Ultrasonic Studies of Ferroelectric Phase Transitions in KTN
- Slides: 15
Ultrasonic Studies of Ferroelectric Phase Transitions in KTN Robert Mech, Betzaida Berrios, Oleksiy Svitelskiy (Physics Department, Gordon College, MA) Gary Pennington, Rajeswari M Kolagani, Grace Yong (Physics Department, Towson University, MD) Lynn A Boatner (Oak Ridge National Lab) This work was partially supported by NSF DMR awards #1709282 and #1709781.
Outline 1) KTa 0. 92 Nb 0. 08 O 3 2) Ultrasound Pulse-Echo Technique 3) Our Research 4) Our Data
KTN • Potassium Tantalate Niobate (KTa 1 -x. Nbx. O 3) is a ferroelectric perovskite. • Ferroelectric behavior strongly dependent on x. • KTN is an archetype for more complicated ferroelectrics (e. g. lead relaxors). • Recently used in optoelectronic devices (e. g. beam deflector for OCT, varifocal lens). KTN 8% Sample (L. Boatner, Oakridge Natl Labs)
KTN – 8% Nb K 2+ Ta/Nb 4+ O 2 - C. B. Di. Antonio and S. M. Pilgrim. Processing, Characterization, and Di-electric Studies on K(Ta 1 -x. Nbx)O 3 for Use at Cryogenic Temperatures. Journal of the American Ceramic Society, Vol. 84, No. 11 (1982).
Ultrasound Pulse Echo L tt = L / v 3 t t = 3 L / v 5 t t = 5 L / v
Ultrasound Pulse Echo • Yellow: Sending Transducer • Blue: Receiving Transducer • Purple: Phase of Ultrasound • Green: Gated Integrator
Apparatus Sample holder for low-temperature, high-voltage measurements Ultrasound is applied longitudinally, electric field applied transversely, [1, 0, 0] – cut crystal Electronics
Data Example Unprocessed Amplitude + Phase Data
Data Transition temperatures TC 3 TC 2 TC 1
Phase Gain and Speed of Sound Relative speed of sound change may be obtained: 0 0 • Ultrasound phase gain Δφ as a function of temperature • Allows us to visualize how electric fields affect phase transitions
Attenuation Data (E-Field Effects) Comparing Amplitude Data Shows: • Transition temperatures tend to decrease with applied electric field • Different Nb site oscillations may explain dual peak
Dual Peak Data Dual Peak Phenomenon: • Right: Shows TC change with respect to voltage • Below: Attenuation of peaks • Different B site oscillations might explain this E Ta/Nb 4+
Long-Term Relaxation Phase and amplitude data shows sample maintains polarization for months
Future Work • Finish Reversed Polarity Measurements • Apply Electric Field Perpendicular • Apply Ultrasound in Transverse Direction • Perform Measurements With Varying KTN Compositions • X-Ray Diffraction
Acknowledgements Gordon College Collaborators: Betzaida Berrios, Oleksiy Svitelskiy (PI) Towson University Collaborators: Gary Pennington, Rajeswari M Kolagani, Grace Yong KTN Crystal grown by: Lynn A Boatner (Oak Ridge National Lab) This work was partially supported by NSF DMR awards #1709282 and #1709781.
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