The thermodynamic and kinetic properties of silver intercalated niobium disulfide

Solid State Ionics 16 (1985) 163-170 North-Holland Publishing Company

THE THERMODYNAMIC

163

AND KINETIC

PROPERTIES

OF SILVER

INTERCALATED

NIOBIUM

DISULFIDE

Henny J.M. BOUWMEESTER Laboratory Nijenborgh

of Inorganic 16, 9747 AG

Chemistry, Groningen,

Materials Science Centre, The Netherlands.

The University

of Groningen,

A study of structures, thermodynamic and kinetic properties of Ag intercalated 2H-NbS2 is reported. The observed phases AgxNbS2, being a dilute gasphase (x < 0.22) and a second- and first-stage phase (0.22 5 x 5 0.30 and 0.55 5 x s 0.76 respectively) are structurally related. Silver atoms reside in tetrahedral holes between neighbouring sandwiches of NbS2. Kinetic parameters of the mobile species (Ag) were obtained from ac response and the Galvanostatic Intermittent current Titration Technique (GITT), using samples of trode in an AgI electrochemical cell above 425 K. Both first- and fast ionic conduction. The relatively low chemical diffusion coeffisient a in the second-stage phase, as compared to that in the first-stage, D M IOto the coupling of the diffusion kinetics with stage conversion in islands type domains.

1. I?!TRODUCTION The layered

properties transition

metals

donating

species

like the alkali

copper

and silver show

or the Ib metals

ionic as well as electronic ionic conduction of the relatively

conduction.

is two-dimensional, large distances

planes of intercalated rated by sandwiches

atoms,

The

the

these being sepa-

TX2. The kinetics

Polycrystalline

of diffu-

samples of AgxNbS2

0.9) were prepared the elements

because

between

2. EXPERIMENTAL

Torr.) at temperatures 5-7 days. The samples and annealed

using a Guinier-HBgg

solid solubility, several quence cess.

distinct of staging

typically

during

and stage conversion

calation.

in these phases

These factors

pro-

influence

are of practical

impor-

use of transition

as cathode materials

in

batteries.

intercalates

MxTX2,

form non-hygroscopic

and are therefore

able solids for case studies. study of structures,

very suit-

In this paper a

thermodynamic

and kinetic

0 167-2738/85/$ 03.30 0 Elsevier Science Publishers (North-Holland Physics Publishing Division)

B.V.

camera

(Jungner

Instruments)

Silicon was used as

standard.

Intensities

of Ag0.60NbS2

(950 ->

(Philips). were grown by

750°C) with a poly-

sample as starting

material

and

(from (NH4)2 PbC16) as transport

agent. The thin hexagonally-shaped have a metallic

gold-like

crystals

lustre. Their

area varied up to 10 mn2, the thickness approximately

and also copper,

to room temperature,

on a diffractometer

Single crystals

chlorine

were powdered

by X-ray powder diffraction

internal calibration were measured

Crystalline

from

tubes (10m5

800 - 1000°C during

with Cu K ~1, radiation.

vapour transport

of the inter-

of the potential

metal dichalcogenides

Silver,

the intercalation to see, how staging

and reversibility

tance, because

secondary

0 < x < 1 for M,TX2,

phases may exist as a conse-

It is of interest

ion transport

In the range of

quartz

at 850°C for l-2 days. After

they were analyzed

electrode.

(0.1 < x c

syntheses

obtained

having been slowly cooled

in an electrochemical

cell with the intercalate

by direct

in evacuated

sion in these phases can be studied conveniently

as solid solution

is presented.

metal dichalcogenides

TX2 (T = Ti, Ta, Nb and X = S, Se) intercalated with electron

of phases AgxNbS2

5 urn. Attempts

under the same conditions

surface being

to grow Ag0.25NbS2,

as mentioned

above,

were not successful. The electrochemical compacts

were performed

experiments

on powdered

in a three electrode

cell of configuration

loaded

Ag/AgI/AgxNbS2/C.

i.e. the working

sample,

electrode,

to the AgI electrolyte,

metal was used as counter trode.

Electrical

whereas

contact

elec-

electrode

of the mobile

ver) in phases AgxNbS2 cation

were obtained

of the Galvanostatic

Titration

Technique

cell voltage current

(Z), in which during

After each current

cell voltage

linear dependence current

passage,

factor

?! and the thermodynamic

W = (alna)/(alnc)

taneously.

rence of other specifiying

nique

interfacial

simul-

the co-occurhence

square-root-of-

a small-signal

during

ac response

the course

tech-

of the titration

AgxNbS2

were washed

samples

with CS2 in order

mm3 and sintered

order

of

at 800°C

ampoule

to prevent

cut in smaller

to remove

- 12 x 3 x 2

with a small volume,

sulphur

in

for about 24 hours in

loss. These bars were

plan parallel

pieces and mounted

in the electrochemical

cell. The lengths

samples were typically

0.5 - 1.5 mm, the sur-

face dimensions

varying

In our laboratory for the application

of the

from 6 to IO mm2.

the experimental

set-up

of GITT and ac small-signal

response

has been realised

computer

systems

on the base of micro-

for control,

constant

AND DISCUSSION

3.1. Structure

and phase relations

Phase analysis

confirm

different

and a first-stage. as deduced

the occurrence phases,

Their

of

being a second-

homogeneity

electrochemically

regions

(see next section)

and agree well with the observations

from X-ray powder diffraction.

The samples were then pressed

a steel die in bars of dimension

in a quartz

3. RESULTS

tively,

free sulphur.

and maintained

Cell

the course

are 0.22 '_ x i 0.30 and 0.55 : x 2 0.76 respec-

experiments. Prior to the measurements,

during

1°C.

two structural

(1 mHz - 400 Hz) (3) was used at regular

intervals

out in high

or helium atmosphere.

were monitored

of the experiment within

control.

were carried

enhancement

impedances,

the diffusional

time-region,

temperatures

are determined

In order to recognize

for potentiostatic

purity nitrogen

or a So-

1186 Electrochemical

All measurements

V, during

diffusion

were performed

an AMEL 551 potentiostat

lartron/Schlumberger

from

of the admittance/impe-

(4). Both techniques

From the

data, the chemical

voltage

circuit were obtained

least squares analyses

with either

on the square root of time

and from stationary coefficient

is established.

of the overvoltage

of an equivalent

Interface

range

30 mV (peak - peak). The elements

the

a new equi-

The

of the working

in the frequency

0.1 mHz - 400 Hz using an excitation

dance data

pulse

by the computer.

dispersion

was measured

current

a constant

(t = 300 sec., 0.2 - 2.5 mA.cme2) librium

by appli-

Intermittent

(GITT)

is monitored

pulse.

ions (sil-

value of dE/dt was less then

frequency

of maximal

(1).

cell

using GITT, was reached

as checked

IE-6 V/min., complex

mical cell type has been given recently parameters

when the absolute

to the sample was

of the electroche-

The new quasi-equilibrium

voltage after decay,

plug. A detailed

of the geometry

Kinetic

and analysis.

silver

and reference

made by use of a graphite description

The

was spring-

data collection

of samples AgxNbS2 regions

indicate

The powder

outside

two-phase

pattern

Powder data

these homogeneity behaviour.

of samples AgxNbS2

(0.22

x L 0.30) could be indexed on a rhombohedral unit cell.

For Ago.25 NbS2 the ccl parameters

(hexagonal

setting)

39.35(l)

a = 3.3423(5)

i and c =

i were found, which are almost

with those of second-stage by Scholz and Frindt in hexagonal

identical

as reported

(5). Since the unit cell

description

NbS2, the phase

AgxTaS2

contains

is designated

six

sandwiches

as GR-AgxNbS2

Good agreement

was obtained

between

and calculated

intensities,

with the atoms in

special

positions

6c of space-group

observed R3m (table 1)

H.J.M. Bouwmeester

/ Kinetic properties of silver intercalated niobium disulfide

Table 1. Observed and calculated powder pattern of GR-AgO 25Nbs2.

.

d-obs

hkl

d-talc

I-obs

I-talc*

of Ag in planes

006 009 0012 011 015 107 018 0111 1013 0114 1016 0021 110 116

6.538 4.366 3.274 2.889 2.716 2.573 2.495 _____ 2.094 2.017

70.9 14.2 13.6 88.0 21.8 17.4 49.0 ___69.7 57.9

1.874 1.669 1.619

23.7 100.0 28.3

119 1022 1112 0027 201 205 027 028 0213

1.562 1.522 1.489 1.459 1.445 1.424 1.402 1.388 1.306

13.5 8.7 1::; 16.8 6.0 8.1 10.8 17.3

6.558 4.372 3.279 2.889 2.717 2.573 2.495 2.250 2.092 2.017 1.874 1.874 1.671 1.619

76.3 18.5 0.1 84.0 30.0 35.2 58.2 18.8 78.4 63.5 0.1 8.3 57.7 12.5

1.560 1.522 1.489 1.457 1.446 1.423 1.402 1.388 1.307

:*: 0:2 5.4 10.1 3.9 5.1

analysis

The powder

-'

pattern

the phase is designated two sandwiches

as 2H-AgxNbS2,

NbS2 are present

cell. Unit cell parameters are a = 3.3503(5) Rotation

and Weissenberg

single crystal described

2H-Ag0,60NbS2,

to the space'group partly,

confirmed

P63/mmc.

using a CAD-4 diffractometer

The intensities

squares P63/mmc,

Calculations

structure

pointed

in P?ml with a slightly

=

different

observed

was obtained occupation

regions,

by silver for first-stage occupied

of neighbouring

sandwiches.

this preference

rather than octahedral,

sulphur

Calculations,

using

6R-AgxNbS2,

for tetrahedral,

coordination

of sites

in the basal plane) form

honeycomb

two interpenetrating

lattice,

consisting

sublattices.

of

The single

X-ray study showed that both sublattices

are statistically Ag,NbS2,

layers

silver. These tetrahedral

(two per unit area

crystal

AgxNbS2,

and empty for the

holes between

a puckered

of which

phase. The silver atoms are in

intercalated

were

between

by intersandwich

the tetrahedral

confirmed

in spacegroup

factors

(6R) and first-

the powder data of second-stage

(6). Least

were started

but a better agreement

and calculated

of a

X-ray analysis,

with the X-ray system

refinemdnts

second-stage

1.

up to sin(e)/h

of second-

(2H) phase are based on sandwiches

and alternatingly

for intensity measurements.

1.35 A-' were measured. performed

stage

are occupied

(Enraf-Nonius)

of reflections

(b)

NbS2 separated

This was, at least

by subsequent

with MO Ko radiation

cell;

because

section,

a\l3

The structures

(0.55

grown as

in the experimental

(5).

FIGURE 1 (11%) sections of (a) 2H-NbS2, (b) GR-Ag,Nb S and (cl 2H-Ag NbS . The origins are displace3 with respect %o ti e original ones in order to demonstrate the paraZZe2 displacements of sandwiches NbS2 during intercalation.

of 2H-Ago 6 NbS2

photographs

structure

(8) from powder data;

a{3 (al

in the unit

i and c = 14.391(9j

the approximate

structure-

and AgO . 60 TaS2 are isostructural

A%.60NbS2

’

5 x 2 0.76) was indexed using a hexagonal

will be given

(7). The above mentioned confirms

factor

report of the structure

of 2HA%.60NbS2

as found by Koertz

168::

of samples AgxNbS2

i.e. 0.56 and

The final agreement

RF was 0.056. A complete

elsewhere

* Calculations were made in space group R%, with all atoms in s ecial positions 6c: :Nb.;o; ;;;6;, z$~~,=,;,".222, zS(2) = Ag

l/2 c apart,

0.60 respectively.

determination

165

whereas

occupied

stage phase do not allow unambigously

in first-stage

the powder data of the second-

between

to distinguish

a statistical

distribution

166

H.J.M. Bouwmrester

/ Kinetic

properties

xin Ag,Nb&

The eZectrochemicaZ t:tyation curve and the thermodynamicfactor W at 450 K, using Agn so~~7bS2 0s starting material. The maximum ZH-NbS2 The present

2H-MoS2.

data indicate

blance of the intercalation into ZH-NbS2 neither

and ZH-TaS2

of Ag

nor electro-

data point to the existence

uptake

of silver by 2H-NbS2

reached,

when Ag,NbS2

metallic

silver,

of higher

ation arises (or Darken)

is

is in equilibrium

with

i.e. EMF = OV. According

fig. 2, and extrapolating

No indications,

from X-ray diffraction,

chemical

the resem-

process

(5).

and

to

to 0 V, this situ-

at x = 0.76. The thermodynamic factor

was calculated

W, also shown in fig. 2,

following

stage phases.

4. ELECTROCHEMICAL

MEASUREMENTS

Fig. 2 shows an almost the electrochemical

where

complete

titration

cycle of

curve measured

at 450 K, using a sample of nominal AgB.50NbS2 curves

as starting

of other

experimental temperature

error.

AgxNbS2,

syntheses,

firm the titration

Titration

at room

prepared

qualitatively

by con-

curve found at 450 K. The

regions

as deduced

from fig. 2

are 0.22 s x 5 0.30 and 0.55 i x 5 0.76 for phases 6R and 2H respectively. two-phase phase

mixture

(Ag present

all sandwiches calation

Below x < 0.22 a

of stage 2 and a dilute in low concentration

of NbS2)

gas-

between

is found. The de-inter-

of silver from the sample was stopped

at this composition, tics observed.

because

X-ray powder

broad diffraction

lines,

ticle size and/or

a highly

of the slow kinepatterns

indicating

show very a small par-

discrdered

stucture.

and F is the Fara-

in W at x = 0.25 can be attri-

buted to an ordering

of silver atoms

in probab-

ly a 2a x 2a superlattice. Preliminary

agree within

EMF measurements

of samples

high temperature

homogeneity

material.

samples AgxNbS2

composition

R is the gas constant

day. The anomaly

measurements

of samples

AgxNbS2,

containing

small amounts

always

of titration

of excess

showed up a constant

sulphur,

voltage

220 mV. This value corresponds

level of

to the decomposi-

tion voltage

of Ag2S at that temperature.

Typical

of the complex

examples

plots of samples AgxNbS2

impedance

from ac measurements

are shown in fig. 3. Theoretically, impedance

should be represented

impedance/admittance least squares circuits According

the total

of the electrolyte/electrode

better fit between

curves

not washed with CS2, thus

interface

by a Randles-circuit.

observed

data was obtained

analyses,

A

and calculated from

using the equivalent

shown in the insets of fig. 3a and b. to these circuits

the contributions

H.J.M. Bouwmeester

-yP

2.6

z d : z Nl

/ Kinetic properties of silver intercalated niobium disulfide

167

J l

0

W3mMm

$12 mHz

l

2

E 1.5

I

l

l

E ;,20

0

I

1

1.5

I

I

a l

-

l l

10 -

972 mHz

8

-

I

l

.5

l

030 9

1 I

.

2 2.5 3 Z-REAL (Ohm1

I

1

3.5

‘0

4

l

-

61.3mHz

l

10 1.1, 20 30I 40I Z-REAL (Ohm1 I

I

50I,

60

FIGURE 3 representations from ac diffusion frequency dispersion measurements of with data from least squares SH-Age feNbS2 Ia.! and GR-AgO 8j NbS2 (b). Observed values coincide caZcu h ons. uszng the eoua0 ent circuits shown. Rb and ZD are the bulk ionic resistance and the diffusionol irnpecla~ce respectively. Complex

impedance

of a charge

transfer

le layer capacitance

Cdl can be ignored. The

form of the diffusional the fitting

procedure

ly by Raistrick

Ret and a doub-

resistance

impedances

has been published

and Huggings

3a and b a diffusion

(9).

controlled

3a clearly diffusion

impedance

shows finite of Ag atoms

derivation

lenghts

behaviour Through

directly

coefficient,

is

hence

of the component

these silver thermodynamic

IT tn K I

for diffusion observed

can

FIGURE 4 The temperature dependence of ionic conductivity (0) and thermodynamic factor W (0) of 2H, as determined from ac measurements

The ionic conductivity

temperature

for 2H-AgO_5ONbS2

o = o. /T exp(-E,/RT).

is a commonly

l&y-&--L IWO/T

(9,lO). diffusion-

the ionic conductivity

shown in fig. 4. and follows

tion energy

1.5

factor W, can

from this capacitative

directly.

reciprocal

behaviour:

of The

IIN = v/W, and use of the Nernst-

equation,

be calculated versus

of fig.

curve dE/dx,

at the lowest frequencies

knowledge

Einstein

effects

in 2H-Ag0.60NbS2.

the value of the thermodynamic be measured

line of

is observed.

represantation

of the titration

recent-

In both fig.

straight

slope almost 45" (ideal Warburg) The complex

ZC used in

found,

an Arrhenius The activaE, = 0.25 eV,

value with respect

intercalation

compounds

factor W decreases

to

(14). The

with increasing

temperature,

indicating

an extending

region at higher temperature

stage phase. From simultaneous measurements

homogeneity

for the firstEMF-temperature

&l(x) and AS(x) of 2H-Ag0,60NbS2

were evaluated,

with use of equation

(l), con-

sidering g(x)

= -F EMF = d(x)

- TV

(2)

A?(x)

= F

dE/dT

(31

Froc fig. 5 it is seen that the chemical diffusion

where AG(x)

= G(x) - G" is the partial

free Gibbs energy relative partial

of silver

in AgxNbS2

to that of pure silver metal molar enthalpy

are defined

molar

AH(x)

(G(x)) G". The

and entropy A?(X)

in a similar way and are respective-lK-1 -1 . Remarkable and 7.3 Jmol

ly -17.9 kJmo1

is the positive teristic phases

value of AS(X),

for silver

(and copper)

which

is charac-

intercalated

(11).

In samples GR-AgxNbS2

contributions

slow interfacial

kinetics,

by the existence

of a passivation

at higher temperatures on prolonged

presumably

layer, appear

(- 530 K), and increase

heating.

The ac response

ments at these high temperatures producible

due to caused

measure-

were not re-

and it was also not possible

obtain accurate

fitting

although

always

positive

temperature

dicating

also a positive

second-stage

phase.

behaviour

be measured

5 at 450 K, obtained

use of the GITT-technique, stage AgxNbS2 100. Results behaviour. domain

differ

from ac response

structure

similar

a factor

confirm

that this

this

is due to a

for the second-stage

in second-stage

AgxTiS2

phase (12)j,

to the island domain model proposed

Daumas and Herold

(12,13) for graphite

lation compounds.

The domain model

in fig. 6. The diffusion AgxNbS2

by

in first- and second-

by approximately

I assume,

(as observed

is relatively

of the necessary

illustrated

by

interca-

is given

in second-stage

slow probably

changes

ches of NbS2 during

because

in stacking

of sandwi-

silver transport,

as is

in fig. 1. In the system AgxTiX2,

E of the first- and second-stage about

of the data. Neither

could the EMF-temperature reproducibly,

to

coefficient

phases are

the same; in this case stage conversion

proceeds

without

displacements

of sandwiches

of TiS2 (14).

a distinctly

coefficient

was found

in-

value of A?(x) for the

Notably,

no

during

DTA and high temperature

800°C)

of samples

transitions X-ray runs (0 -

6R and 2H were observed.

Phc island-model of a second-stage phase, accordinr; to Daumas and Hcrold 1131. as nreswned for SK-& ibS Sandwiches of ‘lJbSz yre ‘indicated by flUL7, meg, whereas circles depzct islands of siZ0cr atoms,iactuaZ size of isZands several n.

+

hundxds

of A).

The measurements

ac-Hall

i.e. resistivity, x I” Ag,NbS,

and magnetic techniques,

properties,

FIGURE 5 The chemical, diffusion coefficient E versus composition of phases AgzNbS2, obtained by means 0-f GITT.

effect

and thermopower,

6R and 2H. The results,

Nb-4d,2

NbS2 by electrons

from intercalated extensively

(15).

in

of filling

band of the host 2H-

will be discussed paper

conduction

with a rigid band formalism

the half filled

tranport-,

using conventional

showed p-type metallic

for both phases agreement

of the electrical

silver,

in a forthcoming

H.J.M. Bouwmeester / Kinetic properties of silver intercalated niobium disulfide

5.

169

LITERATURE

1. B.A. Boukamp and G.A. Wiegers, Solid State

9. I.D. Raistrick and R.A. Huggins, Solid State

Ionics, 9 & 10 (1983) 1193.

2. W. Weppner and R.A. Huggins, J. Electrochem. Sot.

124 (1977) 1969.

3. B.A. Boukamp, 339.

Solid State

4. B.A. Boukamp,

to be published.

Ionics,

11 (1984)

10.

Ionics, 7 (1982) 213.

C. Ho, I.D. Raistrick and R.A. Huggins, J. Electrochem. Sot., 127 (1980) 343.

11. G.A. Wiegers, H.J.M. bouwmeester A.G. Gerards,

5. G.A. Scholz and R.F. Frindt, 15 (1980) 1703.

12. D. Kaluarchchi and R.F. Frindt, 28B (1983) 3663.

Phys. Rev.,

Mat. Res. Bull. 13. N. Daumas and A. Herold, C.R. Acad. Sci. Paris, t 268C (1969) 373.

6. J.M. Stewart, P.A. Machin, C. Dickinson, H. Ammon, L. Heck and H. Flack, The X-RAY 76 system, Tech. Rep. TR-446 Computer Science Centre, Univ. of Maryland, College Park, Maryland. 7. H.J.M. Bouwmeester, F. van Bolhuis Wiegers, to be published. 8. K. Koertz, Acta Cryst.,

and

this issue.

and G.A.

16 (1963) 432.

14. A.G. Gerards, H. Roede, R.J. Haange, B.A. Boukamp and G.A. Wiegers, Synthetic Metals, 10 (1984/85) 51. 15. H.J.M. Bouwmeester, A. Diedering Wiegers, to be published.

and G.A.