Introduction to XRPD Data Analysis
Introduction to X-Ray Powder Diffraction
Data Analysis
Scott A Speakman, Ph.D. Center for Materials Science and Engineering at MIT
speakman@mit.edu
An X-ray diffraction pattern is a plot of the intensity of X-rays scattered at different angles by a sample
X-ray tube
2
sample
? The detector moves in a circle around the sample
? The detector position is recorded as the angle 2theta (2)
? The detector records the number of X-rays observed at each angle 2
? The X-ray intensity is usually recorded as "counts" or as "counts per second"
10000
5000
0
35
40
45
50
Position [?2Theta] (Cu K-alpha)
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? To keep the X-ray beam properly focused, the sample will also rotate. ? On some instruments, the X-ray tube may rotate instead of the sample.
55
Scott A Speakman, Ph.D. speakman@mit.edu
Intensity (Counts)
Each "phase" produces a unique diffraction pattern
Quartz
? A phase is a specific chemistry and atomic arrangement.
Cristobalite
? Quartz, cristobalite, and glass are all different phases of SiO2
? They are chemically identical, but the atoms are arranged differently.
? As shown, the X-ray diffraction
Glass
pattern is distinct for each
different phase.
15 20 25 30 35 40
? Amorphous materials, like glass, do not produce sharp diffraction peaks.
Position [?2Theta] (Cu K-alpha)
The X-ray diffraction pattern is a fingerprint that lets you figure out what is in your sample.
Slide of 20
Scott A Speakman, Ph.D. speakman@mit.edu
The diffraction pattern of a mixture is a simple sum of the diffraction patterns of each individual phase.
Quartz
Mixture
Cristobalite
Glass
15 20 25 30 35 40 Position [?2Theta] (Cu K-alpha)
0
15
20
25
30
35
40
Position [?2Theta] (Copper (Cu))
? From the XRD pattern you can determine:
? What crystalline phases are in a mixture ? How much of each crystalline phase is in the mixture (quantitative
phase analysis, QPA, is covered in another tutorial) ? If any amorphous material is present in the mixture
Slide of 20
Scott A Speakman, Ph.D. speakman@mit.edu
Qualitative Analysis of XRD Data
Slide of 20
Scott A Speakman, Ph.D. speakman@mit.edu
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