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Superprotonic Phase Transitions in Solid Acids: Parameters affecting the presence and stability of superprotonic transitions in the MHnXO4 family of compounds (X=S, Se, P, As; M=Li, Na, K, NH4, Rb, Cs)

Citation

Chisholm, Calum Ronald Inneas (2003) Superprotonic Phase Transitions in Solid Acids: Parameters affecting the presence and stability of superprotonic transitions in the MHnXO4 family of compounds (X=S, Se, P, As; M=Li, Na, K, NH4, Rb, Cs). Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-01292003-150309

Abstract

The present work attempted to uncover the structural and chemical parameters that favor superprotonic phase transitions over melting or decomposition in the MHXO4, MH2ZO4, and mixed MHXO4-MH2ZO4 classes of compounds (X=S, Se; Z=P, As; M=Li, Na, K, NH4, Rb, Cs) and to thereby gain some ability to "engineer" the properties of solid acids for applications. Three approaches are described. First, the general observation that larger cations enable superprotonic transitions was investigated in both the isostructural M2(HSO4)(H2PO4) and non-isostructural MHSO4 family of compounds. The results of these studies confirmed and explained such a cation size effect, and also supplied a crystal-chemical measure for determining the likelihood of a compound undergoing a phase transition. Second, the entropic driving force behind the transitions was explored in the mixed CsHSO4-CsH2PO4 system of compounds. From these investigations, a general set of rules for calculating the entropy change of a superprotonic transition was established and the role of entropy in the transitions illuminated. Finally, the superprotonic phase transition of CsHSO4 was simulated by molecular dynamics, with which means the transition was probed in ways not possible through experimental methods. A sufficiently general approach was utilized so as to be applicable to other (as yet un-synthesized) compounds, thereby speeding up the process of discovering novel superprotonic solid acids. All three approaches increase the fundamental understanding of which chemical/structural features facilitate superprotonic transitions and should aid attempts to create new solid acids with properties ideal for application.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:order-disorder transition; proton conductor; solid acids; superprotonic conduction
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Materials Science
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Haile, Sossina M.
Thesis Committee:
  • Haile, Sossina M. (chair)
  • Ustundag, Ersan
  • Gray, Harry B.
  • Goddard, William A., III
  • Johnson, William Lewis
Defense Date:13 December 2002
Author Email:calum (AT) caltech.edu
Record Number:CaltechETD:etd-01292003-150309
Persistent URL:http://resolver.caltech.edu/CaltechETD:etd-01292003-150309
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:398
Collection:CaltechTHESIS
Deposited By: Imported from ETD-db
Deposited On:20 Feb 2003
Last Modified:26 Dec 2012 02:29

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