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Beyond the Traditional AB2 Laves Phase: Transmission Electron Microscopy Study
Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
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URN: urn:nbn:se:su:diva-23989OAI: diva2:196231
Part of urn:nbn:se:su:diva-624Available from: 2005-08-27 Created: 2005-08-27 Last updated: 2010-01-13Bibliographically approved
In thesis
1. Structure and Stability of Bi1-xSbx and CaAl2-xZnx
Open this publication in new window or tab >>Structure and Stability of Bi1-xSbx and CaAl2-xZnx
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is focused on two intermetallic systems Bi1-xSbx and CaAl2-xZnx. Bi and Sb transform into a peculiar incommensurate composite structure under pressure and our intention was to examine the structure and how alloying influences this incommensurate structure. Our investigation was obscured by the occurrence of a phase separation, which accompanied the transition A7 → Bi III. Most remarkable is the finding that structural parameters of phases with the Bi III composite structure were observed to be almost unaffected by pressure and composition effects.

Secondly, phase and structural stability relations within the AB2 pseudo-binary system CaAl2-xZnx was studied. In CaAl2-xZnx, the C36-type Laves phase was observed for the first time, but not the C14-type, and a VEC induced structural transition C15-type → C36-type takes place with increasing x. The exchange of Al by Zn decreases the size of the B-type atom network surrounding Ca and at concentrations x > 0.95, the Laves phase structure is succeeded by the CeCu2 type structure, which tolerates a larger size ratio A/B. The C15-type → C36-type transformation in the CaAl2-xZnx system is induced by the valence electron concentration VEC.

Through the analysis of MEM/Rietveld from synchrotron powder X-ray diffraction data, the total charge distributions and deformation charge densities were obtained for cubic and 4H hexagonal Laves phases in CaAl2-xZnx and also for orthorhombic CaZn2. The overlap electrons, which take an important role in stabilising the crystal structures, are clearly observed in the Kagome-net between B-net atoms. The Ca atoms are located in the space formed by the B-net atoms.

From the high-pressure experiments it was concluded that at elevated temperatures, 1000-1500 °C, the hexagonal C36 structure type transforms to the C15 structure type between 6.2 and 9.4 GPa, and the orthorhombic CeCu2 phase to a hexagonal Laves phase between 7.5 and 15.5 GPa.

Place, publisher, year, edition, pages
Stockholm: Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi, 2005. 86 p.
National Category
Inorganic Chemistry
urn:nbn:se:su:diva-624 (URN)91-7155-109-3 (ISBN)
Public defence
2005-09-19, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 12 A, Stockholm, 13:00
Available from: 2005-08-27 Created: 2005-08-27 Last updated: 2011-03-10Bibliographically approved

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