FeII-III (oxy)hydroxycarbonate
green rusts;
from ferri- to ferromagnetism
J.-M. R. Génin et al.
Institut Jean Barriol
Laboratoire de Chimie Physique et Microbiologie pour l'Environnement, UMR 7564 CNRS-
Université Henri Poincaré-Nancy 1,
Département Matériaux et Structures, ESSTIN,
405 rue de Vandoeuvre, F-54600 Villers-lès-Nancy, France.
E-Mail:genin@lcpme.cnrs-nancy.fr
“Gütlich, Bill, Trautwein: Mössbauer Spectroscopy and Transition Metal Chemistry@Springer-Verlag 2009”
FeII-III hydroxysalts green rusts, which are layered double hydroxides
(LDH), are constituted of [FeII(1-x) FeIIIx (OH)2 ]x+ layers and [(x/n)An- (mx/n)H2O]xinterlayers that can incorporate various anions such as Cl-, CO32-, SO42-, HCOO-,
C2O42-, SeO42- …
-6
0.25 < x < 0.33
D1 : FeII with no anion
first nearest neighbour
D2 : FeII with one anion
first nearest neighbour
GR1(Cl-)
96
x  0.33 D
1
37%
78 K
94
92
(a)
-4-4
-3 -2-2
100
99
Transmittance %
It is always found that
98
97
Transmittance %
x = FeIII / Fetotal is
obtained directly from
the spectrum (RA of D3)
D2
97
98
D2
32%
31%
-10 0
12 2
Velocity (mm s-1)
GR1(CO32-)
x = 0.33
78 K
96
95
(c)
94
-4
-3 -2
92
D3
34 4
D2
15%
D1
51%
D3
34%
-1
0
1 2
3
Velocity (mm s-1)
4
12%
GR1(CO32-)
x = 0.25
D3
78 K
87
Transmittance (%)
Transmission Mössbauer spectra
measured at 78 K of various Green
Rusts
Transmittance %
For Chloride
GR1(Cl-):
[FeII2FeIII(OH)6]+[Cl-2H2O]Sulphate
GR2(SO42-):
[FeII4FeIII2(OH)12]2+[SO42-8H2O]2Carbonate
GR1(CO32-):
[FeII4FeIII2(OH)12]2+[CO32-3H2O]2There exist two types of space groups as determined by XRD: GR1 [R(-3)m] and GR2 [P(-3)m1] that
depend on the shape of the anion. Mössbauer spectra display 2 ferrous doublets D1 & D2 (large D) and
1 ferric doublet D3 (small D). 100
D1
(b)
82
-46 -3
26%
62%
-2
-1
0
1 2
Velocity (mm s-1)
3
4
3
4
100
98
96
GR2(SO42-)
94
x = 0.33
78 K
92
90
88
(d)
-4 -3
D3
34%
D1
66%
-2 -1 0
1 2
Velocity (mm s-1)
GR1(Cl-)
OH2.5
Fen+
OH-
Cl2
c nm
1.5
OHFen+
OHCl-
OH1
0.5
Fen+
OHClOHFen+
0
OH-
GR1(CO32-)
B
c
A
OHFen+
OH-
a
B
c
A
O2- in ~ a
CO32C in b or c
OHA
n+
b
Fe
C
OH-
A
b
C
c
O2- in ~ c
CO32C in a or b
OHC
n+
a
Fe
B
OH-
C
a
B
b
CO32OH-
B
c
A
Fen+
OH-
O2- in ~ b
C in c or a
B
c
A
GR2(SO42-)
OH-
B
c
A
OH- 1 O2- in c
&
SO42- 23 O in ~ b
1 O2- in c
SO42&
2OH- 3 O in ~ a
B
c
Fen+
A
OH- 1 O2- in c
&
SO423 O2- in ~ b
1 O2- in c
2SO4
&
2OH- 3 O in ~ a
B
n+
c
Fe
A
OHFen+
Stacking sequence at scale
of the Fe cation layers
GR1 [R(-3)m] and
GR2 [P(-3)m1]
(a) Cl- anions and OH- layers
of GR1(Cl-).
(b) CO32- anion interlayers
and OH- layers along the
3-fold axis of GR1(CO32-)
(c) SO42- anion interlayers
and OH- layers along the
3-fold axis of GR2(SO42-);
A, B, C and a, b, c positions
represent the sites in the
hexagonal pavement of ions.
From the relative abundances of the doublets D1, D2 and D3 in the Mössbauer spectra, a long range order
of Fe cations is deduced as due to an order of anions in interlayers. The models are described in the next
figure.
For GR1(CO 2-): a = 0.317588(2) nm and c = 2.27123(3) nm
3
Cl-
FeII
FeIII
(a)
CO32-
FeII
FeIII
(b)
SO42-
FeII
FeIII
(c)
Projections perpendicular to the c axis of the structure of one interlayer, one layer, one interlayer and
3 adjacent interlayers to visualize a repeat for (a) GR1(Cl-), (b) GR1(CO32-) and (c) GR2(SO42-).
The in situ oxidation of the green rust was discovered by pouring H2O2 onto a GR sample, which
became orange. In the example of GR1(CO32-), [FeII4FeIII2(OH)12]2+[CO32-3H2O]2-, by injecting
progressively with a peristaltic pump H2O2 , one monitored the oxidation by Mössbauer spectra
and observed that the two ferrous doublets D1 and D2 transformed progressively into one new
ferric doublet D4 up to completion when it became the fully ferric oxyhydroxycarbonate GR*,
FeIII6O12H8CO3. Meanwhile, the morphology of the hexagonal crystals did not change (TEM) and
diffraction lines of the XRD patterns testified that the structure was essentially conserved. The
oxidation process is due to a deprotonation of OH- ions at the apices of the octahedrons
surrounding the Fe cations that leads to FeII6(1-x) FeIII6x O12 H2(7-3x) CO3.
10
30
40
(b)
10
20
30
Diffraction Angle (2q°)
H2O2
x=1
(c)
0.2 µm
Intensity (a. u)
110 113
012
018
015
20
(a)
Diffraction Angle (2q°)
H2O2
x = 0.50
(b)
0.2 µm
003
006
Intensity (a. u)
(a)
Intensity (a. u)
GR(CO32-)
x = 0.33
40
0.5 µm
(c)
10
20
30
Diffraction Angle (2q°)
40
The in situ oxidation of green rusts by deprotonation
Use a strong oxidant such as H2O2, Dry the green rust and oxide in the air,
Violent air oxidation, Oxide in a basic medium…
0.1
d
b
0.0
-0.1
a
-0.2
0.2
0.4
0.6
0.8
1.0
1.2
{2 × [n(H2O2) / n(Fetotal)] + (1/3)}
96
95
78 K
94
-4
-3
-2
-1 0 1 2
Velocity (mm s-1)
x = 0.33
Transmittance %
92
x ~ 0.63
88
84
-4
(c)
78 K
-3
-2
-1 0 1 2
Velocity (mm s-1)
D4
x ~ 0.63
31 %
D3
3
D1
28 %
(c)
32 %
D2
9%
78 K
-1
0
1
2
100
3
Quadrupole splitting D (mm s-1)
(a)
0
4
D1
D2
17 %
1
2
Quadrupole splitting D (mm s-1)
x ~ 0.78
92
88
-4
(d)
78 K
-3
-2
-1 0 1 2 3
Velocity (mm s-1)
x ~ 0.78
D3
D4
4
(d)
43 %
D1 + D2
35 %
22 %
78 K
-1
0
1
2
3
Quadrupole splitting D (mm s-1)
88
x ~ 0.50
(b)
78 K
-3
-2
-1 0 1 2 3
Velocity (mm s-1)
D3
38 %
D4
16.5 %
78 K
4
D1
(b)
33 %
x ~ 0.50
3
96
84
4
D3
78 K
3
92
84
-4
50 %
33 %
1.4
Probability density (p)
Transmittance %
Probability density (p)
96
D3
(a)
-1
100
Transmittance %
c
x = 0.33
D1
Probability density (p)
0.2
97
D2
12.5 %
-1
0
1
2
3
Quadrupole splitting D (mm s-1)
Transmittance %
e
100
98
x=1
96
(e)
78 K
94
Probability density (p)
Transmittance %
0.3
Probability density (p)
Eh(V)
FeII-III oxyhydroxycarbonate FeII6(1-x) FeIII6x O12 H2(7-3x) CO3
100
100
0<x<1
99
96
H
with
H2O2
2 O2
D2
98
-4
-2
0
2
Velocity (mm s-1)
4
D4
x=1
67 %
(e)
D3
33 %
78 K
-1
0
1
2
Quadrupole splitting D (mm s-1)
“Gütlich, Bill, Trautwein: Mössbauer Spectroscopy and Transition Metal Chemistry@Springer-Verlag 2009”
3
The magnetic properties of ferric oxyhydroxycarbonate GR* and FeII-III hydroxycarbonate GR are
quite different. GR* is ferromagnetic with ordering around 70 K whereas GR at x = 1/3 is
ferrimagnetic with ordering at 5.2 and 7 K for the FeII and FeIII sublattices, respectively.
Components
d (mm s-1) D or e (mm s-1) H (kOe) qb (°) h gb (°) G/2 (mm s-1)
FeII octet (61%)
1.28
2.91
130 ~87 0.1 ~30
0.20-0.38
FeIII sextet (39%) 0.49
0.2
~545 a
0.18
3.5
FeII octet (51%)
1.31
-2.95
121
~87 0.15
0.3-0.4
FeII doublet (9%) 1.31
-2.95
0.25
FeIII sextet (38%) 0.46
-0.21
~510a
0.18
FeIII doublet (2%) 0.46
0.45 0.25
4.2
FeII octet (44%)
1.31
-3.00
110
~84 0.2 ~95
0.3
FeII doublet (17%) 1.31
-3.00
0.25
FeIII sextet (35%) 0.46
-0.3
~500a
FeIII doublet (4%) 0.46
0.45
0.25
5.5
FeII octet (28%)
1.28
2.92
100
0.3-0.4
FeII doublet (34%) 1.28
2.92
0.25
FeIII sextet (29%) 0.46
0.2
~500 a
0.18
FeIII doublet (9%) 0.46
0.45
0.25
12
FeII doublet (64%) 1.28
-2.86
0.19
FeIII doublet (36%) 0.49
0.42
0.17
12c
FeII doublet (49%) 1.29
-2.91
0.17
FeII doublet (19%) 1.29
-2.57
0.17
FeIII doublet (32%) 0.50
0.40
0.17
d: isomer shift with respect to metallic Fe measured at room temperature; D: quadrupole splitting in paramagnetic
state or e: quadrupole shift; H: hyperfine magnetic field; q: angle between the electric field gradient (EFG) axis of
symmetry with hyperfine field H; h: asymmetry parameter and g: angle between one principle axis of EFG and H ;
G/2: half line width at half maximum.
a Hyperfine field distribution maximum value.b Approximately computed value.c Better resolution in 4 mms-1
velocity range from Ref. [10].
Temp. (K)
1.4
When x increases from 0 to 1, three cation sublattices are
progressively filled with FeIII ions replacing FeII. For each
x value, a FeIII cation is surrounded by the minimal number
of other FeIII because of repulsion. This is obtained by long
range order of periodicity a = a03.
100
Doublet fraction (%)
Table of the spectra of the next slide: Mössbauer parameters of stoichiometric
FeII-III hydroxycarbonate FeII4FeIII2 (OH)12CO3 measured at low temperatures
to determine the magnetic ordering.
80
60
40
FeII doublet
FeIII doublet
20
0
0 1 2 3 (K)
4 55 6 7 8 9 10 11 12 13
Temperature
Temperature variations of the proportions of
quadrupole doublets for FeII and FeIII components
within the Mössbauer spectra of GR(CO32-)
1st
2nd
3rd
sublattice
B. Rusch, J.-M. R. Génin, C. Ruby, M. Abdelmoula and P. Bonville, Ferrimagnetic properties in Fe II-III (oxy)hydroxycarbonate green rusts, Solid State Sci. 10 (2008) 40-49.
FeII4 FeIII2 (OH)12 CO3 ferrimagnetism
(a)
1.4 K
99
H = 130 kOe
D = -3 mm s-1
95
100
98
(a)
16 K
-10
(b)
3.5 K
-5
0
5
1
Velocity (mm s-1) 0
Probabability density (au)
100
100
100
S1
S3
34%
51%
S2
(b)
15%
16 K
200 300 400 500 600
Hyperfine Magnetic Field H (kOe)
100
99
95
100
99
98
97
98
(c)
4.2K
96
(c)
97
50 K
95
-10
100
(d)
5.5 K
95
100
94
(e)
12 K
0.8
78 K
-5 Velocity0(mm s-1)5
0.2
2
D1
D3
0.4
(e)
(f)
67%
33%
78 K
0.0
-2
-1
0
1
Velocity (mm s-1)
-10
60 K
-1
0
1
Velocity (mm s-1)
0.6
100
95
-2
1.0
98
x = 0.33
(d)
95
94
-5
0
5
10
Velocity (mm s-1)
96
•
0.014
0.012
0.010
0.008
0.006
0.004
0.002
0.000
Probability density (au)
Transmission (%)
FeIII6 O12 H8 CO3 ferromagnetism
10
Evolution of Mössbauer spectra with measurement
temperature displaying the ferrimagnetic behaviour of
stoichiometric GR(CO32-) between 1.4 and 12 K.
2
-1
0
1
2
3
Quadrupole Splitting D (mm s-1)
Mössbauer spectra of GR(CO32-) sample oxidised violently by H2O2
and named ferric [GR(CO32-)*]1. Measurement temperatures are (a)
16 K, (c) 50 K, (d) 60 K and (e) 78 K. (b) and (f) are the hyperfine field
distribution of (a) and quadrupole splitting distribution of (e) using
a Voigt profile analysis, respectively.
“Gütlich, Bill, Trautwein: Mössbauer Spectroscopy and Transition Metal Chemistry@Springer-Verlag 2009”
FeII-III oxyhydroxycarbonate
(a) x = 0
(b) x = 0.33
Upper
layer
Lower
layer
H2O
OHO2(c) x = 0.67
(d) x = 1
FeII6(1-x) FeIII6x O12 H2(7-3x) CO3
FeII
{
1st sublattice
FeII(CO32-)
FeII(H2O)
FeIII
{
1st sublattice
2nd sublattice
3rd sublattice
Projections perpendicular to the c axis of a Fe layer with octahedrons of OH- ions that can
be deprotonated or protonated for values of x = 0, 0.33, 0.67 and 1. There exist four ordered
types of domain to match any intermediate composition as determined by x.
x=0
x = 0.33
b
0.33 < x < 0.67
H
Ferri
a
FeII
(a)
(b)
FeIII
FeII
0.67 < x < 1
x = 0.67
FeIII
FeII
x=1
Ferro
Ferri
FeIII
FeII
(d)
(c)
FeIII
FeII
(e)
FeIII
(f)
Hexagonal pavements of FeII and FeIII cations in the layers of (a) Fe(OH)2, (b) stoichiometric
GR(CO32-) at x = 1/3, (c) GR(CO32-)* with 1/3 < x < 2/3, (d) GR(CO32-)* at x = 2/3, (e) GR(CO32-)* with
2/3 < x < 1 and (f) fully ferric GR(CO32-)* at x = 1. Long range order is displayed showing magnetic
domains.