low temperature processing of electro-ceramic materials and devices
Open Access
- Author:
- Wang, Dixiong
- Graduate Program:
- Materials Science and Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- December 18, 2019
- Committee Members:
- Susan E Trolier-Mckinstry, Dissertation Advisor/Co-Advisor
Susan E Trolier-Mckinstry, Committee Chair/Co-Chair
Clive A Randall, Committee Member
Qing Wang, Committee Member
Thomas Nelson Jackson, Outside Member
John C Mauro, Program Head/Chair - Keywords:
- Dielectric energy storage
Cold sintering process
Bismuth niobate
Lead zirconate titanate
Ceramic processing
Energy harvesting - Abstract:
- The thesis investigated two low temperature processing methods: Applying deep ultra-violet (DUV) radiation during the sol-gel deposition of Bi3NbO7 (BNO) thin films to facilitate carbon removal, and the cold sintering process (CSP) of Pb(Zr, Ti)O3 (PZT) powder/tape. A DUV treatment between the drying and pyrolyzing steps during sol-gel deposition can effectively eliminate the residual carbon in BNO thin films at < 350 °C, which decreases the porosity, and improves the energy storage densities of the BNO capacitors. As a result, the BNO thin film, when annealed between 350-450 °C, presented energy storage densities of 13-39 J/cm3, which is comparable with many thin films crystallized at 700 °C. Furthermore, by suppressing the maximum heat treatment temperature, high performance thin film capacitors can be directly deposited on the polymer/metal substrates. This will shorten the processing flow of flexible electronics and can be beneficial to the production of wearable devices. The cold sintering process was also employed in order to densify lead zirconate titanate, one of the most widely used piezoelectric materials. The CSP often utilizes a water-based transient liquid phase to either partially dissolve the ceramic powder, creating a liquid phase sintering (LPS) condition; or lubricate the powder to enhance the compaction. Because it is difficult to dissolve PZT powder, moistened Pb(NO3)2 was mixed with PZT to help packing the PZT powder to a relative density over 80% during cold sintering at 300 °C, 500 MPa. The Pb(NO3)2 also decomposes into PbO, which helps to liquid phase sinter the PZT when the cold sintered samples were post-annealed at 700-900 °C. The 900 °C post-annealed PZT showed a relative density ~99% with a room-temperature relative permittivity over 1300 and a d33 ~200 pC/N. Further study also suggested the cold sintering of PZT/Pb(NO3)2 obeys a viscous sintering model, which differs from the cold sintering mechanisms reported for many other materials. The thesis also evaluated the processing of PZT/metal/PZT 2-2 composites via cold sintering and post-annealing. It was found that the cold sintering process can suppress micro-cracking in the PZT layer, presumably by strengthening the ceramic compact at low temperatures. Constrained sintering was observed when PZT was cold sintered on Ni or Cu foils; these could be avoided by laminating tape cast PZT and Cu powder instead. However, the Cu2O interface formed between PZT and Cu is still problematic. The relative permittivity of the 800 °C annealed PZT on Cu is only ~500, with an -e31,f less than 5 C/m2. If future work is able to achieve a clean interface, this process can be helpful for the fabrication of piezoelectric energy harvesters with high open circuit voltages.