Different crystal structures of Engineering materials

This article describes the basic crystal structure of common engineering materials which are now basic building blocks of daily life. Engineering materials like Aluminium, copper, Iron, Cobalt etc are made up of different types of crystal structures like BCC, FCC and HCP. Each structure has its own unique arrangement and based on atomic radius and atomic distance, different crystal structure has different density and so on for other material properties.

Importance of crystal structures

Every physical body in this world is made up of a basic entity called atoms. When these atoms arranged in a regular pattern, unique arrangement, they form lattice structure for crystalline solid/liquid body.The lattice structure finally determines one's physical properties.

Types of lattice structure or crystal structure

Basic of the crystal structure consists of space lattice pattern and basis

Crystal structure = space lattice + basis

Basis may contains one atom per lattice pattern


1) FCC (Space lattice) + 1 Aluminium atom at each lattice point (basis) = FCC Crsystal of Aluminium (Crystal structure)

2) BCC + 1 Iron atom at each lattice point (basis) = BCC Crystal of Iron

  • FCC = Face Centred Cubic
    e.g. Copper, Aluminium, Nickel, Pb, Ag

  • BCC = Body Centred Cubic
    e.g. W, Mo, Cr

  • HCP = Hexagonal close pack
    Mg, Zn, Ti, Cd, Zr

  • Unit Cell:The basic difference between all these pattern lies in the difference between the unit cell which is nothing but the repeatability of each pattern in lattice space.

    Crystal structures of metals FCC BCC HCP

    B.C.C (Body Centred Cubic)

    • 1 atom at centre of cube and one atom each at all the corners
    • No. of atoms per unit cell = Nc/8+Nf/2+Ni/2 Where Nc = No. of atoms at centre, Nf = No. of atoms at face and Ni = No. of atoms inside.
    • Atomic radius = 1.73*a/4, Where a = distance between two adjacent atoms
    • Atomic packing radius = 0.68
    • v, Mo, Ta, W are having BCC structure at room temperature
    • coordination no is 8
    • The nearest distance between two atoms = 1.73*a/2

    BCC Body Centred Cubic

    F.C.C (Face Centred Cubic)

    • 1 atom at each corner of cube
    • 1 atom at the intersection of the diagonal of each of six faces of the cube
    • No. of atoms per unit cell = Nc/8 + Nf/2 + Ni/2 = Four atoms
    • Atomic radius = 1.41*a/4
    • Atomic packing factor = 0.74
    • e.g. Cu, Al, Pb, Ni, Co etc
    • Coordination number = 12
    • Nearest distance between two atoms = a/1.41
    • No. of atoms per unit cell shows the density packedness
    • So, FCC is more density packed than BCC

    H.C.P.(Hexagonal Close Pack)

    • 1 atom at each corner of hexagone
    • 1 atom at each centre of hexagone faces
    • 1 atom at the centre connecting perpendicular s in three rhombuses
    • No. of atoms per unit cell = 6
    • Atomic radius = a/2
    • Atomic packing factor = 0.74
    • Coordination number = 12
    • e.g. Zn, Cd, Mg

    Because of allotropes of iron, it got two different lattice structure at different temperatures.

    • At room temperature crystal structure of Iron is BCC(Body Centered Cubic)
    • At 912 °C the crystal structure changes(Face Centred Cubic) and
    • At 1,394 °C its crystal structure changes to a Body centered cubic (BCC)

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