Crystal defects - definition, its types, example, and diagrammatic representation.

1. CRYSTAL DEFECTS
Presented by Deep Gupta
B.Sc. Geology Honours (1st year)

2. INTRODUCTION
 An ionic crystal which has the same unit containing the same lattice points
throughout the whole of crystal is known as Ideal crystal.
 Such ideal crystals exist only at absolute zero (0 K) temperature.
 Any deviation from completely ordered arrangement of constituent particles in a
crystal is called crystal defects.

3. CLASSIFICATION OF CRYSTAL ACCORDING TO THEIR
GEOMETRY :-
Types of defects
Point defect
Line defect
Planar defect
Bulk defect

4. POINT DEFECTS
“ The defects which arise due to the irregularity or deviations from ideal arrangements
of atoms around a point or an atom in a crystalline substance are called point defects or
atomic imperfections.”
CLASSIFICATION
Stoichiometric crystal defect
Non-stoichiometric crystal
defect
Impurity defect

5. STOICHIOMETRIC CRYSTAL DEFECT
NON-IONIC CRYSTAL
VACANCY DEFECT INTERSTITIAL DEFECT SCHOTTKY DEFECT FRENKEL DEFECT
IONIC CRYSTAL

6. (i) Vacancy Defect
*When some of the lattice sites are vacant.
*Results in decrease in density.
(iii) Schottky Defect
* When some of the ions are missing from
their lattice sites.
* Observed in ionic compounds having high
coordination number & cations and anions
of almost similar sizes.
(ii) Interstitial Defect
*When some constituent particles occupy
vacant interstitial positions .
*Results in increase in density.
(iv) Frenkel Defect
* When an ion is missing from its normal
position and occupies an interstitial site
between the lattice points.
* Observed in compounds having low
coordination number & anionic size is
larger than cationic size.

7. NON-STOICHIOMETRIC CRYSTAL DEFECT
Metal Excess Defects Metal Deficient Defects
* Anion vacancies
* Extra cations occupying
interstitial sites.
* Cation vacancies
* Extra anions occupying
interstitial sites.

8. IMPURITY
DEFECT
* These defects in ionic crystals arise due to the presence of some impurity ions at the
Lattice sites ( in place of host or ions ) or at the vacant interstitial sites.
* Result in increased electrical conductivity in solids.
If molten NaCl containing a little
amount of SrCl2 is allowed to
crystallise, some of the sites of Na+
ions are occupied by Sr2+
ions.

9. LINE DEFECT
“The defects which arise due to irregularities or deviations from ideal
arrangement in entire row of lattice points are called line defects.”
TYPES
EDGE DISLOCATION SCREW DISLOCATION

10. EDGE DISLOCATIONS
* These are caused by the termination of a plane of atoms in the middle of the
crystal. In such a case, the adjacent planes are not straight, but instead bend
around the edge of the terminating plane so that the crystal structure is perfectly
ordered on either side.
SCREW DISLOCATION
* It basically comprises a structure in which a helical path is traced around the
linear defect by the atomic planes of atoms in the crystal lattice.

11. PLANAR DEFECTS
* Grain boundaries occur where the crystallographic direction
of the lattice abruptly changes. This usually occurs when two
crystals begin growing separately and then meet.
* Stacking faults occur in a number of crystal structures, but
the common example is in close packed structures. They are
formed by a local deviation of the stacking sequence of layers
in a crystal.
* A Twin boundary is a defect that introduces a plane of mirror
symmetry on the ordering of a crystal.

12. BULK DEFECTS
* Three dimensional macroscopic or bulk defects, such as pores, cracks,or inclusions.
* Voids – small regions where there are no atoms, and which can be thought of as
clusters of vacancies.
* Impurities can cluster together to form small regions of a different phase. These are
often called precipitates.

13. THANK YOU