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

3. Seven Crystal Systems

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.

5. POINT DEFECT
STOICHIOMETRIC
NON-
STOICHIOMETRIC

6. STOICHIOMETRIC
IN
IONIC
SOLIDS
SCHOTTKY
DEFECT
FRENKEL
DEFECT
IN NON-
IONIC
SOLIDS
VACANCY
DEFECT
INTERSTIT
IAL DEFECT

7. Missing of
Cation
Anion
missing
SCHOTTKY DEFECT
Mass of crystal decreases.
In an ionic crystal of NaCl
type equal number of
cations & anions are missing
from their lattice sites.

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.

10. NON-
STOICHIOMETRIC
BY
METAL
EXCESS
Anion
vacancies
By the presence of
extra cation in
interstitial sites
BY METAL
DEFICIENCY
By removal of
metal cation
from their
lattice site

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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