PbZrO3 (PZ) powders have been prepared by an alkoxide-based sol-gel route, starting from lead acetate, zirconium n-butoxide, and n-butanol as

a solvent, and hydrolysed with different molar ratios of water in neutral and alkaline medium. After drying (150oC/12h) the hydrolysis product is

amorphous as determined by XRD and only after heating (700oC/1h) it crystallizes as perovskite phase*. In the present work we used XAFS for

studying the local environment of metallic atoms in PZ dried powders as function of hydrolysis conditions in order to determine the short range

order and the degree of homogeneity on the atomic level.

Elena-Daniela Ion1, 2, Barbara Malič1, Iztok Arčon3,1, Alojz Kodre4,1, Marija Kosec11 Jožef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia, 2 National Institute of Materials Physics, P.O. Box MG-7, Bucharest-Magurele, Romania

3University of Nova Gorica , Vipavska 13, 5000 Nova Gorica, Slovenia, 4Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000

Ljubljana, Slovenia

XANES: formal oxidation state

coordination chemistryEXAFS: distances, coordination number, type of the neighbours

XANES

EXAFS

k, k2 or k3 - space

FT

R - space

Pb(OAc)2 Zr(OR)4 solvent (ROH)

-(Pb-OAc) + (RO-Zr)- -(Pb-O-Zr)- + ROAc

-(Pb-OAc) + (RO-Zr)- -(Pb-OAc Zr-OR)-

Precursor

solution

Hydrolysis

Drying

150oC/12h

Heating

700oC/1hCeramic powder

Pb ( Zr ) ( O )x ( OAc )2-y ( OR )4-y

Reflux and

Distillation

By-product: ester ( ROAc )Rw = 2, 5 or 15

(Neutral medium pH=6)

Rw =15

(Alkaline medium pH=11)

Rw – molar ratio H2O/Zr(OR)4

pH - PZ – Rw

Z – Rw

e.g. PZ2,

11PZ15

Z5

The XAFS measurements were performed on pellets prepared

from the dried powders and a dilutant, boron nitride (BN). The

amount of each sample was calculated for a total absorption

d~2.

Zr K-edge and Pb L3-edge were measured at ROEMO II (X1)

station, HASYLAB, Hamburg.

All EXAFS spectra were analysed by IFEFFIT program packages

using FEFF6 for ab initio calculation of scattering paths.

Ac = CH3CO-

R = CH3(CH2)3-

M = Zr

Zr(OR)4 solvent (ROH)

Hydrolysis

Basic reactions for one alkoxide group of a metal alkoxide

• Hydrolysis: -M-OR + H2O -M-OH + ROH

• Condensation: -M-OH + RO-M- -M-O-M- + ROH

-M-OH + HO-M- -M-O-M- + H2O

Drying

150oC/12h

Heating

500oC/1h

PZ Z

The Zr XANES spectra of amorphous powders are markedly different in comparison to the spectrum of the PbZrO3, indicating different

local simmetry of Zr atoms.

Pb XANES shows that the coordination of Pb atom in amorphous powders is different from that in the perovskite phase.

The k3 weighted FT of Zr K-edge

EXAFS spectra, _ exp., . . . . fit

0 2 4 6

0

5

10

15

20

25

0 2 4 6

11PZ15

PZ15

PZ5

FT

ma

gn

itu

de

(a

rb.

un

its)

R (A)o

PZ2

Z 5

The k3 weighted FT of Pb L3-

edge EXAFS spectra, _ exp., . . . .

fit

- Zr neighbourhood - modelled by two separate shells. - 1st shell - described by about seven O atoms at two slightly different distances: 2.12 Å and 2.25 Å in both PZ and Z5 powders- 2nd shell in PZ - five Zr atoms at 3.46 Å and one Pb atom at 3.59 Å. - 2nd shell in Z5 - ~six Zr atoms at 3.44 Å-FT of Pb L3-edge

spectra of dried PZ

powder prepared

with different

hydrolysis

conditions are

similar.

- The 1st shell is

composed of two O

atoms at two

slightly different

distances.

- In the 2nd shell one

zirconium atoms is

present at around

3.59 Å.

Zr4+ (CN=6)

18000 18100

0

1

2

3

4

5

PbZrO3

Energy (keV)

no

rm

. X

(E

)

Z 5

11PZ15

PZ15

PZ5

PZ2

Am

orp

hou

s p

ow

ders,

drie

d

at

15

0oC

Cry

stallin

e

pow

der, h

eat

treate

d a

t 7

00

oC/1

h

13000 13050 131000

1

2

3

PbZrO3

11PZ15

PZ15

PZ5

no

rm X(

E)

Energy (keV)

PZ2

Cry

stallin

e

pow

der, h

eat

treate

d a

t 7

00

oC/1

h

Am

orp

hou

s p

ow

ders,

drie

d

at

15

0oC

0 2 4 60

1

2

3

411PZ15

PZ15

PZ5

FT

ma

gn

itu

de

(a

rb

. u

nits)

R (A)o

PZ2

1:1

Zr – O – Pb

1st shell

~5 O ~2 O2nd shell

~5 Zr ~1 PbCentral atom

Zr

2.12 2.25 3.46 3.59

1 2 3 4 R (Å)

Central atomPb

1st shell

~1 O~1 O2nd shell

~1 Zr

2.192.323.59

1234R (Å)

ZrEXAFS:

Pb:EXAFS

From both sides analysis we

found that Zr is linked with

one Pb atom and Pb is linked

with one Zr atom. It is very

probable that an O bridge

connects these two atoms in

the stoichiometry 1:1 and

that all prepared samples are

stoichiometric at atomic

level.

* Ion E.D., et. all., Journal of European Ceramic Society 27, 13-15, (2007) 4349 – 4352. .

An alkoxide-based sol-gel route has been used to prepare PbZrO3

(PZ). The precursor solution is hydrolysed in neutral and alkaline

medium with different Rw. The XAFS investigations show that local

environment of Zr and Pb atoms is not affected by the hydrolysis

condition and is totally different from the environment in the

perovskite phase. The Zr neighbourhood in PZ resembles that of

amorphous precursour for ZrO2 (Z5). The large number of Zr atoms

which are found in the 2nd coordination shell in Zr – EXAFS spectra is

an evidence of the preferred homocondensation of Zr species.

However a link between Zr and Pb is established in the stoichiometry

1:1 which is not destroyed by further condensation of Zr.

This work was supported by the Slovenian Research Agency research programmes P1-0112 and P2-105, and by DESY and the European Community under the FP6 Programme "Structuring the European Research Area" contract RII3-CT-2004-506008 (IA-SFS). Access to synchrotron radiation facilities of HASYLAB (project II-04-065) and expert advice on beamline operation by Edmund Welter of HASYLAB is acknowledged. SICER (G1MA – CT – 2002 - 04029) is also aknowledged for the financial support. The authors wish to thank Jana Padeznik Gomilsek for help in XAFS measurements and Laura Lazarini for help in the experimental work.