This thesis presents the first systematic study of the cobalt site preferences in iron rare-earth based compounds. The Mossbauer source technique employed in this work offers a direct and unambiguous way to quantitatively determine cobalt site preferences in these compounds at extremely low cobalt contents. Data quality as well as counting efficiency for the source ($ sp{57}$Co doped) samples is enhanced by constructing a resonant conversion electron detector utilising 90% $ sp{57}$Fe enriched stainless steel foil. Our results have produced the most convincing evidence that cobalt substitutes preferentially for iron in these compounds. We have demonstrated that the site volume is the dominant factor controlling the preferential cobalt substitutions at transition-metal sites with volume $<$12.2A$ sp3$. The cobalt preference for a site decreases linearly with increasing site volume at a rate of $ sim$0.9A$ sp{-3}$. In general, cobalt shows a preference for sites with volume $<$11.8A$ sp3$. As site volume becomes sufficiently large ($ ge$12.2A$ sp3$), the negative enthalpy of mixing between cobalt and rare-earth plays a significant role in modifying the cobalt site preferences in combination with the site volume effects. This results in cobalt preferring strongly those sites with the highest number of rare-earth nearest-neighbors.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.39786 |
| Date | January 1992 |
| Creators | Liao, Lexiang |
| Contributors | Altounian, Zaven (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Physics.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001326821, proquestno: NN87616, Theses scanned by UMI/ProQuest. |
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