Structure and dynamics of ion-exchanged glasses

E.I. Kamitsos, R. Todorov and C.P. Varsamis

Theoretical and Physical Chemistry Institute

National Hellenic Research Foundation, Athens, Greece

17th Universtity Conference on Glass Science&

1st International Materials Institute Workshop on NEW FUNCTIONALITY IN GLASSES

June 26-30, 2005 / State College, Pennsylvania

Outline of presentation

Ion-exchange process: introduction & relevant literature

Structure of ion-exchanged soda-lime-silica glass

Structure of ion-exchanged 30Na2O-70B2O3 glass

ac conductivity spectra of ion-exchanged 30Na2O-70B2O3 glass

Summary

ION EXCHANGE PROCESS IN GLASS

Applications:

- Chemical strengthening of commercial silicate glass

- Altering optical properties of glass (waveguides, micro-optics)

Open Questions:

- Is there a “mixed-alkali effect” in ion-exchanged glasses?

- How are K+ ions accommodated within the glassy network?

- Can any changes in glass structure occur as a result of ion-exchange below Tg?

M.E. Nordberg et. al.

J. Am. Ceram. Soc.

47 (1964) 215.

ion “crowding”

compressive stress

permanent compression

TTg

0,0 0,2 0,4 0,6 0,8 1,0

10-7

10-6

10-5

10-4

10-3

0C

0.3[xK2O-(1-x)Na

2O]-0.7B

2O

3

310

282

253

239

216

198

180

dc (S

m-1)

K2O/[Na

2O+K

2O]

0,0 0,2 0,4 0,6 0,8 1,0

0,7

0,8

0,9

1,0

0.3[xK2O-(1-x)Na

2O]-0.7B

2O

3

Ea

dc (

eV

)K

2O / [Na

2O+K

2O]

Mixed Alkali Effect (MAE) in melt-grown glasses

1,7 1,8 1,9 2,0 2,1 2,2 2,3 2,4

-18

-16

-14

-12

-10

-8

-6

-4

dc

=0 exp[-E

a

dc/ kT]

x=0.75

x=0.25

x=0.167

x=0.83

x=0.50

x=1.0

x=0.0

0.3[xK2O-(1-x)Na

2O]-0.7B

2O

3

(eV)

Ea

dc = 0.72

Ea

dc = 0.90

Ea

dc = 0.95

Ea

dc = 1.00

Ea

dc = 0.95

Ea

dc = 0.91

Ea

dc = 0.76

ln

dc (

Sm

-1)

1000/T (K-1)

G. Tomandl & H.A. Schaeffer, Non-Cryst. Solids, Trans. Tech. Publ., pp. 480-485 (1977).

Ion-exchanged glasses below Tg do not show the MAE; i.e. resistivity shows a linear

behavior throughout the ion-exchanged layer

Ion-exchange below Tg generates a different “mixed-alkali structure” than the melting

process.

Mixed alkali glasses by ion exchange

0,0 0,2 0,4 0,6 0,8 1,0

4

6

8

10

(K/Na) mixed-alkali soda-lime-silica glasses

solid: melt-grown

dashed: ion-exchanged

T=500°C

T=400°C

log (

cm

)

[K2O]/[K

2O+Na

2O]

T=200°C

T=300°C

Mixed alkali glasses by ion exchange, cont.

C. Windisch & W.M. Risen, J. Non-Cryst. Solids, 44, 345 (1981).

(Na/Li) ion-exchanged Li2O-Al2O3-2SiO2 glasses / Raman spectroscopy

Network structure of ion-exchanged glasses is different from that of melt-grown glasses of

the same stoichiometry

Annealing the ion-exchanged glass leads to network structure identical to that of the melt-

grown glass.

S.N. Houde-Walter, J.M. Inman, A.J. Dent & G.N. Greaves, J. Phys. Chem. 97, 9330 (1993).

(Ag/Na) ion-exchanged Na2O-4SiO2 glasses / X-ray absorption fine structure (XAFS)

CN (Na/O) 5, r(Na-O)=2.30-2.32 Å

CN (Ag/O) 2, r(Ag-O)=2.08-2.23 Å (very similar to the environment of Ag in Ag2O)

metal ions create their own characteristic environments in glass.

G. Berg & A. Ludwig, J. Non-Cryst. Solids, 170, 109 (1994).

(Ag/Na) ion-exchanged soda-lime silica glass / ac conductivity (at 102, 103 Hz)

Concentration dependence of ac conductivity shows the typical mixed cation effect.

M. Dubiel, B. Roling & M. Futing, J. Non-Cryst. Solids, 331, 11 (2003).

(K/Na) ion-exchanged soda-lime glass / ac conductivity spectroscopy (10-2 to 106 Hz)

No MAE for ion-exchange below Tg; but presence of MAE for ion-exchange slightly above Tg

Spectral shape of ac conductivity indicates differences in the ion dynamics between glasses

exchanged slightly above Tg and the corresponding melt-grown glasses.

Mixed alkali glasses by ion exchange, cont.

T. Yano, K. Azegami, S. Shibata & M. Yamane, J. Non-Cryst. Solids, 222, 94 (1997).

(Ag/Na) ion-exchanged Na2O-2SiO2 glasses / X-ray photoelectron spectr. (XPS) & 29Si-NMR

Ag ions induced a large charge redistribution on the glass network & an anomalous change

in the distribution of Qn silicate units

formation of Q2 units at the expense of Q3 units, but no Q4 formation.

Y-K. Lee, Y.L. Peng & M. Tomozawa, J. Non-Cryst. Solids, 222, 125 (1997).

(K/Na) ion-exchanged soda-lime glass / FT-IR reflectance spectroscopy

Shift of the 1050 cm-1 peak is much larger than that caused by changes of the fictive

temperature or composition. Thus, the shift of 1050 cm-1 peak is due mainly to the stress.

A new peak at 950 cm-1 develops with ion-exchange and is attributed to formation of non-

bridging oxygen atoms.

EXPERIMENTAL DETAILS…

Glass Compositions Investigated (mol%)

A. Soda-Lime-Silica Glasses

Oxide

Pilkington

float glass (Tg=558 0C)

(FGS0)

Soft glass

tubing

(T0)

SiO2 71.78 71.62

Na2O 12.44 14.02

CaO 8.76 6.19

K2O 0.38 1.03

MgO 5.88 4.82

BaO none 1.50

Al2O3 0.58 1.49

Fe2O3 0.04 0.02

SO3 0.14 0.22

B. Sodium-Borate Glass: 30Na2O-70B2O3

(Tg=477 0C)

INFRARED SPECTRAL MEASUREMENTS:

Specular reflectance at quasinormal incidence (110)

use the same sample for continuous date acquisition in the mid- & far-IR range

(25-5,000 cm-1)

IMPEDANCE MEASUREMENTS:

5Hz -10MHz, f(T)

ELECTRON MICROPROBE ANALYSIS:

K, Na profiles (Na Kα& Κ Κα Χ-rays produced

by a 15 kV, 20-50 nA, e-beam)

GLASS COMPOSITIONS & SPECTROSCOPIC TECHNIQUES

ANALYSIS OF REFLECTIVITY SPECTRA

0 200 400 600 800 1000 1200 1400

0,0

0,1

0,2

0,3

0.2Na2O-0.8SiO

2

Wavenumbers (cm-1)

Re

fle

ctivity

1,0

1,5

2,0

2,5

0 200 400 600 800 1000 1200 1400

0,0

0,5

1,0

1,5

Wavenumbers (cm-1)

x=0.20

n

n k

0

2

4

200 400 600 800 1000 1200 1400

0

2

4

6

Wavenumbers (cm-1)

'

x=0.20

''

0 200 400 600 800 1000 1200 14000

5

10

15

20

Wavenumbers (cm-1)

x=0.20

(

) (1

03 c

m-1)

Kramers – Kronig

transformation

0 100 200 300 4000,0

0,5

1,0

1,5

2,0

2,5

3,0

Li

CsK

Na110

155

215

Abs.C

oeff

. (1

03 c

m-1)

Wavenumbers (cm-1)

Li2O.2SiO

2

Na2O.2SiO

2

K2O.2SiO

2

Cs2O.2SiO

2

0 200 400 600 800 1000 1200 1400

xNa2O-(1-x)SiO

2

1085

502

250

215

773

7351075

970

1050935

x=0.45

x=0.40

x=0.33

x=0.30

x=0.25

x=0.20

x=0.15

x=0.10

AB

SO

RP

TIO

N (

arb

. u

nits)

x=0

1103

470

810

Wavenumbers (cm-1)

Q4

Q3

Q2

Short-range order structure and metal ion-site vibrations

in silicate glasses

Continuous Random Network (CRN) Model

Na2O-SiO2SiO2

Zachariasen, 1932 Warren-Biscoe, 1938

Q0

Qn tetrahedral units in silicate glasses

0 100 200 300 4000,0

0,5

1,0

1,5

2,0

2,5

3,0

Li

CsK

Na110

155

215

Abs.C

oeff

. (1

03 c

m-1)

Wavenumbers (cm-1)

Li2O.2SiO

2

Na2O.2SiO

2

K2O.2SiO

2

Cs2O.2SiO

2

0 200 400 600 800 1000 1200 1400

xNa2O-(1-x)SiO

2

1085

502

250

215

773

7351075

970

1050935

x=0.45

x=0.40

x=0.33

x=0.30

x=0.25

x=0.20

x=0.15

x=0.10

AB

SO

RP

TIO

N (

arb

. u

nits)

x=0

1103

470

810

Wavenumbers (cm-1)

Q4

Q3

Q2

Short-range order structure and metal ion-site vibrations

in silicate glasses

0 100 200 300 4000,0

0,5

1,0

1,5 230

130

(K)

(Na)

Abs. C

oeff

. (1

03 c

m-1)

F1

F2

F3

F4

F5

Wavenumbers (cm-1)

900 1000 1100 1200 1300

0

5

10

15

20

25

[K+][K

+]

F1

F3

F5

Abs. C

oeff

. (1

03 c

m-1)

Wavenumbers (cm-1)

“Synthetic” float glasses

mol% F1 F2 F3 F4 F5

Na2O 12.44 9.61 6.41 3.21 0.38

K2O 0.38 3.21 6.41 9.61 12.44

Q2 + Q4 2Q3

IR SPECTRA OF “SYNTHETIC” MIXED-CATION (Na+/K+) FLOAT GLASSES

)( /

0

24

4 SiOQ

)( -

/ OSiOQ 23

3

)( -

/

2

222

2 OSiOQ

THERMALLY ION-EXCHANGED FLOAT GLASS: K+/Na+

Q2 + Q4 2Q3

glass structure becomes

more homogeneous

T=475 0C

t=16h

900 1000 1100 1200 13000

5

10

15

20

25 Thermal Exchange

in KNO3, T=475

oC

FGS0

FGS1, t=3 h

FGS2, t=16 h

(

10

3 c

m-1)

Wavenumbers (cm-1)

[K+]

0 100 200 3000,0

0,5

1,0

Thermal Exchange

in KNO3, T=475

oC

FGS0

FGS1, t=3 h

FGS2, t=16 h

(

10

3 c

m-1)

Wavenumbers (cm-1)

[Na+]

[K+]

Tg=558 0C

ANNEALING OF ION-EXCHANGED (K+/Na+) FLOAT GLASS

FGS0: pristine float glass

FGS2: FGS0 thermally exchanged

in KNO3 at 475 0C for 16h

FGS2A: FGS2 annealed in air

at 475 0C for 16 h

0 100 200 3000,0

0,5

1,0

FGS0

FGS2

FGS2A

(

) (1

03 c

m-1)

Wavenumbers (cm-1)

[Na+]

[K+]

900 1000 1100 1200 1300

0

5

10

15

20

FGS0

FGS2

FGS2A

(

) (1

03 c

m-1)

Wavenumbers (cm-1)

[Na+] [Na+]

2Q3 Q2 + Q4

glass structure becomes

less homogeneous

Infrared spectra of singe alkali borate glasses

0 200 400 600 800 10001200140016000

2

4

6

8

10

12

14

16

18

M+-Site vibr.

Network def.

BO3 str.BO

4 str.

M2O.2B

2O

3

Li

Na

K

Rb

Cs

Ab

so

rptio

n C

oe

ffic

ien

t (1

03 c

m-1)

Wavenumbers (cm-1)

IR SPECTRA OF “SYNTHETIC” MIXED-CATION BORATE GLASSES

0.3[xK2O-(1-x)Na2O]-0.7B2O3

0 100 200 300 4000,0

0,5

1,0

1,5230 (Na)

172 (K)

0.3[xK2O-(1-x)Na

2O]-0.7B

2O

3

x=0.0 (Na)

x=0.25

x=0.50

x=0.75

x=1.0 (K)

(

10

3cm

-1)

Wavenumbers (cm-1)

600 800 1000 1200 1400 16000

3

6

9

12

15xK

2O-(0.3-x)Na

2O-0.7B

2O

3

x=0.0 (Na)

x=0.075

x=0.15

x=0.225

x=0.3 (K)

(10

3cm

-1)

Wavenumbers (cm-1)

THERMALLY ION-EXCHANGED 0.3Na2O-0.7B2O3 GLASS: K+/Na+

IR reflectance spectra

0 500 1000 1500 2000 25000,0

0,1

0,2

0,3

0,40.3Na

2O-0.7B

2O

3

offset by 0.07

R

eflecta

nce

Wavenumbers (cm-1)

Ion-exchange in KNO3

at 450 0C for:

t=0 min

t=15 min

t=30 min

t=60 min

THERMALLY ION-EXCHANGED 0.3Na2O-0.7B2O3 GLASS: K+/Na+

IR absorption spectra

600 800 1000 1200 1400 16000

5

10

150.3Na

2O-0.7B

2O

3

(

) (1

03 c

m-1)

Wavenumbers (cm-1)

Ion-exchange in KNO3

at 450 0C for:

t=0 min

t=15 min

t=30 min

t=60 min

0 100 200 300 4000,0

0,5

1,0

1,5

(

) (1

03 c

m-1)

0.3Na2O-0.7B

2O

3

Ion-exchange in KNO3

at 450 0C for:

t=0 min

t=15 min

t=30 min

t=60 min

Wavenumbers (cm-1)

Tg=477 0C

BØ4- BØ2O

-

local structure rearranges

to meet the needs of K+ ions

0 200 400 600 800 1000 1200 1400 16000

4

8

12

16

KNa

0.3Na2O-0.7B

2O

3 (from melt)

0.3Na2O-0.7B

2O

3 ion-exch. KNO

3,

450 oC, 60 min

0.3K2O-0.7B

2O

3(from melt)

(

10

3cm

-1)

Wavenumbers (cm-1)

BØ4-

BØ2O-(C2v)

A1+B2

BØ30 (D3h)

E’

100

101

102

103

104

105

106

107

10-4

10-3

T(°C)

310

296

282

254

268

240

226

217

199

180

0.3Na2O-0.7B

2O

3

f (Hz)

' (S

m-1)

Conductivity spectra of the base glass: 0.3Na2O-0.7B2O3

scaled conductivity spectra

see: B. Roling, A.Happe, K. Funke & M.D. Ingram,

Phys. Rev. Lett. 78 (1997) 2160.

2 4 6 8 10

0,0

0,2

0,4

0,6

0,8

1,0

T(0C)

180

199

217

226

240

254

268

282

296

310

0.3Na2O-0.7B

2O

3

log10

(f/dc

.T) (Hz/Sm-1.K)

log

10 (

'/

dc)

Conductivity spectra of the 0.3Na2O-0.7B2O3 glass ion-exchanged in KNO3

100

101

102

103

104

105

106

107

10-5

10-4

10-3

10-2

Ion-exchanged: KNO3,

450 0C, 30 min.

0.3Na2O-0.7B

2O

3

T (°C)

310

296

282

268

254

240

226

216

198

177

f (Hz)

' (

Sm

-1)

Comparison of conductivity spectra of the base glass 0.3Na2O-0.7B2O3

with those obtained after ion-exchange in KNO3 at 450 0C for 30 min

100

101

102

103

104

105

106

107

10-5

10-4

10-3

10-2

base glass

ion-exch. KNO3

450 0C, 30 min

0.3Na2O-0.7B

2O

3

T(°C)

310

268

216

177

f (Hz)

' (

Sm

-1)

scaled with σdc of the base glass

scaled with low-frequency σdc of

the ion-exchanged glass

K+/Na+ ion exchange below Tg

leads to the development of a highly resistive surface layer

0 2 4 6 8 10-1,0

-0,5

0,0

0,5

1,0

scaled high frequency region

T (0C)

310

296

282

268

254

240

226

216

198

177

0.3Na2O-0.7B

2O

3

t 30 min scaled base glass.opj

log( f / dc

.T) (Hz / Sm-1.K)

log

10( ' /

dc)

Scaled conductivity spectra of the 0.3Na2O-0.7B2O3 glass ion-exchanged

in KNO3 at 450 0C for 30 min

0 2 4 6 8 10

0

1

2

T(0C)

310

296

282

268

254

240

226

216

198

177

0.3Na2O-0.7B

2O

3

3.8.2004 12:41:57t 30 min scaled low freq.opj

log( f / dc

.T) (Hz / Sm-1.K)

log

10( ' /

dc)

10-6

10-5

10-4

10-3

100

101

102

103

104

105

106

107

10-5

10-4

10-3

10-2

30 min15 min

x=0.50

x=0.75

x=0.25

x=1 (K)

x=0 (Na)

T=238oC

x=1 (K)

x=0 (Na)

x=0.75

T=310oC

0.3[xK2O-(1-x)Na

2O]-0.7B

2O

3

30 min15 min

x=0.50

x=0.25

' (

Sm

-1)

f (Hz)

Comparison of conductivity spectra of mixed alkali glasses

0.3[xK2O-(1-x)Na2O]-0.7B2O3 : melt-grown vs ion-exchanged glasses

1,7 1,8 1,9 2,0 2,1 2,2 2,3 2,4

-18

-16

-14

-12

-10

-8

-6

-4

dc

=0 exp[-E

a

dc/ kT]

x=0.75

x=0.25

x=0.167

x=0.83

x=0.50

x=1.0

x=0.0

0.3[xK2O-(1-x)Na

2O]-0.7B

2O

3

(eV)

Ea

dc = 0.72

Ea

dc = 0.90

Ea

dc = 0.95

Ea

dc = 1.00

Ea

dc = 0.95

Ea

dc = 0.91

Ea

dc = 0.76

ln

dc (

Sm

-1)

1000/T (K-1)

Comparison of activation energies for dc conductivity:

melt-grown 0.3[xK2O-(1-x)Na2O]-0.7B2O3 glasses vs ion-exchanged glasses

1,7 1,8 1,9 2,0 2,1 2,2 2,3

-12

-11

-10

-9

-8

-7

-6

-5

Ion-exch. KNO3, 450

0C

0.3Na2O-0.7B

2O

3

Ea

dc=0.72 eV

Ea

dc=0.84 eV

Ea

dc= 0.93 eV

Ea

dc=0.85 eV

Ea

dc=0.76 eV

ln

dc (

Sm

-1)

1000/T (K-1)

0.3Na2O-0.7B

2O

3

15 min

30 min

120 min

0.3K2O-0.7B

2O

3

melt-grown ion-exchanged

Dielectric spectra in the resistivity representation

Dielectric measurements: apply voltage V(ω)=Vmsin(ωt)

measure current I(ω)=Ιm sin(ωt+δ)

Complex impedance:

Complex resistivity:

d=sample thickness; S=electrode area

Complex conductivity:

)(–)(=)( ///* ωiZωZωZ

m

m

I

VZδZZδZZ =,sin=,cos= **//*/

d

SωZωρiωρωρ )(=)(–)(=)( *///*

)(

1=)(+)(=)( *

///*

ωρωσiωσωσ

22 )]([+)]([

)(=)( ///

/

/

ωρωρ

ωρωσ

22 )]([+)]([

)(=)( ///

/

/

ωσωσ

ωσωρ

100

101

102

103

104

105

106

107

102

103

104

T(°C)

310296282

254

268

240226

217

199

180

0.3Na2O-0.7B

2O

3

f (Hz)

' (

m)

1 2 3 4 5 6 7 8

0,0

0,2

0,4

0,6

0,8

1,0

T(0C)

0.3Na2O-0.7B

2O

3

T=310

T=296

T=282

T=268

T=254

T=240

T=226

T=217lo

g(

dc /

')

log(fdc

/T) (Hz/Sm-1K)

Resistivity spectra of the base glass: 0.3Na2O-0.7B2O3

scaled resistivity spectra

100

101

102

103

104

105

106

107

102

103

104

105 0.3Na

2O-0.7B

2O

3T(°C)

base glass

ion-exch. 15 min

ion-exch. 30 min

KNO3, 450

0C

310

268

226

180

f (Hz)

' (

m)

Resistivity spectra of the 0.3Na2O-0.7B2O3 glass ion-exchanged in KNO3

Resistivity spectra of the 0.3Na2O-0.7B2O3 glass ion-exchanged in KNO3

0

200

400

101

102

103

104

105

106

107

0

200

400

T=310°C

Ion-exch. KNO3, 450

0C,15 min

' ion exchange

'' ion exchange

Fit ion-exchanged layer with 3 comp.

K/Na: 3/1, 1/1, 1/3

K/(K+Na): 0.75, 0.50, 0.25

0.3Na2O-0.7B

2O

3

Ion-exch. KNO3, 450

0C, 30 min

T=310°C

', ''

(m

)

f (Hz)

K/Na dei (μm)

15 min 30 min

3/1 0.7 0.9

1/1 1.4 2.5

1/3 1.7 2.7

de 3.8 6.1

0

200

400

101

102

103

104

105

106

107

0

5000

10000

T=310 °C

Ion-exch. KNO3,

450 0C, 15 min

'

''

Fit '

Fit ''

',

'' (

m)

0.3Na2O-0.7B

2O

3

T=216 °C

f (Hz)

“Annealing” of the 0.3Na2O-0.7B2O3 ion-exchanged glass

K/Na dei (μm)

216 0C 310 0C

3/1 1.2 0.7

1/1 1.0 1.4

1/3 0.4 1.7

de 2.6 3.8

“Annealing” of the 0.3Na2O-0.7B2O3 ion-exchanged glass, cont.

0 1 2 3 4 5 6 7 8 9

2,6

2,8

3,0

3,2

3,4

3,6

3,8

4,0

Ion-exch. KNO3,

450 0C, 15 min

T (0C)

0.3Na2O-0.7B

2O

3

310

296

282

268

253

239

226

217

de (m

)

"Annealing" time (hrs)

Structural aspects of ion-exchanged glasses: soda-lime-silica & sodium-borate

Alkali ion motion in the glass matrix below Tg, caused either by ion exchange and/or

annealing, is accompanied by local structural rearrangements/relaxations involving short-

range order structural units (Cation Induced Relaxations Of the Network, CIRON).

The structural rearrangements depend on the nature of the glass network and the

type of the foreign cation introduced into the glass structure:

Soda-lime-silica glass:

K+/Na+: Q2 + Q4 2Q3

Li+, Ag+/Na+: 2Q3 Q2 + Q4

Sodium-borate glass:

K+/Na+: BØ4- BØ2O

-

The structure of an ion-exchanged glass resembles that of the corresponding melt-

grown mixed alkali glass (i.e. similar SRO structure and nature of sites hosting metal

ions).

SUMMARY

Ac conductivity aspects of ion-exchanged glasses: sodium-borate glass

The resistivity of the ion-exchanged (surface) layer can be described in terms of the

resistivities of melt-grown K/Na mixed alkali glasses.

SUMMARY cont.

ACKNOWLEDGMENT

Univ. of Aberdeen, Scotland: M.D. Ingram, J. Davidson, M.H. Wu, A. Coats

NHRF, Athens: J. Kapoutsis, P. Machowski.

Royal Society / NHRF (exchange program)

General Secretariat for Research and Technology / Ministry of

Development in Greece

European Union (project HPMD-CT-2000-00033).