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Mineralogical adventures of a powder diffractionist
Whitfield, Pamela; Roberts, Andy; Mitchell, Lyndon; Le Page, Yvon;
Mills, Stuart; Kern, Arnt; Tait, Kim
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Mineralogical Adventures of a Powder
Diffractionist
Pamela Whitfielda, Andy Robertsb, Lyndon Mitchella,
Yvon Le Pagea, Stuart Millsc, Arnt Kernd and Kim Taite
a NRC, b Geological
Survey of Canada, c University of British Columbia,
d Bruker-AXS, e Royal Ontario Museum
My background in
diffraction?
• My background is inorganic solid-state chemistry
– functional oxides such as lithium battery materials
• Have unique equipment/capabilities for powder diffraction.
– 3 instruments of different configurations (tube anodes Cr Ag)
– custom-built attachments for non-ambient capillary and in-situ
gas pressure work
– beta test software for Bruker-AXS
• Never done single-crystal diffraction and have enough work
that I may never have to!
• Done most powder diffraction techniques up to and including
structure solution from powder diffraction.
– jack of all trades and master of none?
– currently chair of the IUCr Commission for Powder Diffraction
Why is a chemist playing
with minerals?
• Structure determination from lab powder diffraction data not a
common technique in Canada.
• A colleague of a colleague of a colleague in Canada sent me
a sample of a very boring-looking new mineral
– needed capillary geometry - LiNaB3SiO7(OH)
– very fine grained <5 m
– wanted the structure in a couple of weeks for IMA submission!
Bright-field optical image of new mineral
- not very exciting
And?
Crystal structure of jadarite
• Successfully solved the structure
using simulated annealing
• The mineral was jadarite, aka
kryptonite (chemical formula as
per Superman 3) as reported by
the BBC and others
– and the rest is history…
Kryptonite?
Jadarite - dull reality!
What came next?
• Funnily enough some weird and wonderful fine-grained
minerals from Canadian labs have come my way since then….
• The list includes
– stichtite, woodallite, barbertonite, angastonite,
widgiemoolthalite, dypingite, strontiodresserite, montroyalite,
F-altered gibbsite and so on….
• The rest of the presentation consists of a survey of new
techniques and instrumentation to solve the challenges posed
by different mineral samples that have come my way….
Angastonite
CaMgAl2(PO4)2(OH)4.7H2O
•
•
Australian mineral described in 2008.
Lab data
triclinic 2150Å3 unit cell
– new indexing algorithm
Unusual in that lab data much better than synchrotron
– unstable over time and in beam?
50000
0.5mm capillary
Focusing mirror – CuK
Vantec PSD
40000
Intensity (counts)
•
30000
298 K
time
20000
10000
0
5
10 15 20 25 30 35 40 45 50 55 60 65
Two theta (degrees)
Le Bail fit of triclinic cell to lab data
2
3
4
5
6
7
2 (degrees - 0.697 Å)
Synchrotron data from angastonite
Stichtite
Mg6Cr2(OH)16CO3.4H2O
• Stichtite has the hydrotalcite structure
– simple R-3m symmetry but multiple occupancies and vacancies
– also shows hkl-dependent peak broadening (very unpleasant!)
006
012/
009
015
Le Bail fit to data
018
110
113
116
Stichtite
• Seen broadening in R-3m layered battery materials before
– no peak shifts so probably twin faulting in stichtite
Monte-Carlo simulation
of effect of 5% stacking
faults ( ) and twin faults
( )
– previously developed reciprocal-space relationship to model
broadening in R-3m with 1 variable vs 6 spherical harmonics
variables
If H-K
3n = constant
lc*
cos(c* ^ R*)
l = Miller index, c* = c reciprocal space vector, R* = reciprocal space vector
Stichtite
• Structure refinement without the broadening correction..
and with….
1,100,000
1,100,000
1,050,000
1,050,000
1,000,000
1,000,000
950,000
950,000
900,000
stitchtite-3R1 79.18 %
Lizardite 1T 0.56 %
stitchtite-2H1 20.25 %
stitchtite-3R1 87.92 %
Lizardite 1T 0.81 %
stitchtite-2H1 11.27 %
900,000
850,000
850,000
800,000
800,000
750,000
750,000
700,000
700,000
650,000
650,000
600,000
550,000
600,000
500,000
550,000
450,000
500,000
400,000
450,000
350,000
400,000
300,000
350,000
250,000
300,000
200,000
250,000
150,000
200,000
100,000
150,000
50,000
100,000
0
50,000
-50,000
0
-100,000
-50,000
-150,000
10
20
30
40
50
10
60
20
70
30
80
2Th Degrees
40
90
50
100
60
110
70
120
80
2Th Degrees
130
90
100
110
120
130
F-modified gibbsite
(Francon quarry, Montreal)
• Multi-phase (F-gibbsite, corundum, mica, lizardite)
• Gibbsite is layered
anisotropic broadening back again 
• Difficult one to fit and potential correlations are horrendous
280
F-Gibbsite
Corundum
Biotite-mica
lizardite-1T
capillary background
260
240
220
88.16 %
0.50 %
3.96 %
7.38 %
0.00 %
200
Sqrt(Counts)
180
160
140
120
100
80
60
40
20
0
-20
5
•
•
•
•
10
15
20
25
30
35
40
45
50
55
60
65
2Th Degrees
70
75
80
Al(1)-O average bond length = 1.95 Å ,
Al(2)-O average bond length = 1.82 Å,
Al-O6 from bond valence = 1.91 Å,
Al-F6 from bond valence = 1.80 Å,
85
90
95
100
105
110
Fourier difference plot reveals
significant residual electron
density between the layers.
Significant H2O content?
Fluorocronite
very recent IMA submission
•
•
capillary geometry
-1
Cu of 1525 cm !
Had very little material and multi-phase
However mineral of interest is PbF2; has
– CuK a non-starter but wanted to solve with lab equipment
– was going to be named after Lachlan Cranswick but Ron Peterson beat
us to it
35,000
20000
30,000
25,000
16000
20,000
14000
Counts
Intensity (counts)
18000
12000
10000
26.22962
5.046336
7.539469
8.805516
10.11759
11.38644
14.45781
15.05726
17.54717
cassiterite 40.07 %
fluorocronite 59.93 %
15,000
10,000
8000
5,000
6000
0
4000
2000
10
20
30
40
2 (MoK - 0.7Å)
Debye-Scherrer data with MoK .
Likely R with 0.3mm cap still >5 
-5,000
6
8
10
12
14
16
18
20
22
24
2Th Degrees
26
28
30
32
34
36
38
Data from AgK (0.56Å) with focusing
mirror. Likely R with 0.3mm cap <3 
40
Carbonation of CaSiO3
under pressure
• Custom pressure stage built to study
crystallization of polymers under CO2
• Proof of concept study carried out
for sequestration-related work
using wollastonite as a model
60°C
56 bar CO2
In-situ carbonation with 56 bar CO2 of damp CaSiO3
Arrhenius plot for carbonation of CaSiO3
Strontiodresserite
SrAl2(CO3)2(OH)4.H2O
• This sample was supposed to be montroyalite but turned out
to be something else…..
• The data was very good quality to low d-spacings - the ‘heavy’
Sr atom made it a good candidate for charge flipping
Log Intensity
1e+5
4 hemispheres
0.5mm capillary
Focusing mirror
1e+4
1e+3
1e+2
20
1mm hemisphere embedded in sill rock
(Francon Quarry, Montreal)
40
60
80
100
2 (degrees CuK )
Raw data up to 140°2
120
Charge flipping
• Charge-flipping can
be extremely fast –
often get solution in
less than 3 mins
• Sr, Al and many of
the oxygens located
• Info used to
constrain simulated
annealing run to get
rest of the structure
Al
Sr
Atom picking from electron density map generated from
charge-flipping using the tangent formula
Strontiodresserite
structure
•
•
•
•
•
Irregular 9-coordinate Sr-O polyhedra
Octahedral AlO6
Blocks tied together by carbonate anions
Water molecules in a channel along the b-direction
Isostructural with dundasite, PbAl2(CO3)2(OH)4.H2O
• Hydroxides located with
bond valence sums
• DFT calculations to
verify structure and
localize H-bond network
Polyhedral representation of
strontiodresserite structure
Conclusions
• Laboratory powder diffraction equipment and techniques have
improved considerably in recent years
– Detectors, optics, software, new algorithms, etc
• Information can now be extracted in the lab from samples that may
previously have been intractable or only possible using a
synchrotron beamline
• The continuing evolution of powder diffraction guarantees it will
play an increasingly important role in the analysis of both new
minerals and in revisiting some old ones…
Acknowledgements
• Chris Stanley and co for the kryptonite adventure
– and everyone in the powder diffraction community who will never
let me forget it!
• Peter Stephens (SUNY/Brookhaven) for valiantly trying to get
some decent data from the angastonite on his beamline
• Hugues Guerault of Bruker-AXS for collecting the AgK data
Questions?