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

• Calibration of variable autotransformer indirectly

• Linear relationship is found

• E = V/t0-5

5-10

10-15

Geometry

K181 Sample #71,72

Sample #33,44

Sample #3,5

K182

Sample #13,15

Initial Run

180

165

d1_failure 330

d1_failure 331

2 1041 Cycles_failure

1 10 100 1 103

1 104

1 105

165

170

175

180

# 33 1.4kV/mm#44 1.4 kV/mm

K181 d33 vs Cycles to Failure

Cycles

d33

Cycled at 1.4kV/mm• K181 t = .0848in

d = .965in

• Fail mode cracking• NO significant

degradation of d33• Early in cycling 10^4

Second Run

212.3

2.7

d 33_5i j

p C

N

d 33_2i j

p C

N

d 33_215k

p C

N

d 33_213k

p C

N

1 1061 Cycles

i j Cyclesi j Failure_2

k

1 10 100 1 103

1 104

1 105

1 106

62.5

125

187.5

250

K181 #5K181 #2K182 #15K182 #13

1.2kV/mm Cycling Field

Cycles

d33

(p*C

/N)

Cycled 1.2kV/mm• K182 Fail

t = .0839ind = .843in

• K181 degrades

t = .0848ind = .841in

Sample Failure

Trouble Shooting

• Time constraints K182 is abandoned to focus further on K181

• Current is candidate for FailureOhms law I = V/R

• Resistance is geometry dependent - longer length = higher R

- smaller area = higher R

Last Run

210

175

d1_failure 332

d1 33_72k

1.72 1041 Cycles_failure Failure_72

k

1 10 100 1 103

1 104

1 105

180

190

200

210

K181 #71 @1.4kV/mmK181 #72 @1.24kV/mm

Cycles

d33

(p*C

/N)

• 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 samplesLarge 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.