Segregation and space charge model (poster2) · 2015. 7. 20. · Space charge effect and dopant...
Transcript of Segregation and space charge model (poster2) · 2015. 7. 20. · Space charge effect and dopant...
Space charge effect and dopant segregation in acceptor-doped BaZrO3 proton conductors
M. Shirpour1, B. Rahmati2, W. Sigle2, P. A. van Aken2, R. Merkle1, and J. Maier1
1Max Planck Institute for Solid State Research, Stuttgart, Germany,
2Max Planck Institute for Metals Research, Stuttgart, Germany
•• BlockingBlocking effecteffect at at thethe GB and GB and spacespace chargechargemodelmodel::
•• AsAs--preparedprepared samplesample: Spark Plasma Sintered (SPS) at 1600°C / 5min / 50MPa
•• AnnealedAnnealed samplesample: SPS sample annealed at 1700°C / 20 h ρ ≈ 98% ρth
No grain growth during annealing
Secondary phases Inhomogeneous dopant distribution
Symmetry reduction
Positive core charge
Barium loss ...
?BaV ′′
BaV ′′
BaV ′′
BaV ′′ •BaY
BaV ′′BaV ′′
BaV ′′
•BaY
•BaY
•BaY
•BaY
1.0 1.5 2.0 2.5 3.0
-8
-6
-4
-2
0
800 600500 400 300 200 100
0.46eV
0.81eV
T / °C
log(
Tσ /
Scm
-1K
)
1000T-1 / K-1
0.73eV
BulkBulk
PH2O=20 mbar
GBGB--annealedannealedGBGB--asas--preparedprepared
I) High I) High temperaturetemperature annealingannealing II) Dopant II) Dopant segregationsegregation
Depletion and Accumulation of charge carriers
(as-prepared) (annealed)0.2 µ
Bulk
Bulk
TEM image
GB composition by EDXS-TEM
annealed samples:• Same σH+ for bulk, strongly increasedσH+ for GB• Lower space charge potential• Comparable effect for Y- and Sc-doped BaZrO3
as-prepared:slight Y excess at GB
annealing: dopant segregation to GB core and space charge zone⇒ decreased proton depletion
in space charge zone
6at.% Y-doped BaZrO3
1.0 1.5 2.0 2.5 3.0
-8
-6
-4
-2
0
800 600500 400 300 200 100
0.47eV
T / °C
log(σ
T / S
cm-1K
)
1000T-1 /K-1
1.04eV
0.71eVBulkBulk
GBGB--annealedannealed
GBGB--asas--preparedprepared
PH2O=20 mbar
6at.% Sc-doped BaZrO3 annealed:strong Y segregation to GB region
ZrY′
•OH •OH
ZrY′
annealing: dopant segregationto GB core and space charge zone
decreased proton depletion in space charge zone
Sc3+ GB excess ≈ Y3+ GB excess(r = 0.72 Å) (r = 0.90 Å)
electrostatic driving force dominatesover elastic contribution
•• Potential reasons for blocking grain boundaries (Potential reasons for blocking grain boundaries (GBsGBs))
Grain size distribution