Impedance spectroscopy of mixed conductors: modelling and experiments

J. Jamnik

National Institute of Chemistry, Hajdrihova 19, Ljubljana, Slovenia

Max-Planck Institut für Festkörperforschung, Heisenbergstr. 1, Stuttgart,

Germany

Polycrystalline mixed conductors with blocking grain boundaries

Electrochemical parameters of interest: Parameters of no interest?

Grains Grain boundaries Electrodes

ionR

eonR gbionR gb

eonR ctionR ct

eonR

C

C gbCdlC

Different parametrisation possible, for example:

eonion

eonion RR

Rt

CRR

LD

eonion )(

2

1

c

Energydissipation

Energystorage

Impedance spectroscopy: theory

Local description generalised equivalent circuits derived from Nernst-Planck-Poisson equations(J. Jamnik & J. Maier, PCCP 3, 1668 (2001)) .

Assumptions: •continuum model •2-mobile charge carriers•internal reactions in local equilibrium

Microstructure Brick layer model

Introductory remarksAn important strength of IS is that the electrode effects appear separated from the bulk and grain boundary response!??

bulk g.b.

materials response

electroderesponse

Re(Z)-I

m(Z

)

(independent ofthe electrode material)

bulk

Re(Z)

-Im

(Z)

R1R2

R1+R2

Pure ionic orelectronic conductors

Mixed conductors: Single crystals first

Completely blocking or completely reversible electrodes

Ideal selectively blocking electrodes

Electrode effects in single crystals: Résumé

electrode effects in single crystals grain boundary effects in polycrystals

but

poly2single n

C

RR

RRgb

gb

J. Jamnik, SSI 157, 19, 2003

Experiment: bicrystal

13 grain boundary:•strongly blocking for ions•weakly blocking for holes

J. Jamnik, X. Guo, J. Maier, APL, in press.

Consistency test: