Diffraction

Attachments
I- Purpose/Objective:

Diffraction is another core technique in Materials Science. Here we will introduce powder diffraction method, and use it for the analysis of the crystal structure of several materials. Some specific objectives are:

  1. Review basic diffraction theory and examine their application for materials characterization.
  2. Index the diffraction pattern of a cubic crystal phase manually.
  3. Acquire diffraction patterns, and identify unknown single-phase and two-phase materials
  4. Correlate diffraction patterns to microstructure.
  5. Experience designing procedures for open ended or ambiguous tasks.
  6. Determine the confidence levels and accuracy of gathered data.
  7. Develop skills in constructing team technical reports.

II - Experimental Procedure:

The unit is short, only two lab meetings. It is organized into several lessons, each a different task.

 

Activity #1: Manual indexing

Each student will be supplied with a raw diffraction pattern of a cubic phase, showing intensity in counts/second vs. diffraction angle 2q. You will manually the peaks as relative intensity, calculate their d-spacings, and index the pattern to determine the Miller Index (hkl) of the plane corresponding to that peak.

Activity #2: Diffraction patter acquisition and analysis

Each student will obtain diffraction patterns of two samples:  a single phase material and a two-phase material. You will learn to use the JADE search/match software to identify your sample. We have one diffractometer available – a Rigaku Miniflex- and one station for use of the JADE search/match software. Each group will prepare two powder diffraction patterns using the Miniflex.

 

Please choose one of the single phase powder unknowns from the vials labeled A, B,…N. Prepare the sample for diffraction using the method suggested by the GSI. Load the sample into the Rigaku Miniflex. While your sample is being loaded, be sure to look at the design of the goiniometer inside the Miniflex to compare with the other diffractometers in XMAL.  Collect the pattern over a wide 2-Q range (30-90 degrees) with a fast scan rate. (Usually slow scans over smaller ranges are preferred, but we are trading speed for quality in this case.)  Use JADE to analyze the pattern and identify the material.  Index the pattern so that every peak is associated with the (hkl) plane. If there are missing peaks or extra peaks, make note of them. Comment on whether the d-spacings are consistent with the lattice parameters of the phase.[1]


Also take one of the two phase unknowns, in vials labeled 2A, 2B, 3C, etc. and prepare that for analysis. Use JADE to solve the two phase pattern, again accounting for every possible peak.

  • SOP's:

Activity #3: Diffraction by visible light
You will set up a simple apparatus for visible light diffraction using a laser pointer. You will record the diffraction pattern (a Fraunhofer pattern) from a CD, a DVD, or some similar pattern of regular objects with a periodicity on the order of the wavelength of light. Calculate the wavelength of light (llaser) and the periodicity of the pattern (dCD, dDVD, or dsomething else). Compare that with what you see by direct observation in a microscope.

 

This is not a pre-designed lab experiment.  Rather we ask you to figure it out yourselves (with some basic guidance from the instructional team.  I will supply some CD and DVDs – if you have Blu-ray discs or Playstation 3 discs, bring them in for comparison. But other items having periodicity on the order of visible light may also be used (feather, opals, diffraction gratings, etc)  Have fun. Your grade on this portion of the lab will depend heavily on the creativity and thoroughness of your approach.

 

Activity #4: Advanced X-ray techniques
We will tour the X-ray diffraction laboratory (which we call “XMAL” because it is an XRD version of the Electron microbeam analysis lab “EMAL”).  We will examine three state-of-the-art instruments, the Bruker D8 Discovery, the Bede, and the Bruker NanoStar SAXS device, as well as a Rigaku diffractometer with a rotating anode source. Take careful notes on the diffraction geometry, source, detector, and characteristics of each instrument. Note applications for each XRD technique. You will include them in your report, comparing and contrasting these diffraction instruments.

 


[1] This is not quite the correct procedure for determining lattice parameters, since we are doing fast scans.  Proper lattice parameter determinations will combine many peaks, and often use ‘internal standards’ to correct for non-ideal goiniometer alignments and other errors.


III - Theory/Background Information:

The diffraction unit should coincide with lectures on diffraction in MSE 350.  Refer to your MSE 350 book and notes, and standard sources such as Cullity and Stock Elements of X-Ray Diffraction, 3rd Edition.

 


IV - Theory/Background References:


V- Activity Schedule:

Date/Time

Group 1

Group 2

Group 3

Group 4

Day 1

first half

1:30-3:30

Activity #1

indexing pattern

Activity #2

search/match

Activity #3

laser pointer

Activity #4

XMAL

Day 1

second half

3:30-5:30

Activity #2

search/match

Activity #3

laser pointer

Activity #4

XMAL

Activity #1

indexing pattern

Day 2

first half

1:30-3:30

Activity #3

laser pointer

Activity #4

XMAL

Activity #1

indexing pattern

Activity #2

search/match

Day 2

second half

3:30-5:30

Activity #4

XMAL

Activity #1

indexing pattern

Activity #2

search/match

Activity #3

laser pointer


VI -Format and Important Questions for Lab Report: