Experiment No.

Title: Study of crystal structure: Diamond, ZnS &NaCl.Aim: To study crystal structure of Diamond , ZnS & NaCl.Apparatus: Plastic Models of Diamond, ZnS & NaCl crystal structures.

Theory:

Diamond:The diamond lattice can be described as being build up from two identical interpenetrating FCC sub lattices, one of which is displaced from the other by ¼ of the length along body diagonal. The atomic basis is two atoms per lattice point, one located at (0,0,0) and other at (¼,¼,¼).

ZINC SULPHIDE (ZnS):

The zinc blend(ZnS) structure is same as that of diamond with a minor difference is the two interpenetrating sub –lattices are of different elements (zinc and sulphide structure, Zn atoms replace carbon atoms of one FCC sub lattice and S atoms replace the carbon atoms of another FCC sub- lattice of diamond unit cell.

SODIUM CHLORIDE (NaCl):

Sodium Chloride crystal is an ionic crystal is an ionic crystal. In the sodium chloride lattice, positively charged sodium ion and negatively charged chlorine ion are situated side by side. It consists of two FCC sublattices. One of the chlorine ion has its origin at (0, 0, 0) point while sodium ion has its origin midway along the cube edge at (a⁄2, 0, 0) point as shown in fig. Due to the electrostatic force between sodium and chloride ions, the two ions are attracted towards each other. When the two ions come closer, their outer electron shell come close proximity giving rise to strong force of repulsion. Thus, the attraction and repulsion are counter balanced at particular distance of separation and equilibrium is obtained.

Experiment No.

Diamond structure

Experiment No.

Observation Table:

Sr.No. Parameter Observation

Diamond ZnS NaCl1. Lattice

2. Basis

3. No.of atoms per unit cell(n)

4. Atomic Radius( r )

5. Co-ordination Number

6. Atomic Packing Factor(APF)

7. Void Space

8. Density (ρ )

Experiment No.

Calculation:

No.of atoms per unit cell (n) =

Atomic Radius ( r ) =

Atomic Packing Factor (APF) =

Void space =

Density (ρ) =

Definition of Atomic Packing Fraction (APF) It is defined as ratio of volume occupied by atoms to the total volume of unit cell. When APF is expressed in percentage it is called Packing efficiency.

Formula: APF = Volumeof atomsVolumeof unit cell

Procedure: 1.Observe the crystal models of Diamond ,ZnS and NaCl crystal structure.2.Note down the number of atoms present at corner, at body centre, face centre and edges positions.3.Calculate the number of effective atoms per unit cell

4.Calculate atomic radius in terms of Lattice Constant ‘a’

5.Calculate the atomic packing fraction (APF) for individual unit cell and their respective void spaces.

Experiment No.Result : We have calculated various aspects regarding crystal structure of Diamond ,ZnS and NaCl as shown in observation table.

Experiment No.

Title: Study of HCP crystal structure.Aim: To study crystal structure of HCP.Apparatus: Plastic Model of HCP crystal structure.

Theory:

HCP: In a layer of close packed spheres, each sphere is in contact with six neighbour spheres. The line joining centres of the six neighbour spheres forms a hexagon. In a Hexagonal close packed (HCP) structure; one atom is present at each corner, one atom at each centre of the hexagonal faces and three more atoms within the body of the unit cell.

Definition of Atomic Packing Fraction (APF)It is defined as ratio of volume occupied by atoms to the total volume of unit cell. When APF is expressed in percentage it is called Packing efficiency.

Formula: APF = Volumeof atomsVolumeof unit cell

Procedure: 1Observe the crystal models of HCP crystal structure.2Note down the number of atoms present at corner, at body centre, face centre and edges positions.3Calculate the number of effective atoms per unit cell .4Calculate atomic radius in terms of Lattice Constant ‘a’.5Calculate c/a ratio for HCP.

6.Calculate the atomic packing fraction (APF) for individual unit cell and their respective void spaces.

Result : We have calculated various aspects regarding crystal structure of HCP as shown in observation table.

Experiment No.

Experiment No.Observation Table: HCP.

Sr.No. Parameter Observation

1. Lattice

2. Basis

3. No.of atoms per unit cell(n)

4. Atomic Radius ( r )

5 c/a Ratio

6. Co-ordination Number

7. Atomic Packing Factor(APF)

8. Void Space

9. Density ( ρ )

Calculation:n =

r =

APF=

Void Space =

ρ =

c/a =

Result : We have calculated various aspects regarding crystal structure of HCP as shown in observation table.

Experiment No.