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Fry_Allyson_dissertation_Final_2.pdf (8.68 MB)
ETD Abstract Container
Abstract Header
Controlling the ordering of the polar building units
M
O
3
F
3
3-
(
M
=Mo,W) with three counter ions,
A
3-x
B
x
M
O
3
F
3
Author Info
Fry, Allyson Marie
Permalink:
http://rave.ohiolink.edu/etdc/view?acc_num=osu1376867125
Abstract Details
Year and Degree
2013, Doctor of Philosophy, Ohio State University, Chemistry.
Abstract
This research focuses on understanding and controlling the orientational ordering of the polar building unit
M
O
3
F
3
3-
(
M
=Mo,W). The orientational ordering of these polar building units have been the interest of researchers for almost a century due to the potential of being useful in the creation of polar materials. These polar building units (PBU) has been incorporated in many perovskite structures, as mentioned in Chapter 6, that do not have any long range orientational ordering. This work focuses on several perovskite related compounds that show orientational ordering and therefore advances our ability to design new polar materials. Chapter 2 and Chapter 3 use powder diffraction techniques, laboratory and synchrotron X-ray and time-of-flight neutron diffraction, to explore the incorporation of
M
O
3
F
3
3-
(
M
=Mo,W) into the LiNbO
3
structure. Hard and soft interactions are employed to control the cation and anion ordering in the compound Na
1.5
Ag
1.5
M
O
3
F
3
(
M
=Mo,W). Preferentially the fluoride face of the
M
O
3
F
3
3-
(
M
=Mo,W) anion coordinates sodium and the oxygen face silver, which results in anti parallel orientational ordering of the PBU. In Chapter 3 the compositional flexibility of this cation and anion ordered LiNbO3 structure is further investigated by substitution of additional alkali metals, with partial substitution of potassium investigated in detail. This study indicates that the interlayer spacing has a large impact on the interactions of the PBU and thus the structure that forms. Chapter 4 explores the complex low temperature structure of two compounds, α-K
3
MoO
3
F
3
and α- Rb
3
MoO
3
F
3
, which are part of a relatively small family of ferroelectric materials, but had incorrectly been assigned a non-polar structure. These compounds were found to be the first examples of anion ordered compounds that possess non-cooperative octahedral tilting (NCOT). This form of tilting has only been observed in a small number of compounds and is the result of large amplitude rotations of the rigid
B'X
6
octahedra around some or all of the perovskite axes. The structure was determined through combined refinements of synchrotron and time-of-flight neutron data. Due to the large size of the unit cells, 13,103.94(4) Å
3
and 14,576.23(6) Å
3
for the potassium and rubidium analogs respectively, and the number of crystallographically independent sites, 104, both constraints and restrains had to be employed to correctly determine the anion ordering as well as stabilize the refinement. Preliminary laboratory X-ray powder diffraction was performed on several additional compounds and they are suggested to adopt similar NCOT structures which would more than double the number of compounds that adopt this type of octahedral tilting. Most of this work addresses the long range structure of compounds containing PBU, however structures may possess local ordering which may help to elucidate structural differences that are not understood when probed by diffraction techniques. In Chapter 5 the PBU in the compounds described in earlier chapters are investigated by Raman scattering. The PBU give several strong Raman bands that are sensitive to the local ordering of the PBU as well as the
B
and
B'
cation identities. The asymmetric stretching modes give rise to a diffuse collection of bands that are sensitive to ordering of the PBU. The number of bands present in this region of the Raman spectra in the high temperature cubic phase suggests the presence of short range ordering of PBU that is not detectable by traditional diffraction. The Raman of the anion ordered LiNbO
3
structures presented in Chapter 2 and Chapter 3 are collected and compared to the Raman of LiNbO
3
as well as perovskite related compounds. The final chapter presents metrics that can be used to predict the formation of perovskite related structures, LiNbO
3
and those that exhibit NCOT. The tolerance factor has been used for some time to predict when a structure will form hexagonal, cubic, or tilted perovskites, but two additional metrics are needed to predict the formation of LiNbO
3
and NCOT structures. Both of these metrics are based on cation radii and not only do they address a means of predicting the formation of these structures they also reveals structural driving forces that stabilize the formation of these technologically important materials.
Committee
Patrick Woodward, PhD (Advisor)
Pages
161 p.
Subject Headings
Chemistry
;
Inorganic Chemistry
Recommended Citations
Refworks
EndNote
RIS
Mendeley
Citations
Fry, A. M. (2013).
Controlling the ordering of the polar building units
M
O
3
F
3
3-
(
M
=Mo,W) with three counter ions,
A
3-x
B
x
M
O
3
F
3
[Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1376867125
APA Style (7th edition)
Fry, Allyson.
Controlling the ordering of the polar building units
M
O
3
F
3
3-
(
M
=Mo,W) with three counter ions,
A
3-x
B
x
M
O
3
F
3
.
2013. Ohio State University, Doctoral dissertation.
OhioLINK Electronic Theses and Dissertations Center
, http://rave.ohiolink.edu/etdc/view?acc_num=osu1376867125.
MLA Style (8th edition)
Fry, Allyson. "Controlling the ordering of the polar building units
M
O
3
F
3
3-
(
M
=Mo,W) with three counter ions,
A
3-x
B
x
M
O
3
F
3
." Doctoral dissertation, Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1376867125
Chicago Manual of Style (17th edition)
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Document number:
osu1376867125
Download Count:
243
Copyright Info
© 2013, all rights reserved.
This open access ETD is published by The Ohio State University and OhioLINK.