H. Giefers, University of Paderborn Introduction XAFS 12 in Malmö 24. June 2003 High-pressure EXAFS and XRD investigation of unit cell parameters of SnO

H. Giefers, University of Paderborn

Introduction

XAFS 12 in Malmö24. 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


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


SnO under pressure

D.M. Adams et al., Phys. Rev. B46, 11358 (1992).

N.R. Serebryanaya et al., Dokl. Akad. Nauk SSSR 187, 307 (1969).

E.V. Kapitanov, E.N. Yakovlev, Phys. Stat. Sol. A51, 641 (1979).

a

b

cc

a

b

- 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


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: 0.2×0.2 mm2

- diamond anvil cell- liquid N2 as pressure transmitting medium- Gold powder as pressure marker - sample size Ø 0.4 mm2



30 35 40 45 50 55 60

p = 11.5 GPaK 1,

2

111 21

1

11220

0

Au2

00

002

Au1

11110

101

Energy (keV)

p = 4.65 GPaK 1,

2

211

112

200

Au2

00Au1

1100

2

11010

1

ambient pressure = 3.912°

211

112

200

Au2

00Au1

1100

2

110

101K 1,

2

norm

. In

tens

ity (

a.u.

)

- 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

300 280 260 240 220 200 180

different pressure transmitter

Au200

112NaCl220

200

MgO200

Au111

SnO @ 2 GPa

110

NaCl200

101

d (pm)

norm

. Int

ensi

ty (

a.u.

) lN2 2.0 GPa NaCl 1.6 GPa MgO 2.2 GPa


0 2 4 6 8 10 12

1.16

1.18

1.20

1.22

1.24

1.26

1.28 (b)

Pressure (GPa)

c/a

0.88

0.92

0.96

1.00 (a)

a/a 0

c/c 0

a/a 0

, c/

c 0

0 2 4 6 8 10 12

0.85

0.90

0.95

1.00EOS: Birch

p (GPa)

V/V

0

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




C u B e98 2

brass

B C4

C u

stee l

10 m m

- 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)



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 0.8×0.8 mm2


29.1 29.4 29.7 30.0 30.30.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6SnO

10 GPa 0.0 GPa

Energy (keV)

norm

. Int

ensi

ty (

a.u.

)

25.5 25.8 26.1 26.4 26.7

10 GPa 0.0 GPa

Ag

Energy (keV)

4 6 8 10 12 14-1.0

-0.5

0.0

0.5

1.0

k (Å-1)

(k)

·k2

4 6 8 10 12 14

-1

0

1

k (Å-1)

(k)

·k2


EXAFS of:

sample SnOandpressure marker Ag

together in the HP cell


0 1 2 3 4 5 6

SnO

10 GPa

9.6 GPa

9.2 GPa

8.4 GPa

7.5 GPa

6.8 GPa

5.7 GPa

5.1 GPa

3.9 GPa

2.1 GPa

1.0 GPa

0.8 GPa

0.0 GPa

FT

[ (

k)·k

2 ]

R' (Å)1 2 3 4 5

Ag

10 GPa

9.6 GPa

9.2 GPa

8.4 GPa

7.5 GPa

6.8 GPa

5.7 GPa

5.1 GPa

3.9 GPa

2.1 GPa

1.0 GPa

0.8 GPa

0.0 GPa

R' (Å)




0 2 4 6 8 102.17

2.18

2.19

2.20

2.21

2.22

p (GPa)

RS

n-O (

Å)

0 2 4 6 8 10

4.5

5.0

5.5

p (GPa)

2 (10

-3 Å

2 )

- 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 orthorhombic structure


Combination of EXAFS and EDXRD results of SnO

- a and c from EDXRD- RSn-O from EXAFS

c

aRSnz

22OSn 25.0

- 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

0 2 4 6 8 10

0.24

0.25

0.26

0.27

p (GPa)

z(S

n)

1.00

1.02

1.04

1.06

1.08

1.10

1.12

1.14

z/z0


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

Documents

H. Giefers, University of Paderborn Introduction XAFS 12 in Malmö 24. June 2003 High-pressure EXAFS and XRD investigation of unit cell parameters of SnO