CHE-0211029,
  DOE-DE-FG02-97ER45651

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Obtaining the PDF
Structure function
Raw data
PDF
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Observing Domains in the PDF
r1 ltlt x
r2 x/2
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What is the PDF?

• Sit on an atom and look at your neighborhood
• G(r) gives the probability of finding a neighbor
  at a distance r
• PDF is experimentally accessible
• PDF gives instantaneous structure.

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Crystallographic bond-lengths Caveat Emptor

• Silica quartz at the a to b transition at 846K
• Crystallographic bond lengths shorten
• Real bonds (obtained directly from PDF) lengthen
  modestly
• The explanation
• Work by Dave Keen and Martin Dove