CHEMICAL SOLUTION DEPOSITION OF POTASSIUM SODIUM NIOBATE THIN FILMS
Open Access
- Author:
- Jacques, Leonard
- Graduate Program:
- Materials Science and Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- October 23, 2020
- Committee Members:
- Susan E Trolier-Mckinstry, Thesis Advisor/Co-Advisor
Clive A Randall, Committee Member
Veronika Kovacova, Committee Member
John C Mauro, Program Head/Chair - Keywords:
- Chemical Solution Deposition
Thin Film
KNN
Processing
Metal Oxide
Activation Energy
Nucleation
Composition Segregation
Kinetics - Abstract:
- Potassium sodium niobate (KNN) shows promise as a lead-free alternative for lead zirconate titanate, a material utilized in piezoelectric thin films. However, the successful production of these films via the Chemical Solution Deposition (CSD) process remains challenging. This thesis presents detailed solution methods for KNN deposition via CSD. It was found that the electrical properties of 0.5% Mn-doped KNN films depended on both the composition homogeneity and the heat treatment. The best films exhibited breakdown fields over 600 kV/cm and showed well-developed ferroelectric hysteresis loops. The nucleation and growth phenomena in KNN thin films produced by CSD were studied to obtain activation energies for KNN perovskite phase transformation and growth. The films were annealed in a rapid thermal processor (RTP) with a hold step in a temperature range of 500 to 550°C. During early crystallization of KNN films, it was found that individual nuclei grow as circular regions called rosettes. FESEM was used to determine the size of KNN rosettes, the volume fraction crystallized, and the number of rosettes on partially crystallized samples prepared to determine the activation energies for nucleation, growth, and phase transformation. The results show a linear growth rate with rate law exponents of 1.4, 1.3, and 1.1 at 550°C, 525°C, and 500°C, respectively. The rate laws suggest rapid growth, possibly due to excess alkali additions to the chemical solution. The activation energies for perovskite transformation and growth are 687 ± 13 kJ/mol and 194 ± 10 kJ/mol. The effective activation energy for nucleation calculated from these is 493 ± 23 kJ/mol. Crystallization in KNN is nucleation-limited, and the crystallization temperature can be reduced by crystallizing on a seed layer. Energy dispersive spectroscopy (EDS) revealed the segregation of excess sodium acetate during the drying steps and subsequent transformation to oxalates during pyrolysis as the source of composition segregation.