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LY_final_thesis_draft.pdf (7.36 MB)
ETD Abstract Container
Abstract Header
Synthesis and Characterization of A
2
Mo
3
O
12
Materials
Author Info
Young, Lindsay Kay
Permalink:
http://rave.ohiolink.edu/etdc/view?acc_num=toledo1431517117
Abstract Details
Year and Degree
2015, Master of Science, University of Toledo, Chemistry.
Abstract
Negative thermal expansion (NTE) materials have attracted considerable research interest in recent decades. These unique materials shrink when heated, offering a potential means to control the overall thermal expansion of composites. Several families of materials display this behavior, the largest of which is the A
2
Mo
3
O
12
family (also called the scandium tungstate family), in which A is a trivalent cation and M is molybdenum or tungsten. These materials show NTE in an orthorhombic structure, but many members transform to a monoclinic structure with positive expansion at low temperatures. Many properties of these materials are dependent on their elemental composition, especially the identity of the A
3+
cation. This includes the magnitude of NTE, as well as the phase transition behavior as a function of temperature and pressure. It is also possible to create "mixed site" cation A
2
Mo
3
O
12
materials, in which the A site is occupied by two different cations. These are described as A
x
A'
2-x
M
3
O
12
materials, as the composition A:A' can vary. Creating these new compositions may result in different phase transition properties or the ability to tune the NTE properties of these materials. In this work, the focus was on synthesis and characterization of indium gallium molybdate (In
x
Ga
2-x
M
3
O
12
). The non-hydrolytic sol-gel (NHSG) method was used to synthesize indium gallium molybdate while exploring a variety of reaction parameters. While the goal was to create stoichiometric, homogenous materials, it was found that this could not be accomplished using easily accessible parameters during NHSG reactions. However, it was discovered that certain conditions allowed unusually low temperature (230 °C) crystallization of these materials. Similar conditions were explored for single cation A
2
Mo
3
O
12
materials, and it was determined that crystallization of indium molybdate, iron molybdate, and scandium molybdate was possible at temperatures of 230 or 300 °C. This extremely low temperature crystallization may provide the opportunity for exploring the in situ synthesis of polymer composites containing these materials, as the crystallization temperatures are compatible with many polymer systems. In the second part of this thesis, the high pressure behavior of a number of A
2
Mo
3
O
12
and AA'Mo
3
O
12
materials was studied. The open frameworks of NTE compounds are generally prone to pressure induced phase transitions. NTE materials may have to withstand high pressures during production or regular use of composites, thus understanding the high pressure behavior of these materials is necessary for effective application. Irreversible transitions to new phases or amorphization at high pressures could lead to failure of composites, as these phases are not expected to exhibit any NTE properties. Studies were carried out at the Advanced Photon Source at Argonne National Laboratory at pressures up to 5-7 GPa using a diamond anvil cell. The materials investigated could be divided into three groups based on distinct types of high pressure behavior. The room temperature monoclinic Group1 compounds (A
2
= Al
2
, Fe
2
, FeAl, AlGa) underwent a similar sequence of reversible subtle phase transitions before undergoing a major structural transition to a common high pressure structure. The unit cell of this high pressure phase was successfully indexed, and the transition was found to be reversible upon decompression. Phase transition pressures increased with decreasing A-site cation radius. In contrast, Group2 materials (A = Cr, Y) retained their low temperature monoclinic structures up to the highest pressures investigated. The remaining materials (A
2
= In
2
, InGa) underwent a different sequence of subtle transitions followed by an irreversible transition at higher pressures. The patterns belonging to these high pressure phases are unlike those of the first group. No patterns similar to InGaMo
3
O
12
were found in the literature, while In
2
Mo
3
O
12
may transform to the same high pressure polymorph as In
2
W
3
O
12
. The classification of A
2
Mo
3
O
12
materials into several groups with distinct high pressure behavior adds pertinent knowledge to the field that may help elucidate the structures of previously studied materials, and ultimately may help predict the behavior of compositions that have not yet been explored.
Committee
Cora Lind-Kovacs, PhD (Committee Chair)
Eric Findsen, PhD (Committee Member)
Jon Kirchhoff, PhD (Committee Member)
Pages
175 p.
Subject Headings
Chemistry
;
Materials Science
Keywords
negative thermal expansion
;
scandium tungstate
;
high pressure
;
phase transitions
;
low temperature crystallization
;
molybdates
;
tungstates
;
non-hydrolytic sol-gel
;
NHSG
Recommended Citations
Refworks
EndNote
RIS
Mendeley
Citations
Young, L. K. (2015).
Synthesis and Characterization of A
2
Mo
3
O
12
Materials
[Master's thesis, University of Toledo]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1431517117
APA Style (7th edition)
Young, Lindsay.
Synthesis and Characterization of A
2
Mo
3
O
12
Materials.
2015. University of Toledo, Master's thesis.
OhioLINK Electronic Theses and Dissertations Center
, http://rave.ohiolink.edu/etdc/view?acc_num=toledo1431517117.
MLA Style (8th edition)
Young, Lindsay. "Synthesis and Characterization of A
2
Mo
3
O
12
Materials." Master's thesis, University of Toledo, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1431517117
Chicago Manual of Style (17th edition)
Abstract Footer
Document number:
toledo1431517117
Download Count:
1,180
Copyright Info
© 2015, some rights reserved.
Synthesis and Characterization of A
2
Mo
3
O
12
Materials by Lindsay Kay Young is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. Based on a work at etd.ohiolink.edu.
This open access ETD is published by University of Toledo and OhioLINK.