Nanoprecipitates Flashcards
Describe the Hume Rothery criteria for when you may expect to have a complete solid solubility between two compounds. Give two examples; one metallic system and one oxide system for which you will argue that there is full solid miscibility.
H-R Criteria:
- Max 15% difference in atoms
- Same (with minor differences) crystal structure
- Same oxidation state for involved cations/anions
- No major difference in eletronegativity (chemical bonding)
Fcc-metals: Rh - Pt
Rock salt: MgO - NiO
Perovskites: LaAlO3 - LaCoO3
Consider the system MgO (rock salt) - ZnO (wurtzite), and describe solid solubility in the system.
Not same crystal structure –> not miscible
What is heterovalent (aliovalent) substitution? Which types of defects are connected with such substitution?
Substitution of host-atom with atom of different valence (oxidation state).
Defect: Vacancies, interstitials (charge compensators)
Imagine that you substitute Fe(II) into ZnO at high temperature. Draw a figure showing how the solid solubility depends on temperature. Describe what will happen if you rapidly or slowly cool a sample which at high temperature contains a substantial amount of Fe(III), see lecture slides for relevant phase diagrams.
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Can you generalize this (question 4) to what can be expected on rapid and slow cooling of supersaturated solid solutions?
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Imagine that you have incorporated some Fe(II) into an oxide matrix by ion implantation, and that you subsequently heat treat the sample at specific (different) temperature and oxygen partial pressure. How will the magnetic preoperties of the sample depend on the conditions for the treatment?
Which methods may you use for identifying the oxidation state of iron in these samples?
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How are nanoprecipitates formed in Al-based light metal alloys, and how do the presence of these influence the properties of the alloys?
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