Materials Science Glossary - L

laminar composite. A series of two-dimensional sheets, each having a preferred high-strength direction, fastened one on top of the other at different orientations; strength in the plane of the laminate is highly isotropic.

large-particle composite. A type of particle-reinforced composite wherein particle-matrix interactions cannot be treated on an atomic level; the particles reinforce the matrix phase.

laser. Acronym for light amplification by stimulated emission of radiation— a source of light that is coherent.

lattice. The regular geometrical arrangement of points in crystal space.

lattice parameters. The combination of unit cell edge lengths and interaxial angles that defines the unit cell geometry.

lattice strains. Slight displacements of atoms relative to their normal lattice positions, normally imposed by crystalline defects such as dislocations, and interstitial and impurity atoms.

lever rule. A mathematical expression, whereby the relative phase amounts in a two-phase alloy at equilibrium may be computed.

light-emitting diode (LED). A diode composed of a semiconducting material that is p-type on one side and n-type on the other side. When a forward-biased potential is applied across the junction between the two sides, recombination of electrons and holes occurs, with the emission of light radiation.

linear polymer. A polymer produced from bifunctional monomers in which each polymer molecule consists of repeat units joined end to end in a single chain.

liquid crystal polymer (LCP). A group of polymeric materials having extended and rod-shaped molecules that, structurally, do not fall within traditional liquid, amorphous, crystalline, or semicrystalline classifications. In the molten (or liquid)

state they can become aligned in highly ordered (crystal-like) conformations. They are used in digital displays and a variety of applications in electronics and medical equipment industries.

liquidus line. On a binary phase diagram, the line or boundary separating liquid and liquid / solid phase regions. For an alloy, the liquidus temperature is the temperature at which a solid phase first forms under conditions of equilibrium cooling.

longitudinal direction. The lengthwise dimension. For a rod or fiber, in the direction of the long axis.

lower critical temperature. For a steel alloy, the temperature below which, under equilibrium conditions, all austenite has transformed to ferrite and cementite phases.

luminescence. The emission of visible light as a result of electron decay from an excited state.