The document discusses crystal structures and defects. The key points are:
- A crystal is a solid with a regularly repeating pattern of atoms or molecules extending in three dimensions, known as the unit cell.
- Point defects occur when atoms or ions are misplaced or replaced at a single point in the crystal structure. Non-stoichiometric defects occur when the crystal does not have the proper ratio of elements.
- Common point defects include vacancies, when an atom is missing from its normal site, and interstitials, when an atom occupies a space between normal lattice sites.
2. UNIT CELL :
A crystal is a solid in which the constituent
atoms, molecules,ions are packed in a
regularly ordered, repeating pattern of
‘building blocks’, extending in all three
spatial dimensions.
-the ‘building block’ is known as the unit
cell.
The line of dots is called the lattice, and each
lattice point (dot)
must have identical surroundings
LATTICE
4. CRISTAL DEFECTS
POINT DEFECT LINE DEFECT
Defect will be on a
certain point or
position.
If ions or atoms are
misplaced or replaced by
other atoms along a line.
8. Missing ion
present in
interstitial site
Missing cation
FRENKEL DEFECT
An ion is missing from its
lattice site and occupies the
interstitial site.
Mass and volume of crystal
are not changed.
Density of solid remains
unaffected.
9. Particle in the
interstitial site
INTERSTITIAL DEFECT
some foreign atoms are
trapped in interstitial
voids of lattice .
Mass of crystal
increases.
11. Metal excess defect by Anion
vacancies
If no. of missing anions are more than no. of
missing cation .
Anion may be missing from its lattice site leaving
a hole which occupied by an electron to maintain
electrical neutrality .
The location of electron where it is trapped i.e.
anion vacancies called F – Centers
12. F - Centers
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F-center
F = farbe a German word means
‘colour’
F centers are responsible for imparting
color to the crystal.
Example ; at room temperature ZnO is
white in color when it heated some O
ions get released in the form of O2 &
electrons are trapped at their location
due to this it appears yellow .
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