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Lesson 7Publishing XRD Results
Nicola Döbelin(‘s humble opinions…)
RMS Foundation, Bettlach, Switzerland
October 16 – 17, 2013, Uppsala, Sweden
…totally irrelevant to the rest of the world
Relevant Topics
2
- Accuracy of Rietveld refinement results
- Graphs
- «Experimental» section
Accuracy of Rietveld Refined Data
3
Standard procedure:
- Do multiple measurements
- Calculate mean and standard deviation
How good is your analysis?
Is there a systematic error / bias? Caused by:
- Your instrument configuration
- Your sample preparation
- Your refinement strategy
Much trickier question:
Accuracy of Rietveld Refined Data
4
- Often no complementary analyticaltechnique available
- Hardly any reference materials available
- Refinement: Highly operator dependent
XRD / Rietveld refinements are very difficult to validate:
One option: Participate in round robins
� Compare your results with other labs
Round robin on CaP phase quantificationorganized by RMS Foundation / Nicola Döbelin
Accuracy of Rietveld Refined Data
5
Round Robin (unpublished):
- Simple 2 phase system: HA + β-TCP
- Very homogeneous distribution
- No texture
- No micro-absorption
- Highly crystalline
- Mean cryst size ~200 nm
0.01 0.1 1 10 1000
2
4
6
8
10
Qua
ntity
[%]
Particle Diameter [µm]
Volume Number
0.01 0.1 1 10 1000
2
4
6
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10
Qua
ntity
[%]
Particle Diameter [µm]
Volume Number
� Nearly «Best Case» Scenario
Accuracy of Rietveld Refined Data
6
5 Samples measured on Bruker D8 at Ångström Lab
Sample β-TCP [wt-%] HA [wt-%]
1 28.44 71.56
2 28.72 71.28
3 28.90 71.10
4 28.70 71.30
5 28.62 71.38
Mean (Std. Dev) 28.68 (0.17) 71.32 (0.17)
Round Robin
10 Labs with 21 different instruments / configurationsanalyzed the same powder
27.0
27.5
28.0
28.5
29.0
29.5
30.0
b-T
CP
[rel
. wt-
%]
27.0
27.5
28.0
28.5
29.0
29.5
30.0
b-T
CP
[rel
. wt-
%]
27.0
27.5
28.0
28.5
29.0
29.5
30.0
111 3
JJIHHGCBAAA
b-T
CP
[rel
. wt-
%]
A B C DLab E F G H I J
Instrument 1 2 31 2 1 2 1 2 1 2 1 2 1 2 1 2
27.0
27.5
28.0
28.5
29.0
29.5
30.0
111 3
JJIHHGCBAAA
b-T
CP
[rel
. wt-
%]
A B C DLab E F G H I J
Instrument 1 2 31 2 1 2 1 2 1 2 1 2 1 2 1 2
27.0
27.5
28.0
28.5
29.0
29.5
30.0
111 3
JJIHHGCBAAA
b-T
CP
[rel
. wt-
%]
A B C DLab E F G H I J
Instrument 1 2 31 2 1 2 1 2 1 2 1 2 1 2 1 2
27.0
27.5
28.0
28.5
29.0
29.5
30.0
111 3
JJIHHGCBAAA
b-T
CP
[rel
. wt-
%]
A B C DLab E F G H I J
Instrument 1 2 31 2 1 2 1 2 1 2 1 2 1 2 1 2
Accuracy of Rietveld Refined Data
7
D8 Ångströmlabn=5
28.68 (±0.17) %
Meann=105
28.17 (±0.53) %
p < 0.01
Accuracy of Rietveld Refined Data
8
Results for this scenario* (Round Robin 2-phase sample):
* only for this scenario!
Repeatability:
- Same Lab
- Same Instrument
- Same Configuration
- Same Operator
- Same Refinement Software
- Same Refinement Strategy
� σQuantification = 0.21 wt-%
Reproducibility:
- Different Lab
- Different Instrument
- Different Configuration
- Different Operator
- Different Refinement Software
- Different Refinement Strategy
� σQuantification = 0.53 wt-%
σ will increase for more complex samples
Accuracy of Rietveld Refined Data
9
[1] Doebelin, N. «Round robin on calcium phosphate phase quantification by powder diffraction», in preparation.
[2] Stutzman, P. «Powder diffraction analysis of hydraulic cements: ASTM Rietveld round-robin results on precision.» Powder Diffraction, 2005, 20(2): 97-100.
Sr = Reproduced Standard Deviation (different lab / instrument / config / operator / software / refinement strategy)
sr = Repeated Standard Deviation (same lab / instrument / config / operator / software / refinement strategy)
The round robin has demonstrated:
- Small standard deviation ≠ accurate results
- Most labs obtain biased results(from insignificant to highly significant bias)
- Rule of thumb: [1] and [2] show that for phase quantificationsSr ≈ 2 · sr
In a nut shell:
Accuracy of Rietveld Refined Data
10
General consensus in the Rietveld Community:For n=1: Forget about the decimals!
Publish as:
HA: 100 wt-%
betaTCP: not detected
- Do multiple measurements and report Std. Dev. σ(ignore bias)
- Do multiple measurements and report [1]:Repeatability R = 2.77 · sr(more realistic error bars)
- Do a full test validation to calculate accurate and realistic σ(extremely difficult and time consuming)
3 options to report refined phase quantities in publications:
Probably themost feasibleProbably themost feasibleProbably themost feasible
[1] ASTM E177-13: «Standard Practice for Use of theTerms Precision and Bias in ASTM Test Methods».
10 15 20 25 30 35 40 45 50 55
Inte
nsity
(a.
u.)
Diffraction Angle (°2θ)
10 15 20 25 30 35 40 45 50 55
Inte
nsity
(a.
u.)
Diffraction Angle (°2θ)
Methods… phase quantities
were calculatedfrom XRD data…
Graphs: XRD / Rietveld are «visual» methods
11
Is the data
good
enough?
Your friendly reviewer
Graphs: XRD / Rietveld are «visual» methods
12
Methods… XRD data was
analyzed byRietveld
refinement…
How good
was the
refinement?
10 20 30 40 50 60-1000
-500
0
500
1000
1500
2000 Iobs Icalc Idiff Background
Inte
nsity
[cou
nts]
Angle [°2theta]
10 20 30 40 50 60
0
500
1000
1500
Iobs Icalc Idiff Background
Inte
nsity
[cou
nts]
Angle [°2theta]
Graphs: XRD / Rietveld are «visual» methods
13
10 20 30 40 50 60
0
500
1000
1500
Iobs Icalc Idiff Background
Inte
nsity
[cou
nts]
Angle [°2theta]
10 20 30 40 50 60
0
500
1000
1500
Iobs Icalc Idiff Background
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nsity
[cou
nts]
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10 20 30 40 50 60
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Iobs Icalc Idiff Background
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nsi
ty [
coun
ts]
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10 20 30 40 50 60
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ts]
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ts]
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coun
ts]
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10 20 30 40 50 60
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Iobs Icalc Idiff Background
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nsity
[cou
nts]
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10 20 30 40 50 60
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Iobs Icalc Idiff Background
Inte
nsity
[cou
nts]
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10 20 30 40 50 60
0
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Iobs Icalc Idiff Background
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nsi
ty [
coun
ts]
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10 20 30 40 50 60
0
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nsi
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coun
ts]
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10 20 30 40 50 60
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coun
ts]
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Iobs Icalc Idiff Background
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nsi
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coun
ts]
Angle [°2theta]
Recommendation:
- Show all your raw data(documents your data quality)
- Show 1 full refinement(documents your refinement quality)
- All the information is in the raw data
- Only additional information in refinement plots (Icalc, Idiff, Bkgr):
«The refinement was done right»
Graphs: XRD / Rietveld are «visual» methods
14
10 15 20 25 30 35 40 45 50 55
25 °C
1000 °C
950 °C
900 °C
850 °C
800 °C
750 °C
700 °C
650 °C
600 °C
550 °C
525 °C
575 °C
25 °C
Inte
nsity
(a.
u.)
Diffraction Angle (°2θ)
500 °C
HAα-TCPβ-TCP
10 15 20 25 30 35 40 45 50 55
25 °C
1000 °C
950 °C
900 °C
850 °C
800 °C
750 °C
700 °C
650 °C
600 °C
550 °C
525 °C
575 °C
25 °C
Inte
nsity
(a.
u.)
Diffraction Angle (°2θ)
500 °C
HAα-TCPβ-TCP
10 20 30 40 50 60
0
500
1000
1500
Iobs Icalc Idiff Background
Inte
nsity
[cou
nts]
Angle [°2theta]
10 15 20 25 30 35 40 45 50 55
25 °C
1000 °C
950 °C
900 °C
850 °C
800 °C
750 °C
700 °C
650 °C
600 °C
550 °C
525 °C
575 °C
25 °C
Inte
nsi
ty (
a.u.
)
Diffraction Angle (°2θ)
500 °C
HAα-TCPβ-TCP
30 31 32 33 34 35 36
0
500
1000
1500
Iobs Icalc Idiff Background b-TCP HA
Inte
nsity
[co
unts
]
Angle [°2theta]
Combine your raw patterns
30 31 32 33 34 35 36
0
500
1000
1500
Iobs Icalc Idiff Background b-TCP HA
Inte
nsity
[cou
nts]
Angle [°2theta]
30 31 32 33 34 35 36
0
500
1000
1500
Iobs Icalc Idiff Background b-TCP HA
Inte
nsity
[cou
nts]
Angle [°2theta]
Show more graphs if themanuscript improves
«Materials and Methods» Section
15
Used for phase identification
Match the level of detail to the relevance of XRD for the study
- Basic intrument parameters:
- Instrument / Manufacturer
- Scan range (start, end, step size)
- References to PDF / ICDD / COD phaseentries
«Materials and Methods» Section
16
10 20 30 40 50 60
0
500
1000
1500
Iobs Icalc Idiff Background
Inte
nsity
[cou
nts]
Angle [°2theta]
«Materials and Methods» Section
17
Used for phase quantification
- Detailed intrument parameters:
- Instrument / manufacturer
- Scan range (start, end, step size [°2θ])
- Radiation, filter / monochromator, divergence slit
- References to sources of crystal structures
- Rietveld software (program name, version, reference)
«Materials and Methods» Section
18
«Materials and Methods» Section
19
Used for advanced refinements(structural parameters, amorphous fractions, crystallite size analysis, texture analysis etc.)
- Detailed intrument parameters:
- Instrument / manufacturer
- Scan range (start, end, step size [°2θ])
- Radiation, filter / monochromator, divergence slit
- … (detector, masks, ASS, Soller slits, generator sett ings…)
- References to sources of crystal structures
- Rietveld software (program name, version, reference)
- Refinement strategy
- Any non-standard calculations, sample preparations, measurement conditions, etc…
«Materials and Methods» Section
20
Refinement strategy
«Materials and Methods» Section
21
Special calculations
Summary: DOs and DON’Ts in Manuscripts
22
Do:
- Show your raw data (stacked plots)
- Show one full refinement
- Give details according to the relevanceof XRD data for the manuscript
Don’t:
- Spam the manuscript with refinement plots
- Publish results from non-standard samples
- Publish results from poor refinements!!!
23
Thank you !