View
256
Download
5
Category
Preview:
Citation preview
Department of Materials Engineering at Isfahan University of Technology
ISSUES TO ADDRESS...
• How to make a stereographic for a crystal
structure?
• What is a stereographic projection?
• What is application of the stereographic
projection in crystallography?
CHAPTER 7: The Stereographic Projection
Department of Materials Engineering at Isfahan University of Technology
Crystals are made of lattice planes and angles
Crystals information can be illustrated from their planes and angles
between planes.
Stereography is a graphical method to find angular relationship
between lattice planes and directions
With stereographic projection, a 3-Dimension perspective of a crystal
can be illustrated in a 2-Dimension plaper.
The Stereographic Projection
Stereography
Department of Materials Engineering at Isfahan University of Technology
The angle between two crystal faces
as the angle between lines that are
perpendicular to the faces. Such a
lines are called the poles to the crystal
face.
The Stereographic Projection
Crystallographic Angles
Department of Materials Engineering at Isfahan University of Technology
The Stereographic Projection
Crystallographic Angles
Department of Materials Engineering at Isfahan University of Technology
From each crystal face (in the
centre of sphere) we draw a line
perpendicular to the face
The Stereographic Projection
Stereographic Projection
We define this face (010) as having a φ angle of
0o. For any other face, the φ angle will be
measured from the b axis in a clockwise sense in
the plane of the equator.
We define the ρ angle, as the angle between the c
axis and the pole to the crystal face, measured
downward from the North pole of the sphere. In the
diagram shown here, a crystal face has a ρ
angle measured in the vertical plane containing the
axis of the sphere and the face pole, and a ρ angle
measured in the horizontal equatorial plane. Note
that the (010) face has a ρ angle = 90o.
Department of Materials Engineering at Isfahan University of Technology
These angular measurements are
similar to those we use for latitude
and longitude to plot positions of
points on the Earth's surface. For the
Earth, longitude is similar to the φ
angle, except longitude is measured
from the Greenwich Meridian, defined
as φ = 0o. Latitude is measured in
the vertical plane, up from the
equator, shown as the angle ρ.
The Stereographic Projection
Stereographic Projection
Department of Materials Engineering at Isfahan University of Technology
Example, the ρ and φ angles for the
(111) crystal face in a crystal model is
shown here. Note again that the ρ
angle is measured in the vertical
plane containing the c axis and the
pole to the face, and the φ angle is
measured in the horizontal plane,
clockwise from the b axis.
The Stereographic Projection
Stereographic Projection
Department of Materials Engineering at Isfahan University of Technology
The Stereographic Projection
Angles between two planes
Department of Materials Engineering at Isfahan University of Technology
The Stereographic Projection
Stereographic Projection Method
Department of Materials Engineering at Isfahan University of Technology
The Stereographic Projection
Stereographic Projection Method
1. The plane C is represented by its normal CP.
2. The normal CP is represented by its pole P, which
is its intersection with the reference sphere.
3. The pole P is represented by its stereographic
projection P’
Department of Materials Engineering at Isfahan University of Technology
Stereographic Projection Method
The Stereographic Projection
Department of Materials Engineering at Isfahan University of Technology
Stereographic Projection of Main
Planes
The Stereographic Projection
Department of Materials Engineering at Isfahan University of Technology
The Stereographic Projection
The Wulff Net
Department of Materials Engineering at Isfahan University of Technology
The Stereographic Projection
Wulff net Drawn for 2°intervals
The Wulff Net
Department of Materials Engineering at Isfahan University of Technology
Applications:
Example 1: Finding zone circle of two known poles
The Stereographic Projection
Reminder:
A family of faces all parallel to some particular line
is called a zone, and the line is called the zone axis
Department of Materials Engineering at Isfahan University of Technology
Applications:
Example 2: Finding pole of plane of a given trace
The Stereographic Projection
Department of Materials Engineering at Isfahan University of Technology
Applications:
Example 3: Finding Angle between two planes
The Stereographic Projection
Department of Materials Engineering at Isfahan University of Technology
Applications:
Example 4: Finding area of all planes of α angle with P
The Stereographic Projection
Department of Materials Engineering at Isfahan University of Technology
Applications:
Example 5: Finding a plane with α and β angle with P1 and P2
The Stereographic Projection
Department of Materials Engineering at Isfahan University of Technology
Example 6: Plotting F and rUsing a Wulff NetPlotting F and r
Suppose you measured r = 60o and F = 30o
The pole for (010) is on the eastern edgeMeasure F = +30o clockwise along the circumference x
Rotate tracing paper so x falls over E-W diameterPlot r = 60o in from center
x
Tracing paper over a Wulff Net,
rotating about a thumb tack at the center
The Stereographic Projection
Department of Materials Engineering at Isfahan University of Technology
Miller indices of a poleMiller indices are a convenient way to represent a direction or a plane
normal in a crystal. Directions are simply defined by the set of multiples of
lattice repeats in each direction. Plane normals are defined in terms of
reciprocal intercepts on each axis of the unit cell.
When a plane is written with
parentheses, (hkl), this indicates a
particular plane normal: by
contrast when it is written with
curly braces, {hkl}, this denotes a
the family of planes related by the
crystal symmetry. Similarly a
direction written as [uvw] with
square brackets indicates a
particular direction whereas
writing within angle brackets ,
<uvw> indicates the family of
directions related by the crystal
symmetry.
Department of Materials Engineering at Isfahan University of Technology
Miller indices of Unknown Poles
N
S
WE
Department of Materials Engineering at Isfahan University of Technology
Miller indices of Unknown Poles
N
S
WE
Procedure:
1. Draw great circles which pass
through at least three points
2. Draw great circle (zone) of each
pole
3. 3. Find degree of (Fold)
symmetry
2-fold symmetry: PA=PB
Department of Materials Engineering at Isfahan University of Technology
Miller indices of Unknown Poles
3-fold symmetry:
PA=PB=PC
AB=BC=CA
4-fold symmetry:
PA=PB=PC=PD
AB=BC=CD=DA
Department of Materials Engineering at Isfahan University of Technology
Miller indices of Unknown Poles
Procedure:
4. Find a triangle which the highest
number of great circles passed
through the poles
Department of Materials Engineering at Isfahan University of Technology
Cube Component = {001}<100>
{110}
{100}
{111}
Department of Materials Engineering at Isfahan University of Technology
Rotation of a Crystal
Department of Materials Engineering at Isfahan University of Technology
Standard Projection of cubic
crystals
The Stereographic Projection
Department of Materials Engineering at Isfahan University of Technology
Standard Projection of cubic
crystals
The Stereographic Projection
Department of Materials Engineering at Isfahan University of Technology
We have 8 tetrahedral position per an fcc unit cell.
We have (6 · 4)/2 = 12 positions per an BCC unit cell
Tetrahedral Positions
Department of Materials Engineering at Isfahan University of Technology
We have 12/4 +1 = 4 positions per an fcc unit cell.
We have 12/4 + 6/2 = 6 positions per an bcc unit cell
Octahedral Positions
Recommended