XRD analysis

1
XRD analysis

• Instruments and data acquisition
• Getting data and data formats
• Analysis software
• Phase ID

2
Equipment

• Scintag PAD-V
• Pole-Figure attachment
• Scintillation detector
• Scintag XDS-2000
• Theta-Theta goniometer
• i-Ge energy-dispersive detector
• Bruker D8
• GADDS area detector

3
Data Acquisition

• Assumption infinite, randomly distributed
  particles
• Size
• watch for preferred orientation
• Sample on rotation axis
• Good statistics!
• Standards important for precision work

4
Acquisition issues

• Statistics

5
Poisson 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

6
S/N ratio

• Any point on a scan will have a fixed count rate
  ? total counts (I) are proportional to time.

7
(No Transcript)
8
(No Transcript)
9
(No Transcript)
10
(No Transcript)
11
(No Transcript)
12
S/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?

13
Uncertainty propagation
Source P.R. Bevington Data Reduction and
Analysis for the Physical Sciences, 2nd ed., p. 50
14
Case when absolute variances add
If B is large, then the remainder after
subtraction will be small and the relative
uncertainty will be very large.
15
Acquisition issues

• Statistics
• Fluorescence effects

16
Fe sample with Cu radiation
17
What is the difference in the S/N of the net
intensity?
18
Acquisition issues

• Statistics
• Fluorescence effects
• Geometric Effects
• Off-axis
• Absorption depth (sampling depth)

19
Aberrations

• 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

20
(No Transcript)
21
h Illustrate correction process later
22
Acquisition issues

• Statistics
• Fluorescence effects
• Geometric Effects
• Off-axis
• Absorption depth (sampling depth)
• Spectral Contamination
• Cu Kb, W La radiation

23
Ni 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!

24
Spectral 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

25
(No Transcript)
26
(No Transcript)
27
Data 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

28
ALL2EVA

• 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

29
ALL2EVA shortcut
30
Phase 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

31
EVA

• tour

32
EVA

• displacement_1.eva

33
Phase ID steps

• Read .RAW file
• Subtract background, Strip Ka2
• 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.

34
EVA

• Single phase (min11-01.raw)
• Elements Mg and O

35
EVA

• TQ019-01.raw
• Pure Mg, Si, O used in the processing

36
EVA

• DA029.raw
• Multi component, initially unknown elements
• SEM EDS

37
(No Transcript)
38
(No Transcript)
39
(No Transcript)
40
EVA

• DA029.raw
• SEM EDS
• Ti, Si, Mn, O, F
• K, Na, Al, Mg, Fe