Phononen in Fe65Ni35 Temperatur- und Druckabh

1
Introduction
XAFS 12 in Malmö 24. June 2003
High-pressure EXAFS and XRD investigation of
unit cell parameters of SnO
Hubertus Giefers
Physics Department, University of Paderborn,
D-33095 Paderborn, Germany
2
Survey
?? SnO under pressure ? Energy dispersive
X-ray diffraction (EDXRD) of SnO ? EXAFS of SnO
under high pressure ? Combination of EXAFS and
EDXRD results for determination of z(Sn) ?
Conclusion Acknowledgment
3
SnO under pressure

• only a few high pressure (HP)
• studies on SnO in the literature
• a tetragonal to orthorhombic phase
• transition is controversially discussed
• no HP study on the atom position
• parameter z(Sn) is reported in the
• literature

c
c
a
a
b
b
N.R. Serebryanaya et al., Dokl. Akad. Nauk SSSR
187, 307 (1969).
D.M. Adams et al., Phys. Rev. B46, 11358 (1992).
E.V. Kapitanov, E.N. Yakovlev, Phys. Stat. Sol.
A51, 641 (1979).
4
Energy dispersive X-ray diffraction (EDXRD) of SnO
High pressure (HP) EDXRD at beamline F3 at
HASYLAB/DESY

• EDXRD spectra recorded with lN2 cooled
  Ge-detector
• in this case beam 0.20.2 mm2
• diamond anvil cell
• liquid N2 as pressure transmitting medium
• Gold powder as pressure marker
• sample size Ø 0.4 mm2

5
Energy dispersive X-ray diffraction (EDXRD) of SnO

• strong texture with c-axis parallel to load axis
• no obvious phase transition with pressure
• but lines (hkl) with h?k broaden with pressure
• the broadening depends on the pressure
• transmitting medium
• we attribute this line broadening to
• nonhydrostatic conditions in the HP cell
• SnO is very sensitive to shear stress

6
Energy dispersive X-ray diffraction (EDXRD) of SnO
Birch equation-of-state for SnO
K0 33.5(11) GPa
K0 6.1(5) compared to
SnO2 with K0 205 GPa
K0 3.1
due to the strong preferred orientation of SnO
in the HP cell, the free atomic position
parameter z(Sn) could not be determined from
the diffraction intensities that
is the reason why we performed the EXAFS study
7
EXAFS of SnO under high pressure

• versatile high pressure cell with B4C anvils
• anvil flat diameter 2.5 mm
• sample diameter 1.3 mm
• gasket material Cu
• polyethylene as pressure transmitting medium
• Ag powder as pressure marker
• pressure determination with EXAFS of Ag at Ag-K
  edge (25.5 keV)

8

EXAFS of SnO under high pressure
EXAFS at beamline X1 at HASYLAB/DESY

• Si (311) double monochromator
• energy resolution of 14 eV at 29 keV
• EXAFS at Sn-K edge (29.2 keV)
• beam size of 0.80.8 mm2

9
EXAFS of SnO under high pressure
EXAFS of sample SnO and pressure marker
Ag together in the HP cell
10
EXAFS of SnO under high pressure
11
EXAFS of SnO under high pressure

• the Sn-O distance
• decreases only by
• about 2
• compressibility of the
• Sn-O bonding is quite
• small
• the decrease is linear
• with pressure
• the 2nd cumulant
• decreases continuously
• with pressure ?
• contradicts a phase
• transition to ortho-
• rhombic structure

12
Combination of EXAFS and EDXRD results of SnO
- a and c from EDXRD - RSn-O from EXAFS

• z(Sn) increases due to the strong compression of
  the
• c-axis and the small reduction of the Sn-O
  distance
• when the Sn-O-Sn layers come closer with
  pressure
• the repulsion increases and the increase of
  z(Sn) flattens
• in the same way as the decrease of the c-axis

13
Conclusion Acknowledgment

• SnO shows no obvious tetragonal to orthorhombic
  phase transiton with lN2
• as pressure transmitting medium under pressure
• XRD line broadenings are induced by
  nonhydrostatic conditions in the HP cell
• SnO is very sensitive to shear stresses
• the combination of XRD and EXAFS reveals all 3
  cell parameters (a, c, z(Sn))
• of SnO under pressure

• Thanks to
• Felix Porsch
• Gerhard Wortmann
• Edmund Welter and the EXAFS HASYLAB team