grain size effects on the electromechanical properties of ... · critical grain size critical grain...

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


Grain size: 2.2 µm Grain size: 0.52 µm

Electromechanical properties

Bipolar strain hysteresis Unipolar hysteresis



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


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



(200) Reflex group

1.70 µm

1.25 µm

0.52 µm

0.37 µm

Grain size:

Crystal structure

PZT 52/48

Effective donor


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.

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