Complex Functional Oxides Prepared
by Mild Hydrothermal Synthesis
Richard Walton
Department of Chemistry, University of Warwick, UK
Functional Inorganic Materials: Strategy
SYNTHESIS
New Reaction Conditions
temperature - pressure
solution formation
control of crystallisation
STRUCTURAL
CHARACTERISATION
Atomic-Scale Structures
long-range: crystallography
short-range: spectroscopy
PROPERTY
MEASUREMENT
Bulk Properties
redox / catalysis
mechanical
sorption & separation
Inorganic Materials at Warwick
Complex
Oxides
Metal Organic
Frameworks
Nanoporous
Materials
X-ray Diffraction at Warwick
Suite of 7 diffractometers
• Siemens D5000 with MRI heating stage (1000 oC)
• Bruker D8 with Anton-Parr chemical reaction chamber (10 bar)
• Siemens D5005 with Phoenix cryostage (5 K)
• Panalytical Expert Pro MRD for high resolution data
• Oxford Diffraction CCD (Single crystal)
• Panalytical Expert Pro MRD for reflectivity
• Panalytical Expert Pro MRD for high resolution / high temperature
New Chemistry-Physics Research Building (£24M)
Open October 2011
Central Facilities for Advanced Characterisation
Diamond Light Source
X-ray diffraction
X-ray spectroscopy
ISIS Neutron Source
neutron diffraction
ESRF
X-ray diffraction
X-ray spectroscopy
ILL Reactor
neutron diffraction
Transition-Metal Oxides: Synthesis
Conventional Synthetic Approach
High-temperature > 1000 oC, (+ pressure)
Solid-Solid Reactions: Interparticle Diffusion
Thermodynamically Stable Products Formed
BaO
BaTiO3
TiO2
Transition-Metal Oxides by Chimie Douce
Sol-Gel / Co-Precipitation Synthesis
(1) Amorphous precursor
(2) Firing to induce crystallinity (< 1000 oC)
Topochemical Modification
(1) Preparation of crystalline precursors (high temperature synthesis)
(2) Ion-exchange / reduction / oxidation
Molten Flux Synthesis
(1) Molten hydroxides as reaction media (~ 500 oC)
(2) Washing to remove excess hydroxide
Solvothermal Reaction Vessels
Teflon-lined Parr type (25 ml)
(T < 240 oC)
With increasing T:
viscosity of water is lowered
dielectric constant decreases
Inconnel Multicell Reactor (5 x 40 ml)
(T < 500 oC P < 300 bar)
Solubilisation, transport, and reaction of
otherwise un-reactive materials
P-T Curves for Sealed Vessels (Pure Water)
90 % fill
10000
80 % fill
9000
8000
70 % fill
Pressure / bar
7000
6000
5000
60 % fill
4000
50 % fill
3000
40 % fill
30 % fill
2000
1000
20 % fill
10 % fill
0
0
100 200 300 400 500 600 700 800 900 1000
o
Temperature / C
C.W. Burnham, J.R.Holloway, N.F. Davis, Geol. Soc, Am. Spec. Paper 132, 96 (1969)
Transition-Metal Oxides: Solvothermal Synthesis
BaTiO3
TiO2(s)+ Ba(OH)2 • 8H2O(aq) BaTiO3(s)
• 80 - 250 oC in water, sealed autoclave
• rapid reaction: minutes - hours
• small particle size: nanoscale - submicron
• deposition of films
• tetragonal polymorph in small crystallites
ABO3
perovskite
R. E. Riman, W. L. Suchanek,
and M.M. Lencka, Annales de
Chimie, 27 (2002) 15
Solvothermal Synthesis of BaTiO3
Ba(OH)2 + TiO2 T > 80 oC
Nanospheres
Clark et al. J. Mater. Chem. 9 (1999) 83
Nanotube Arrays
Yang et al. Nanotech. 20 (2009) 055709
Plates
Feng et al. Chem. Mater., 13 (2001) 290
Continuous Films
on Polymer Support
Hou et al. Chem. Mater., 21 (2009) 1214
Dendritic morphology
Maxim et al. Cryst. Growth Des., 8 (2008) 3309
Hydrothermal Synthesis of NaNbO3
ilmenite NaNbO3
< 1 M NaOH (aq)
NaNbO3
T > 200
oC
Nb 2O5
> 1 M NaOH (aq)
T > 150
oC
perovskite NaNbO3
NaNbO3
(Pbcm polymorph)
Structural Characterisation of Ilmenite NaNbO3
0.12
Diffracted Intensity (arbitrary units)
0.11
Observed
Calculated
Difference
0.10
0.09
0.08
0.07
4 µm
0.06
0.05
0.04
0.03
0.02
0.01
0.00
-0.01
4
6
8
10
12
14
16
Total Time of Flight (ms)
powder neutron structure refinement
(GEM, ISIS)
23Na
solid-state NMR
one single octahedral Na site
D.R. Modeshia, R.J. Darton, S.E. Ashbrook and R.I. Walton, Chem. Commun. (2009) 68
Collapse of Ilmenite NaNbO3 to Perovskite
o
Temperature ( C)
in situ laboratory thermodiffractometry: Bruker D8 with VÅNTEC detector
1000
950
900
850
800
750
700
650
600
550
500
450
400
350
300
250
200
150
100
P
111
200
Al2O3
I
006
115
I
110
Al2O3
I
113
11-3
P
201
Al2O3
I I
021 202
P
207
400
I
107
I
024
I
116
205
31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
Diffraction angle (2θ)
orthorhombic perovskite formed at ~ 500 oC: irreversible transition
In Situ X-ray Diffraction of NaNbO3 Crystallisation
Energy-Dispersive X-ray Diffraction
solid-state
detector
‘white’
X-ray beam
2θ
z
y
sample
x
diffraction
lozenge
'white' X-ray beam
using synchrotron radiation:
Daresbury SRS, UK Station 16.4
HASYLAB, Germany Beamline F3
In Situ X-ray Diffraction of NaNbO3 Crystallisation
Ed sin θ = ½ hc
⇒
E keV = 6.199
d Å sinθ
In situ EDXRD of NaNbO3 Crystallisation
1 g Nb2O5 + 8 mL 1 M NaOH (aq) 240 oC
Station 16.4, Daresbury SRS
In situ EDXRD of NaNbO3 Crystallisation
1 g Nb2O5 + 8 mL 1 M NaOH (aq) 240 oC
Station 16.4, Daresbury SRS
Nb2O5
In situ EDXRD of NaNbO3 Crystallisation
1 g Nb2O5 + 8 mL 1 M NaOH (aq) 240 oC
Station 16.4, Daresbury SRS
Na7(H3O)Nb6O19.14H2O
In situ EDXRD of NaNbO3 Crystallisation
1 g Nb2O5 + 8 mL 1 M NaOH (aq) 240 oC
Station 16.4, Daresbury SRS
Na2Nb2O6.2H2O
In situ EDXRD of NaNbO3 Crystallisation
1 g Nb2O5 + 8 mL 1 M NaOH (aq) 240 oC
NaNbO3 ilmenite
NaNbO3 Hydrothermal Crystallisation
Rapid Dissolution of Nb2O5 in NaOH at 240 oC
Na7(H3O)Nb6O19.14H2O
"Lindqvist Ion"
Na2Nb2O6.2H2O
Sandia Octahedral Molecular Seive
low pH
high pH
un-identified phase
perovskite NaNbO3
long reaction time
ilmenite NaNbO3
Manganite Perovskites
AMnIIIO3
A1-xA’xMn(3+x)O3
A = La, Pr, Nd etc.
LaMnIIIO
3:
Distorted Perovskite
A’MnIVO3
A’ = Ca, Sr, Ba
BaMnIVO3: ‘2H Perovskite’
Hydrothermal Synthesis of Manganites
Ln1-xAxMn(3+x)O3
x = 0.5 (‘half doped’ phase): Mn3.5
Hydrothermal Reaction
KMnO4/MnCl2/A(OH)2/Ln(NO3)3/KOH/H2O
240 oC, 25 mL Parr-type autoclave, 24 hours
3 MnO4- : 7 Mn2+ ⇒ average Mn oxidation 3.5
Solid-State Reaction
Ln2O3 + ACO3 + Mn2O3
• T > 1200 oC with controlled O2 partial pressure
• repeated cycles of heating and grinding
• reaction time: days - weeks
Manganite Perovskites: Crystallisation Model
3KMnO4 + 7MnCl2 + 5Ba(OH)2 + 5La(NO3)3 + KOH + H2O
'K0.5MnO2.nH2O'
La0.5Ba0.5MnO3
(1) precipitation
of layered
birnessite-type
intermediate
Mn3.5+
(2) dissolution
(3) crystallisation
of perovskite
edge-shared
{MnO6}
J. Spooren, R.I. Walton, F. Millange, J. Mater. Chem. 15 (2005) 1542
corner-shared
{MnO6}
Cerium Oxides by Hydrothermal Synthesis
(Na0.33CeIV0.67)2TiIV2O7
A2B2O7 pyrochlore
TiF3
H2O2
NaCeIIITiIV2-xVIVxO6
ABO3 perovskite
TiF3 / VCl3
T > 100 oC
CeCl3.7H2O
NaOH
H2O
NaBiO3
240 oC
CeIV1-xBiIIIxO2-x/2
AO2 fluorite
T > 200 oC
VCl3 / H2O2
T > 200 oC
ZrOCl2.8H2O
H2O2
T > 200 oC
Na0.1CeIV0.9-xZrIVxO1.85
AO2 fluorite
CeIIIVVO4
ABO4 zircon
Hydrothermal Synthesis of NaCeIIITiIV2O6
Intensity
CeCl3 .7H2 O + 2.5TiF3 + NaOH + H2 O >100 oC
40
10
20
30
40
50
50
60
60
70
70
80
90
80
100
90
100
o
Diffraction Angle / 2 θ
Pnma, a = 5.45077(18) Å, b = 7.72797(16) Å, c =5.45596(14) Å
C.S. Wright, R.I. Walton, D. Thompsett, J. Fisher, Inorg. Chem. 43 (2004) 2189.
Solvothermal Synthesis of NaCeIIITiIV2O6
Intensity
CeCl3 .7H2O + 2.5TiF3 + NaOH + 1,4-butanediol >100 oC
10
20
30
40
50
60
70
o
Diffraction Angle / 2θ
Scherrer Analysis: 30 nm crystallites
BET surface area: ~20 m2g-1
80
90
100
Hydrogen Uptake (arbitrary units)
(Na1/3CeIV2/3)2TiIV2O7 : A Novel Redox-Active Solid
Temperature
Programmed
Reduction
TPR 3
mild
oxidation
TPR 2
mild
oxidation
TPR 1
100
Material
200
300
400
500
Reduction
CeO2
500 oC
CeO2/Rh
150 - 200 oC
Ce1-xZrxO2
200 − 350 oC
(Na1/3Ce2/3)2Ti2O7 100 – 200 oC
600
700
o
Temperature / C
D. Thompsett, J. Fisher C.S. Wright, R.I. Walton, International Patent WO2006/030179, 23/3/2006
Cerium Titanate Pyrochlore: Ce LIII-edge XANES
Ce(III)
4.0
Normalised Absorption
3.5
CeCl3.7H2O
3.0
2.5
NaCeTi2O6
Ce(IV)
2.0
(Na1/3Ce2/3)2Ti2O7
CeO2
1.5
1.0
0.5
0.0
5705
5710
5715
5720
5725
5730
Energy /eV
Station 7.1 Daresbury SRS and BM26A ESRF
5735
5740
5745
5750
In situ XANES of Cerium Titanate Pyrochlore
Station 7.1. Daresbury SRS
10 minutes per spectrum
120
TPR2
100
TPR under 10 % H2 in N2:
large and reversible reduction
80
TPR1
60
40
20
0
100
200
300
400
o
Temperature / C
XRD under 5 % H2 in N2:
phase separation to Bi metal
500
Intensity/arbitrary units
Hydrogen Uptake / arbitrary units
Redox Properties of Bismuth-Doped Ceria
(b)
Metallic Bi
o
30 C
o
200 C
o
400 C
o
400 C
o
200 C
o
30 C
40
30
50
o
Diffraction Angle / 2θ
K. Sardar, H.Y. Playford et al. Chem. Mater., 22, 6191 (2010).
60
Alkali-Earth Iridium Oxides and Hydroxides
Sr2Ir(OH)8
‘Synthesis Map’
Na0.27Sr0.73IrO3.77
KSbO3-type structure
195 oC
9-14 days
BaIr(OH)6.H2O
H2O2
HF
240oC
48 h
IrCl3.5H2O
M(NO3)2.nH2O
NaOH(aq)
80 oC
9 days
Na2O2 or H2O2
Ca2IrF(OH)6.OH
NaF
240 oC
6 days
240 oC/ 96 h
Sardar et al. Chem. Sci. (2011)
(Na0.27Ca0.58)2Ir2O6.nH2O
pyrochlore-type structure
Current Challenges
1. Exploratory Synthesis
of New Materials
Novel combination of metals
Control of metal oxidation state
Oxides – sulfides – nitrides
2. Control of Crystal Size, Shape and Form for Applications
Nanoscale – microscale
Hierarchical order / Porosity
3. Scalability of Synthesis
Lab-scale (< 5g) – large scale (cf. zeolite synthesis)
Batch reactors or continuous flow?
Films and coatings