the structure of ges3-ag glassesnphys/rmc5/talks/ratkai.pdfthe structure of ges 3-ag glasses...

The structure of GeS3-Ag glasses

László Rátkai

MTA Wigner Research Centre for PhysicsInstitute for Solid State Physics and Optics

Budapest, RMC-5 Conference20th September, 2012

László Rátkai (Wigner RCP) The structure of GeS3-Ag glasses

Table of Contents

Application and sample preparationMeasurements dataRMC simulation setupFit qualitiesPair correlation functionsCoordination numbers and conclusions


Application and sample preparation

Ge-S-Ag can be used as electrochemical electrodes or theirmembranes for sensors for potentiometric determination of ions

4 samples: GeS3 and doped with 15, 20, 25 at% Aghigh purity elements: Ge (5N), S (4.5N), Ag (3N)in quartz evacuated ampoules in rocking furnace

0

200

400

600

800

1000

0 5 10 15 20 25

Tem

pera

ture

(°C

)

Time (hours)

Thermal history of GeS3-Ag glasses

Samples: Jakub Kolar and Tomas Wagner, University of PardubiceLászló Rátkai (Wigner RCP) The structure of GeS3-Ag glasses

Measurements - Neutron diffraction

LLB Saclay, France, 7C2 diffractometer

-1

0

1

2

3

4

0 2 4 6 8 10 12 14 16

S(Q

)

Q (Å-1)

GeS3

GeS3-15Ag

GeS3-20Ag

GeS3-25Ag

Measured by Brigitte BeuneuLászló Rátkai (Wigner RCP) The structure of GeS3-Ag glasses

Measurements - X-ray diffraction

BW5 beamline, HASYLAB, Hamburg, Germany

-2

-1

0

1

2

3

4

0 5 10 15 20 25

S(Q

)

Q (Å-1)

GeS3GeS3-15Ag

GeS3-20Ag

GeS3-25Ag

Measured by Ivan KabanLászló Rátkai (Wigner RCP) The structure of GeS3-Ag glasses

Measurements - Ge-EXAFS

X1 beamline, HASYLAB, Hamburg, Germany

-8-6-4-2 0 2 4 6 8

10

4 5 6 7 8 9 10 11 12

k3χ(

k)

k (Å-1)

Ge K-edge EXAFS

GeS3-Ag15-Ag20-Ag25

Measured by Iva Voleská and Jóvári PálLászló Rátkai (Wigner RCP) The structure of GeS3-Ag glasses

Measurements - Ag-EXAFS

X1 beamline, HASYLAB, Hamburg, Germany

-1.5

-1

-0.5

0

0.5

1

1.5

4 5 6 7 8 9 10 11 12

k3χ(

k)

k (Å-1)

Ag K-edge EXAFS

GeS3-15AgGeS3-20AgGeS3-25Ag

Measured by Iva Voleská and Jóvári PálLászló Rátkai (Wigner RCP) The structure of GeS3-Ag glasses

RMC simulations

simulation box contains 12000 atomscut off distances: [Å]

Ge-Ge Ge-S Ge-Ag S-S S-Ag Ag-Ag

GeS3 3.1 2.0 1.95Ag 15,20,25 2.35 2.0 3.15 1.95 2.2 2.85

constraints:NGe = 4no S-S between 2.15 and 2.7 Å to avoid overlap with Ge-Sand Ag-S

backscattering factors for EXAFS calculated with FEFF 8.4


-1.2

-0.8

-0.4

0

0.4

0.8

0 2 4 6 8 10 12 14

S(Q

)

ND fit for GeS3

fitexperiment

-1.2

-0.8

-0.4

0

0.4

0.8

0 5 10 15 20 25

XRD fit for GeS3

fitexperiment

-1.6

-1.2

-0.8

-0.4

0

0.4

0.8

0 2 4 6 8 10 12 14

S(Q

)

Q (Å-1)

ND fit for GeS3-25Ag

fitexperiment

-1.2

-0.8

-0.4

0

0.4

0.8

0 5 10 15 20 25Q (Å-1)

XRD fit for GeS3-25Ag

fitexperiment


-8-6-4-2 0 2 4 6 8

4 5 6 7 8 9 10 11 12

k3χ(

k)

k (Å-1)

Ge EXAFS fit for GeS3-25Ag

fitexperiment

-1.5

-1

-0.5

0

0.5

1

1.5

4 5 6 7 8 9 10 11 12k (Å-1)

Ag EXAFS fit for GeS3-25Ag

fitexperiment

-8-6-4-2 0 2 4 6 8

10

4 5 6 7 8 9 10 11 12

k3χ(

k)

k (Å-1)

Ge EXAFS fit for GeS3


Are there any Ge-Ge bonds?

Ge EXAFS fits in GeS3-25Ag for the two cases:

-8-6-4-2 0 2 4 6 8

4.5 5 5.5 6 6.5 7

k3χ(

k)

k (Å-1)

with Ge-Ge

fitexperiment

-8-6-4-2 0 2 4 6 8

4.5 5 5.5 6 6.5 7k (Å-1)

without Ge-Ge

fitexperiment

R-factor was 40% higher without Ge-Ge bonds for Ag > 15at. %rGe-Ge = 2.4Å, as expected


GeS3 PPCF

0

2

4

6

8

10

12

1 2 3 4 5 6 7 8r (Å)

rGe-S = 2.23ÅrS-S = 2.08Å

S-S

Ge-S Ge-GeGe-S

S-S


GeS3-25Ag PPCF

0

2

4

6

8

10

12

1 2 3 4 5 6 7 8r (Å)

rGe-Ge = 2.40ÅrS-Ag = 2.54Å

rAg-Ag = 2.95Å

S-S

Ge-S

Ge-Ge

S-AgAg-Ag

Ge-GeGe-S

Ge-AgS-S

S-AgAg-Ag


0

1

2

3

4

5

6

7

2 2.5 3 3.5 4 4.5 5

g ij(r

)Ge-Ge PPCF GeS3

-Ag15-Ag20-Ag25

0

2

4

6

8

10

12

1.5 2 2.5 3 3.5 4 4.5

Ge-S PPCF GeS3-Ag15-Ag20-Ag25

0

1

2

3

4

5

6

7

1.5 2 2.5 3 3.5 4 4.5

g ij(r

)

r (Å)

S-S PPCF GeS3-Ag15-Ag20-Ag25

0 0.5

1 1.5

2 2.5

3 3.5

4

2 2.5 3 3.5 4 4.5r (Å)

S-Ag PPCF -Ag15-Ag20-Ag25

0 0.5

1 1.5

2 2.5

3 3.5

4

2.5 3 3.5 4 4.5 5r (Å)

Ag-Ag PPCF -Ag15-Ag20-Ag25


0

1

2

3

4

5

6

7

1.5 2 2.5 3 3.5 4 4.5

g ij(r

)

r (Å)

S-S PPCF GeS3-Ag15-Ag20-Ag25

0 0.5

1 1.5

2 2.5

3 3.5

4

2 2.5 3 3.5 4 4.5r (Å)

S-Ag PPCF -Ag15-Ag20-Ag25

0 0.5

1 1.5

2 2.5

3 3.5

4

2.5 3 3.5 4 4.5 5r (Å)

Ag-Ag PPCF -Ag15-Ag20-Ag25


Coordination numbers

NGe-Ge NGe-S NS-Ge NS-S NS-Ag NAg-S NAg-Ag NS NAg

GeS3 - 3.90 1.30 0.86 2.16-15Ag 0.64 3.20 1.07 1.06 0.51 2.17 0.73 2.64 2.90-20Ag 0.69 3.30 1.10 0.96 0.95 2.86 0.82 3.01 3.68-25Ag 0.75 3.25 1.08 0.95 1.27 2.86 0.93 3.30 3.79

NGe-Ge+NGe-S and NS-Ge + NS-S remain the same for theAg-doped alloysNS and NAg increase with Ag content


Molar volumes

13 13.5

14 14.5

15 15.5

16 16.5

17 17.5

18

0 5 10 15 20 25 30

mol

ar v

olum

e (c

m3 )

Ag at%

alloymatrix

Density measurement: Tomas Wagner et al.László Rátkai (Wigner RCP) The structure of GeS3-Ag glasses

Conclusions

GeS3-Ag glasses were studied by RMC simulation with 4experimental data setsGe-Ge bonds are necessary to obtain good fit quality forAg > 15 at%Ag atoms avoid Ge atomsAg atoms don’t enter the Ge-S covalent network but inducesome rearrangement

NGe-Ge +NGe-S ≈ 4NS-Ge +NS-S ≈ 2


Thanks for the attention!

Acknowledgements:Brigitte Beuneu, Iva Voleska, Ivan Kaban, Jakub Kolar,

Jóvári Pál, Tomas Wagner


the structure of ges3-ag glassesnphys/rmc5/talks/ratkai.pdfthe structure of ges 3-ag glasses...

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