Elena Dimitriu, Rodica Ramer, Alin Iuga

1
Elena Dimitriu, Rodica Ramer, Alin Iuga
EFFECT OF PROCESSING CONDITIONS ON THE PROPERTIES
OF PIEZOCERAMICS
National Institute for Material Physics,
Magurele, Romania School of Electrical
Engineering, University of South Wales, Sydney
2052, Australia
AIM OF WORK
A review is given on the effect of processing
conditions on the properties of some lead oxide
based ferroelectrics, prepared by the usual
ceramic technique. All processing conditions, as
milling, thermal treatment and poling contribute
to transform the oxides into piezoelectric
materials with a broad series of applications.
PZT- and PT-type materials with different dopants
are selected as examples for studying the
influence of the thermal treatment on the
microstructure and physical properties. The
materials with different compositions are
sintered in a specific temperature range. Results
on microstructure, density, dielectric
permittivity, remanent polarization, and
piezoelectric constants of these materials are
reported.
EXPERIMENTAL
SAMPLE PROCESSING
CAN WE PREDICT THE CERAMIC PROPERTIES? YES
Materials investigated PZT- SMS-CE Pb0.98
(Sr0.02Mn0.017Sb0.033) (Zr0.48 Ti0.47)O3 0,15
Ce2O3 1 2 3 4 Pb 1 PZT-WL
Pb(Zr0.51Ti0.465W0.015Li0.01)O3 2 PT-ND
Pb0.88Nd0.036Dy0.044Ti0.98Mn0.02O3 3 PT-Eu
Pb0.94Eu0.04Ti0.98Mn0.02O3 4
OPTIONS FOR PROCESSING 1.Chemical formula ? a
composition in the proximity of the morphotropic
phase boundary favors strong piezoelectric
effects. 2.Impurities in row materials ? act as
dopants and could cause the occurrence of
vacancies and/or holes or even could stabilize a
phase of the crystalline lattice, with
implications in the values of a specific
property. 3. The solvent for mixing The raw
materials mixed in methanol showed less size of
the particles and the slurry dries easier. 3. The
agate mill ? The SiO2 from the agate balls
decrease the sintering temperature, but favors
the occurrence of the pyrochlor phase.
Weighting the stoichiometric quantities of raw
materials Mixing the oxides or carbonates in
mills with a solvent Drying Calcining the dried
mixture Milling the calcined product Pressing
the milled powder as disks or other shapes
Mechanically processing the sintered samples
Electrodes deposition Poling the samples
Measuring the physical properties.
INFLUENCE OF THE SINTERING TEMPERATURE ON THE
MICROSTRUCTURE
General aspect of the fracture surface (x573)
material (PT-Eu) -sintered at 1180oC
Morphology and dimensions of grains (x4580)
material (PT-Eu) sintered at 1200oC
SEM pattern for the sample sintered at 1280oC
(PZT-WL)
SEM pattern for the sample sintered at 1305oC
(PZT-WL
Local concentration of W atoms on the sample
surface (PZT-WL, TS1280oC)
Local concentration of W atoms on the sample
surface (PZT-WL, TS1305oC)
TS 1220oC
TS 1220oC
TS 1170oC
TS 1170oC
Morphology and dimensions of the grains (x2400)
(material PT-ND)
Split image SEI DyL? X-ray map of the grains
(x2400) (material PT-ND)
MAGNETIC PROPERTIES
Remanent polarization vs. transition temperature
CORRELATION MICROSTRUCTURE- DIELECTRIC
PROPERTIES (PZT-WL ceramics )
DIELECTRIC PROPERTIES
MODELING
The influence of the defects (un-reacted raw
materials, inclusions with gradient of chemical
elements concentration , pores, etc.) might be
calculated by treating the substances as
composite materials with a connectivity 3-0. The
quantities referring to the nonporous ceramic
have been computed. By applying the formula
correlating the dielectric properties of the
composite with the dielectric properties of its
components it is possible to reconstitute the
dielectric properties of the ideal materials
and the influence of each impurity on the
obtained dielectric material
PZT- SMS-CE with lead deficiency
PZT- SMS-CE with lead excess
PZT- SMS-CE
YES, WE CAN PREDICT THE CERAMIC PROPERTIES
The unity cell proper for the 0-3 connectivity
used for the computation of piezoelectric
coefficients
REFERENCES
M.Alexe, C.Tanasoiu, E.Dimitriu, C. Cojocaru,
Materiaux de constructions, XXVII,2, 107-111
(1997) R.Ramer, E.Dimitriu, E. Boerasu, A. Iuga,
8-th ECERS, Istanbul, 2003 E.Dimitriu,
C.M.Bunescu, A.Iuga, R.Ramer, Ferroelectrics 270,
45-50, 2002 E. Dimitriu, E. D. Ion, S.
Constantinescu, M. Bunescu, R. Ramer,
Ferroelectrics, in press
4.The heat treatment is specific for each
chemical composition and is determinant for
a)the microstructure (crystalline lattice,
phases, distribution of additives) b)physical
properties (density, dielectric, piezoelectric,
magnetic properties). 5. Milling the calcined
product ? less size of the particles 6. Hot
pressing the powder ? less sintering temperature
The measured physical quantities for porous
ceramic and the calculated ones for the nonporous
material (sintering temperature 1220oC and 1170o
C).
ACKNOWLEDGEMENTS
POLECER Network is acknowledged for the financial
support