Lecture handout including QS - Department of Materials Science ...
Lecture handout including QS - Department of Materials Science ...
Lecture handout including QS - Department of Materials Science ...
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BH57 Course B: <strong>Materials</strong> for Devices BH57<br />
Magnetostriction coefficient, Λ : fractional change in length on changing magnetisation from zero<br />
to saturation (dimensionless).<br />
Monomer: the simple chemical unit which, when many are joined together, form a polymer.<br />
Nematic: spontaneously anisotropic liquid, composed <strong>of</strong> rod-shaped molecules with parallel<br />
alignment.<br />
Optic Axis: for a birefringent sample, a direction along which no birefringence is observed, i.e. a<br />
direction perpendicular to an isotropic section. The optic axis <strong>of</strong> a nematic liquid crystal is along<br />
the Director.<br />
Optical Path Difference: the extra distance traveled by the fast ray outside an anisotropic material<br />
in the time it takes for the slow ray to reach the edge <strong>of</strong> the sample (m).<br />
Order parameter: describes the orientational order <strong>of</strong> a liquid crystalline material, taking account <strong>of</strong><br />
the deviation <strong>of</strong> orientation <strong>of</strong> individual molecules from the Director (zero for complete disorder;<br />
unity for perfect order).<br />
Paramagnetism: the net magnetic moment caused by alignment <strong>of</strong> the electron spins when a<br />
magnetic field is applied.<br />
Permitted Vibration Directions: two perpendicular directions in an anisotropic material along<br />
which the transverse electric field <strong>of</strong> light can vibrate.<br />
Permittivity, ε : describes how an electric field is affected by a dielectric (F m -1 ).<br />
Perovskite: family <strong>of</strong> ABX 3<br />
compounds which commonly show displacive phase transitions by<br />
octahedral tilts or atomic displacements.<br />
Phase: a part <strong>of</strong> a system, homogeneous in composition and structure.<br />
Phase diagram: a diagram showing the equilibrium phases and phase compositions at each<br />
combination <strong>of</strong> temperature (and/or pressure) and overall composition.<br />
Photoelasticity: stress-induced birefringence. In a polymer, this is caused by stress-induced<br />
alignment <strong>of</strong> polymer chains.<br />
Piezoelectricity: the application <strong>of</strong> stress produces a change in the dielectric polarisation <strong>of</strong> a<br />
material or, conversely, application <strong>of</strong> an electric field results in strain. Piezoelectric materials must be<br />
non-centrosymmetric.<br />
Piezoelectric coefficient, d: measure <strong>of</strong> the rate <strong>of</strong> change <strong>of</strong> dielectric polarisation with applied<br />
stress (C N -1 ).<br />
Pitch: the distance it takes for the Director in a cholesteric / chiral nematic liquid crystal to go<br />
through one complete 360° rotation (m).<br />
Polar material: a material with crystal symmetry such that it contains one (or more) unique<br />
direction.<br />
Polarization, P: the dipole moment per unit volume in a medium, or charge per unit area (C m -2 )<br />
Polarization (<strong>of</strong> light): the property <strong>of</strong> electromagnetic waves that describes the direction <strong>of</strong> the<br />
transverse electric field.<br />
Polarized light: light that has passed through a sheet <strong>of</strong> polarizer, and has a transverse electric field<br />
that vibrates in one direction only.