Chapter 3 - Structure of Crystalline Solids Flashcards
What materials have crystalline structures?
All metals, most ceramics, some polymers
What are noncrystalline materials called?
Amorphous
When atoms are modeled as solid spheres, what is the model called?
Atomic Hard Sphere Model
What is the smallest pattern observed in a crystal structure called?
Unit Cell
How many total atoms does a FCC unit cell have?
4 atoms (1/2 atoms at each face, 1/8 atoms at each corner)
What is the unit cell length of a FCC structure?
2Rsqrt(2)
What is the Atomic Packing Factor of an BCC unit cell
0.68
What is a coordination number?
The number of atoms an atom is bonded to
What is the coordination number for a FCC unit cell
12
How can you tell an atom has an FCC structure from its indices?
The indices are all odd, or all even
How can you tell an atom has an FCC structure from the first 2 diffraction angles?
The ratio of the first 2 sin^2(theta) are 0.75
Which crystal structure’s unit cell is composed of 2 whole atoms?
Body Centered Cubic
What is the unit cell length of BCC structures?
4*R/sqrt(3)
Which crystal structure(s) has an atomic packing factor of 0.74?
Both FCC and HCP
Alpha, Gamma, and Delta irons, have what crystal structures?
Alpha and Delta have BCC, Gamma has FCC
What is the coordination number for BCC structures?
8
How can you tell if a structure is BCC based on its indices?
The sum of the indices is even
Given the ratio of the first 2 sin^2(theta) is 0.5, what is the crystal structure?
BCC
How many atoms does a HCP structure contain?
6 total atoms
What is the ideal ratio of the lengths of the short and long sides (a and c respectively)
1.633
What do you call a material that can have multiple crystal structures?
Polymorphism
What is allotropy?
Polymorphism that occurs within an elemental solid
What are the reflection indices for BCCs first 3 planes?
(110), (200), (211)
Given the first 3 sums of the squared indices are 3, 4, 8, the crystal structure is what?
fCC
Given the sum of the squared indices of the first 3 planes are 2, 4, 6, what is the crystal structure?
BCC
What is the pattern of the planes of a simple cubic structure?
(x00), (x10), (x11) where x starts at 1 and increases every 3 planes
What do the relative intensities given by x-ray diffraction imply within the unit cell?
The arrangements in atoms
What does Bragg’s Law describe?
The relationship between wavelength, and angle of diffraction, and distance between atoms given planar indices and unit cell length.
What is a single crystal?
A crystal with no grain boundaries
What is isotropy?
When there is no directionality
What is the pattern of stacked planes in FCC?
ABC pattern
What is the pattern of stacked planes in BCC?
ABAB
What is the pattern of stacked planes in HCP?
ABAB
