Investigating Disorder and Dynamics in Solids: Multinuclear Solid-State NMR and First-Principles Calculations

EPJ Web of Conferences 30, 04003 (2012) DOI: 10.1051/epjconf/20123004003

© Owned by the authors, published by EDP Sciences, 2012

This is an Open Access article distributed under the terms of the Creative Commons Attribution License 2.0, which

Organized by

Thibault Charpentier

[email protected]

Patrick Berthault

[email protected]

Constantin Meis

[email protected]

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EŽǀĞŵďĞƌ ϮϴƚŚʹ ĞĐĞŵďĞƌ Ϯ

ŶĚ

_ϮϬϭϭ

/E^dEʹ ^ĂĐůĂLJ͕&ƌĂŶĐĞ

Sharon Ashbrook

University of St Andrews, UK

Investigating disorder

and dynamics in solids

Multinuclear solid-state NMR

and first-principles calculations

[04003]

Investigating Disorder and Dynamics in Solids: Multinuclear

Solid-State NMR and First-Principles Calculations

Sharon Ashbrook

School of Chemistry and EaStCHEM

University of St Andrews, UK

Solid-state NMR

δiso

MAS (I = 1/2)

MAS (I > 1/2)

C_Q,ηQ, δiso

Orthoenstatite

MAS

MQMAS

41 ppm 2.9 MHz 0.19

46 ppm 2.8 MHz 0.29

52 ppm 2.9 MHz 0.53

56 ppm 2.9 MHz 0.29

60 ppm 4.2 MHz 0.78

70 ppm 4.8 MHz 0.80

δiso |CQ| ηQ

MgSiO₃ (50 mg, 75% 17_O)

9.4 T (MQMAS, 54 hours)

J. Am. Chem. Soc. 129, 13213 (2007)

First-principles calculations

•  Calculation of NMR parameters from first principles can aid experimentalists in a range of ways

•  Spectral interpretation

•  Spectral assignment

•  Verification of NMR parameters

•  Additional information difficult to extract from experiment

•  Spectral prediction

•  Assessment of experimental feasibility

•  Flexible way to study the dependence of NMR parameters upon structure

•  Testing of structural models

Shielding δiso, ΔCSA, ηCS, (α, β, γ)

Quadrupole C_Q, η_Q, (α, β', γ')

J coupling J_iso, J_aniso

CASTEP

•  Planewave DFT code which exploits the inherent periodicity of many solids

•  Pseudopotentials are employed to separate core/valence interactions

•  Use of GIPAW formalism to calculate chemical shifts

CASTEP code

Pseudopotentials: Ultrasoft

Functional: GGA (PBE)

k-point spacing: 0.04-0.05 Å–1

Energy cut off: 50-60 Ry

Extended solids: 12-250 atoms in unit cell

EaStCHEM Research Computing Facility (148 cores, 2.4 GHz)

Research group Cluster - Pickard

Orthoenstatite

41 ppm 2.9 MHz 0.19

41 ppm 3.06 MHz 0.21

46 ppm 2.8 MHz 0.29

47 ppm 2.96 MHz 0.29

52 ppm 2.9 MHz 0.53

53 ppm 3.03 MHz 0.62

56 ppm 2.9 MHz 0.29

57 ppm 3.03 MHz 0.35

60 ppm 4.2 MHz 0.78

62 ppm 4.35 MHz 0.78

70 ppm 4.8 MHz 0.80

73 ppm 5.0 MHz 0.81

O1/O11

O2/O12

O4/O22

O3/O21

O5/O31

O6/O32

δiso |CQ| ηQ MAS

MQMAS

Overview

•  We apply a combination of multinuclear solid-state NMR experiments and first-principles DFT calculations to study structure, disorder and dynamics in a range of materials

•  Microporous phosphate frameworks

•  Ferroelectric perovskites

•  Metal-organic frameworks

•  Ceramics for waste remediation

•  High-pressure silicate minerals

175 180 ppm

C2

C1 C1 C7 C3

C3 C2

C6 C5 C4

STAM-1

1000 900 800 700 600 500 400 300 200 100 0 –100 –200 δ (ppm)

HKUST-1

20 16 12 8 4 0

(ppm)

DQ

(ppm)

10 8 6 4 2 0

–250 –500 0

250 500

(ppm)

1. Disorder in Pyrochlore Ceramics

Introduction

•  From 1941-2004

More than 1400 tons of Pu have been generated throughout the world

236 nuclear power plants generating 70-80 tons of new spent Pu each year

Range of long-lived isotopes of actinides and lanthanides need to be contained

•  Ceramic wasteforms

High crystal chemical flexibility

Tolerant of defects, substitutions and variable oxidation states High waste loading

Low leach rates

Natural analogues enable study of long-term behaviour

•  Pyrochlores

Present in the ceramic wasteform SYNROC > 500 synthetic compositions

Pyrochlore structure

•  Pyrochlore: A₂B₂O₇

•  Ordered superstructure of fluorite with 1/8 O removed in an ordered manner (Fd–3m)

•  2 cation sites VIII_{A 2+, 3+}

VI_{B 5+, 4+}

•  3 oxygen sites 8a (vacant), 8b and 48f

B site Sn/Ti/Zr/Hf

Experimental methods

•  Y₂Ti_2–xSn_xO₇ pyrochlore solid solution

Y3+ _{an NMR-active model non-radioactive cation}

Ti-bearing pyrochlores have good chemical durability

Sn-bearing pyrochlores have increased tolerance to radioactive decay

•  Stoichiometric amounts of Y₂O₃/SnO₂/TiO₂ ground and pressed into pellets and heated at 1500 °C for 48 h, reground and reheated for 96 h

•  Basic characterisation by powder XRD and electron microscopy

30 40 50 60

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

Normalised I

n

tensit

y

Two Theta / Degrees

Y2Ti2O7

Y2Sn2O7

Experimental methods

89_Y 119_Sn

Spin quantum number 1/2 1/2

Abundance (%) 100 8.6

γ (rad T–1_s–1_{) –1.3 × 10}7 _{–10.0 × 10}7

Receptivity (rel. to 13_{C) 0.7 26.6}

T₁ relaxation (s) 1000-10,000 ~10-100

Chemical shift range (ppm) ~2200 ~900

•  Experimental conditions

14.1 T (29.4 MHz for 89_{Y and 223.7 MHz for} 119_Sn)

4-mm MAS probe (5-14 kHz)

Y

₂

Ti

_2–x

Sn

_x

O

₇

:

89

_{Y NMR}

J. Phys. Chem. B 110, 10358 (2006)

100 50 0

150 200 250

δ (ppm)

100 50 0

150 200 250

δ (ppm)

x = 2.0

x = 0 x = 1.2

x = 0.4 x = 1.6

x = 0.8 Y₂Sn₂O₇

6 Sn NNN

Y₂Ti₂O₇ 6 Ti NNN

Field strength:

14.1 T

MAS rate:

14 kHz

Transients added:

24-1080

Relaxation time:

300 s

Expt. time:

2 hrs – 4 days

Spectral interpretation

•  Can we determine if Y is found only on the A site?

What would the chemical shift be if Y was on the B site?

•  Is the chemical shift we see determined only/primarily by the number of surrounding Sn/Ti? How does the shift change as a NNN Sn/Ti is substituted?

•  Does the spatial arrangement of the Sn/Ti have any effect on the chemical shift? Is there a shift difference between the different arrangements?

•  How significant are longer range differences in the environment?

For the same NNN arrangement how different can the chemical shift be? 250 200 150 100 50 0

(ppm)

Y2Ti1.2Sn0.8O7

DFT calculations:

89

_Y

δ

iso

•  Calculations were converged as far as possible with respect to both k-point spacing and cut-off energy

•  Series of simple model systems considered to assess accuracy

J. Phys. Chem. C 113, 18874 (2009)

Y2Ti2O7

Y2Sn2O7

Model systems

Y₂O₃ (2) Y₂Ti₂O₇ Y2Sn2O7 YAlO₃ Y₂O₂S YF₃

β-Y₂Si₂O₇

α-Y2Si2O7 (4)

89_{Y NMR}

Y2O3 used as a reference

A/B site occupancy

•  Comparison of experimental shift ranges to those from calculation show that Y is confined solely to the A site and Sn solely to the B site

experimental data

0 ppm 100

200 300

400

89_{Y δ} iso (ppm)

B site species A site species

Swap A and B site in Y₂Sn₂O₇/Y₂Ti₂O₇

Computational method for disordered materials

Y2Sn2O7/Y2Ti2O7 geometry optimisation / NMR

embed cluster into unit cell

1,2-Sn4Ti2

Sn6 Sn5Ti 1,3-Sn4Ti2 1,4-Sn4Ti2 1,2,3-Sn3Ti3 1,2,4-Sn3Ti3

1,3-Sn2Ti4

1,3,5-Sn3Ti3 1,2-Sn2Ti4 1,4-Sn2Ti4 SnTi5 Ti6

0 1 2 3 4 5 6

60 70 80 90 100 110 120 130 140 150 160

Sn6 Sn5Ti 1,2-Sn4Ti2 1,3-Sn4Ti2 1,4-Sn4Ti2 1,2,3-Sn3Ti3 1,2,4-Sn3Ti3 1,3,5-Sn3Ti3 1,2-Sn2Ti4 1,3-Sn2Ti4 1,4-Sn2Ti4 SnTi5 Ti6

δ_iso (ppm)

Sn NNN

Y

₂

Ti

_2–x

Sn

_x

O

₇

:

89

_{Y calculations}

Y₂Sn₂O₇ cell

0 1 2 3 4 5 6 60 70 80 90 100 110 120 130 140 150 160 Sn6 Sn5Ti 1,2-Sn4Ti2 1,3-Sn4Ti2 1,4-Sn4Ti2 1,2,3-Sn3Ti3 1,2,4-Sn3Ti3 1,3,5-Sn3Ti3 1,2-Sn2Ti4 1,3-Sn2Ti4 1,4-Sn2Ti4 SnTi5 Ti6

δ_iso (ppm)

Sn NNN

Y

₂

Ti

_2–x

Sn

_x

O

₇

:

89

_{Y calculations}

Y₂Sn₂O₇ cell

J. Phys. Chem. C 113, 18874 (2009)

0 1 2 3 4 5 6 60 70 80 90 100 110 120 130 140 150 160 Sn6 Sn5Ti 1,2-Sn4Ti2 1,3-Sn4Ti2 1,4-Sn4Ti2 1,2,3-Sn3Ti3 1,2,4-Sn3Ti3 1,3,5-Sn3Ti3 1,2-Sn2Ti4 1,3-Sn2Ti4 1,4-Sn2Ti4 SnTi5 Ti6

δ_iso (ppm)

Sn NNN

Y

₂

Ti

_2–x

Sn

_x

O

₇

:

89

_{Y calculations}

Y₂Sn₂O₇ cell Y2Ti2O7 cell

Y

₂

Ti

_2–x

Sn

_x

O

₇

:

89

_{Y calculations}

•  Deviation of 6-10° away from linear for O_8b–Y–O_8b bond angle

•  Lengthening of a number of the Y–O48f bonds

•  Why do these distortions occur? lattice fixed to be Y₂Sn₂O₇ or Y₂Ti₂O₇ local substitution of different size cations substitutions reproduced periodically

•  Does this have any impact upon the experimental analysis?

over 500 89_{Y shifts calculated}

anomalous shifts present in <3% of cases

J. Phys. Chem. C 113, 18874 (2009).

Y

₂

Ti

_2–x

Sn

_x

O

₇

: spectral analysis

250 200 150 100 50 0 (ppm)

Y2Ti1.2Sn0.8O7

5 4

3 2 1

0

J. Phys. Chem. C 113, 18874 (2009) 0 20 40 60 80 100 0 1 2 3 4 5

6 6 5 4 3 2 1 0

Y₂Sn₂O₇

Y₂Sn_1.6Ti_0.4O₇

Y₂Sn_1.2Ti_0.8O₇

Y₂Sn_0.8Ti_1.2O₇

Y₂Sn_0.4Ti_1.6O₇

Y₂Ti₂O₇

Intensity %

n Sn NNN n Sn NNN

Experimental Theoretical

Y

₂

Ti

_2–x

Sn

_x

O

₇

: spectral analysis

250 200 150 100 50 0 (ppm)

Y2Ti1.2Sn0.8O7

P(n Sn NNN) = pn _{(1 – p)}6–n

number of permutations p probability of finding Sn (x/2)

5 4

3 2 1

0

J. Phys. Chem. C 113, 18874 (2009)

•  No evidence for anything other than a random distribution of Sn/Ti on the pyrochlore B sites

0 20 40 60 80 100 0 1 2 3 4 5

6 6 5 4 3 2 1 0

Y₂Sn₂O₇

Y₂Sn_1.6Ti_0.4O₇

Y₂Sn_1.2Ti_0.8O₇

Y₂Sn_0.8Ti_1.2O₇

Y₂Sn_0.4Ti_1.6O₇

Y₂Ti₂O₇

Intensity %

n Sn NNN n Sn NNN

Experimental Theoretical

Y₂Sn₂O₇ Y₂Sn_1.6Ti_0.4O₇ Y₂Sn_1.2Ti_0.8O₇ Y₂Sn_0.8Ti_1.2O₇ Y₂Sn_0.4Ti_1.6O₇ Y₂Ti₂O₇

Conclusions

•  Solid-state NMR is an excellent probe of local environment and disorder, and complex spectra can be interpreted with the aid of first-principles calculations

•  In Y₂(Sn,Ti)₂O₇:

Evidence for random disordering of the B-site cations, rather than clustering or ordering

No evidence for A/B disorder, with 89_{Y present only on the A site}

Although easier to acquire, 119_{Sn NMR spectra are less informative owing to}

considerable overlap of the spectral resonances

•  Current/ongoing work

Use of 89_{YCSA to provide additional support for assignment}

Experimental measurement using CSA-amplified PASS experiments and use of DFT calculations

2. Disorder and Dynamics in Silicate Minerals

Collaborators: Andrew Berry, Imperial UK, ANU Australia Stephen Wimperis, Glasgow UK

Chris Pickard, UCL UK Jonathan Yates, Oxford UK

The inner Earth

•  The inner Earth is composed

primarily of silicates; aluminosilicates in the crust and magnesium silicates in the mantle

•  Water plays a key role in crustal and surface geology but little is known about its role in the Earth’s interior

•  The mantle is presumed to contain a vast amount of water

•  Thought to be located within the

structure of the nominally anhydrous minerals (NAM) in the mantle

Mg₂SiO₄ 0.9-3 wt%

Experimental challenges

•  High-temperature (~1500 °C) and high-pressure (up to 25 GPa) synthesis

•  Requires multi-anvil apparatus

•  Only small (3-40 mg) amounts of material

25

_Mg

29

_Si

17

_O

I = 5/2

10% abundance

γ = 0.06 of 1_H

Q = 19.94 fm2

I = 5/2

0.037% abundance

γ = 0.136 of 1_H

Q = –2.56 fm2

I = 1/2

4.7% abundance

γ = 0.199 of 1_H

•  Isotopic enrichment of materials using 35% (£500 / g), 70% (~£1200 / g) or 90% (~£2000 / g) H₂17_{O during synthesis}

Aims and objectives

Aims and objectives

(i) Characterise high-pressure anhydrous minerals using NMR

(ii) Study known hydrated minerals as models for water incorporation

Humite minerals

•  Proposed as possible models for defect H incorporation into mantle silicates, but synthesized at relatively low pressure

•  Humite minerals have the general formula

nMg₂SiO₄.Mg(OH)₂

•  where n = 1 (norbergite), 2 (chondrodite), 3 (humite) and 4 (clinohumite)

chondrodite

clinohumite

Humite minerals:

17

_{O NMR}

9.4 T MAS

Forsterite

Chondrodite

Clinohumite

J. Am. Chem. Soc. 123, 6360 (2001)

9.4 T MQMAS

O1 O3 O2

O4 O3/2 O1

O1 O5 O7/8 O3/4 O2/6

Chem. Phys. Lett. 364, 634 (2002)

Humite minerals: structure

•  Four possible 1_{Harrangements within one unit cell}

•  Two 1_{H sites H1 and H2}

•  50% occupied by diffraction

•  Two nearby H1 cannot be occupied simultaneously

Humite minerals:

17

_{O calculations}

9.4 T MQMAS

Chondrodite

Clinohumite

Experiment Calculated sum Calculated mean

O4 O3/2 O1

O1 O5 O7/8 O3/4 O2/6

Humite minerals:

17

_{O calculations}

•  1H dynamics cause a change in the magnitude/orientation of 17O quadrupolar tensors

•  This will cause a change in the quadrupolar splitting for any one crystallite, ΔνJ

•  If the rate constant is comparable to ΔνJ _{this will cause motional broadening in}

experiments which utilise satellite transitions

•  Broadening (interference effects) in STMAS but fast averaging in MAS/MQMAS spectra

Humite minerals:

17

_{O calculations}

ΔνRMS _{= (Δν}J₎2 _sinβ

1 dβ1 dγ1

β1=0

π

∫

γ1=0 2π

∫

β1=0

π

∫

γ1=0 2π

∫

Powder averaged frequency jumps: Chondrodite

Clinohumite

Calculate motional broadening expected in STMAS spectrum

for each O resonance

Δν1/2

Humite minerals:

17

_{O calculations}

•  Good agreement when log₁₀(k / s–1_{) ~ 5.5}

•  Estimate rate constant for H1 - H2 interchange k ~ 3.2 × 105 _s–1

J. Phys. Chem. C 113, 465 (2009)

•  Can utilise CASTEP calculations (quadrupolar parameters/tensor orientations) to

calculate powder averaged ΔνJ _{and corresponding line broadening to simulate spectrum}

Humite minerals: summary (1)

•  17_{O NMR (experimental and first-principles calculations) suggests that there is dynamic}

(μs timescale) rather than static disorder of the 1_{H positions in the humite minerals}

•  Suggests exchange of the H1 and H2 species

2_{H NMR is the classic method for probing motion in the solid state}

Humite minerals:

2

_{H NMR}

2_{H NMR of brucite (9.4 T)} 2_{H NMR of clinohumite (9.4 T)}

Phys. Chem. Chem. Phys. 12, 2989 (2010)

Humite minerals:

2

_{H NMR}

2_{H NMR of brucite (9.4 T)} 2_{H NMR of clinohumite (9.4 T)}

CASTEP calculations

•  Differences in NMR parameters (in particular the quadrupolar coupling) are very small

•  Reorientation of tensor is ~180°

•  Only small changes to the broad static quadrupolar lineshape

Phys. Chem. Chem. Phys. 12, 2989 (2010) site δiso (ppm) CQ / kHz ηQ

H1 2.1 276.3 0.027

Humite minerals:

2

_{H MAS NMR}

2_{H MAS (14 kHz) NMR of clinohumite (9.4 T)}

clinohumite

brucite

EA = 40 kJ mol–1

Estimated rate constant k ~ 1.3 × 105 _s–1

(3.2 × 105 _s–1 _for 17_{O NMR)}

Phys. Chem. Chem. Phys. 12, 2989 (2010)

Humite minerals: substitution

•  In nature, humite minerals can have substantial amounts of F or Ti incorporated

•  By diffraction, only a single 1_{H species is}

observed in substituted humites

•  In F-humites hydrogen bonding in the ordered structure restricts 1_{H to the H1 site}

1 H species and 1 F species 2_{H MAS (12.5 kHz) NMR}

F-humite minerals:

19

_{F NMR}

19_{F MAS (30 kHz) NMR of F-clinohumite (14.1 T)}

F_A F_B F_C F_D

F_0.5(OD)_0.5 clinohumite F_1.0 clinohumite

F_A F_B F_C F_D

J. Am. Chem. Soc. 132, 15651 (2010)

F-humite minerals:

19

_{F calculations}

J. Am. Chem. Soc. 132, 15651 (2010)

site δisoexp <δisocalc,scaled>

F_A –166.4 –166.6

F_B –169.3 –169.2

FC –175.1 –174.4

Humite minerals:

19

_{F disorder}

Composition not exactly F_0.5(OD)_0.5?

Presence of OH-rich regions?

electron microprobe analysis shows composition to be F_0.54(OD)_0.46

dynamics in these regions?

100 °C

2_{H MAS (12.5 kHz) NMR} F_0.5(OD)_0.5 clinohumite (14.1 T)

25 °C

Humite minerals: summary (2)

•  For fluorinated humites:

Little motional broadening in 2_{H MAS NMR spectra} 19F MAS NMR indicates disorder and four F species

Preference for forming F…HO hydrogen bonds but not a strict rule Subsequent observation of motionally-broadened resonance in 2_{H MAS}

spectra at higher temperatures

•  Solid-state NMR is an excellent probe of local environment and disorder, and complex spectra can be interpreted with the aid of first-principles calculations

•  For humite minerals:

17_{O NMR suggests a dynamic not a static disorder of the} 1_{H positions, with}

exchange of the H1 and H2 species

MQMAS and STMAS confirm dynamics are on the μs timescale (k ~ 3.2 × 105 _s–1₎

Little information from wideline 2_{H NMR but motional broadening observed in} 2_H

Humite minerals in nature?

•  Is the disorder in the synthetic substituted minerals a kinetic effect?

Natural clinohumite (Tajikistan)

Mg8.805Fe0.01Ti0.2(Si3.94O16)O0.4F0.97(OH)0.63

19_{F MAS (30 kHz, 14.1 T)}

Acknowledgements

Mitchell _Daniel

Dawson Olivia Steward Valerie Seymour St Andrews Martin Mitchell Simon Reader John Griffin Andrew Miller

Karl Whittle, ANSTO Chris Pickard, UCL

Andrew Berry, Imperial College Stephen Wimperis, Glasgow

Dr John Griffin Scott Sneddon Martin Peel Lauren Jamieson Dr Sharon Ashbrook Martin

Mitchell _Daniel