Mineralogical adventures of a powder diffractionist

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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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Pamela Whitfielda_{, Andy Roberts}b_{, Lyndon Mitchell}a_,

Yvon Le Pagea_{, Stuart Mills}c_{, Arnt Kern}d _{and Kim Tait}e

a _NRC,b _{Geological Survey of Canada,}c _{University of British Columbia,} d _Bruker-AXS,e _{Royal Ontario Museum}

Mineralogical Adventures of a Powder

Diffractionist

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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?

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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

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And?

• 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…

Crystal structure of jadarite

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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….

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Angastonite

CaMgAl

₂

(PO

₄

)

₂

(OH)

₄

.7H

₂

O

• 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?

Le Bail fit of triclinic cell to lab data

2 (degrees - 0.697 Å)

2 3 4 5 6 7

time

Synchrotron data from angastonite

Two theta (degrees)

5 10 15 20 25 30 35 40 45 50 55 60 65 Intensity (counts ) 0 10000 20000 30000 40000 50000 298 K 0.5mm capillary

Focusing mirror _{– CuK}

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Stichtite

Mg

₆

Cr

₂

(OH)

₁₆

CO

₃

.4H

₂

O

• Stichtite has the hydrotalcite structure

– simple R-3m symmetry but multiple occupancies and vacancies – also shows hkl-dependent peak broadening (very unpleasant!)

018 110 113 ₁₁₆

006

015 012/

009 Le Bail fit to data

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Stichtite

• Seen broadening in R-3m layered battery materials before

– no peak shifts so probably twin faulting in stichtite

– previously developed reciprocal-space relationship to model broadening in R-3m with 1 variable vs 6 spherical harmonics variables

Monte-Carlo simulation of effect of 5% stacking faults ( ) and twin faults ( )

If H-K 3n = constant lc* cos(c* ^ R*)

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Stichtite

• Structure refinement without the broadening correction..

and with….

2Th Degrees70 80 90 100 110 120 130 60 50 40 30 20 10 1,100,000 1,050,000 1,000,000 950,000 900,000 850,000 800,000 750,000 700,000 650,000 600,000 550,000 500,000 450,000 400,000 350,000 300,000 250,000 200,000 150,000 100,000 50,000 0 -50,000 -100,000 -150,000 stitchtite-3R1 87.92 % Lizardite 1T 0.81 % stitchtite-2H1 11.27 % 2Th Degrees70 80 90 100 110 120 130 60 50 40 30 20 10 1,100,000 1,050,000 1,000,000 950,000 900,000 850,000 800,000 750,000 700,000 650,000 600,000 550,000 500,000 450,000 400,000 350,000 300,000 250,000 200,000 150,000 100,000 50,000 0 -50,000 stitchtite-3R1 79.18 % Lizardite 1T 0.56 % stitchtite-2H1 20.25 %

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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

• 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,

2Th Degrees55 60 65 70 75 80 85 90 95 100 105 110 50 45 40 35 30 25 20 15 10 5 S qr t( C ou nts) 280 260 240 220 200 180 160 140 120 100 80 60 40 20 0 -20 F-Gibbsite 88.16 % Corundum 0.50 % Biotite-mica 3.96 % lizardite-1T 7.38 % capillary background 0.00 %

Fourier difference plot reveals significant residual electron density between the layers.

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Fluorocronite

very recent IMA submission

• Had very little material and multi-phase → capillary geometry • However mineral of interest is PbF2; has Cu of 1525 cm-1 !

– 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 2 (MoK - 0.7Å) 10 20 30 40 Inten sity (co un ts) 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000

Debye-Scherrer data with MoK .

Likely R with 0.3mm cap still >5  _{mirror. Likely R with 0.3mm cap <3 }Data from AgK (0.56Å) with focusing

2Th Degrees20 22 24 26 28 30 32 34 36 38 40 18 16 14 12 10 8 6 C o u n ts 35,000 30,000 25,000 20,000 15,000 10,000 5,000 0 -5,000 5.046336 7.539469 8.805516 10.11759 11.38644 14.45781 15.05726 17.54717 26.22962 cassiterite 40.07 % fluorocronite 59.93 %

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Carbonation of CaSiO

₃

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

In-situ carbonation with 56 bar CO₂ of damp CaSiO₃

60°C

56 bar CO₂

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Strontiodresserite

SrAl

₂

(CO

₃

)

₂

(OH)

₄

.H

₂

O

• 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

1mm hemisphere embedded in sill rock

(Francon Quarry, Montreal) _{Raw data up to 140° 2}

2 (degrees CuK ) 20 40 60 80 100 120 Log Intens ity 1e+2 1e+3 1e+4 1e+5 4 hemispheres 0.5mm capillary Focusing mirror

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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

Sr Al

Atom picking from electron density map generated from charge-flipping using the tangent formula

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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

Polyhedral representation of strontiodresserite structure • Hydroxides located with

bond valence sums • DFT calculations to

verify structure and

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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…

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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

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