Graduate Thesis Or Dissertation
 

Cation Substitution Effects in Complex Transition Metal Oxides

Public Deposited

Downloadable Content

Download PDF
https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/1j92gf23r

Descriptions

Attribute NameValues
Creator
Abstract
  • Understanding structural evolution in solids as composition changes is essential to materials properties prediction. Such structure-properties relationships are the theme of solid state chemistry. Materials scientists and chemists have utilized an abundance of simple crystal structures to enhance understanding of chemical and structural origins of properties in materials for decades. Low symmetry and large site systems have often been left inadequately investigated due to complications of relating the structural changes within such materials to the emergent properties. However, as more advanced materials are required for emerging applications it is necessary to develop better working frameworks for these structurally complex materials. The hibonite structure and triclinic iridate double perovskites are interesting hosts for cation substitutional investigations as the origin of properties is multi-faceted. Both hibonites and iridate perovskites are under-explored systems due to their high structural complexity and difficulty in producing samples for inquiry.The effects of iron substitution into the hibonite structure (CaAl12O19) was investigated due to an interest in the resultant magnetic and dielectric properties. The related hexaferrite, BaFe12O19, is an excellent hard magnet used commercially, but suffers dielectric loss due to the large amount of iron. Iron substitution by the formula, CaAl12−xFexO19 was successful up to x = 5:5. Magnetic susceptibility measurements reveal paramagnetic behavior for x ≤ 3 and ferrimagnetic behavior for x ≥ 4 with increasing Curie Temperature. The ferrimagnetic transition is unlike other iron-containing hexaferrite and is likely the result of spin-freezing due to the low iron site-preference, rather than a highly ordered magnetic structure. Increasing iron content also increases dielectric loss. Cobalt-titanium co-substitution into the hibonite structure revealed striking deepblue coloration. Compositions of CaAl12−2xCoxTixO19 were successfully synthesized for x ≤ 1. Structural analysis revealed high site preference for both Co2+ and Ti4+ for the tetrahedral (and trigonal bipyramidal) and face-shared octahedral sites, respectively. UV-Vis and Near-IR spectroscopy showed intense d-d transitions related to tetrahedral Co2+. The deep blue coloration was therefore attributed to Co2+ in tetrahedral coordination. The lack of green hue compared to CoAlO4 was related to the presence of Co2+ in trigonal bipyramidal coordination, blue-shifting the visible absorbance. Barium substitution into La2CuIrO6, double perovskite, was performed to further explore the effects of charge balance and A-site size mismatch on the low-symmetry host structure. A solid solution for CaxLa2−xCuIrO6 and BaxLa2−xCuIrO6 was found to exist for x ≤ 0:6 and x ≤ 1, respectively. Increasing Ca and Ba content reduces the magnetic moment, coinciding with the oxidation of Ir4+ to Ir5+, only. Ba substitution also causes an increase in symmetry, from triclinic to monoclinic. High temperature resistivity measurements show all samples remain semiconducting.
Contributor
License
Resource Type
Date Issued
Degree Level
Degree Name
Degree Field
Degree Grantor
Commencement Year
Advisor
Committee Member
Academic Affiliation
Rights Statement
Publisher
Peer Reviewed
Language
Embargo reason
  • Intellectual Property (patent, etc.)
Embargo date range
  • 2020-06-08 to 2022-07-09

Relationships

Parents:

This work has no parents.

In Collection:

Items

Thumbnail Title Date Uploaded Visibility Actions
file details DuellBrettA2020.pdf 2020-06-08 Public Download