Space charge effect and dopant segregation in acceptor-doped BaZrO 3 proton conductors
M. Shirpour
1, B. Rahmati
2, W. Sigle
2, P. A. van Aken
2, R. Merkle
1, and J. Maier
11
Max Planck Institute for Solid State Research, Stuttgart, Germany,
2
Max Planck Institute for Metals Research, Stuttgart, Germany
•
• Blocking Blocking effect effect at at the the GB and space GB and space charge charge model
model: :
••
As- As -prepared prepared sample sample
:Spark Plasma Sintered (SPS) at 1600°C / 5min / 50MPa•
•
Annealed Annealed sample sample
:SPS sample annealed at 1700°C / 20 hρ
≈98%ρ
thNo grain growthduring annealing Secondary phases Inhomogeneous
dopant distribution
Symmetry reduction
Positive core charge
Barium loss ...
Ba
?
V′′
V′′Ba
V′′Ba V′′Ba •
YBa V′′Ba
V′′Ba V′′Ba
• YBa
• YBa
• YBa
• YBa
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
Bulk Bulk
PH2O=20 mbar
GB GB--annealedannealed GB-GB-asas--preparedprepared
I) High
I) High temperature temperature annealing annealing II) Dopant II) Dopant segregation segregation
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 increased σH+for GB
• Lower space charge potential
• Comparable effect for Y- and Sc- doped BaZrO3
as-prepared:
slight Y excess at GB
annealing: dopant segregationto 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(σT / Scm-1K)
1000T-1 /K-1 1.04eV
0.71eV Bulk Bulk
GB GB--annealedannealed GB-GB-asas--preparedprepared
PH2O=20 mbar
6at.% Sc-doped BaZrO3 annealed:
strong Y segregation to GB region
Y′Zr
OH• OH•
YZr′
annealing: dopant segregation to 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 dominates over elastic contribution
• • Potential reasons for blocking grain boundaries ( Potential reasons for blocking grain boundaries (GBs GBs) )
Grain size distribution
