Title: XRD analysis
1XRD analysis
- Instruments and data acquisition
- Getting data and data formats
- Analysis software
- Phase ID
2Equipment
- Scintag PAD-V
- Pole-Figure attachment
- Scintillation detector
- Scintag XDS-2000
- Theta-Theta goniometer
- i-Ge energy-dispersive detector
- Bruker D8
- GADDS area detector
- Philips XRD-3000 generator
- Laue camera and film recording
3Data Acquisition
- Assumption infinite, randomly distributed
particles - Size lt 30mm (320 grit)
- watch for preferred orientation
- Sample on rotation axis
- Good statistics!
- Standards important for precision work
4Acquisition issues
5Poisson distribution
- Describes processes where each event is
independent and has a constant probability of
occurring within a time interval. - Standard Deviation (s) (I)½
- Var (I) s2 I
6S/N ratio
- Any point on a scan will have a fixed count rate
? total counts (I) are proportional to time.
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12S/N continued
- We usually want NET intensity rather than GROSS
intensity. - Need to subtract the background
- What uncertainty do we have in the NET intensity?
13Uncertainty propagation
Source P.R. Bevington Data Reduction and
Analysis for the Physical Sciences, 2nd ed., p. 50
14Case when absolute variances add
If B is large, then the remainder after
subtraction will be small and the relative
uncertainty will be very large.
15Acquisition issues
- Statistics
- Fluorescence effects
16Fe sample with Cu radiation
17What is the difference in the S/N of the net
intensity?
18Acquisition issues
- Statistics
- Fluorescence effects
- Geometric Effects
- Off-axis
- Absorption depth (sampling depth)
19Aberrations
- Bragg-Brentano goniometer is a para-focusing
geometry. - All elements must be precisely located.
- If the sample is displaced from the rotation
axis, there is a peak shift
20Bragg-Brentano Focusing Circle
21Displacement shift
22Displacement Shift
h lt 100mm
Illustrate correction process later
23Absorption Equation
Where r is the density and m is the mass
absorption coefficient.
24Absorption Depth
Where G is the fraction of the diffracted signal
and m is the linear (not mass) absorption
coefficient.
2599 Sampling Depth
2699 Sampling Depth
27Acquisition issues
- Statistics
- Fluorescence effects
- Geometric Effects
- Off-axis
- Absorption depth (sampling depth)
- Spectral Contamination
- Cu Kb, W La radiation
28Ni Filter
- Ka/Kb intensity ratio is 9
- Ni filter attenuates Kb more than Ka
- MAC of Ni for Cu Kb 283 cm2/g
- MAC of Ni for Cu Ka 49 cm2/g
- A 20mm Ni filter will produce a Kb/Ka ratio of
about 500 while attenuating the Ka by a factor of
2. - Kb intensity is not 0!
29Spectral Contamination
- Multiple Cu peaks
- Ka1 1.540562Å
- Ka2 1.54439Å
- Average 1.5418Å
- CuKb 1.392218Å
- W deposits on anode (filament contamination)
- W La1 1.47639Å
30Ka2 peak
31Periclase (MgO)
32MgO
33Data Format
- EVA needs .RAW
- Scintag - creates .RD
- VAX data acquisition computer. Need to download
data. - Convert to .RAW with ALL2EVA
- Convert to ASCII with RD2ASCII (to read into
Excel) - Bruker - .RAW
34ALL2EVA
- Converts all .RD files (up to 100) in a folder to
.RAW - DOS program - 8 character filename
- Tips
- Set up your ftp program to download to one
directory. - Setup an ALL2EVA shortcut to point to the
appropriate directory
35ALL2EVA shortcut
36Phase ID
- EVA or Jade software
- EVA available in er6 lab
- EVA Jade in CEOF computer lab
- ICDD database (formerly JCPDS)
- Tutorials
- www.matter.org.uk/diffraction/x-ray
- www.ccp14.ac.uk/educate.htm
37er6 procedure
- Download and convert data
- Go to the CEOF web page (www.ceof.ohio-state.edu)
, select file servers and the Scintag window.
Enter the appropriate username and password. - Copy the file to the C\TEMP. Ensure that the
saved filename conforms to the DOS 8 character
format, that the extension is .RD, and that there
is no 1 appended to the extension. - Select Start All Programs Databases X-ray
Diffraction All2EVA. - Copy these .RD and .RAW files to your home
directory on the Z drive. - Select Start All Programs Databases X-ray
Diffraction DIFFRAC Plus Evaluation Eva - Select File Open, set the file type to .RAW,
and select your file name. - Select View Settings Master Database File.
Enter G\Diffplus\PDF1\JCP2.CAT.
38EVA
39EVA
40Phase ID steps
- Read .RAW file
- Subtract background, Strip Ka2 (append)
- Use background subtracted scan for Peak Search
Use Ka2 stripped scan for Peak Match. - Match dominant peaks displacement shift if
necessary - If displacement shift return to RAW data and
correct.
41EVA
- Single phase (min11-01.raw)
- Elements Mg and O
42EVA
- TQ019-01.raw
- Pure Mg, Si, O used in the processing
43EVA
- DA029.raw
- Multi component, initially unknown elements
- SEM EDS
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47EVA
- DA029.raw
- SEM EDS
- Ti, Si, Mn, O, F
- K, Na, Al, Mg, Fe