Fundamental Understanding of Crystallographic Texturing and Defect Engineering for High Power Piezoelectric Ceramics
Open Access
- Author:
- Leng, Haoyang
- Graduate Program:
- Materials Science and Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- August 17, 2022
- Committee Members:
- John Mauro, Program Head/Chair
Qiming Zhang, Outside Unit & Field Member
Shashank Priya, Chair & Dissertation Advisor
Clive Randall, Major Field Member
Long-Qing Chen, Major Field Member - Keywords:
- Crystallographic texturing
Defect engineering
High power
Piezoelectric - Abstract:
- Piezoelectric ceramics with combinatory soft and hard characteristics are highly desired for high-power applications. However, it remains grand challenge to achieve simultaneous presence of hard (e.g. high coercive field, Ec; high mechanical quality factor, Qm) and soft (e.g. high piezoelectric constant, d; high electromechanical coupling factor, k) piezoelectric properties in piezoelectric ceramics since the mechanism controlling the hard behavior (pinned domain walls) will significantly reduce the soft behavior. In this dissertation, the challenges in design of high performance high-power piezoelectric ceramics are addressed and issues related to transition of developed high-power piezoelectric ceramics are investigated. First, a synergistic design strategy that combines composition/phase selection, crystallographic texturing and defect engineering was developed to fabricate high performance high-power piezoelectric ceramics. Specifically, the <001> textured MnO2 and CuO co-doped Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) ceramics can exhibit ultrahigh combined soft and hard piezoelectric properties (d33 = 713 pC/N, k31 = 0.52, Qm≈950, Ec = 9.6 kV/cm, tan δ = 0.45%). The outstanding electromechanical properties are explained by considering composition/phase selection, crystallographic anisotropy, and defect engineering. Phase-field model in conjunction with high resolution electron microscopy and diffraction techniques is utilized to delineate the contributions arising from intrinsic piezoelectric response, domain dynamics, and local structural heterogeneity. These results will have significant impact in the development of high-power transducers and actuators. Next, the electrical fatigue behavior of high-power textured PIN-PMN-PT piezoelectric ceramics was investigated to evaluate the electric field stability. It was found that high-power textured ceramics exhibit better fatigue resistance behavior in comparison with the random counterpart. The superior fatigue resistance of textured ceramics originates from its smaller domain size with high domain wall density, favorable domain wall switching and internal stress relaxation during the electric field cycling process. Both mechanical damage and domain wall pinning mechanisms were found to play an important role in influencing the fatigue behavior of high-power textured ceramics. Detailed microstructural analysis along with electrical fatigue measurement under bipolar and unipolar mode was conducted to confirm the mechanisms controlling the degradation as a function of varying field and temperature. High-resolution electron microscopy results demonstrate that BaTiO3 (BT) templates present within the high-power textured ceramics do not induce mechanical damage during electric field cycling. Scaling the manufacturing of textured piezoelectric ceramics is difficult as the piezoelectric properties vary with size. In this dissertation, manufacturing of large dimension high-power textured PIN-PMN-PT piezoelectric ceramics is investigated. The large-size high quality high-power textured PIN-PMN-PT piezoelectric ceramics were fabricated by optimizing the ceramic processing conditions. The piezoelectric properties of fabricated large size textured ceramics are close to that of small size counterparts, demonstrating the high reproducibility of textured PIN-PMN-PT piezoelectric ceramics. A tonpilz transducer was built using the fabricated high-power textured PIN-PMN-PT piezoelectric ceramics. The textured PIN-PMN-PT based transducer was found to show much higher coupling coefficient keff along with good electric field stability in comparison with both commercial hard PZT and textured MnO2 doped PMN-PT counterparts, indicating the higher sensitivity of textured PIN-PMN-PT transducer in high power applications. These experimental results clearly demonstrate the promise of high-power textured PIN-PMN-PT ceramics in industrial applications. Next, both <001> and <111> textured PIN-PMN-PT ceramics were successfully fabricated through templated grain growth (TGG) method to investigate the effects of the crystallographic orientation on high-power properties of PIN-PMN-PT ceramics. It is shown that <001> textured ceramics possess higher d33 compared to <111> textured counterparts, while the Qm is strongly enhanced in <111> textured ceramics due to less favored polarization rotation. MnO2 doping is shown to further improve the Qm values for both <001> and <111> textured ceramics because of the restricted polarization switching induced by the defect dipole. Doped <001> textured ceramics can exhibit the high d33 and moderate Qm (d33 = 725 pC/N, Qm = 716) in comparison with <111> textured ceramics exhibiting low d33 and high Qm (d33 = 350 pC/N, Qm = 1495). Owing to the combinatory soft and hard piezoelectric properties, the doped <001> textured ceramics exhibit 1.5× higher vibration velocity (~ 0.90 m/s) in comparison with commercial hard PZTs. Interestingly, a slightly higher vibration velocity (~ 0.94 m/s) can be obtained in doped <111> textured ceramics, which is mainly attributed to the high Qm and low elastic compliance s11. These results demonstrate the promise of textured piezoelectric ceramics for high-power applications. The poling process is crucial in obtaining the piezoelectric properties in piezoelectric ceramics after manufacturing. The poling of hard and high-power piezoelectric ceramics is not an easy process due to the pinned domain walls or polarization rotation induced by the existence of defect dipoles inside the piezoelectric ceramics. Considering the wide applications of piezoelectric ceramics in various electromechanical devices, it is quite necessary to design a poling technique, which can not only improve the piezoelectric properties of piezoelectric ceramics but also provide simplified experimental setup to reduce cost and time. In this study, a water quenching-assisted poling technique was designed by combining water quenching treatment and room temperature AC/DC poling process for soft, hard, and high-power piezoelectric ceramics. This poling technique can not only improve the piezoelectric properties of soft PIN-PMN-PT ceramics but also provide the saturated piezoelectric properties of hard and high-power PIN-PMN-PT ceramics in short duration at room temperature. Extensive microstructural characterizations were conducted with high resolution electron microscopy and diffraction techniques in conjunction with phase field modeling to uncover the mechanisms for enhanced piezoelectricity due to poling ability arising from the quenching-induced rhombohedral phase formation and disordered charged point defects. It is expected that this new poling technique will make a significant contribution on the industrial applications of piezoelectric ceramics. As mentioned earlier, high-power piezoelectric materials should simultaneously possess the soft properties (high piezoelectric coefficient, d33; high voltage coefficient, g33; high electromechanical coupling factor, k) and hard properties (high mechanical quality factor, Qm; low dielectric loss, tan δ) along with wide operation temperature (e.g. high rhombohedral-tetragonal phase transition temperature Tr-t) for covering off-resonance (figure of merit (FOM), d33×g33) and on-resonance (FOM, Qm×k2) applications. However, achieving hard and soft piezoelectric properties simultaneously along with high transition temperature is quite challenging since these properties are inversely related to each other. Here, through a synergistic design strategy of combining composition/phase selection, crystallographic texturing, defect engineering and water quenching technique, the fabricated <001> textured 2 mol.% MnO2 doped 0.19PIN-0.445PSN-0.365PT ceramics can exhibit giant FOM values of Qm×k_31^2 (227 – 261) along with high d33×g33 (28 – 35 × 10-12 m2 /N), low tan δ (0.3 – 0.39%) and high Tr-t of 140 – 190 oC, which is far beyond the performance of the state-of-the-art piezoelectric materials. Further, the water quenching room temperature poling technique provides enhanced piezoelectricity of textured MnO2 doped PIN-PSN-PT ceramics. Based upon the experiments and phase-field modeling, the enhanced piezoelectricity is explained in terms of the quenching-induced rhombohedral phase formation. These findings will have tremendous impact on development of high performance off-resonance and on-resonance piezoelectric devices with high stability.