| Term | Definition |
| Allotropy | Polymorphism in elemental solids |
| Amorphous | Lacking any distinct structure |
| Atomic Packing Factor (APF) | fraction of solid sphere volume in unit cell (APF =volume of atoms in a unit cell/total unit cell volume) |
| Axis | Spacial direction |
| Body-Centered Cubic (BCC) | Bravais Lattice involving 8 corner atoms and one center atom |
| Bragg equation | Equation used to determine plane positions using x-ray diffraction (d=?(?/sin ?)) |
| Close Packed Plane | Direction of closest atoms, often the slip plane |
| Constructive Interference | sum of multiple waves results in total greater than original waves |
| Coordination Number | number of nearest neighbors |
| Crystallography | The study of crystals |
| Cubic | One atom at each corner (lattice point) |
| Degree of crystallinity | Percentage of material in crystal form (not amorphous) |
| Destructive Interference | sum of multiple waves results in total less than original waves |
| Face-Centered Cubic (FCC) | Bravais Lattice of an atom at every corner and in the center of every face (physically 2 cubic lattices offset by half a lattice in all three directions |
| Interference | result of multiple waves. May be constructive or destructive |
| Lattice | three-dimensional array of atoms |
| Long-range order | Continuous periodicity |
| Mirror Plane | Reflects the face of a crystal from one side to the other |
| Nearest Neighbor | atoms or ions closest to the atom or ion of discussion |
| Orthogonal | perpendicular, at right angles, or 90? to each other |
| Period | distance between atoms in a lattice |
| Periodicity | Repetition of lattice |
| Plane | two-dimensional flat surface or direction |
| Polymorphism | having more than one possible crystal structure |
| Unit Cell | formation of atoms that repeats itelf within a crystal, hases the most geometrical symmetry |
| X-ray | Form of energy (Energy = ) |
| X-ray diffraction | Method used to determine crystal structures by aiming x-rays at the material and determining at what angles they are detected at |
| Rotational axis | Imaginary axis that crystal can be rotated around and continue to look like the same crystal (atomically) |
| x-ray | A relatively high-energy photon having a wavelength in the approximate range from 0.01 to 10 nanometers. |
| x-ray diffraction | The scattering of x-rays by crystal atoms, producing a diffraction pattern that yields information about the structure of the crystal. |
| Interference | The variation of wave amplitude that occurs when waves of the same or different frequency come together. |
| Diffraction | Change in the directions and intensities of a group of waves after passing by an obstacle or through an aperture whose size is approximately the same as the wavelength of the waves. |
| Fourier series | An infinite series whose terms are constants multiplied by sine and cosine functions and that can, if uniformly convergent, approximate a wide variety of functions. |
| Bragg equation | Relates the angles at which X-rays are scattered from a crystal to the spacing between the layers of molecules. |