Chapter 4: Crystal Structure

Question 1

Structure of materials

Answer 1

Arrangement of atoms in a material to minimize bond energy.

Question 2

Short ranged order (SRO)

Answer 2

Regular and predictable arrangement of atoms over a short distance. Based on the coordination number of atoms.

Question 3

Short ranged order (SRO) examples

Answer 3

amorphous materials (wax, glass, liquids)

Question 4

Long ranged order (LRO)

Answer 4

Regular and predictable arrangement of atoms over infinitely great distances.

Question 5

Long ranged order (LRO) examples

Answer 5

Crystalline solids, tempered chocolate

Question 6

Crystalline materials

Answer 6

3D structures where the material is arranged regularly. (SRO & LRO)

Question 7

Amorphous materials

Answer 7

Solids that are non-crystalline

Question 8

Metallic structures

Answer 8

Crystalline

Question 9

Ceramic structures

Answer 9

Crystalline and/or amorphous

Question 10

Polymer structures

Answer 10

Amorphous and/or partially crystalline

Question 11

Semiconductor structures

Answer 11

Crystalline

Question 12

Composite structures

Answer 12

Crystalline and amorphous

Question 13

Unit cell

Answer 13

Smallest indivisible group of atoms of a substance that has the overall symmetry of a crystal. A group of unit cells is a LRO crystal structure.

Question 14

Mass density

Answer 14

Representation of the amount of mass (or the number of particles) of a substance.

Question 15

Mass density formula

Answer 15

p = (nM)/(VNa)

Question 16

Lattice parameters

Answer 16

Edge length of a unit cell

Question 17

Lattice

Answer 17

3D network of points

Question 18

Crystal basis

Answer 18

Repeating unit centered on lattice points

Question 19

Bravis lattice

Answer 19

Array of discrete points with an arrangement and orientation that look exactly the same from any of the discrete points. Each point has the same surroundings

Question 20

Atomic packing factor

Answer 20

APF = (Volume of atoms in unit cell) / (Volume of unit cell)

Question 21

Simple cubic (SC) structure

Answer 21

Quarter atoms at each corner, 2 atoms in the unit cell. CN = 6, a = 2r, APF = 0.52

Question 22

Linear packing factor

Answer 22

LPF = (length of vector covered by atom) / (length of vector)

Question 23

Face centered cubic (FCC) structure

Answer 23

Quarter atoms in each corner, half atoms on each face, 4 atoms in the unit cell. CN = 12, a = 2sqrt(2)r, APF = 0.74. Close packed bravis lattice with sequence ABCABC

Question 24

Planar packing factor

Answer 24

PPF = (area covered by atoms) / (area of atom)

Question 25

Body centered cubic (BCC) structure

Answer 25

Quarter atoms in each corner, 1 atom in the center, 3 atoms in the unit cell. CN = 8, a = 4/sqrt(3)r, APF = 0.68. Bravis lattice.

Question 26

Hexagonal close packed (HCP) structure

Answer 26

7 close packed atoms on alternating layers with 3 atoms in the hollows, 6 atoms in the unit cell. CN = 12, a = 2r, APF = 0.74. Close packed with sequence ABAB

Question 27

Packing sequence and ductility

Answer 27

The closer packed atoms are, the more ductile the material. FCC is more ductile than HCP since slip is possible in every direction.

Question 28

Miller indices

Answer 28

Way to describe points, lines, planes in 3D space using h, k, l. Negative numbers are written with bars above them.

Question 29

Directions

Answer 29

Written without commas inside square brackets. Families use pointed brackets.

Question 30

Points

Answer 30

Written with commas and no brackets. Range from 0 to 1.

Question 31

Planes

Answer 31

Written without commas inside brackets. Families use curly brackets and rely on spacing

Question 32

Crystal defects

Answer 32

Control diffusion and plasticity. Eliminated to reduce total energy.

Question 33

Point defects

Answer 33

Crystal disturbances at a single point.

Question 34

Vacancies

Answer 34

Empty lattice sites that occur spontaneously.

Question 35

Vacancy ratio

Answer 35

Nv/Nt = e^(-Q/RT)

Question 36

Solute atoms

Answer 36

Atoms dissolved into the crystal lattice to remove vacancies, forms a solid solution.

Question 37

Substitutional solute atoms

Answer 37

Atoms replace the solute on the lattice site due to being a similar size/electronegativity.
EX: nickel in gold

Question 38

Interstitial solute atoms

Answer 38

Small atoms go in between lattice atoms.
EX: Carbon in steel

Question 39

Atomic vibrations

Answer 39

Atoms vibrate about their lattice positions at 10^13Hz and release the extra energy responsible for thermal activation.

Question 40

Line defects/dislocations

Answer 40

Atom planes are distorted so that half planes end inside the crystal. Motion produces slip and plastic deformation.

Question 41

Interfacial defects

Answer 41

Phase and orientation changes between grain boundaries

Question 42

Volume defects

Answer 42

Void formation at grain boundaries

Question 43

Bregg’s law

Answer 43

Describes the interaction of x-rays and crystal lattices.

Question 44

Bregg’s law formula

Answer 44

nλ = 2d(hkl)sinθ

Question 45

Interplanar spacing formula

Answer 45

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

Question 46

X-Ray diffraction

Answer 46

Used to determine crystal structure. Crystalline structures have many diffraction angles while amorphous ones have few.