xrd analysis
DESCRIPTION
RSA analizaTRANSCRIPT
XRD analysis• Instruments and data acquisition
• Getting data and data formats
• Analysis software
• Phase ID
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
Data Acquisition • Assumption: infinite, randomly distributed
particles– Size < ~30m (320 grit)– watch for preferred orientation
• Sample on rotation axis
• Good statistics!
• Standards important for precision work
Acquisition issues• Statistics
Poisson distribution
• Describes processes where each event is independent and has a constant probability of occurring within a time interval.
• Standard Deviation () = (I)½
• Var (I) = 2 = I
S/N ratio• Any point on a scan will have a fixed count rate
total counts (I) are proportional to time.
timeN
S
thus
II
II
N
S
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S/N = 20/18 = 1 (2)
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S/N = 400/80 = 5 (2)
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?
Uncertainty propagation
uvvux
uvx
uvvux2
2
2
2
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2
uvvux
vux
uvvux2
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/
222222 2 uvvux abba
bvaux
Source: P.R. Bevington Data Reduction and Analysis for the Physical Sciences, 2nd
ed., p. 50
Variances add
Cross terms = 0 for independent
variables
Relative Variances add
Case when absolute variances add
222222 2 uvvux abba
bvaux
22BPBP
If B is large, then the remainder after subtraction will be small and the relative uncertainty will be very large.
Acquisition issues• Statistics
• Fluorescence effects
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Fe sample with Cu radiation
FURNACE DUST - File: 715-03.RAW - Type: 2Th/Th unlocked - Start: 15.000 ° - End: 75.000 ° - Step: 0.030 ° - Step time: 4.5 s - Temp.: 25 °C (Room) - Time Started: 0 s - 2-Theta: 15.000 ° - Theta:
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What is the difference in the S/N of the net intensity?
Acquisition issues• Statistics
• Fluorescence effects
• Geometric Effects – Off-axis– Absorption depth (sampling depth)
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
cos2
2R
h
Operations: Y Scale Mul 0.712 | Strip kAlpha2 0.514 | Background 1.000,1.000 | Import
QUARTZ OFFSET - File: 715Q-01.RAW - Type: 2Th/Th unlocked - Start: 15.000 ° - End: 69.990 ° - Step: 0.030 ° - Step time: 0.2 s - Temp.: 25 °C (Room) - Time Started: 0 s - 2-Theta: 15.000 ° - Theta:
Operations: Strip kAlpha2 0.514 | Background 1.000,1.000 | Import
QUARTZ - File: Q091506.RAW - Type: 2Th/Th unlocked - Start: 18.000 ° - End: 72.000 ° - Step: 0.030 ° - Step time: 0.2 s - Temp.: 25 °C (Room) - Time Started: 0 s - 2-Theta: 18.000 ° - Theta: 0.000 ° -
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Operations: Y Scale Mul 0.712 | Strip kAlpha2 0.514 | Background 1.000,1.000 | Import
QUARTZ OFFSET - File: 715Q-01.RAW - Type: 2Th/Th unlocked - Start: 15.000 ° - End: 69.990 ° - Step: 0.030 ° - Step time: 0.2 s - Temp.: 25 °C (Room) - Time Started: 0 s - 2-Theta: 15.000 ° - Theta:
Operations: Strip kAlpha2 0.514 | Background 1.000,1.000 | Import
QUARTZ - File: Q091506.RAW - Type: 2Th/Th unlocked - Start: 18.000 ° - End: 72.000 ° - Step: 0.030 ° - Step time: 0.2 s - Temp.: 25 °C (Room) - Time Started: 0 s - 2-Theta: 18.000 ° - Theta: 0.000 ° -
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h < 100m
Illustrate correction process later
Acquisition issues• Statistics
• Fluorescence effects
• Geometric Effects – Off-axis– Absorption depth (sampling depth)
• Spectral Contamination– Cu K, W L radiation
Ni Filter• K/K intensity ratio is 9
• Ni filter attenuates K more than K– MAC of Ni for Cu K = 283 cm2/g– MAC of Ni for Cu K = 49 cm2/g
• A 20m Ni filter will produce a K/K ratio of about 500 while attenuating the K by a factor of ~2.
• K intensity is not 0!
Spectral Contamination• Multiple Cu peaks
– K1 = 1.540562Å
– K2 = 1.54439Å
– Average =1.5418Å
– CuK = 1.392218Å
• W deposits on anode (filament contamination)– W L = 1.47639Å
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Cu K W L
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
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
Set to your download directory
ALL2EVA shortcut
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
EVA• tour
EVA• displacement_1.eva
Phase ID steps• Read .RAW file
• Subtract background, Strip K2
• Use background subtracted scan for Peak Search; Use K2 stripped scan for Peak Match.
• Match dominant peaks; displacement shift if necessary
• If displacement shift; return to RAW data and correct.
EVA• Single phase (min11-01.raw)
– Elements: Mg and O
EVA• TQ019-01.raw
– Pure Mg, Si, O used in the processing
EVA• DA029.raw
– Multi component, initially unknown elements– SEM EDS
EVA• DA029.raw
– SEM EDS• Ti, Si, Mn, O, F• K, Na, Al, Mg, Fe