Term
|
Definition
|
|
Term
| definition of temperature |
|
Definition
equilibrium concept in heat
measure of avergae kinetic energyassociated with atoms in a substance |
|
|
Term
|
Definition
elastic waves in a material
have quantized energy E=hν |
|
|
Term
| internal energy and enthalpy |
|
Definition
|
|
Term
|
Definition
energy required to change the temp. of 1 mole of a substance by 1 degree Celsius
units: J/molK |
|
|
Term
|
Definition
| energy required to change the temp. of 1 kg of a substance by 1 degree Celsius |
|
|
Term
|
Definition
|
|
Term
| heat capacity at constant V |
|
Definition
|
|
Term
| heat capacity at constant T |
|
Definition
|
|
Term
| differences between constant V and constant T heat capacity |
|
Definition
for ideal gases: CP=CV+ R (effects of P are important)
for solids: CP≈CV (effects of P are small)
|
|
|
Term
|
Definition
as T increases,
there amplitude of atomic vibrations in a solid increase,
so solid expands |
|
|
Term
CTE
coefficient of thermal expansion |
|
Definition
|
|
Term
|
Definition
as bond strength ↑ α ↓
as energy ↑ α ↓
as melting point ↑ α ↓
as temp. ↑ α usually ↑
also depends on crystal structure |
|
|
Term
| defintion of thermal conductivity |
|
Definition
| it describes the ability to transfer heat |
|
|
Term
| Fourier's law for heat flux |
|
Definition
.
Q/A = -k(dT/dx)
where k=thermal conductivity |
|
|
Term
| thermal conductivity mechanisms |
|
Definition
atomic vibrations: stronger bonds and closer stomic spacing facilitates heat transfer
conduction of free electrons: KE is transferred via mobile electrons |
|
|
Term
|
Definition
metals usually have higher k than nonmetals because they have both mechanisms
exception exist for very strongly bonded crystals like diamond |
|
|
Term
| definition of thermal shock |
|
Definition
| fracture of material due to sudden temp change (usually cooling) |
|
|
Term
|
Definition
a problem with using brittle materials at high T
depends on thermal expansion
thermal conductivity
fracture toughness |
|
|
Term
| mechanisms of thermal shock |
|
Definition
thermal expansion of a constrained material leads to failure stress
rapid T change produces Temp. gradients with a material, resulting in non-uniform expansion/contraction -> internal stress
ex: rapid cooling leads to tensile stress at surface |
|
|
Term
|
Definition
material composed of two or more individual materials (not chemically reacted) to obtain unique properties not available in a pure material
means artificially created structures, not multi-phase equilibrium microstructures |
|
|
Term
| connectivity of composites |
|
Definition
thin, short fiber sprinkles oriented randomly in a continuous matrix: 0D fibers, 3D matrix
thin, continuous fibers all aligned in the same direction in a continuous matrix: 1D fibers, 3D matrix
thin, continuous fibers all aligned in the same direction in a continuous matrix: 1D fibers, 3D matrix
flat "sheet" of woven fibers in a continuous matrix: 2D fibers, 3D matrix |
|
|
Term
|
Definition
layered components with 2D connectivity
(meaning the matrix is also a layered component with 2D connectivity) |
|
|
Term
|
Definition
depends only on volumes fractions (not connectivity)
ρc= Σρivi
where ρ= density
v= volume fraction |
|
|
Term
|
Definition
depends only on mass fractions (not connectivity)
Cc=ΣmiCi
|
|
|
Term
| [property averaging rules in composites] |
|
Definition
|
|
Term
| classification of electronic materials |
|
Definition
conductors
semiconductors
superconductors
dielectrics (insulators) |
|
|
Term
|
Definition
V=IR
σ=JE
where J=current density
σ=conductivity
ρ=resistivity |
|
|
Term
|
Definition
depends on concentration of charge carriers
mobility of charge carriers |
|
|
Term
|
Definition
|
|
Term
|
Definition
μe = vd/E = σ/(nqe)
where n=# free electrons/volume
qe= charge of electron (1.602E-19 C)
|
|
|
Term
| about charge carrier mobility |
|
Definition
depends on carrier type (electron, hole, ion, vacancy)
structure (composition, crystallinity, lattice type)
defects
temp. (because of phonon scattering)
*anything that scatters moving charges decreases mobility |
|
|
Term
| [resistivity in metals vs. resistivity in semiconductors] |
|
Definition
|
|
Term
| intrinsic vs. extrinsic semiconductor |
|
Definition
intrinsic- pure materials, where conductivity depends on excitation of electrons across the bandgap
extrinsic- conductivity depends on impurities |
|
|
Term
|
Definition
insulator: band gap E: over 2.5 eV
semiconductor: band gap E: under 2.5 eV
metal: band gap E: 0 eV |
|
|
Term
| [how free carries are generated in intrinsic and extrinsic semiconductors] |
|
Definition
|
|
Term
|
Definition
| how many occupiable states exist in the bands |
|
|
Term
| about Fermi-Dirac function |
|
Definition
describes the probability that an electron will have a given energy based on thermal activation
below the "Fermi level," all occupiable states are filled at T= abs. zero |
|
|
Term
|
Definition
| F(E) = [1 + e^((E - EF)/kT)]-1 |
|
|
Term
| equilibrium carrier concentration eqns |
|
Definition
n = Nce^[-(Ec-EF)/kT]
p = Nve^[-(EF-Ev)/kT]
where c= conduction band
v= valence band |
|
|
Term
| A quantum of energy resulting from vibrational waves in a solid is a _____ |
|
Definition
|
|
Term
| temperature is a measure of _____ energy associated with atoms/molecules in a substance |
|
Definition
|
|
Term
| _____ is a materials property that represents the amount of _____ absorbed/released per mass to raise/lower the material's temp. by 1 degree |
|
Definition
|
|
Term
| a maerial's CTE _____ as bond strength increases, so it is _____ proportional to _____ and _____ that depend on bond strength |
|
Definition
decreases
inversely
melting pt.
Young's modulus |
|
|
Term
| thermal conductivity describes the ability of a material to _____ and has units of _____ |
|
Definition
|
|
Term
| metals usually have higher thermal conduvtivity than ceramics because _____ |
|
Definition
| they have heat transfer by mobile electrons and by atomic vibrations, but ceramics only have the latter |
|
|
Term
How could crystallographic defects affect thermal conductivity?
give an example. |
|
Definition
Crystal defects usually decrease thermal conductivity.
substitutional inpurities, dislocations, and grain boundaries will decrease it |
|
|
Term
| Why does rapic cooling of a material make it more susceptible to thermal sghock than rapid heating? |
|
Definition
| because cooling makes the outer surface contract faster than the inside, which puts the surface under tensile stress, and brittle fracture occurs more readily for tensile stress than for compressive |
|
|
Term
| the conductivity of a meaterial is a function of the _____ and the _____ of charge carriers |
|
Definition
|
|
Term
| when electrons in a conductor are accelerated in an electric field, _____ events cause a loss of _____ energy, and the electrons will attain a speed called the _____ |
|
Definition
scattering
kinetic
drift velocity |
|
|
Term
| the carrier mobility is the ratio of _____ to _____ |
|
Definition
drift velocity
electric field |
|
|
Term
| when atoms are brought together in a solid, _____ interactions cause energy levels to split into closely spaced states called _____ |
|
Definition
electron-electron interactions
energy bands |
|
|
Term
| the _____ band is the highest band normally filled with electrons, above it is the _____ band |
|
Definition
|
|
Term
| the probability that an electron will have a given energy above the Fermi level is given by the _____ |
|
Definition
|
|
Term
in a semiconductor, the transition of an electron from the valence band to the conduction
band (or vice versa) requires absorption/release of _____ which can be in the form of _____ or _____ |
|
Definition
|
|
Term
| A ______ is an impurity in a semiconductor that substitutes for an atom in the host crystal with a different _____ state, which results in the _____or ______ of an electron by the impurity. |
|
Definition
dopant
valence
donation
borrowing |
|
|
Term
| Large organic molecules (and polymers) can be electrically conductive and semiconductive when they have a _____ bond structure which means there is a pattern of alternating ______. |
|
Definition
conjugated
double and single bonds |
|
|
Term
Dielectric materials are electrically ______, but are
______ in an electric field, by mechanisms which may include
______, _______, ________, or _______ |
|
Definition
insulating
polarizeable
electronic polarization
dipolar polarization
space charge polarization |
|
|
Term
| The _____ polarization mechanism is present in all substances and is the related to the index of refraction. |
|
Definition
electronic polarization
ionic polarization |
|
|
Term
| The ______ polarization mechanism exists in some materials and is the basis of microwave heating. |
|
Definition
|
|
Term
| The _______ polarization mechanism exists in _____________ materials and can be exploited in IR spectroscopic characterization techniques. |
|
Definition
|
|
Term
| ______ materials have spontaneous polarization below a critical temperature known as the ______ temperature. |
|
Definition
|
|
Term
| [calculate values of E or n in relating given data to the Arrhenius nature of the intrinsic carrier concentration] |
|
Definition
|
|
Term
| relative permittivity (or dielectric constant) |
|
Definition
| indicates degree of polarizability of a material |
|
|
Term
|
Definition
εr
same thing as
dielectric constant, K
|
|
|
Term
polarization mechanisms:
Electronic Polarization |
|
Definition
occurs when, in the presence of an electric field, there is a slight displacement b/t nucleus of an atoms and its electron cloud, creating a dipole moment.
present in all materials
gives rise to the refractive index of a material in the
visible range of the EM spectrum
frequency: under 1E16 Hz |
|
|
Term
polarization mechanisms:
Ionic Polarization |
|
Definition
occurs when bonds between anions and cations deform, moving ions further away/closer together.
present in ionic materials
basis of IR spectroscopic characteriztaion of
materials
frequency: under 1E13 Hz |
|
|
Term
polarization mechanisms:
Dipolar (or Orientation) Polarization |
|
Definition
occurs when permanent dipoles realign in the presence of an electric field
occurs in polar materials
basis of microwave heating
frequency: under 1E9 Hz |
|
|
Term
polarization mechanisms:
Space Charge Polarization |
|
Definition
occurs when mobile charges (including electrons and ions) pile up at interfaces or grain boundaries, leaving their compensating charges back in the lattice.
not a common mechanism for most materials. |
|
|
Term
[Explain how an impurity can be a donor or acceptor of electrons in a semiconductor crystal and
how to determine the density of both majority and minority carriers] |
|
Definition
|
|
Term
[Describe the regions (i.e. different slopes) on a plot of carrier concentration vs. 1/T for an
extrinsic semiconductor] |
|
Definition
|
|
Term
[Understand the basic principle and electrical characteristics of a semiconductor diode.
Understand the basis of light emission from a light-emitting diode or the generation of electrical
current from a solar cell.] |
|
Definition
|
|
Term
| permittivity and capacitance |
|
Definition
Electric field across dielectric: E=V/d
C = Q/V = (εoA)/d
chrage density: D = εoE |
|
|
Term
| effects of polarization in materials on capacitance of parallel electrode structures. |
|
Definition
| charge density increases by K |
|
|
Term
|
Definition
quality factor, Q=energy stored/energy used = 1/tan(δ)
where energy stored = ½cv2
|
|
|
Term
|
Definition
Piezoelectric materials develop a voltage under mechanical stress and vice-versa
Occurs in crystals with no center of symmetry (Non-centrosymetric)
All ferroelectric materials are piezoelectric (but not all piezoelectric materials are ferroelectric)
used for sonar, touch sensors, strain gauges, and microphones |
|
|
