Polarization Orientation Dependence of Piezoelectric Loss and Proposed Crystallographic Characterization Methodology
Open Access
- Author:
- Choi, Minkyu
- Graduate Program:
- Materials Science and Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- October 08, 2018
- Committee Members:
- Kenji Uchino, Dissertation Advisor/Co-Advisor
Kenji Uchino, Committee Chair/Co-Chair
Clive A Randall, Committee Member
Susan E Trolier-Mckinstry, Committee Member
Wenwu Cao, Outside Member - Keywords:
- PZT
piezoelectric loss
piezoelectric characterization
anisotropy
negative loss - Abstract:
- Piezoelectric materials are widely utilized in small devices, and low loss is essential for further miniaturization with desired power density. Due to large piezoelectric loss, the mechanical quality factor of Pb(Zr,Ti)O3 (PZT) ceramics at antiresonance frequency is much higher than the one at resonance frequency. Thus, driving the piezoelectric resonator at the antiresonance frequency is recommended to reduce the required electric power for generating the same level of mechanical vibration. Unfortunately, piezoelectric loss has not been studied intensively, and the physical origin is yet unclear. Assuming the origin of loss is from domain dynamics, it is essential to understand the piezoelectric loss behavior by polarization orientation. The change in the piezoelectric loss factors by polarization orientation was investigated using a conventional characterization method with effective k31 and k33 mode structures. 1% Nb-doped PZT ceramics (PNZT) were prepared in tetragonal rhombohedral and MPB structure with 0, 15, 30, 45, 60, 75 and 90 degree polarization angles in collaboration with PI Ceramics, Germany. As a result, it was determined that the intensive piezoelectric loss increases more than intensive dielectric and elastic losses by angling the polarization. However, two serious issues were found in the k33 structure with small motional capacitance, which are: 1. Large relative error from indirect calculation and large structural impedance of the k33 rod. 2. Error in 3dB method used to define the mechanical quality factor. Consequently, a new analysis procedure to obtain anisotropic loss tensors is proposed using effective vibration modes of ceramic bar with canted polarization. The proposed methodology contains 1) off-resonance dielectric measurements, 2) effective k31 mode analysis, 3) off-resonance d33 measurements and 4) effective k15 mode analysis. The effective k31 and k15 vibration mode should be separated from other modes to use the method. A bandwidth between maximum and minimum susceptance and reactance, which is known as the quadrantal bandwidth, is suggested as the half-power bandwidth to determine the mechanical quality factors at resonance and antiresonance, respectively. ATILA/FEA (Micromechatronics Inc., PA, USA) simulation was made with the change of piezoelectric d constant. The new method showed better accuracy of the quality factor and loss determination especially in the low coupling condition. The independent intensive properties of prepared PNZT are obtained with the suggested methodology. Piezoelectric loss showed larger anisotropy in all structures compared to the dielectric or elastic loss. Using the rotation matrix, polarization angle dependent effective properties were calculated. Although the elastic and piezoelectric properties differ from the result obtained with the conventional method, the piezoelectric loss showed the largest changes by canting the polarization. Considering 3-dimensionally clamped and electrically open-circuited condition of material, extensive loss parameters were additionally obtained. Negative extensive piezoelectric loss was discovered in a tetragonal PNZT with largely angled polarization and electric field, for both k31 and k15 vibration mode. In is known that positive piezoelectric loss is considered to compensate the dielectric and elastic losses, thus the heat generation under anti-resonant drive is less than the one under resonant drive when the piezoelectric loss is large. The negative extensive piezoelectric loss contributes to the overall phase lag, which could be observed in the contribution of extensive loss factors to the intensive elastic loss. The negative piezoelectric loss may be related with the domain wall dynamics and could motivate theoretical physicists to a new understanding.