Université Montpellier II

Ion diffusion in chalcogenide glasses

Application in ionics and optics

Michel RIBES and Annie PRADEL

Laboratoire de Physicochimie de la Matière Condensée

UMR 5617 CNRS

Université Montpellier II, Montpellier FRANCE

An IMI Video Reproduction of Invited Lectures

from the 17th University Glass Conference

Chalcogenide Glasses

Chalcogenide homologous of oxide glasses

SiO2 ; GeO2 --> SiS(e)2 ; GeS(e)2

Ia 01

HIIa IIIa IVa Va VIa VIIa 2

He3

Li4

Be5

B6

C7

N8

O9

F10

Ne11

Na12

MgIIIb IVb Vb VIb VIIB VIIIb Ib IIb 13

Al14

Si15

P16

S17

Cl18

Ar19

K20

Ca21

Sc22

Ti23

V24

Cr25

Mn26

Fe27

Co28

Ni29

Cu30

Zn31

Ga32

Ge33

As34

Se35

Br36

Kr37

Rb38

Sr39

Y40

Zr41

Nb42

Mo43

Tc44

Ru45

Rh46

Pd47

Ag48

Cd49

In50

Sn51

Sb52

Te53

I54

Xe55

Cs56

Ba57

La72

Hf73

Ta74

W75

Re76

Os77

Ir78

Pt79

Au80

Hg81

Tl82

Pb83

Bi84

Po85

At86

Rn87

Fr88

Ra89

Ac104

Unq105

Unp106

Unh107

Uns

58

Ce59

Pr60

Nd61

Pm62

Sm63

Eu64

Gd65

Tb66

Dy67

Ho68

Er69

Tm70

Yb71

Lu90

Th91

Pa92

U93

Np94

Pu95

Am96

Cm97

Bk98

Cf99

Es100

Fm101

Md102

No103

Lr

Chalcogenide glasses are glasses containing chalcogens (Se, S, Te).

They exhibit semiconductor properties and thus form a large group of amorphous semiconductorsIntrinsically metastable, they can undergo various structural transformations under the action of external stimuli, in particular light.

Presence of S, Se, Te --> polarisable environment with lone-pair (LP)

Specific property of chalcogenide glasses compared to oxide ones

Chalcogenide Glasses

Semiconductor

Transparency in the IR

Photoinduced phenomena

hn -> hole-electron pair -> change in n

Ovshinsky effect(amorphous state <-> crystalline state)

As2S3 glass ~ 10-14 Scm-1

Eg ~ 2,15 eV

Application of ion diffusion in chalcogenide glasses

Interface ion exchange

Ion sensors

Diffusion under E

Electrochemical energy storage : batteries

Diffusion under photons hn

Photoinduced phenomena

Diffusion under E and hn

PMC memories

Principle of a sensor

Analyteanalysis

and

treatment

system

Electrical

signalsensitive part Transductor

Characteristic

information

CHEMICAL or PHYSICAL SENSOR

Membrane Potentiometric

FET

Sensitivity, reversibility, selectivity and stability

Ion exchange : Chemical Sensor

Ion-selective electrode

D. L.

i

i

0 aLogFz

RTEE

Potentiometric analysis of a chemical sensordepends on the relationship between theconcentration of the species and the e.m.f.The ideal relationship is known as the Nernstequation :

determination of e.m.f between the ISE and a reference electrode.

Typical calibration curve of an ion-selective electrode obtained with the wellknown addition method.

Linear range and detection limit

Slope of the response

Development of ISE chemical microsensors

Analytical device for Cu2+ ion detectionbased on (1-X)Sb12Ge28Se60 - XCu glassy thin films.

epoxy resine

Cr

Si/Si3N4

Silver paste

metal connection

substrate

ion-sensitive

membrane

.

ion-sensitive

membrane

10 cm

epoxy resine

metal connection

C.Cali,D.Foix,E.Siebert,D.Gombeau,A.Pradel, M. Ribes; Solid. State. Engineering C21 (2002) 3-8

Elaboration of the (Sb-Ge-Se)/(Cu) material

Thin films produced by r.f. sputtering of a composite target

Film thickness varies from 0.4 to 1 µmdepending on sputtering conditions andsputtering time.

S.E.M cross sectional view of a thin film

copper(Sb12Ge28Se60)Target Chemical composition of thin films

1 (Sb11.3Ge30.4Se58.3)40(Cu)60

2 (Sb11Ge29Se60)50(Cu)50

Electrode response

Interfering Ion log K Cu2+ / j

K+ -5.1

Na+ -5.3

Ca2+ -5.1

Ni2+ -4.1

Cd2+ -4.1

Pb2+ -2.5

Mn2+ -3.4

-7 -6 -5 -4 -3

40

60

80

100

120

140

160

x=0.6

x=0.5

E (

mV

) vs

EC

S

Log [Cu2+

]

29 mV / pCu

D. L. 810-7 mol.l-1

Influence of pH on electrode response

Mixed solution method with constant a interfering ion concentration.

2 3 4 5 620

30

40

50

60

70

80

90

100

110

120

130

10-5 mol.l

-1

10-4 mol.l

-1

10-3 mol.l

-1

10-2 mol.l

-1

E (

mV

) vs.

EC

S

The material with x = 0.6 gives the best electrode performance.

Log [Cu2+]

pH

Diffusion under E : chemical energy storage

Superionic Conductive Glasses

Conductivity 100-1000 times larger than that of their oxide counterpart

r > 10 (Weak electrolyte theory)

Ag+ ~ 10-2 Scm-1

Li+ ~ 10-3 Scm-1

Application: all solid state batteries based on solid electrolytes

Rocking-chair Li-ion batteries for various portable equipments

Safety: prevent from igniting and leaking (liquid combustible organic solvent)

miniaturisation

-9

-8

-7

-6

-5

-4

-3

-2

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

EFFECT of MODIFIER

x M2S-(1-x) GeS2

X (M2S)2

Log

(Scm

-1)

Ag

Li

Na

At the begining: Li batteriesour first works (1983) Li/LiI-Li2S-GeS2(g)/V2O5

Eveready (USA)(90 ’s) Li/ sulfide (oxysulfide) (g)/various cathodic materials

Now Li-ion batteries (mainly japanese teams)Minami-Tatsumisago group (Osaka)

In/Li2S-P2S5glass-ceramics/LiCoO2 (Chem.Letters 2002)

Takada et al (NIMS-Tsukuba)

C/LiI-Li2S-P2S5 (g)//Li3PO3-Li2S-SiS2(g)/ LiCoO2 (SSI 2003)

Li-ion battery

Li+

Li+

Li+

Li+

Li+

e-

e-

e- e-

e-

e-

Electrolyte

Anode

Cathode

collector

Collector

Thin-films lithium battery developped at ORNL

Neudecker BJ, Dudney NJ and Bates JB ; J. Electrochem. Soc. 147 (2000) 517

Levasseur group Bordeaux Fr; Industrialization HEF Group (SVF Gazette du Vide 2 march 2003)

Li (or Li-ion) microbattery

Reduction of power supply of electronics devicesActive power sources:implantable medical devices, remote sensors, miniature transmitters, smart cards

Standby power sources:CMOS-SRAM memory devices (few mWh.cm-2 are required to back up a CMOS memory chip)

Photodissolution (« photodoping »)

Illumination of a chalcogenide film in contact with silver-> rapid penetration of the metal into the semiconductor(Kostyshin (1966))

Typical features :•large amount of Ag can be dissolved 30-40 at%, and even 57% in GeS3

•rate of dissolution depends on chalcogenide composition (excess in chalcogen)

Diffusion under photons hn: Photoinduced phenomena

Ag+

Light

Ag film ionization of Ag(semiconductor presence of holes or electrons)Ag + h+ Ag+ Ag Ag+ + e-

reduction of chalcogenide2Ag + Se Ag2Se DG°

298 ~ -25 kJ/mol4Ag + 2As2Se3 2Ag2Se + As4Se4 DG°

298 ~ -12 kJ/mol

Photo-enhanced solid state reaction

Mechanism

hn close to bandgap energy

T. Kawaguchi, K. Tanaka and S.R.Elliott; Handbook of advanced electronic and photonic materials and

devices AP, N.H Nalwa ed. (2001) p 91

Solubility of doped region in alkaline solvents much reduced

Local change in chemical composition

photoresists

etched gratings

Application of photodissolution

Very sharp edges between doped and undoped regions

Local creation of pairs « electron-hole » + small diffusion length of free carriers

Hardly any lateral diffusion

Photomigration - Photodeposition

Phenomenon observed in highly doped chalcogenide: Ag-Ge-S(e), Ag-As-S(e). For example in (Ge0.3S0.7)100-xAgx films when x > 0.45

lower silver content (x < 0.45) higher silver content (Ag45As15S40)

Illumination

increase in Ag density in the illuminated part

Reversible processAnnealing dissolution of the Ag clusters

precipitation of Ag

Small clusters or crystals 10nm in diameter and 1nm in thickness

200mW/cm2 530mW/cm2

T. Kawaguchi et al JNCS 212 (1997) 1666

Mechanism of photomigration-photodeposition

Point of view of chemist

Photodecomposition = decomposition of an oversaturated Ag solid solution

Under illumination the metastable system approaches equilibrium with excess Ag segregation.

Annealing at higher temperature allows Ag to dissolve again in the solid solution

Point of view of physicist

Illumination

creation of pair « electron-hole »

Ag+ + e- Ag h+ moves away from illuminated spot

Ag+

Ag

Particle

Ag+

Light

Application of photomigration-phodeposition

Increased reflectivity for Ag rich regionphotoexpansion

Au addition increase in the photosensitivity of photodeposition by two orders of magnitude (Au clusters = nucleation centers for Ag)

Gratings/ microlenses Optical memories

X= Se

x=35

illuminated

30 min

X= S

x=60

as-prepared

X= S

x=60

illuminated

5 min

Agx(Ge0.3X0.7)100-x

110 mW/cm2

T. Kawaguchi, K. Tanaka and S.R.Elliott; Handbook of advanced electronic and photonic

Materials and devices AP, N.H Nalwa ed. (2001) p 91

Photocrystallisation (phase change)

Exist in chalcogenide with or without ionGe-Sb-Te (GST-Ge2Sb2Te5)

Ag-In-Sb-Te (AIST)

Disordered state

amorphous AgSbTe2

+ amorphous In-Sb

Ordered state

crystalline AgSbTe2

+ amorphous In-Sb

hn

laser beam Critical cooling rate

3.4 K/ns

Different reflectivity for amorphous and crystalline AgSbTe2

Pulse structure

Application of photocrystallisation

Rewritable optical disk memoryPhase change: Write/Erase phenomena

Laser-induced

annealing/melting

Ge-edge data (Ge2Sb2Te5)

Very big change in EXAFS and XANES

The transition

between the

crystalline and

amorphous states

can be viewed as an

umbrella-switch of

Ge atoms from a

octahedral to

tetrahedral

symmetry position

within the Te fcc

sublattice

A.Kolobov et al, 2004,

Nature Mater. 3, 703

T. Ohta, JOAM 2001

Polycarbonate disc

Protection layer ZnS-SiO2

Protection layer ZnS-SiO2

Active layer (GST, AIST)

Reflection layer (heat sink)

UV resin

Real disc structure

WHY PHOTOSTRUCTURAL CHANGES OCCUR ONLY IN AMORPHOUS

CHALCOGENIDES?

•Excitation of lone-pair electrons is a trigger of the structural change - presence of LP-electronsis crucial - group VI elements (chalcogens);

•Localization of photo-excited carriers and hence disorder is important - amorphous;

•Low coordination number is beneficial since it makes the structure floppy.

Amorphous chalcogenides are the only materials that satisfy all these requirements

Diffusion under E and hn : PMC memories

« Programmable Metallization Cell Memory Devices » bias accumulation of silver metal creating a conductive link (« on » state) -Ag is oxidised at the anode and reduced at the cathode

Reversing the bias breaks down the silver and restore the initial resistive state (« off » state)

Solid electrolyte: Ag photodissolution

in GeS(Se)y

Cathode: inert metal (Cr,Ni..)

Anode: Ag or Ag-containing material

M. N. Kozicki, M. Mitkova, M. Park, M. Balakrishnan, C. Gopalan,

Superlattices and Microstructures 34 (2003) 459.

Ionic conductive chalcogenide glasses

Glasses exist in large composition domains

evolution of conductivity with compositionnon-Arrhenius behaviour (log 1/T)

Ag (Na)- based chalcogenide glasses

Ag2S - GeS2

Ag2S – GeS - GeS2

Ag2Se - GeSe2*

Ag2S - As2S3

Na2S - GeS2

Ag (Na) content varying from 0.01 - 30 at%

Former ModifierYX2 + M2X

(Y = Si, Ge…X = S, Se) (M = Li, Na, Ag..)

Covalent bonds Ionic bonds

(Glass)X- X-

Y X Y X

X- X-

X

M+ M+

M+M+

*M.Kawasaki, Kawamura J, Y. Nakamura and M. Aniya; SSI 123 (1999) 259

M.A. Urena, A.A Piarristeguy. M. Fontana and B. Arcondo; SSI 176 (2005) 505

Change in the transport regime at about 1 at % in sodium(electronic to ionic ?)

3 different behaviours

Na2S-GeS2 :

-14

-12

-10

-8

-6

-4

0.001 0.01 0.1 1 10 100

Na2S – GeS2

-16

-14

-12

-10

-8

-6

-4

-2

0.001 0.01 0.1 1 10 100

Ag2S-GeS-GeS2

60GeS-40GeS2

t = 1.93

Ag (Na) concentration (Atomic %)

-2

-16

-14

-12

-10

-8

-6

-4

0.001 0.01 0.1 1 10 100

Ag2S – GeS2

Ag2S – As2S3

GeS

Ag-Ge-Se

log

(S

cm

-1)

Ag-based glasses:large increase of 4-5 orders of magnitude in the conductivity at about 5-8 at % in silver

Ag2S-GeS-GeS2 and Ag-based glasses: Change in the transport regime at about 5-8 at % in silver

Variation of conductivity (298 K) with Ag(Na) content (at %) in Ag(Na)-X-Y glasses (X=Ge,As; Y=S,Se)

A. Pradel, N. Kuwata, M. Ribes, 2003, J.Phys.: Cond. Mat. 15, S1561; M.A. Urena, A.A Piarristeguy. M. Fontana and B. Arcondo; SSI 176 (2005) 505

FE-SEM (Field Effect - Scanning Electron Microscopy)

Chemical inhomogeneities

EFM (Electric Force Microscopy) Surface potential imaging

and surface electric modification

Electrical inhomogeneities

Ag2S-GeS-GeS2 and Ag-based glassesStructural studies (microscopic, nanoscopic scale)

16.7at.%

8.3at.%

5.8at.%0.8at.%

Ag2S-GeS-GeS2

FE-SEM (LEO-982 )

No phase separation

-16

-14

-12

-10

-8

-6

-4

-2

0.001 0.01 0.1 1 10 100

Ag2S-GeS-GeS2

Lo

g( C

on

du

ctivity)

Scm-1

60GeS-40GeS2

t = 1.93

-16

-14

-12

-10

-8

-6

-4

-2

0.001 0.01 0.1 1 10 100

Ag2S-As2S3

Lo

g( C

onductivity)

Scm

-1

Silver Concentration [At.%]

GeS2

Ag-Ge-Se

Ag-based glasses showing a large increase (4-5 orders of magnitude) in the conductivity at about 5-8 at % in silver

Ag2S-GeS2

Ag2S - As2S3

FE-SEM (LEO-982 )

4at.%

7at.%

1.2at.%

9.8at.%

Glasses are phase separated

Ag-rich phase

Ag-poor phase

the change in the conductivity regime occurswhen the Ag-rich phase starts connecting

FE-SEM (LEO-982 )

Ag2S - GeS2

2at.%

5at.% 5at.%

15at.%

1at.% 3at.%

4at.%

7at.% 33at.%

Glasses are phase

separated

the change in the conductivity regime occurswhen the Ag-rich phase starts connecting

Ag-poor phase

Ag-rich phase

543210

5

4

3

2

1

0

X[µm]

Y[µ

m]

543210

5

4

3

2

1

0

X[µm]

Y[µ

m]

5%Ag

Clear areas

(Ag-rich

phase)

d~0,3µm

Dark areas

(Ag-poor

phase)

d~0,8-0,9µm

Comparison FE-SEM / EFM (Ag2S-GeS2 glasses)

15%Ag5%AgEFM -3V

Weak conductivity domain : Ag-poor phase connected

High conductivity domain : Ag-rich phase connected

Clear-areas

(Ag poor

phase)

Dark areas

(Ag-rich

phase)

EFM -3V

15%Ag

543210

5

4

3

2

1

0

X[µm]

Y[µ

m]

(Ge25Se75)Ag:10%

1.0µm 1.0µm

Electrons retrodiffusés

EFM

-3V +5V Topo

Clear areas (Ag-

rich phase in a

Ag-poor matrix)

Dark areas in a clear

matrix but a weaker

contrast !

(Ge25Se75)Ag:15%Electrons retrodiffusés

EFM

d~1µm

1.0µm 1.0µm1.0µm

-3V +4V Topo

1.0µm1.0µm1.0µm

(Ge25Se75)Ag:25%Electrons retrodiffusés

EFM

-3V +5V Topo

Variation of conductivity (298 K) with Ag content (at %) in Ag2S - GeS2 and Ag2S - As2S3 glasses

The glasses are phase separated

The jump in the conductivity occurswhen the phase previously embedded in the connecting phase becomes the connecting one

percolation threshold with the Ag-poor phase (Ag-rich phase) being responsible for the conductivity at low silver (high silver) content

Nature of the charge carriers (electrons to ions)?EMF <---> Tracer diffusion coefficient

At low Ag content, power law dependence: = Cxt

Ag2S - As2S3 glasses

Conductivity 110mAg tracer diffusion coefficient

Log-log plots

Cxt

D CDxtD

tD = t - 1

tD = -0.29

118.8°C

tD = 0.78

25°C

-14

-12

-10

-8

-6

-4

0.01 0.1 1 10 100Silver Concentration (at. %)

Con

du

ctiv

ity (

S c

m-1

)

low silver content: conductivity mainly ionic high silver content: conductivity purely ionic t > 0.99(same conclusions for: Ag2S-GeS2 and Ag2S-GeS-GeS2)

Bychkov E, Tsegelnik V, Vlasov Y, Pradel A and Ribes M., JNCS 208 (1996) 1.

Bychkov E, Bychkov A, Pradel A and Ribes M., SSI 113-115 (1998) 691.

Non-Arrhenius behaviour (log 1/T) in glasses and more generally

in super-ionic conductors

-12

-10

-8

-6

-4

-2

0

2

0 2 4 6 8 10 12

0.5Ag2S+0.5GeS20.8Na2S+0.2B2S30.56Li2S+0.44SiS20.7Li2S+0.3B2S30.525Ag2S+0.475(B2S3:SiS2)0.2AgI+0.8[0.525Ag2S+0.475(B2S3:SiS2)]0.3AgI+0.7[0.525Ag2S+0.475(B2S3:SiS2)]0.4AgI+0.6[0.525Ag2S+0.475(B2S3:SiS2)]60AgI+13.3Ag2O+26.7MoO374AgI+8.7Ag2O+17.3MoO3

1000/T

Arrhenius plots of for different « superionic » glasses(temperatures below Tg)

Arrhenius plots of for different « superionic » Crystallised phases

Ag7GeSe5I Renaud

Ag7GeSe5I Abdel

Ag8GeSe6

Ag7PSe6

Ag8SnSe6

Ag8SiSe6

Li0.5La0.5TiO3

Nab"Al2O3

Ag7GeS5I

a-AgI

RbAg4I5

BiMeVOx1

BiMeVOx2

BiMeVOx3

BiMeVOx4

SnCl2

CaF2

SrF2

BaF2

-12

-10

-8

-6

-4

-2

0

2

0 2 4 6 8 10 12

1000/T [K-1

]

F

Because of super-Arrhenius behaviour below Tg in glasses one can think that it exists a « Mobile ion » glass transition

Such a transition cannot be observed easily because itsweakness. (To date it has only been reported by Hahashi and Ojuni – AgPO3-AgI glass at ~80K).

It is also possible to imagine a « mobile ion Tg »for superioniccrystalline compounds with disorder in the mobile ionsub-lattice (for temperature higher than this hypotheticaltemperature ions move in a quasi-liquid sub-lattice)

For temperature greater than that of « mobile ion Tg » cooperative cation motions super-Arrhenius behaviour

Scaled Arrhenius plots of for different « superionic » Glass and Crystalline compounds

Work done withAusten Angell ASU - Tempe

In the absence of experimental data one can tentatively take for « mobile ion Tg » the temperature where the conductivity is about 10-9 Scm-1, allowing a scaling of the variation of the conductivity

(log T(= 10-9) / T)

-9

-8

-7

-6

-5

-4

-3

-2

-1

0

1

0 0.2 0.4 0.6 0.8 1

Ag7GeSe5I RenaudAg7GeSe5I AbdelBiMeVOx1BiMeVOx2BiMeVOx3BiMeVOx40.8Na2S+0.2B2S30.56Li2S+0.44SiS20.7Li2S+0.3B2S360AgI+13.3Ag2O+26.7MoO374AgI+8.7Ag2O+17.3MoO3Li0.5La0.5TiO3Ag8GeSe6Ag7PSe6Ag8SnSe6Ag8SiSe6SnCl2

T10-9 /T