Evaluation of Large Signal Minor Loop Behavior in PMN-PT Ceramics

1. Evaluation of Large Signal Minor Loop Behavior in PMN-PT Ceramics Harold C.Robinson and Elizabeth A.McLaughlin NAVSEA Undersea Warfare Center Division Newport 1176 Howell Street, Newport RI 02841

2. abstract • The stress and polarization behavior (lanthanum doped PMN-PT) ▶ evaluate using unipolar, biased drive of up to 1.3MV/m under varying temperature and mechanical stresses • The strain vs. field 와 polarization vs. field loops (minor loops biase / full loops biase) • minor loops: rotate around the midline of the major loop ▶ smaller values for the large for the large signal piezoelectric and dielectric constants than major loop alon • Energy density, electromechanical coupling factor, dielectric loss factor DC bias 와 AC drive field의 함수로 계산 ▶ the strain energy density, electromechanical coupling factor (DC bias: increasing, AC drive: decreasing) ▶ dielectric loss factor (DC bias: decreasing, AC drive: increasing)

3. I. Introduction • The large signal electromechanical properties of electroactive materials  PZT,PMT-PT ceramics  transducer, actuator design  measuring under small signal condition(book value)  Not relevant to the conditions of their actual use. • Properties of linear materials(PZT) have exhibited considerable dependence upon AC drive field, prestress, temperature • Nonlinearities(the strain, polarization response<--hysteresis) can inaccurate determinations(result of a single large signal, all condition) • For accurately device performance(under actual condition) • actual condition에서 material properties 값을 측정 가능. •측정치가 적다면 material properties를 결정할 타당성의 범위 확정.

4. I. Introduction • A series of biased minor loop measurements ▶ perform using NAVSEA Newport’s SDECS ▶ using combinations of two temperatures, four prestress levels, four DC bias levels, seven AC drive levels ▶ the stress, polarization : measured as a function of the applied field The large signal electromechanical properties (piezoelectric constant, dielectric constant, dielectric loss factor) The Young’s modulus as a function of applied DC bias (at each temperature from the stress-strain response) ▶ so, the large signal properties were used to compute the equivalent coupling factor, energy density of the material SDECS: Stress Dependent Electromechanical Characterization System

5. II.MEASUREMENTS • <<Typical field and polarization waveform>> • be subjected to two cycles of full unipolar drive • the initial electrical conditions were the same(for each biased minor loop) • AC drive field was reduced to measure the minor loop response over six cycle • The sample had returned to its original state • The first and last cycles(minor loop segment) were discarded to remove the effects of any transients

6. << the strain and polarization in minor loops >> II.MEASUREMENTS 3kpsi at PMN-PT is 0.34MV/m(bias level) • 이하: see the character of the minor loops • 이상: hysteresis 감소, minor loops are indistinguishable the initial two cycles followed the outermost loop • The AC drive level was reduced the polarization and strain loops be different than that predicted from the slope of the major loop ∴ major loop만의 data로 제작한 transducer는 예상치 못한 결과를 낳는다.

7. III. MATERIAL PROPERTIES • The large signal material properties • The piezoelectric constant • relative permittivity • dielectric loss factor • electromechanical coupling factor • the strain energy density

8. III. MATERIAL PROPERTIES 1. 3kpsi에서 piezoelectric constant 와 relative permittivity 의 특성 곡선 3kpsi(21Mpa)의 압축응력 DC bias(4): △,□ (at ) ▲,■ (at )

9. 2. 3kpsi에서 Dielectric loss factor 와 coupling factor 의 특성 곡선 III. MATERIAL PROPERTIES

10. III. MATERIAL PROPERTIES 3. 3kpsi에서 Strain energy density 의 특성 곡선

11. conclusion • The minor loops tend to rotate about the center line of the major loop • Major loop만으로 측정된 material properties는 device의 성능을 정확히 예측하기 어렵다.(in hysteretic situation) • Dielectric loss factor는 온도가 상승하면 감소되고 또한, 일정한 온도에서 DC bias와 AC drive를 증가시키면 감소된다 • Coupling factor와 strain energy density 적당한 drive에서 최고치를 가지고, DC bias와 ac drive가 증가하면 감소.