Piezoelectric Materials

1
Piezoelectric Materials

• Derek Sanderson
• Tulane University Chemical Engineering
• Advisor Prof. Keith Bowman

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Cancerous Tissue Ablation

• Idea
• array of ultrasound transducers
• concentrate energy
• destroy cancerous tissue
• Needs
• ablation strength pulse
• Restrictions
• close proximity
• small size
• internal body temp

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Perovskite Structure

• Simple cube of As face-centered Cs
  body-centered B
• A B C
• Pb2 (Zr/Ti)4 O32-
• cubic
• central B-site cation
• paraelectric
• not lowest energy
• tetragonal/rhomb.
• shifted B-site cation
• ferroelectric
• lower energy

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Microscopic

• cubic structure at high temp.
• cooling below Curie temp. (Tc)
• tetra./rhomb.
• non centrosymmetric
• c/a lt 1.005

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Macroscopic

• neighboring dipoles align to form domains
• 6 possible domains per grain
• infinite possible domains per species ? random
  orientations ? no net dipole ? not piezoelectric

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Poling
P
x

• strong field applied
• field removed net dipole recedes slightly
• not all domains within a grain will switch

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Poling contd- XRD
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Hysteresis

• Initial polarization (virginal)
• saturation polarization
• remanent polarization
• shows a barrier in displacement of B-cation
• proof of mechanism for piezoelectricity
• application of AC causes vibration

Hysteresis curve for Philips PXE 52
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Piezoelectricity

• Direct Effect
• mechanical strain ? electrical pulse
• Sensors- proportional response
• force, engine knocking, crash, microphones
• Generators- conversion of energy
• igniters
• Converse Effect
• electrical pulse ? mechanical strain
• Actuators- proportional response
• fuel injection valve, speakers
• Transducers- conversion of energy (high intensity
  ultrasound)
• medical imaging
• tissue ablation

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PMN-PZT

• Pb (Mn,Nb) O3 Pb (Zr,Ti) O3
• (soft) (hard)
• xPMN-(1-x)PZT ceramic system
• No mean value theorem

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Equipment

• Berlincourt meter- d33 tester
• Pennebaker Model 8000
• design and operation

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Setup

• Set Parameters
• tightness of clamp 105o
• calibration set for post-warming
• interval time (min) 1,5,15,60 for 30 sec.
• cooling time
• Variables
• warming time
• sample thickness, weight, atmosphere

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Results
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Results
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Results
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Results
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Results
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Current Theory

• Possible Explanations
• operator error
• reproduced
• equipment error
• unknown phenomenon

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Current Theory

• Equipment Error
• Values of d33 are significantly lower (up to 50)
  of reported values by Keramos.
• Keramos has noticed the same decrease but not
  further investigated
• Tests to be conducted at Keramos with 2 different
  models of Berlincourt meter

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Future Work

• Conclude decreasing piezoelectric constant due to
  equipment error
• Determine cause of the defect
• Prepare method of obtaining accurate d33 values
  with current Pennebaker model

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Acknowledgements

• Dr. Keith Bowman
• Thomas Key
• Piezo Technologies- Keramos Division
• NSF REU Grant

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Questions?