Lesson 10 - Publishing XRD - Profex | Open Source XRD and...
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Transcript of Lesson 10 - Publishing XRD - Profex | Open Source XRD and...
Lesson 10
Publishing XRD Results
Nicola Döbelin(‘s humble opinions…)
RMS Foundation, Bettlach, Switzerland
…totally irrelevant to the rest of the world
January 14 – 16, 2015, Bern, Switzerland
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 Döbelinin 2012/2013
Accuracy of Rietveld Refined Data
5
Round Robin Reference Sample:
- 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 10 100
0
2
4
6
8
10
Qua
ntity
[%
]
Particle Diameter [µm]
Volume
Number
0.01 0.1 1 10 100
0
2
4
6
8
10
Qua
ntity
[%
]
Particle Diameter [µm]
Volume
Number
� Nearly «Best Case» Scenario
Accuracy of Rietveld Refined Data
6
Sample β-TCP [wt-%] HA [wt-%]
1 28.01 71.99
2 28.22 71.78
3 28.49 71.51
4 28.29 71.71
5 28.20 71.80
Mean (Std. Dev) 28.24 (0.17) 71.76 (0.17)
Round Robin
12 Labs with 26 different instruments / configurationsanalyzed the same powder
n=5
Accuracy of Rietveld Refined Data
7
A:I A:II A:IIIA:IV B:I B:II B:III B:IV C:I C:II D:I E:I E:II F:I G:I G:II H:I H:II H:III I:I I:II J:I J:II J:III K:I L:I
70
71
72
73
74
**
*
*
**
**
**
**
**
**
**
HA
Phase Q
uantity
[re
l. w
t-%
]
Laboratory:Configuration
*
* p < 0.05** p < 0.01
71.97 (0.54)
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 = 0.29 wt-%
Reproducibility:
- Different Lab
- Different Instrument
- Different Configuration
- Different Operator
- Different Refinement Software
- Different Refinement Strategy
� σQuantification = 0.60 wt-%
σ will increase for more complex samples
Accuracy of Rietveld Refined Data
9
Parameter �� ��� �� �� � �
Weigth Fraction β-TCP [wt-%] 28.03 0.54 0.29 0.60 0.81 1.67
Weigth Fraction HA [wt-%] 71.97 0.54 0.29 0.60 0.81 1.67
Unit Cell Length β-TCP a [nm] 1.04099 0.00027 0.00005 0.00027 0.00015 0.00077
Unit Cell Length β-TCP c [nm] 3.73561 0.00102 0.00024 0.00104 0.00066 0.00292
Unit Cell Length HA a [nm] 0.94221 0.00026 0.00005 0.00026 0.00013 0.00073
Unit Cell Length HA c [nm] 0.68845 0.00019 0.00003 0.00019 0.00009 0.00054
Crystallite Size β-TCP [nm] 212.87 110.30 31.04 113.74 86.91 318.48
Crystallite Size HA <001> [nm] 106.99 16.67 6.69 17.72 18.74 49.60
Crystallite Size HA <100> [nm] 92.69 14.38 4.54 14.95 12.72 41.85
�̿: Average of Cell Averages̅: Standard deviation of Cell Averages�: Repeatability standard deviation : Reproducibility standard deviation�: 95% repeatability limit�: 95% reproducibility limit
Precision statistics according to ASTM E691 - 13
Accuracy of Rietveld Refined Data
10
[1] Doebelin, N. «Interlatoratory study on the quantification of calcium phosphate phases by Rietveld refinement», 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 = Repeatability Standard Deviation (same lab / instrument / config / operator / software / refinement strategy)
Sr = Reproducibility Standard Deviation (different 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
11
General consensus in the Rietveld Community:For n=1: Forget about the decimals!
Publish as:
HA: > 99 wt-%
betaTCP: < 1 %
- 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 the
most feasible
Probably the
most feasible
Probably the
most 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 calculated
from XRD data…
Graphs: XRD / Rietveld are «visual» methods
12
Is the data
good
enough?
Your friendly reviewer
Graphs: XRD / Rietveld are «visual» methods
13
Methods
… XRD data was
analyzed by
Rietveld
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 [co
un
ts]
Angle [°2theta]
10 20 30 40 50 60
0
500
1000
1500
Iobs
Icalc
Idiff
Background
Inte
nsity [co
un
ts]
Angle [°2theta]
Graphs: XRD / Rietveld are «visual» methods
14
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
Inte
nsity
[cou
nts
]
Angle [°2theta]
10 20 30 40 50 60
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500
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1500
Iobs Icalc
Idiff Background
Inte
nsi
ty [
coun
ts]
Angle [°2theta]
10 20 30 40 50 60
0
500
1000
1500
Iobs Icalc
Idiff Background
Inte
nsi
ty [
coun
ts]
Angle [°2theta]
10 20 30 40 50 60
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Iobs Icalc
Idiff Background
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nsi
ty [
coun
ts]
Angle [°2theta]
10 20 30 40 50 60
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Iobs Icalc
Idiff Background
Inte
nsi
ty [
coun
ts]
Angle [°2theta]
10 20 30 40 50 60
0
500
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1500
Iobs Icalc Idiff
Background
Inte
nsity
[cou
nts
]
Angle [°2theta]
10 20 30 40 50 60
0
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1500
Iobs Icalc Idiff
Background
Inte
nsity
[cou
nts
]
Angle [°2theta]
10 20 30 40 50 60
0
500
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1500
Iobs Icalc
Idiff Background
Inte
nsi
ty [
coun
ts]
Angle [°2theta]
10 20 30 40 50 60
0
500
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Iobs Icalc
Idiff Background
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nsi
ty [
coun
ts]
Angle [°2theta]
10 20 30 40 50 60
0
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1500
Iobs Icalc
Idiff Background
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nsi
ty [
coun
ts]
Angle [°2theta]
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0
500
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1500
Iobs Icalc
Idiff Background
Inte
nsi
ty [
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
15
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 [
co
unts
]
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
nsity (
a.u
.)
Diffraction Angle (°2θ)
500 °C
HAα-TCP
β-TCP
30 31 32 33 34 35 36
0
500
1000
1500
Iobs Icalc Idiff Background
b-TCP HA
Inte
nsity [co
un
ts]
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 [
co
un
ts]
Angle [°2theta]
30 31 32 33 34 35 36
0
500
1000
1500
Iobs
Icalc
Idiff
Background
b-TCP
HA
Inte
nsity [
co
un
ts]
Angle [°2theta]
Show more graphs if themanuscript improves
«Materials and Methods» Section
16
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 phase
entries
«Materials and Methods» Section
17
10 20 30 40 50 60
0
500
1000
1500
Iobs
Icalc
Idiff
Background
Inte
nsity [co
un
ts]
Angle [°2theta]
«Materials and Methods» Section
18
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
19
«Materials and Methods» Section
20
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 settings…)
- 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
21
Refinement strategy
«Materials and Methods» Section
22
Special calculations
Summary: DOs and DON’Ts in Manuscripts
23
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!!!