Cold Sintering of Lead Zirconate Titanate Based Composites
Open Access
- Author:
- Gupta, Shruti
- Graduate Program:
- Materials Science and Engineering (MS)
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- May 21, 2021
- Committee Members:
- Susan E Trolier-Mckinstry, Thesis Advisor/Co-Advisor
Clive A Randall, Committee Member
John Mauro, Program Head/Chair
Michael T Lanagan, Committee Member - Keywords:
- Cold sintering process
ceramic process
piezoelectricity
composites
ultrasound transducers
sintering process - Abstract:
- Medical ultrasound and other devices that require transducer arrays are difficult to manufacture, particularly for high frequency devices (>30 MHz). To enable focusing and beam steering, it is necessary to reduce the center-to-center element spacing to half of the acoustic wavelength. Conventional methodologies prevent co-sintering ceramic-polymer composites due to the low decomposition temperatures of the polymer. Moreover, for ultrasound transducer arrays exceeding 30 MHz, methods such as dice-and-fill cannot provide the dimensional tolerances required. Other techniques in which the ceramic is formed in the green state often fail to retain the required dimensions without distortion on firing the ceramic. This dissertation explores use of the cold sintering process to produce dense lead zirconate titanate (PZT) ceramics for application in high frequency transducer arrays. PZT-polymer 2-2 composites were fabricated by cold sintering tape cast PZT with Pb nitrate as a sintering aid and ZnO as the sacrificial layer. PZT beams of 35 μm width with ~5.1 μm kerfs were produced by this technique. The ZnO sacrificial layer was also found to serve as a liquid phase sintering aid that led to grain growth in adjacent PZT. This composite produced resonance frequencies of > 17 MHz. This dissertation also explored cold sintering of PZT using alternative sintering aids. It was shown that lead acetate trihydrate lowers the optimum cold sintering temperatures to 200°C. Densification entailed a 2 step process: cold sintering of PZT with Pb acetate trihydrate and post annealing the as cold sintered PZT ceramics. Unlike in the case of lead nitrate, PZT densification with lead acetate trihydrate occurs by a liquid phase assisted sintering mechanism, leading to an as-cold sintered relative density of 84% at 200°C. After performing a post anneal step at 900°C, >97% relative densities were achieved in samples that were cold sintered with Pb acetate trihydrate. This step not only densified PZT but also refined the grain boundaries. In the post-annealed samples, the room temperature relative permittivity at 100 Hz was ~1600, slightly higher than that reported in samples that used lead nitrate as a sintering aid; the loss tangent was about 3.8%. For measurements at 10 Hz, the remanent polarization in both cases was ~28µC/cm2. Both Rayleigh analysis and ageing studies showed that a higher irreversible contribution to the permittivity exists in samples that used Pb nitrate as a cold sintering aid.