Untitled Quiz

Crystal Structure

• Crystal structure describes the ordered arrangement of atoms, ions or molecules in a crystalline material.
• Crystallography is the experimental science of determining the arrangement of atoms in crystalline solids.
• A crystalline solid is a solid material whose constituents are arranged in a highly ordered microscopic structure.
• The smallest group of particles in the material that constitutes the repeating pattern is called the unit cell.
• The unit cell completely defines the symmetry and structure of the entire crystal lattice, which is built up by repetitive translation of the unit cell along its principal axes.
• The repeating patterns are said to be located at the points of the Bravais lattice.

Simple Cubic Lattice

• Coordination number = 6
• Packing Efficiency = 52%
• 1/8 atom at each of 8 corners

Body-centered Cubic Lattice

• Coordination number = 8
• Packing Efficiency = 68%
• 1 atom at the center of the unit cell

Face-centered Cubic Lattice

• Coordination number = 12
• Packing Efficiency = 74%
• 1/2 atom at each of the 6 faces

Summary of Cubic Lattices

• Simple Cubic: 1 atom per unit cell; Packing Efficiency = 52.4%; Empty Space = 47.6%
• Body-centered Cubic: 2 atoms per unit cell; Packing Efficiency = 68%; Empty Space = 32%
• Face-centered Cubic: 4 atoms per unit cell; Packing Efficiency = 74%; Empty Space = 26%

Defects in Crystals

• Crystal defect: an imperfection in the regular geometrical arrangement of the atoms in a crystalline solid.
• Defects can result from deformation of the solid, rapid cooling from high temperature, or high-energy radiation.
• Defects influence the mechanical, electrical, and optical behavior of the solid.

Polymorphism

• Polymorphism: the ability of a solid material to exist in more than one form or crystal structure.
• Polymorphism can be found in any crystalline material including polymers, minerals, and metals.
• Examples include glycine, calcite, and aragonite.