Lesson 5 Advanced Refinements Advanced Profex...

Lesson 5

Advanced Refinements

Advanced Profex Features

Nicola Döbelin

RMS Foundation, Bettlach, Switzerland

June 13 – 15, 2018, Bettlach, CH

Topics


Bi-modal crystallite sizes

Linked parameters

Chemical substitutions(by Bastien Le Gars Santoni)

Internal standard quantification


Text blocks

Refinement presets

Base lines

«Scan Math»

FullProf.2k

2

Bi-modal Crystallite Sizes

3


4

Highly-crystalline hydroxyapatite (HA)

Nano-crystalline hydroxyapatite (HA)


5

Peak broadening cannot

be described with a

single crystallite size


6

Two HA phases refined

(= Two independent

crystallite sizes)


7

Works, but introduces a lot of refined parameters:

- Unit cell dimensions

- Crystallite size

- Micro-strain

- Texture

- Atomic coordinates

- Site occupancies

- …

BGMN Features: Sub-Phases

Allows to refine only certain parameters bi-modal.


8


9

RefMult=2

RP=4 k1=0 PARAM=k2=0_0^0.0001

PARAM=B1[1]=0_0^0.01

PARAM=B1[2]=0_0^0.05

PARAM=GEWICHT[1]=0_0


Activates 2 sub-phases

Instead of refining one crystallite size (B1)

for the hydroxyapatite phase, we can

refine individual B1 for the sub-phases:

B1[1], B1[2]


10

RefMult=2

RP=4 k1=0 PARAM=k2=0_0^0.0001

PARAM=B1[1]=0_0^0.01

PARAM=B1[2]=0_0^0.05



k2 (micro-strain) is not refined

individually for the sub-phases

But two B1 (crystallite size) are

refined for each sub-phase

The weight fraction (GEWICHT)

for both fractions is refined

GOAL:HAp=(GEWICHT[1]+GEWICHT[2])*ifthenelse(ifdef(d),exp(my*d*3/4),1)

The total weight fraction of hydroxyapatite is the

sum of the nano- and micro-crystalline sub-phases


11

Much better fit

But no anisotropic refinements possible

(B1=ANISO, GEWICHT=SPHARn, etc.)

Limitation by BGMN


12

Workaround for bimodal crystallite sizes with

anisotropic shape and texture


13



RP=4 k1=0 PARAM=k2=0_0^0.0001 B1=ANISO^0.01 GEWICHT=SPHAR8 //

RefMult=2

PARAM=pB1=5_1^50

B1[1]=B1

B1[2]=pB1*B1

PARAM=pG=0.5_0.05^0.95

GEWICHT[1]=pG*GEWICHT

GEWICHT[2]=(1-pG)*GEWICHT

Refine anisotropic parameters

for the entire phase

(as if no sub-phases were defined)


14



RP=4 k1=0 PARAM=k2=0_0^0.0001 B1=ANISO^0.01 GEWICHT=SPHAR8 //

RefMult=2

PARAM=pB1=5_1^50

B1[1]=B1

B1[2]=pB1*B1

PARAM=pG=0.5_0.05^0.95

GEWICHT[1]=pG*GEWICHT

GEWICHT[2]=(1-pG)*GEWICHT

Define the sub-phase parameters

as multiples of the phase parameters

Refine the multiplicator


15

Refined with anisotropic B1[1] and B1[2],

and texture for GEWICHT[1] and GEWICHT[2]

Profex Feature: Text Blocks

16

1

2

3

4 Restart Profex


17

1 place cursor here

2 3


18

Linked Parameters

19

Scenario:

- α-TCP (α-Ca3(PO4)2) sample

- Test for impurities of:

- β-TCP (β-Ca3(PO4)2)

- β-CPP (β-Ca2P2O7)

«Test for impurities» = refining phases that are potentially not present

Linked Parameters

20

α-TCP: 84.36 ± 0.75 %

β-TCP: 12.74 ± 0.70 %

β-CPP: 2.89 ± 0.26 %

Linked Parameters

21

β-TCP refinement

unreliableCrystallite Size = 8.5 nm

after sintering at 1350°C

???

Linked Parameters

22

β-TCP signal too weak (or absent)

to refine crystallite size

Unstable refinement

Best guess for β-TCP crystallite size:

Same as α-TCP

Link B1 of β-TCP to B1 of α-TCP

Linked Parameters

23

PHASE=alphaTCP // 04-010-4348

…

RP=4 k1=0 k2=pk2 B1=pB1 GEWICHT=SPHAR6 //

…

PHASE=betaCaPyrophosphate // 04-009-3876

…


…

PHASE=betaTCP // 04-008-8714

…


…

Structure files (*.str)Control file (*.sav)

…

EPS1=0

PARAM[1]=EPS2=0_-0.01^0.01

EPS3=0

PARAM[2]=pB1=0_0^0.01

PARAM[3]=pk2=0_0^0.0001

alpha3ratio=0.020

betaratio=0.005

NTHREADS=8

PROTOKOLL=Y

SAVE=N

…

Linked Parameters

24

α-TCP: 94.93 ± 0.27 %

β-TCP: 2.02 ± 0.19 %

β-CPP: 3.05 ± 0.19 %

Exercise after lunch: further optimize the refinement

Chemical Substitutions

25

X-rays are scattered at the electron shell of atoms/ions (elastic scattering)

More electrons = more scattering

Heavier atoms/ions = more scattered intensity

Structure factor amplitude

|Fhkl| says:

«Scattered intensity

corresponds to 17.937 electrons»

Crystal structure model says:

«at this position we expect

a Ca2+ ion»

Rietveld refinement says:

«Then the site occupancy

is 0.9965»


26

Structure factor amplitude

|Fhkl| says:

«Scattered intensity

corresponds to 17.937 electrons»

Crystal structure model says:

«at this position we expect

a Sr2+ ion»

Rietveld refinement says:

«Then the site occupancy

is 0.4990»

XRD only sees clouds of electrons

The crystal structure model determines how to

interpret the number of electrons


27

Goal for refinement of site occupancies:

- Establish a structure model that describes

the number of electrons found…

- … while maintaining charge balance


28

Presentation by Bastien

Internal Standard Quantification

Only crystalline phases create a distinct diffraction pattern

XRD is «blind» to amorphous phases

Phase quantifications usually report «relative weight-%»

(= relative to all crystalline phases)

Internal standard quantification = spiking with a crystalline phase in

a known quantity

Can be used to normalize relative quantities to absolute values

29

100% − 𝑄𝑎𝑏𝑠𝑜𝑙𝑢𝑡𝑒 = 𝑄𝑎𝑚𝑜𝑟𝑝ℎ𝑜𝑢𝑠


30

Partially

amorphous

SiO2

Add 20 wt-%

Al2O3

20.0 %

XRDQtz

40.0 %

20.0 %

Absolute

quantities

normalize

Qtz

66.7 %

Al2O3

33.3 %

Relative

quantities

Amorph∙20.0

33.3

60.0 %

100 - 60

= 40.0 %

Qtz

40.0 %

20.0 %

Absolute

quantities

Amorph

40.0 %

normalize

∙100.0

100.0 − 20.0

Qtz

50.0 %

Amorph

50.0 %

These calculations can be

done in Profex using GOALs


31

Sample contains:

- X % Glass

- Y % Hydroxyapatite

20 wt-% Al2O3 (Corundum)

were added as internal standard


32

Step 1: Quantify all

crystalline phases


33

Step 2: Define Al2O3 as the

internal standard phase


34

GOALs section will

be modified

sum=Corundum+HAp

QCorundum=Corundum/sum

QHAp=HAp/sum

GOAL[1]=QCorundum

GOAL[2]=QHAp

ISTD=Corundum

ISTDQ=0.2000

sumabs=ISTD*(1-ISTDQ)/ISTDQ

QabsHAp=HAp/sumabs

QabsAmorph=1-(HAp)/sumabs

GOAL[1]=QabsHAp

GOAL[2]=QabsAmorph

Then repeat the refinement


35

Reports absolute phase quantities

without the internal standard


36

Exercise for the afternoon:

Improve the fit


37

PhasePhase quantity [abs wt-%]

Mixed Internal standard External standard

Hydroxyapatite 50.00 46.56 45.49

MgO - 0.11 0.12

Amorphous 50.00 53.33 54.39

Explanation:

A mixture of 50 wt-% hydroxyapatite + 50 wt-% glass was prepared.

But the hydroxyapatite raw material contained traces

of MgO and 9 wt-% amorphous or undetected phases.

External standard quantification see: …\Handouts\ExternalStandard.pdf

Topics


Bi-modal crystallite sizes

Linked parameters

Chemical substitutions(by Bastien Le Gars Santoni)

Internal standard quantification


Text blocks

Refinement presets

Base lines

«Scan Math»

FullProf.2k

38

Profex Feature: Refinement Presets

39

Profex Feature: Refinement Presets

40

Refinement Presets:

- Consistent refinement strategies

- Eliminate user influence

- Shared preset repository

Profex Feature: Base Line

41

Warning: DO NOT subtract base lines for Rietveld refinement!

Project Add Base Line…

2 Optimize parameters

1 Select base line algorithm

3 Check for smooth base line

4 Append base line to project

Profex Feature: Base Line

42

Base line is added as a new scan, but not yet saved to disk.

Use right mouse button «Export Scan» to save to disk.

Profex Feature: Scan Math

43

«Tools Scan Math»: Perform mathematical operations

on scans within a project.

Example: Subtract base line from scan


44

«Tools Scan Math» 1 Enter equation

2 Generate Scan


45

«Tools Scan Math»

New scan is generated

Profex Feature: Fullprof.2k

46

https://www.ill.eu/sites/fullprof/


Download and install Fullprof Suite

Select the fullprof executable «fp2k.exe» in the

preferences

47

Set to «Fullprof», restart Profex

«Run Refinement» will call fp2k.exe


48

Warning: Fullprof only accepts datasets measured with

fixed divergence slit!

When to use Fullprof instead of BGMN:

- When setting up an instrument configuration for BGMN fails

(Fullprof uses empirical profile functions, not fundamental parameters)

- Some features are easier to use in Fullprof

(distance and angle constraints)

- When you like Fullprof better than BGMN

Lesson 5 Advanced Refinements Advanced Profex...

Documents

Transcript of Lesson 5 Advanced Refinements Advanced Profex...