Sol-gel processing, perovskite phase development and properties of relaxor-based thin layer ferroelectrics
Francis, Lorraine Falter
This item is only available for download by members of the University of Illinois community. Students, faculty, and staff at the U of I may log in with your NetID and password to view the item. If you are trying to access an Illinois-restricted dissertation or thesis, you can request a copy through your library's Inter-Library Loan office or purchase a copy directly from ProQuest.
Permalink
https://hdl.handle.net/2142/21451
Description
Title
Sol-gel processing, perovskite phase development and properties of relaxor-based thin layer ferroelectrics
Author(s)
Francis, Lorraine Falter
Issue Date
1991
Doctoral Committee Chair(s)
Payne, David A.
Department of Study
Materials Science and Engineering
Discipline
Materials Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Materials Science
Language
eng
Abstract
This thesis reports on the preparation and properties of thin layer ceramics in the Pb ((Zn$\sb{1/3}$Nb$\sb{2/3})\sb{\rm 1-x}$Ti$\sb{\rm x}$) O$\sb3$ (PZNT) and Pb ((Mg$\sb{1/3}$Nb$\sb{2/3})\sb{\rm 1-x}$Ti$\sb{\rm x}$) O$\sb3$ (PMNT) systems for capacitor and ferroelectric applications. Sol-gel methods were used to prepare thin layers by spin-casting partially hydrolysed alkoxide-based solutions on platinized Si substrates. As-deposited layers were amorphous, and formed a nonferroelectric pyrochlore phase or a ferroelectric perovskite phase, depending on the processing route. Since the perovskite structure is required for ferroelectric properties, the phase development and processing methods for perovskite formation were investigated in detail for thin layers and powders.
Crystalline phase development in sol-gel derived powders and thin layers was studied by thermal analysis and X-ray diffraction. All compositions crystallized first into a cubic pyrochlore phase. Pb$\sb2$ ((M$\sb{1/3}$Nb$\sb{2/3})\sb{\rm 1-x}$Ti$\sb{\rm x}$) $\sb2$O$\sb6$ and at higher temperatures, formed the perovskite phase Pb ((M$\sb{1/3}$Nb$\sb{2/3})\sb{\rm 1-x}$Ti$\sb{\rm x}$) O$\sb3$ (M is Mg or Zn). For powders, the gelation conditions affected the rate of perovskite formation. The unit cell parameters and formation temperatures for the pyrochlore and perovskite phases were found to depend on composition. The evolution of structure with heat-treatment was explained in terms of a general model of thermally activated processes.
With optimized processing, thin layers in the entire PMNT system could be prepared in the perovskite structure. The most effective processing method was spin-casting, followed by rapid heat-treatment to a temperature sufficiently high for the perovskite structure to crystallize, without the formation of the pyrochlore phase. Solution additives (HNO$\sb3$, NH$\sb4$OH and benzoic acid) also affected perovskite content and microstructure. Dielectric and ferroelectric properties of thin layers were determined and related to composition, microstructure and phase content. PMN rich thin layers had high dielectric constants (K) and low remanent polarization (P$\sb{\rm r}$) values (e.g., 90 PMNT: K $\sim$ 2200, tan $\partial$ $<$ 0.03; P$\sb{\rm r}$ = 3 $\mu$C/cm$\sp2$, E$\sb{\rm c}$ = 18 kV/cm), whereas PT rich thin layers had relatively high P$\sb{\rm r}$ values with lower dielectric constants (e.g., 30PMNT: K $\sim$ 500, tan $\partial$ $<$ 0.03, P$\sb{\rm r}$ $\sim$ 12 $\mu$C/cm$\sp2$, E$\sb{\rm c}$ = 40 kV/cm). Thin layers in the PMNT system have potential for thin layer capacitor and ferroelectric memory applications which can now be integrated directly onto semiconductors by sol-gel methods.
Use this login method if you
don't
have an
@illinois.edu
email address.
(Oops, I do have one)
IDEALS migrated to a new platform on June 23, 2022. If you created
your account prior to this date, you will have to reset your password
using the forgot-password link below.
