Transcript Piezoelectric Materials

Piezoelectric Materials
Chris Petorak
REU
Dr. Bowman and J.Jones
Piezoelectric Materials
•
•
•
•
Below Curie Temp
Perovskite unit cell
Unit electric dipole
Poling of dipoles in
single direction allows
for piezoelectric
properties
Piezoelectric Properties
• Apply an external
stress = a voltage
difference between top
and bottom electrode
• Applied Voltage = a
strain in the direction
of the applied electric
field.
Common Applications
• Sensors
ex. Microphones and Hydrophones
• Actuators
• Ultrasound technology
Fatigue of Ferroelectric
Properties
• Narrowing of
Hystersis loop
• Decreasing switchable
polarization and d33
• Increasing # of cycles
leads to greater
reduction in
ferroelectric properties
Zhang,N. Li,L. Gui,Z. Degredation of piezoelectric and dielectirc relaxation
properties due to electric faitgue in PLZT ferroelectric capacitors
Domain Wall Pinning
• Oxygen Vacancies
• Results in Space Charge
• Space Charge accumulate to pin domain
walls
• Reduce domain wall mobility
• Therefore reducing switch able polarization
Cycling Setup Considerations
•
•
•
•
Electrical Loading
Hystersis loop
Apply alternating field
180 domain
reorientation
• Parallel plate capacitor
• Lower Cost & Easier
to find Parts
• Compressive Loading
• Stress vs. Strain
• Apply stress to get 1%
deformation
• 90  domain
reorientation
• Compressive jig setup
highly sensitive and
expensive
Cycling Setup Considerations
• High Voltage
• Electric field higher
than Ec
• Closer to saturation
the greater the fatigue
• Low Frequency
• More time for E to
affect domains and
difficult movement
• Domains become set =
greater internal
stresses to be
overcome in reverse
cycle
Building the Setup
• 1st Setup – DC power source 1.4kV/mm
Sinusoidal oscillator 20Hz
• 2nd Setup – AC power source 60Hz
Tube transformer 1.4kV/mm
Variac
• Parallel plate capacitor setup under constant
stress
Building the Setup
Trouble Shooting
10-15
600
Vsample
i0
Voltage
• Calibration of variable
autotransformer
indirectly
• Linear relationship is
found
• E = V/t
O ut pu t Vo l tag e vs. Vari ac sett in g
656 800
Vsample
i1
400
5-10
200
0-5
Vsample
i2
40
0
0
1
2
0
3
i
Increments
0 -5 Vari ac
5 -1 0 Variac
1 0-15 Vari ac
4
5
5
Geometry
K181
Sample #71,72 
Sample #33,44 
Sample #3,5 
K182
Sample #13,15
Initial Run
Cycled at 1.4kV/mm
• K181
t = .0848in
d = .965in
K 18 1 d 33 v s Cycl es to Fail ure
180 180
d33
 0  175
d1_failure33
1 
d1_failure33
170
165
165
1
1
10
3
100
1 10
C ycles_failure
C ycles
# 33 1.4 kV/ mm
# 44 1.4 kV/ mm
4
1 10
5
1 10
4
2 10
• Fail mode cracking
• NO significant
degradation of d33
• Early in cycling 10^4
Second Run
212.3
1 .2k V/mm C ycl in g Field
250
d 33_5
ij
p C
N
187.5
d33 (p*C/N)
d 33_2
ij
p C
N
d 33_215
k
p C
125
N
d 33_213
k
p C
62.5
N
2.7
1
1
10
K 18 1 # 5
K 18 1 # 2
K 18 2 # 15
K 18 2 # 13
100
3
1 10
C ycles  C ycles  Failure_2
ij
ij
k
C ycles
4
1 10
5
1 10
Cycled 1.2kV/mm
• K182 Fail
t = .0839in
d = .843in
• K181 degrades
t = .0848in
d = .841in
6
1 10
6
1 10
Sample Failure
Trouble Shooting
• Time constraints K182 is abandoned to
focus further on K181
• Current is candidate for Failure
Ohms law I = V/R
• Resistance is geometry dependent
- longer length = higher R
- smaller area = higher R
Last Run
210
210
d33 (p*C/N)
200
2 
d1_failure33
d1 33_72
k
190
180
175
1
1
10
3
100
1 10
C ycles_failure
 Failure_72
k
C ycles
K 18 1 # 71 @ 1.4 kV/ mm
K 18 1 # 72 @ 1.2 4k V/mm
4
1 10
5
1 10
4
1.7210
•
•
•
•
•
Area Considerations
 = R*A/t
E = V/t
E*t = I*  *t/A
A increases so does I
because  is
independent of
geometry
Area and Current
• Current Macrolevel – seems to support
theory
• Current Microlevel – current/unit area
leaves a hole in argument.
• Probability of defects in greater in larger
Volume
• Porosity
Recommendations
• Cycle further samples
Large A large t at 1.2kV/mm
Small A large t at 1.4kV/mm
• Establish relationship for sample’s R at low
I and low V. Use this to predict the Current
flow through at high voltage.