The document discusses defects in solids, categorizing them into stoichiometric and non-stoichiometric defects, which include vacancy and interstitial defects. Stoichiometric defects maintain the balance of constituent particles, while non-stoichiometric defects result from an imbalance, such as metal excess or deficiency due to cation or anionic vacancies. Examples like Frenkel and Schottky defects illustrate how these structural anomalies affect the material properties and composition of crystals.

1. Defect in solids
Line defect & Point defect

2. Point & Line defect

3. Point defects in solids

4. Stoichiometric defects
 These are the point defect that do not disturb the
stoichiometry of the constituent particles in the
crystal.
 They are called intrinsic or thermodynamic
defect.
 This defect is of two types.

5. Types of Stoichiometric defect
Non-ionic compound
(a) Vacancy defect
(b) Interstitial defect
Ionic compound
These solids must always
maintain electrical neutrality.
(a) Frenkel defect
(b) Schottky defect

6. Vacancy Defect
 When some of the lattice
sites are vacant,
the crystal is said to have
vacancy defect .
 This results in decrease
in density of the
substance.
 This defect can also
develop when
a substance is heated.

7. Interstitial defect
 When some constituent
particles (atoms or
molecules) occupy an
interstitial site, the
crystal is said to have
interstitial defect
 This defect increases the
density of the substance.


8. Frenkel defect
 Smaller size ion is
missing (dislocating)
from its correct lattice
sites (causing a vacancy
or a hole) and occupies
an interstitial site.
 Electrical neutrality as
well as stoichiometry of
the compounds are
maintained.
Hole

9. Frenkel defect
 Dislocation defect
 No change in density of
solid
 Large difference in the
size of cation and anion
 Example : ZnS, AgCl,
AgBr,

10. Schottky defect
 In the ionic crystal of the
type A+ B-, equal number
of cations and anions are
missing from their lattice
point . It is called
Schottky defect.
 It maintain the electrical
neutrality of the
compound.

11. Schottky defect
 Density of the crystal
decreases.
 The size of the Cation
and anion is almost
similar.
 Example : NaCl, KCl,
CsCl, AgBr.
 Example: In NaCl,
there are approximately
106 Schottky pair per cm3
at room temperature. In
1 cm3 there are about
1022 ions. Thus, there is
one Schottky defect per
1016 ions.

12. Difference

13. Impurity Defect
 If molten NaCl is
crystallized with a little
amount of SrCl2, some of
the sites of Na+ ions are
occupied by Sr2+ ion.
 Each Sr2+ ion replaces
two Na+ ion.
 Number of vacancy
produced, is equal to that
of Sr2+ ions.

14. Non-Stoichiometric defect
 Metal Excess defect
 It is of two types:
(a) Metal excess defect due to
anionic vacancies
(b) Metal excess defect due to
the presence of extra
cation
 Metal deficiency
defect

15. Non-Stoichiometric defect

16. Metal excess defect due to anionic vacancies
 A crystal of NaCl is heated in
sodium vapour, it acquires a
yellow colour.
 This yellow colour is due to the
formation of a non-
stoichiometric compound of
sodium chloride in which there
is a slight excess of sodium
ions.
 The anionic sites occupied by
the unpaired electron are called
F - centres
F - Centre

17. Metal excess defect due to anionic vacancy

18.  The colour results by the
excitation of these
electrons, when they
absorb energy from visible
light.
 LiCl crystal appear pink.
 KCl crystal appear violet.

19. Metal excess defect due to the presence of extra cation
 On heating ZnO loses O2
and turns yellow.
 Formula Zn1+xO
 Zn2+ and electron moves
to the different
interstitial sites.

21. Metal Deficiency defect
 One of the positive ions is missing from its lattice
site and the extra negative charge is balanced by
some nearby metal ion acquiring two charges
instead of one.
 This type of defect is generally found in the
compounds of transition metals which can
exhibit variable valency.
 Crystals of FeO, FeS and NiO show this type of
defects.

23. Composition is Fe0.95O

24. THANKS