Mössbauer Spectroscopy of
Geological Materials
Enver Murad
Marktredwitz, Germany
197Au
2%
121Sb
2%
119Sn
18 %
Others
5%
57Fe
64 %
Mössbauer publications: environmentally relevant isotopes
(total in June 2006: > 46 000)
MEDC 06/2006
100
Fe2+
Melanterite
FeSO4 7H2O
98
96
Transmittance (%)
94
92
90
100
Fe3+
Schwertmannite
Fe8O8(OH)6SO4
98
96
94
92
-5
-2.5
0
Velocity (mm/s)
2.5
5
Hematite @ 4.2 K
Transmission
Mössbauer
spectrum of
antiferromagnetic
hematite (red) with
a quadrupole
interaction of
+0.41 mm/s,
and simulated
hematite spectrum
(black, dotted)
fitted with the
same hyperfine
field but zero
quadrupole
interaction
[ 0.00mm/s ]
0.41 mm/s
-10
-5
0
Velocity (mm/s)
5
10
Kaolin / Jari @ 295 K
100
Transmission (%)
99.5
99
98.5
98
-7.5
-5
-2.5
0
2.5
5
7.5
Velocity (mm/s)
The inner doublet (green doublet) refers to pure kaolinite. The measured
spectrum shows considerable broadening due to paramagnetic relaxation.
Kaolin / Jari @ 4.2 K
Transmission (%)
100
99
98
97
-10
-5
0
5
10
Velocity (mm/s)
The Mössbauer spectrum at 4.2 K shows, in addition to the doublet of
pure kaolinite, a sextet arising from a paramagnetically relaxing
component. This sextet is not to be confused with that of magnetically
ordered hematite
Kaolin CMS KGa-1 @ 295 K
Transmission (%)
100
99.9
99.8
Fe3+
Fe2+
99.7
-5
0
Velocity (mm/s)
5
Kaolin “Wolfka” @ 4.2 K
100.0
Transmission (%)
99.8
99.6
.
99.4
100.0 -I
I
99.8
99.6 Goethite removed by
Na dithionite extraction
-10
-5
−0.11 %
goethite
0
Velocity (mm/s)
5
10
Kaolin / Jari
Mössbauer spectra (at 295 K)
as function of firing temperature
2.0
Kaolin / Jari @ 295 K
,  (mm/s)
1.5

1.0
0.5

0.0
0
200
400
600
800
Firing temperature (°C)
1000
1200
Fe3+ oxides, oxyhydroxides and hydroxide that occur in nature
Unit-Cell Dimensions (Å)
c
b
a
Structure
Space
Group
corundum
R3c
5.034
Fe3O4
inverse spinel
Fd3m
8.396
γ-Fe2O3
disordered spinel
Fd3m / or
P422
Composition
Mineral
Occurrence
Hematite
very common α-Fe2O3
Magnetite
common
Maghemite
common
Goethite
very common α-FeOOH
Diaspore
Pnma
Akaganéite
very rare
β-FeOOH
hollandite
I2/m
Lepidocrocite common
γ-FeOOH
boehmite
Feroxyhite
very rare
δ’-FeOOH
disordered CdI2
Ferrihydrite
common
Fe5HO8∙4H2O
disordered corundum
Bernalite
extremely
rare
Fe(OH)3
disordered ReO3
13.752
8.3474
8.347
25.01
9.956
3.0215
4.608
10.600
3.034
10.513
Bbmm
3.071
12.52
3.873
P3m1
2.93
4.56
2.955
9.37
Immm
7.544
7.560
7.558
Mössbauer characteristics of naturally-occurring Fe3+ oxides sensu lato
Mineral
TN, TC
MAG
Bhf
(K)
δ/Fe
Δ
Δ
Bhf
Room Temperature
4.2 K
Hematite
955
wfm
51.8
0.37
-0.20
53.5
or 54.2
-0.20
0.41
Magnetite
850
fim
49.2
46.1
0.26
0.67
50.6
36 – 52
0.00
1.18-(-0.79)
~ 950
fim
50.0
50.0
0.23
0.35
≤ | 0.02 |
≤ | 0.02 |
≤ | 0.02 |
≤ | 0.02 |
Goethite
400
afm
38.0
0.37
Akaganéite
299
afm
–
77
afm
Feroxyhite
450
Ferrihydrite
Bernalite
Maghemite
Lepidocrocite
52.0
53.0
≤ | 0.02 |
≤ | 0.02 |
-0.26
50.6
-0.25
0.38
0.37
0.55
0.95
47.3
47.8
48.9
-0.81
-0.24
-0.02
–
0.37
0.53
45.8
0.02
fim
41
0.37
-0.06
53
52
115
25
spm
–
–
0.35
0.35
0.62
0.78
50
47
427
wfm
41.5
0.38
≤ | 0.01 |
56.2
~ 0.0
~ 0.0
-0.07
-0.02
≤ | 0.01 |
Hematite and goethite: Al-for-Fe
substitution
Al3+
Fe3+
(r = 53.5 pm)
(r = 64.5 pm)
Hematite (Fe1-xAlx)2O3 0 ≤ x ≤ ~ 0.15
Goethite Fe1-xAlxOOH 0 ≤ x ≤ 0.33
100
Transmission (%)
95
90
85
80
-10
-5
0
Velocity (mm/s)
5
10
The effect of
Al substitution
is obvious in
the spectrum
of a hematite
with 0.43 %
substitution at
4.2 K, which
displays
coexisting
components
that have
(blue subspectrum)
and have not
(red subspectrum)
passed
through a
Morin
transition.
60
Bhf (T)
40
Goethite
20
-10
-5
0
5
10
Hematite
-10
0
0
200
-5
0
400
5
10
600
T (K)
The graph shows
the temperaturedependence of
the magnetic
hyperfine fields
of hematite (red)
and goethite
(black).
The vertical lines
correspond to 295
and 77 K and the
insets show
room-temperature
Mössbauer
spectra of a pure
goethite and a
pure hematite
800
1000
Transmission (%)
100
100
98
97
96
94
94
91
92
P (Bhf) (%)
-10
-5
a
0
5
10 -10
Velocity (mm/s)
-5
b
0
5
10
Velocity (mm/s)
40
40
20
20
0
0
20
25
30
35
40
20
25
30
35
40
Transmission (%)
100
100
99
99
98
98
97
96
97
95
P (Bhf) (%)
-10
-5
c
0
5
10 -10
Velocity (mm/s)
-5
d
0
5
10
Velocity (mm/s)
40
40
20
20
0
0
20
25
30
Bhf (T)
35
40
20
25
30
Bhf (T)
35
Mössbauer spectra
of goethite are
characterized by
asymmetric distributions of magnetic
hyperfine fields.
40
The graph shows
room-temperature
spectra and the
corresponding
hyperfine field
distributions of
goethites of mean
particle sizes in the
[111] direction of 97
nm (a), 55 nm (b),
19 nm (c), and 25 nm
(d). Sample a is a
natural fibrous
goethite and d was
synthesized in the
presence of Si.
Ferrihydrite, Fe5HO8·4H2O,
displays the following phenomena:
paramagnetism,
superparamagnetism,
blocking temperatures,
speromagnetism,
hyperfine field distributions,
recoil.
The following two slides show Mössbauer spectra and hyperfine
distributions of the two limiting ferrihydrite types, one exhibiting only
two X-ray diffraction peaks (“2-p” sample; particle size ~ 2 nm) and
the other exhibiting six X-ray diffraction peaks (“6-p”; particle size
~ 7 nm) recorded at room temperature and 4.2 K, respectively.
Ferrihydrite @ 295 K
30
100
6-p
99
20
10
97
0
30
100
20
99
2-p
10
98
0
-2
-1
0
Velocity (mm/s)
1
20
1
2
 (mm/s)
3
P () (%)
Transmission (%)
98
Ferrihydrite @ 4.2 K
20
100
6-p
Transmission (%)
96
12
94
8
92
4
90
0
20
100
16
99
2-p
98
12
8
97
96
4
95
0
-10
-5
0
Velocity (mm/s)
5
10 36
40
44
48
Bhf (T)
52
56
P (Bhf) (%)
16
98
A commercial iron
oxide catalyst
(“Nanocat ®”),
which consists of
isolated “FeOOH”
(more probably
ferrihydrite)
particles ~ 3 nm
in size shows
decreasing
absorption of
gamma radiation
and no Mössbauer
spectra at all
above 50 K
because of
particle recoil.
100
Transmission (%)
99.5 45 K
100
99
98
97
10 K
-12
-8
-4
0
Velocity (mm/s)
4
8
Adapted from
12 Ganguly et
al.,1994
Magnetite and Maghemite, Fe3O4
and -Fe2O3
display the following phenomena:
ferrimagnetism,
Verwey temperature,
non-stoichiometry.
100
Magnetite, Fe3O4
Fetet3+[Fe2+Fe3+]octO4
99
The spectrum measured at room
temperature can be separated into
two sextets. One sextet arises
from Fe3+ ions in tetrahedral sites,
the other from iron in octahedral
sites with fast electronic fluctuation
between Fe2+ and Fe3+ in
octahedral sites.
98
Transmission (%)
97
295 K
96
.
95
100
Below the Verwey transitions
(ca. 120 K), Mössbauer spectra
of magnetite are very complex
due to a variety of lattice sites
with different surroundings. The
spectrum taken at 4.2 K has been
deconvoluted into five sextets.
99
98
97
4.2 K
96
-10
-5
0
Velocity (mm/s)
5
10
100
Magnetite @ 160 K
Transmission (%)
97
Bext = 0
94
91
100
98
96
Bext = 6 T // 
94
92
-14
-7
0
Velocity (mm/s)
7
14
Magnetite @ 295 K
100
Mössbauer spectra (at 295 K)
as a function of aging time.
98
+ 6 months
Fe3+ [Fe3+1.28Fe2+0.570.14] O4
Transmission (%)
96
94
100
+ 99 months
Fe3+ [Fe3+1.39Fe2+0.410.20]O4
98
96
94
-10
-5
0
Velocity (mm/s)
5
10
With increasing ageing time, Fe2+ is
increasingly oxidized to Fe3+, as
shown by the relative increase of
the intensity of the Fe3+ sextet
(larger field) compared to that of
Fe“2.5 +” (red arrows).
Maghemite @ 295 K
Transmission (%)
100
The room temperature
spectrum can be
separated into two
magnetic sextets, one
(dotted line) arising from
Fe3+ in tetrahedral and
one (dashed line) from
Fe3+ ions in octahedral
sites.
99
98
97
96
Fe2O3 = Fe[Fe5/3□1/3]O4
-10
-5
0
Velocity (mm/s)
5
10
“Green rusts”, Fe2+-Fe3+-double
layered hydroxides (“DLHs”),
display the following phenomena:
temporal instability,
rapid oxidation, therefore
problematic identification in nature,
characteristic Mössbauer parameters.
“Green rust” (Fex2+Fe23+(OH)2x+4 CO3 (x-2)H2O)
@ 120 K
Relative Transmission (%)
100
96
92
88
84
-4
-3
-2
-1
0
Velocity (mm/s)
1
2
3
4
Natural green rust (“fougerite”)
J.-M.R. Génin
100
96
Oxidation of the Fe2+Fe3+
hydroxycarbonate green
rust shown in the
previous slide as a
function of reaction at
room temperature
(all spectra recorded at
120 K).
t=0
92
88
84
Transmission (%)
100
96
t = 20 min
92
88
84
100
t = 40 min
96
92
88
-4
-2
0
Velocity ( mm/s)
2
4
Complex natural systems
Room-temperature
Mössbauer spectra of
a “standard” bauxite
before (top) and after
(bottom) 3 treatments
with dithionite-citratebicarbonate (DCB) to
remove iron oxides
(in the present case
hematite).
100
Transmittance (%)
98
Bauxite BX-N
96
100
99
After 3 DCB
treatments
295 K
98
-10
-5
0
Velocity (mm/s)
5
10
These treatments
reduced the Fe2O3
contents of the
sample from 22.88 %
to 1.50 mass %.
The bottom spectrum
shows the remnant
hematite to be
identical to that which
was extracted.
100
98
Mössbauer spectra
of the clay fraction
(< 2 µm) of a red soil
from the northern
Alpine foreland taken
at the indicated
temperatures.
295 K
96
94
Transmission (%)
92
120 K
100
98
96
100
77 K
98
96
100
4.2 K
98
96
-10
-5
0
Velocity (mm/s)
5
10
The spectra show
the iron oxides
(hematite, αFe2O3,
outer sextet and
goethite, αFeOOH,
inner sextet)
contained in the soil
to order magnetically
over a broad range
of temperatures
as a result of
superparamagnetic
relaxation.