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MAT SCI > TEST 2 > Flashcards

TEST 2 Flashcards

1
Q

What are the four main point defects?

A

Vacancy
Interstitial
Interstitial foreign atom
Substitutional foreign atom

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2
Q

What is a vacancy

A

when an atom is missing so adjacent atoms try to compensate

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3
Q

What is an interstitial defect?

A

When a foreign atom that is smaller than lattice atoms is present in lattice

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4
Q

How does Nv/N correlate with Gibbs Free Energy?

A

There should be some point where at a certain Nv/N, G is at a minimum

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5
Q

formula for vacancy concentration?

A

Nv/N= exp(-delta(Hv)/RT)= exp(-Q/kT)

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6
Q

What criteria is used for metal alloys?

A

Hume Rothery Rules

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7
Q

What are the Hume Rothery Rules?

A

1) Atomic Radii should be within 15% of each other
2) Crystal structure should be the same
3) Electronegativity of solute and solvent should be similar
4) Valence of solute and solvent should be the same

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8
Q

What are the point defects in ceramics?

A

Cation interstitial
Cation Vacancy
Anion Vacancy

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9
Q

What is Cation Interstitial?

A

Extra cation in lattice

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10
Q

What is cation vacancy?

A

Cation absence

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11
Q

What is anion vacancy?

A

Anion absence

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12
Q

If an Na+ is missing in an NaCl ceramic lattice, what kind of particle must replace an Na+?

A

at least one particle with +2 charge.

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13
Q

If three Fe2+ are missing from an iron oxide consisting of Fe2+ and O2-, how many Fe3+ particles should be presdnt

A

two +3 particles
Why? there will be a net charge of 6- so there must be two Fe3+ particles to make up the difference

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14
Q

Formula for point defect probability

A

Ndef/N= exp[-Qdef/(2kT)]

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15
Q

What is a burgers vector

A

Vector that describes the magnitude and direction of the lattice distortion associated with a dislocation

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16
Q

What are the three types of linear dislocation

A

edge dislocation
screw dislocation
mixed dislocation

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17
Q

What is edge dislocation

A

Linear defect that centers around and perpendicular to the plane of the page
Imagine a line of particles perpendicular to page is removed

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18
Q

does a burgers vector tend to be large or small

A

Dislocations will always tend towards the smallest possible burgers vector

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19
Q

What takes more energy, larger or smaller burgers vector?

A

larger

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20
Q

What is a screw dislocation?

A

When the lattice planes trace a helical path around the dislocation line

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21
Q

What are the types of 2D imperfections?

A

Grain boundaries

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22
Q

What is a grain boundary

A

lattice pattern is constant but at an angle making a boundary

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23
Q

Why do things diffuse?

A

to reach an optimum energy state (a lower energy state usually)

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24
Q

How do atoms diffuse?

A

Atoms will fill neighboring vacancies

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25
Q

What does diffusion rate depend on?

A

Diffusion rate depends on
#vacancies
activation energy for atom jumps

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26
Q

Does it take energy to diffuse>

A

Yes, there is a certain E that acts as a kinetic barrier for atoms jumping vacancies

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27
Q

What is interstitial diffusion?

A

Diffusion with an atom that is much smaller so they can diffuse between atoms

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28
Q

What is faster, interstitial or vacancy diffusion>

A

Interstitial; energy it takes to move is much lower because of smaller size

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29
Q

what is this equation:
D= Do * exp[-Qd/RT]

A

Function of diffusion constant in regards to time

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30
Q

What happens when temperature increases in terms of diffusion?

A

High temperature leads to increase in energy, therefore movement of molecules
This increases the rate of diffusion

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31
Q

What are the units for this equation D= Do * exp[-Qd/RT]
D:
Do:
Qd:
R:
T:

A

D: Diffusion coefficient m^2/s
Do: pre-exponential constant m^2/s
Qd: activation energy J/mol
R: gas constant J/K*mol
T:temp K

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32
Q

What is this formula and what is z, λ, and v
(1/6)zλ^2v

A

Pre-exponential constant formula for diffusion (Do)
z: number of potential sites for jumps
λ: distance of diffusive jumps
v: atomic vibration frequency

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33
Q

What 5 factors influence diffusion?

A
  1. Interstitial vs vacancy
  2. The interacting substances (Do and Qd is different for every particle)
  3. Temperature
  4. Crystal Phase
  5. Microstructure; diffusion is faster in polycrystalline materials
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34
Q

What can Fick’s first Law tell us
J= -D (dC/dx)
D: diffusion constant
J: Flux across plate
C: concentration

A

Substances will diffuse from areas of high concentration to lower concentration
J=Mass/(area*time)

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35
Q

What can Fick’s 2nd law tell us
dC/dt = D (d^2C/dx^2)

A

+ : concentration will increase
-: concentration will decrease

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36
Q

What does this proportion mean?
x proportional to sqrt(Dt)

A

t increases –> depth of penetration increases

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37
Q

penetration depth of diffusion formula for 1D, 2D, 3D?

A

sqrt(2Dt)
sqrt(4Dt)
sqrt(6Dt)

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38
Q

What is required to diffract light for a lattice?

A

Lattice spacing must be comparable to the wavelength of the incident wavelength

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39
Q

What is this equation and what are its variables?
nλ= 2dhkl *sin theta

A

Bragg’s diffraction law
n: wavelength number (take it as 1 usually)
λ: wavelength
dhkl: spacing between planes

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40
Q

What does Bragg’s diffraction law tell us?

A

Constructive interference (max diffraction) will occur if path difference between rays is equal to nλ

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41
Q

formula for dhkl?

A

d= λ/(2sintheta)
theta: critical scattering angle

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42
Q

Formula for dhkl without theta?

A

dhkl = a/sqrt(h^2 + k^2 + l^2)

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43
Q

how does h, k, and l relate to interplanar spacing?

A

hkl increases —> interplanar spacing decreases

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44
Q

How are the incident and reflection angle related to each other in an x ray diffractometer

A

reflection angel should be twice the incident angle therefore if theta is the incident angle, 2theta is the diffraction angle

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45
Q

What kind of intensity vs diffraction angle will a crystal have?

A

approximately at a constant low level with distinct jumps in intensity at certain angles

46
Q

What kind of intensity vs diffraction angle will a liquid/amorphous substance have?

A

one absolute maximum with the change being fairly gradual

47
Q

What kind of intensity vs diffraction angle will a semi-crystalline solid have?

A

it will look like an amorphous graph with peaks like a crystal;
will have spikes in intensity but will not be at a constant low intensity usually

48
Q

when will SCC not have diffraction?

A

none; all hkl will diffract

49
Q

when will FCC not diffract?

A

when hkl is either all even or all odd

50
Q

when will BCC not diffract?

A

When the sum of hkl is even

51
Q

What can x ray diffraction determine?

A

can determine crystal structure and interplanar spacing (lattice constant)

52
Q

What is electric conductivity range of metals?

A

σ> 10^5 (Ohm*m)^-1

53
Q

What is electric conductivity range of semiconductors?

A

10^-6 <σ< 10^5 (Ohm*m)^-1

54
Q

What is electric conductivity range of insulators?

A

σ<10^-6 (Ohm*m)^-1

55
Q

Do electrons have a net force?

A

No; electrostatic force is canceled out by force that results from bumping into obstacles

56
Q

what does σ=neu mean>

A

σ: conductivity
n: number density of carriers
e: carrier charge
u: carrier mobility

57
Q

what is the trend for neu of metals compared to semiconductors

A

n: (lots of carriers)
e: same
carreir mobility: lower

58
Q

trend for neu of semiconductors:

A

n: low amt of carriers
e: same
u: high

59
Q

5 Factors that affect resistivity?

A

grain boundaries
dislocations
impurities
vacancies
lattice vibrations

60
Q

Resistivity increases with:

A

temp
% impurity
% cold work

61
Q

p=?

A

p= pthermal+ pimpurity + pdeformation

62
Q

What would a graph of % impurity vs resistivity look like between two metals\

A

would look like an upside down parabola
resistivity increases until the “impurity” becomes the majority which is when resistivity begins to decrease again

63
Q

Compare conductivity of metals and semiconductors

A

σmetal» σsemiconductor
Metals have a lot of carriers but are limited by their mobility
Semiconductors have lots of mobility but are limited by lack of carriers

64
Q

What is an electron energy band structure

A

band shows allowed energies for electrons from each atoms when interacting with each other

65
Q

What will a band structure look like for metals

A

The highest occupied band will be partially filled or bands will overlap

66
Q

What does it mean when two bands overlap?

A

electrons in the overlapped band mean they are in different states but have the same energy, meaning that they can switch bands

67
Q

What is Fermi Energy

A

Highest filled state when at 0 K
Every energy state below Ef will be filled and all above will be empty

68
Q

What is a filled band? Can the electrons in a filled band conduct?

A

a filled band is an energy state where all allowed energies are taken up. Electrons in a filled band cannot conduct because there is no energy level they can jump to

69
Q

Why can’t electrons below fermi energy conduct?

A

in order to conduct, electrons must use energy from the electric field to jump to a higher energy state. However, since all the energies below Ef are occupied, there are no energy states to jump to.

70
Q

what is a band gap

A

band gaps are electron energy states that can NOT be filled

71
Q

What will a band diagram for a insulator look like

A

The valence band will be completely filled with a large band gap. There will be no states that electrons can jump to because the gap is too big (the gap will be greater than 2 eV

72
Q

What will band diagram for semiconductor look llike

A

valence band will be completely filled but the band gap energy will be very small (Eg<2 eV

73
Q

What are the types of charge carriers in semiconductors

A

electrons: negatively charged particle
holes: positively charged vacant state from an electron

74
Q

What is an intrinsic semiconductor?

A

conductor without any dopant

75
Q

relationship between holes and electrons?

A

amt of electrons and holes will be equal;

76
Q

what does n=p=ni= n0 * exp[-Eg/(2kT)]

A

n= no density of free electrons
p= no density of free holes
the expression shows how n and p change with T

77
Q

how does T and conductivity relate

A

T increases –> conductivity decreases

78
Q

relationship between lattice spacing and band gap?

A

lattice spacing decreases –> band gap increases

79
Q

What is an extrinsic Semiconductor

A

doped semiconductor

80
Q

What is a p type semiconductor

A

semiconductor doped to increase amount of holes
p»n

81
Q

what is an n type semiconductor

A

semiconductor doped to increase amount of mobile e-
n»p

82
Q

relationship between carrier mobility and impurity concentraiton

A

impurity concentration increases –> mobility decreases

83
Q

Carrier mobility vs temp

A

temp increases –> mobility can decrease or have a maximum depending on concentration

84
Q

how to find threshold condition for absorption of light by semiconductors?

A

Egap<_ hc/λ —–> λ<_ hc/Egap
c/λ= frequency

85
Q

What are three types of semiconductor devices?

A

solar cell
MOSFET
LED

86
Q

What is a p-n junction

A

boundary between two semiconductor material types; usually a p type and n type

87
Q

What is a diode

A

device that acts as a one way switch for current. It allows current to flow freely in one direction but severely restricts the opposite direction

88
Q

What is forward bias flow diode

A

charge carriers will flow through both p and n regions; holes and electrons recombine at junction
thus CURRENT FLOWS

89
Q

what is reverse bias flow diode

A

charge carriers will flow away from junction; junction region depleted of carriers
little current flows

90
Q

What is Moore’s Law

A

the amt of transistors in a CPU will double every two years
therefore amt of computing power will double every two years

91
Q

What is an LED

A

light emmiting diode

92
Q

is an LED in forward or reverse bias

A

emits light when forward biasedd

93
Q

How does LED emit light

A

when recombining, the electron and hole are eliminated and a photon is emitted

94
Q

How do solar cells work

A

pn junction in reverse bias;
holes and electrons flow away from junction as more energy is introduced from incident light

95
Q

Band gap vs intrinsic semiconductor lattice constant

A

decrease lattice constant –> increase in band gap

96
Q

Band gap vs difference in electronegativity

A

large difference in EN –> larger Eg

97
Q

What is a dielectric material

A

-An insulator that contains electric dipole; positive and negative charges are separated at an atomic level
-An electric field will cause dipoles to align which will affect the material properties

98
Q

What is capacitance

A

ability to store charge across a potential difference

99
Q

What does a capacitor do

A

One plate will have an excess of charge causing a net charge on both plates.
The charge will remain even if the battery in the circuit is removed.
If a resistor is added charge will flow again until there is no net charge on plates (kinda like a battery)

100
Q

what is this formula
ℨo(A/l)

A

capacitance formula
ℨ: dielectric constant for a vacuum between two plates
A: area of plate
l: distance between plates

101
Q

what is this formula ℨr= ℨ/ℨo

A

formula for dielectric constant if there is no vacuum

102
Q

What is polarization

A

When internal charges are moved from their equilibrium positions by a strong electric field

103
Q

What is electronic polarization

A

displacement of electron clouds from the positive nucleus.
Occurs in all materials
requires electric fields

104
Q

Ionic polarization

A

occurs in ionic materials
applied electric field displaces cations and anions in opposite directions

105
Q

orientation polarization

A

alignment of permanent dipoles from random directions

106
Q

What is a ferroelectric material

A

materials where polarization remains permanently, even after removing electric field

107
Q

What is a piezoelectric material

A

Material where polarization can be varied by mechanical force

108
Q

What is M=Xm H

A

Formula for magnetization field of material
M: Internal magnetiation field of material
Xm: Magnetic susceptibility
H: applied (external) magnetic field

109
Q

What does Xm depend on?

A

Depends on magnetic force per atom
alignment of magnetic force among atoms

110
Q

As you increase the frequency of an applied alternating electric field to a dielectric material, its
dielectric constant begins to decrease as different polarization mechanisms become non-responsive to the
alternating field. The order in which these mechanisms freeze out from low to high frequency is

A

orientation ionic electronic
OIE

MAT SCI (5 decks)

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