Crystals and Crystalline Structure

Crystalline Structure

• Many solid substances, including metals, have a crystalline structure, meaning their basic particles are arranged in a definite 3D pattern of rigid geometrical form, repeated many times.
• Crystals take on a distinctive geometric form when allowed to grow freely.
• Non-crystalline solids, such as pitch, glass, and some plastic materials, are amorphous (without shape) and can be considered as extremely viscous liquids.

Crystal Structure and Unit Cell

• The structure of crystals can be understood by considering their constituent atoms as spherical in shape.
• A simple cubic crystal can be built up from eight spherical particles, with the unit cell being the geometric figure that illustrates the fundamental grouping of particles in the solid.
• The unit cell is repeated many times to form the space lattice, which characterizes crystalline materials.
• The regular, repetitive pattern of particles is a key characteristic of crystalline materials.

Bravais Space Lattices

• All crystal structures can be analyzed into fourteen basic lattices, known as the Bravais space lattices.
• The Bravais space lattices can be classified into two types: P-type and C-type.
• P-type lattices are primitive and shown in Figure 1.6 (a).
• C-type lattices are centred on the "ab" face and shown in Figure 1.6 (b).