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【正文】 is more possible A B C D (a) (b) Diffusion of vacancysolute plexes (4) 3. Vacancyinterstitial solute plexes in bcc crystals (1) A ? B, then C ? D Migration energy of plex ? (solute atom migration energy + vacancysolute binding energy) or vacancy migration energy (2) C ? D, then A ? B Migration energy of plex ? (vacancy migration energy + vacancysolute binding energy) or solute atom migration energy Diffusion of vacancysolute plexes (5) 3. Vacancyinterstitial solute plexes in fcc crystals (c) A B C D A B C E (a) (b) (d) Migration energy of plex ? vacancy migration energy or solute atom migration energy Complex migration does not need its partial dissociation Diffusion in Ionic Materials (1) Diffusion occurs by vacancy mechanism and involves two types of ions with opposite charges Formation of vacancies: ? Schottky defects Diffusion in Ionic Materials (2) FeO ? Nonstoichiometry Diffusion in Ionic Materials (3) ? Substitutional impurities . in NaClCa solid solution Replacement of a sodium ion by a calcium ion creates an extra positive charge. To maintain the electroneutrality, the formation of a sodium vacancy is required Diffusion processes: The diffusive migration of a single ion is the transport of electrical charge. To maintain the electroneutrality near the moving ion, another species with equal and opposite charges is required to acpany this ion’s diffusive motion Possible charged species: vacancy or electronic carrier like free electron or hole Diffusion in Ionic Materials (4) Concepts: free electron, hole Semiconductors – ntype semiconductor and ptype semiconductor ntype semiconductor: electron conduction (an extra valence electron – excitation of the electron – a free electron) ptype semiconductor: hole conduction, a deficiency of one valence electron (hole) FeO Assignments Problems , , and
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