Studies in PZT piezoelectrics

By Adam MyersAdvisor: Prof. Bowman

Piezoelectrics: PZT, [ ]

A piezoelectric is a material that produces an electric field when subjected to a mechanical stress, and vice versa.

PZT is shorthand for Lead Zirconate Titanate,

X-ray Diffraction

Prof S.A.Nelson, Tulane University

n2d*sin(

Constructive interference

Destructive interferenceBragg’s Law:

X-ray Diffraction cont.

Useful in finding planar orientationsShow mechanical surface damagesShow poling effects

002

020

200

020

200

002

Poling Direction

Away from poling Direction

A

A

B

B

X-Rays

Poling MechanismThe central shifting ion in the tetragonal unit cell of PZT allows the material to be a dielectric and a piezoelectric.

+4

+4

a

a

c

Poling DirectionSince the central ion can only move in the cdirection, the domains must align so this canoccur. Poling direction domains effectivelygrow.

Polishing effects

Sample was subjected to different polishing media and annealing temperatures in order to study crystal structure changes.It was found that the 0.05 micron alumina polishing produced a sample texture closest to the as-received sample texture.Longer annealing times may have produced a more random sample.

{002} Planes

Decreasing mechanicaldamage

Ferroelastic material:Mechanical poling or just surface damage.

Poling of thin K550 sample

Thin K550 PZT was placed in a silicone oil bath at 120 degrees C.A 250 volt potential difference was applied across the electrodes for 2 minutes.Sample was washed with solvent to remove the silicone oil, and nitric acid to remove the electrodes.

Peaks of interest: {002}-Split peak caused by tetragonal unit cell.-Poling shown by higher (002) peak

Electro-optic effects

The K550 is an electro-optic PZT. Electro-optic materials can transmit or block light according to different electric fields and poling conditions.Wanted to see if there was a difference in the index of refraction of a poled and unpoled sample.

AirN1

WaterN2

light

Index of Refraction:N1*sin(Theta1)=N2*sin(Theta2)

Theta1

Theta2

Laser

Top View

Screen

PZT: Poled Unpoled

Light was scattered, no measurabledata was obtainable

Alternate method was considered, but not used because ofinability to polish samples down to at least 50 microns andlack of prior knowledge of a close value.

Sample Thinning-Silver electrodes were removed from samples with nitric acid, leaving about 120 microns of PZT for the thin samples.-Polishing went slowly until 600 grit polishing paper was used.-Sample shattered due to epoxy expansion in acetone. Relatively large piece at 88 microns was recovered for transmission XRD.-Results were uncertain due to possibility of reflection from micro-cracks.

Multiples of a Random Distribution

Shows exactly what it says: The multiple of times something occurs compared to its occurrence in a randomly distributed sampleData was normalized to 3, the number of orthogonal planes in the {002} family

MRD plot of Poled Navy II sample Produced with encouragement from Andy Smith

90 degrees 45 degrees 25 degrees

Checked different Navy II and VI samples poledin different fields for increased poling.

Results seem to show that the increased poling fields do notincrease the poled texture.

d33 measurements on the samples seem to confirm the MRD results.

d33 measurements area measure of the efficiency of the piezoin converting mechanicalto electrical energy.

Thanks to….

Profs. Slamovich and BowmanPurdue UniversityDave RobertsAll of my fellow REU students*

Pete, Jake, and Harry