Introduction
This presentation is the property of its rightful owner.
Sponsored Links
1 / 25

Introduction PowerPoint PPT Presentation


  • 95 Views
  • Uploaded on
  • Presentation posted in: General

Introduction. 14 th ESRF User Meeting Phonons in Crystalline Materials Workshop 9. February 2004. Phonon DOS in oriented hcp iron and SnO from high-pressure NIS. Hubertus Giefers. Physics Department, University of Paderborn, D-33095 Paderborn, Germany. Survey.

Download Presentation

Introduction

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Introduction 3937578

Introduction

14th ESRF User Meeting

Phonons in Crystalline MaterialsWorkshop

9. February 2004

Phonon DOS in oriented hcp iron and SnO from high-pressure NIS

Hubertus Giefers

Physics Department, University of Paderborn, D-33095 Paderborn, Germany


Introduction 3937578

Survey

 Experimental setup and high-pressure cell for NIS

(Nuclear Inelastic Scattering)

 Iron under high pressure, texture in hcp iron

 High pressure NIS-experiments with iron up to 130 GPa

 Subtraction method: projected DOS of hcp iron

 Sound velocity in hcp iron

 SnO under pressure

 Texture of SnO

 Orientational dependent DOS-spectra of SnO

 Phonon modes in SnO

 Conclusion/Acknowledgment


Introduction 3937578

Experimental setup for NIS

Kirkpatrick-Baez-mirror:

Focusing essential

for high pressure studies

SR spot of 10x10µm2 at sample


Introduction 3937578

High-pressure cell for NIS

  • large openings for APD detector

  • diamonds without support ring → large scattering angle

  • Be-Gasket → transmission of Ka,b x-ray fluorescence

  • scattering geometry parallel and perpendicular to the HP-cell axis


Introduction 3937578

pressure

≈ 13 GPa

e-phase

hcp structure

a-phase

bcc structure

e-Fe at 220 GPa

pressure

H.-R. Wenk et al., Nature 405, 1044 (2000).

Iron under high pressure

- a/e-phase transition at 13 GPa

- after the a/e-phase transition e-Fe is preferentially oriented

with the hcp c-axis along the load axis


Introduction 3937578

Iron in the Earth

  • Fe is of actual geophysical interest

  • the solid inner core consists mainly

  • of e-Fe

  • longitudinal sound velocity vp from

  • north to south is faster (3-4 %) than

  • from east to west

  • - assumption: e-Fe is textured in the

  • inner core


Introduction 3937578

High pressure NIS-experiments with iron

APS Experiments 1999: DE = 2 meV

ESRF Experiments 2003: DE = 3 meV

H. Giefers et al., to be published.

H.-K. Mao et al., Science 292, 914 (2001).


Introduction 3937578

Phonon density-of-state (DOS) of oriented hcp-iron


Introduction 3937578

40 GPa

Subtraction method: projected phonon DOS of iron

e-Fe

40 GPa


Introduction 3937578

Comparison: theory ↔ experiment

B1g

E2g

calculation: D. Alfè

in

Giefers et al.,

High Press. Res. 22,

501 (2002).


Introduction 3937578

projected DOS of iron


Introduction 3937578

gB1g=1.68(9)

gE2g=1.44(3) [Merkel]

gE2g=1.43(9)

Mode-specific analysis of the phonon spectra


Introduction 3937578

Sound velocity in e-iron


Introduction 3937578

Sound velocity in e-iron


Introduction 3937578

Sound velocity vp and vs of e-Fe


Introduction 3937578

e-phase

hcp structure

Difference of sound velocities in hcp-iron

Difference in sound velocities vp:

from measured DOS-spectra at 130 GPa :

0°: 9.87(14) km/s

75°: 9.74(14) km/s

difference: 1.3 %

from subtracted DOS-spectra at 130 GPa :

c-axis: 10.58(19) km/s

a,b-plane: 9.55(19) km/s

difference: 9.7 %


Introduction 3937578

Tin oxide SnO

a = 3.800 Å

c = 4.836 Å

z(Sn) = 0.236

- layer structure

- weak van der Waals

binding between

Sn-O-Sn layers

Sn

O

Sn

Sn

O

Sn

Sn

O

Sn

Sn

O

Sn


Introduction 3937578

XRD and EXAFS measurements

Unit cell parameters of SnO under pressure

  • strong elastic anisotropy

  • no phase transition up to 50 GPa

  • Birch-EOS: K0=35(1) GPa, K0‘=6.1(2)


Introduction 3937578

Texture of SnO studied by EDXRD

  • SnO shows (001)-texture:

  • the c-axes of the

  • graphite-like

  • crystallites

  • are perpendicular to the

  • sample plane

- texture occures even

at ambient pressure

- this texture is used

for an orientation

dependent NIS-study

like in e-Fe


Introduction 3937578

Orientation dependent NIS-spectra of SnO


Introduction 3937578

Orientation dependent phonon-DOS of SnO

the spectra resemble

each other → SnO

becomes more isotropic


Introduction 3937578

1 acoustic

2 optic

3 optic

1 acoustic

2 acoustic/optic

3 optic

Phonon modes in SnO: theory ↔ experiment

← S. Koval, Phys. Rev. B 54,

7151 (1996).


Introduction 3937578

Mode-Grüneisen parameter

gi = 0.8 for 1 2

gi = 0.5 for 3

gi = 4.4 (0-1.3 GPa),

1.9 (1.3-6.1 GPa)

for 1

Phonon modes in SnO


Introduction 3937578

Conclusion

  • - The new difference method for NIS-DOS-spectra from textured samples

  • allows a direction dependent analysis of the phonon DOS as demonstrated for

  • -Fe and SnO.

  • - This difference method delivers results similar to those obtained by single crystal

  • studies, for instance with INS or IXS; this method allows also, together with

  • theoretical calculations, for a mode selective analysis of the DOS-spectra.

  • Textured -Fe was investigated up to 130 GPa, the mode-specific analysis of

  • the E2g mode shows very good agreement with a Raman study, the sound

  • velocity is at 130 GPa faster along the c-axis by almost 10% than in the

  • a,b-plane.

  • - Application of the difference method to SnO reveal drastic differences in the

  • phonon DOS seen parallel and perpendicular to the c-axis; pressure reduces

  • this anisotropic behaviour, reflected in a soft mode, and makes the

  • phonon DOS more isotropic.


Introduction 3937578

Acknowledgment

Paderborn group : G. Wortmann

U. Ponkratz

K. Rupprecht

R. Lübbers

iron at ESRF : A.I. Chumakov

O. Leupold

A. Barla

SnO at APS : W. Sturhahn

M.Y. Hu

E.E. Alp

SnO at HASYLAB : F. Porsch


  • Login