xrd analysis

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

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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

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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