Transcript REMcassie - University of Florida

Development and Implementation of a Polarization Measurement System
Cassandra Llano, Elena Aksel, Anderson D. Prewitt, Shruti Banavara Seshadri, Jennifer Forrester
and Jacob L. Jones
Department of Materials Science and Engineering, University of Florida, Gainesville, FL 32611, USA
Explanation of Polarization Measurement:
Motivation:
Polarization of a piezoelectric material gives insight into
many of its structure-property relationships, for example
the permittivity is directly proportional to polarization.
An apparatus that measures polarization will provide an
avenue to comprehend these properties.
Sawyer-Tower Circuit
To measure polarization, a Sawyer-Tower circuit is used
The voltage is cycled by the function generator in a specific waveform
The reference capacitor and the sample are in series, so the voltage across the
reference capacitor is measured
Thus the charge on the sample (polarization) can be measured by:
Q= C x V
Where Q is charge, C is capacitance, and V is voltage
Surface Charge = (C x V)/surface area of sample
We can show the polarization of a material in an oscillating electric field by plotting
the electric field applied to the material on the x-axis, and the polarization of the
The point of polarization
material on the y-axis
The remnant
polarization, Pr left on
the sample at zero
field.
Oscilloscope
saturation, Ps where the
maximum amount of
domains in the sample are
aligned in the direction of
the field.
Reference Capacitor
Earth
Piezoelectric
Sample
Set-Up:
The oscilloscope shows the applied
wave function and the response
from the sample (Figure 3 middle).
Pb0.97Sm0.02Zr0.3(TiO3)0.7
Pb0.97Sm0.02Zr0.2(TiO3)0.8
Pb0.925Sm0.05Zr0.2(TiO3)0.8
Electric field (kV/mm)
 Compare hysteresis loops of 2% and 5% Sm doped PZT at
different Zr/Ti ratios
 Pb0.97Sm0.02Zr0.2(TiO3)0.8 shows conductivity in the sample
NBT with BT
Solid Solutions
Na0.5Bi0.5TiO3
0.96(Na0.5Bi0.5TiO3)
0.04(BaTiO3)
0.94(Na0.5Bi0.5TiO3)
0.06(BaTiO3)
0.93(Na0.5Bi0.5TiO3)
0.07(BaTiO3)
0.91(Na0.5Bi0.5TiO3)
0.09(BaTiO3)
0.87(Na0.5Bi0.5TiO3)
0.13(BaTiO3)
Function Generator
Figure 5. Sawyer-tower circuit diagram
Figure 6. Example of Sawyer-tower
reference capacitor
Figure 1. Polarization apparatus with cage
The function generator allows the
user to select the specific wave
functions (sine, square, triangular),
as well as the voltage and frequency
that needs to be applied to the
sample (Figure 3 top).
The voltage amplifier receives the
signal from the function generator
and sends the appropriate
voltage/frequency to the probe on
the sample (Figure 3 bottom).
Pb0.97Sm0.02Zr0.45(TiO3)0.55
The coercive field, Ec is
the points where
domain switching starts
to occur.
Figure 7. Polarization Vs. Electric Field
Experimental:
• The following samples were tested in the PE set up: Sm-doped lead zirconate titanate
(PZT) and sodium bismuth titanate (NBT) with barium titanate (BT) solid solutions
• The measurements were done using a triangular waveform at 1 Hz.
• All samples were cycled at incremental electric fields, starting from a low field, until a
full PE loop was observed.
Figure 2. platform, probe and holder
Figure 3. Function generator, Oscilloscope
and Voltage amplifier
(top to bottom)
 Compositions made by Dr. Forrester in Dr. Jacob Jones’ lab
 NBT and NBT-9BT show some conductivity in the samples
NBT with BT
Solid Solutions
0.94(Na0.5Bi0.5TiO3)
0.06(BaTiO3)
0.93(Na0.5Bi0.5TiO3)
0.07(BaTiO3)
0.91(Na0.5Bi0.5TiO3)
0.09(BaTiO3)
0.88(Na0.5Bi0.5TiO3)
0.12(BaTiO3)
Electric field (kV/mm)
Conclusions:
 Built a set-up that measures polarization with the following capabilities:
Voltage
Frequency
Wave function
Electric field (kV/mm)
Polarization (pC/cm2)
The polarization apparatus, probe
and platform was placed in a plexiglass cage, which has a safety onoff sensor that only permits the high
voltage to run if the cage door is
closed (Figures 1 and 2).
Sm doped PZT
Polarization (pC/cm2)
To develop a device that can accurately
measure the polarization of materials at
various electric fields and frequencies in
order to acquire a better understanding of
the structure-property relationships in
piezoelectric materials.
Polarization vs. Electric Field:
Polarization (pC/cm2)
Objective:
0kV-10kV AC
10 mHz- 100 kHz
sine, triangle, square
 Sm-doped PZT at the Morphotropic phase boundary has a lower Ec than
rhombohedral PZT
 The addition of Sm to a PZT sample with a .2/.8 Zr/Ti ratio decreases sample
conductivity
 Samples prepared in the J. Jones lab showed comparable property results to those
from Darmstadt, Germany
 The addition of 6-7 mol% BT to NBT significantly reduces Ec while Maintaining Pr
 Compositions made by Dr. Wook Jo’s in Darmstadt, Germany
 0.91(Na0.5Bi0.5TiO3) 0.09(BaTiO3) had large conductivity
Future Work:
Setting up a linear
variable displacement
transducer (LVDT)
The LVDT will be able to measure the strain
as well as the polarization of a sample at the
same time
Figure 8. LVDT
References: http://www.doitpoms.ac.uk/tlplib/ferroelectrics/printall.php?question=4&type=1 Acknowledgments: Research Experience in Materials (REM) ; Howard Hughes Medical Institute- Science for Life Program; NSF award #DMR-0746902 ; U.S. Department of the Army award # W911NF-09-1-0435