grain size effects on the electromechanical properties of ... · critical grain size critical grain...
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Fine grained PZT powder by using conventional PbOand ZTH as raw materials
0.125%
0.50%
Doping of PZT ceramics :
TS= 900°C TS= 1050°C
1 µm
Effective
donor content:
1 µm 1 µm
mol% 0.125VV contentdonor eff.
V0.51La :donor)-site-(A La
0.375V0.75Fe :aceptor)-site-(B Fe
OPb
Pb
3
O
3
=−′′=
′′=
=
••
+
••+
SEM600nm
Calcined PZT powder
nm 201d BET50, ≈TEM100nm nm 5d BET50, ≈
Zirconia Titania Hydrate
Auer, et al., United States PatentPub. No.: US 2009/0060831 A1
sieving calcination shaping sinteringZTH
PbO
attrition milling
Dopants
Effective donor content
Synthesis and microstructure
Grain Size Effects on the Electromechanical
Properties of donor-doped PZT-Ceramics
G. Picht1,2, W. Rheinheimer2, M. J. Hoffmann2
1 Robert Bosch GmbH, Stuttgart, Germany, 2 Ceramics in Mechanical Engineering, Institute of Applied
Materials, Karlsruhe Institute of Technology, Karlsruhe, Germany
Piezoelectric ceramics of the solid solution PbZr1-xTixO3 (PZT) are state of the art materials in sensor applications such as accelerometers and ultrasonic sensors. It is known
from literature that their electromechanical properties are grain size dependent.
The current study analysed the grain size effect for different Zr/Ti-ratios and different donor concentrations. Dense ceramics with a grain size between 0.3 – 10.0 µm were
obtained by varying the sintering temperature from 875°C to 1250°C. Hereby the Ti content was varied between 45 to 52 mol% with a fixed concentration of 1 mol% La as
dopant. In a second step the Ti content was fixed at 47 mol% and the doping content was varied from 1 mol% La to co-doping with 1 mol% La and 0.75 mol% Fe.
While decreasing the grain size of the material a critical size was found, at which the domain structure changes significant from complex 3-D structures to simple lamellar
patterns. This is in correlation with a suppression of the distortion of the perovskite lattice below the critical grain size as shown by XRD and Raman experiments. Small and
large signal dielectric and piezoelectric properties show changes in non-180° domain switching as well as changes of the intrinsic piezoelectric properties by decreasing the
grain size. It is demonstrated that the critical grain size is mostly related to the amount of donor dopant.
PFM analysis of the domain structure
in plane in plane
500nm
Change from complex domain structure to a simple lamellar domain structure by decreasing grain size.
PZT 53/47
Effective donor
concentration: 0.5 mol%.
Topography In plane
Grain size: 7-12µm
(conventional preparation)5 µm 1µm
Topography In plane
Large grained sample Small grained sample
Grain size: 0.89 µm
500nm
PZT 53/47Effective donor
concentration: 0.5 mol%.
Grain size: 2.2 µm Grain size: 0.52 µm
Electromechanical properties
Bipolar strain hysteresis Unipolar hysteresis
PZT 53/47Effective donor
concentration: 0.5 mol%.
Decreasing the grain size of the PZT ceramics below a critical value leads to larger coercive fields and
lower remanent strain. Both extrinsic and intrinsic contributions drop down at very low grain sizes.
Influence of grain size on intrinsic and
extrinsic contributions
General trend of the grain size effect on the large field strain
for different donor concentrations
The critical grain size is strongly influenced by the amount of effective donor dopant.
1.00
0.25
0.125
0.50
PZT 53/47Effective donor
concentration:
Critical grain size
Critical grain size
Tsurumi, Appl. Phys. Let. 2010
Grain size: 1.7 µm Grain size: 0.37 µm
Decrease in tetragonal phase content and c/a-ratio by decreasing the grain size.
La
ttic
e p
ara
met
er
Distance from the center of the domain
CubicTetragonalGradient
layer
c1
a1
c2
a2
a3
Zr4+, Ti4+
O2-
[001]
[100]
Pb2+
Critical grain size
PZT 53/47Effective donor
concentration: 0.5 mol%.
(200) Reflex group
1.70 µm
1.25 µm
0.52 µm
0.37 µm
Grain size:
Crystal structure
PZT 52/48
Effective donor
concentration: 0.5 mol%.
The difference in the slope in the range between 101-
108 Hz is probably caused by a different domain wall
contribution to the permittivity. This implies a higher
degree of disorder in the small grained sample.
The relaxation frequency is influenced by the domain
size and is therefore shifted towards higher
frequencies by decreasing grain size.
Acknowledgement: Dragan Damjanovic, Li Jin, EPFL Lausanne
Frequency dispersion of the permittivity Conclusions
A decrease in the grain size leads to a change in the complexity of the domain structure.
The performed x-ray analysis shows a decreasing c/a-ratio for smaller grain sizes. This can
be explained by an increase of the domain wall density and the pseudocubic structure close
to the domain walls. This is in agreement with the frequency dependence of the
permittivity showing a larger slope for a small grain size which implies a more disordered
structure.
The change in the domain structure and lattice parameter cause a decrease in the
electromechanical properties. Below a critical grain size the intrinsic and extrinsic
contributions are strongly reduced. The critical grain size is affected by the effective donor
content.
Motivation, Methods and Objectives
1 µm1 µm1 µm
Control of the grain size by sintering parameters and effective donor content.