Chemistry Reference
In-Depth Information
Table 3.8
RT hyperfine parameters of FeS
2
and related minerals
Mineral
Formula
d
Fe
(mm/s)
D (mm/s)
Pyrite
FeS
2
0.31
0.61
Marcasite
FeS
2
0.27
0.50
Marcasite (Se)
FeSe
2
0.40
0.58
Marcasite (Te)
FeTe
2
0.47
0.50
Löllingite (Sb)
FeSb
2
0.45
1.28
Löllingite (As)
FeAs
2
0.31
1.68
Mispickel
FeAsS
0.26
2.10
Table 3.9
Representative hyperfine parameters at RT of various sulfides
Mineral
Formula Fe
1 - x
S
B (T)
2e or D (mm/s)
d
Fe
(mm/s)
Triolite
FeS
30-32
-0.3
0.7-0.9
Intermediate
pyrrhotite
Fe
11
S
12
;Fe
10
S
11
Fe
9
S
10
(x = 0.83; 0.091; 0.100)
22.0-23.5
0.05
0.55
25.5-26.5
0.05
0.55
27.5-31.5
0.10
0.55
Pyrrhotite
monoclinic
Fe
7
S
8
(x = 0.125)
22.9
0.08
0.77
26.7
0.03
0.79
31.1
0.15
0.79
34.5
-0.09
0.81
Smythite
Fe
9
S
11
(x = 0.182)
22.4
0.33
0.58
25.9
0.04
0.58
30.3
0.17
0.47
Greigite
Fe
3
S
4
(x = 0.250)
31.3
0.0
0.17
31.3
-0.08
0.42
Mackinawite
Fe
1.01
S - Fe
1.07
S
(0.02)
(0)
Pentlandite
Fe
9
S
8
0.36
0.30-0.37
0.60-0.68
0
(x = 0.100), These intermediate pyrrhotites all have a hexagonal structure based
on NiAs exhibiting different kinds of ordering of the vacancies [
110
,
141
,
142
].
Concerning the magnetic properties the compounds close to FeS still exhibit an
antiferromagnetic behavior, but from x = 0.08 on the presence of ferrimagnetism
has been observed. It has been shown that from about that composition on, these
sulfides undergo a 90 spin-flip resulting in a antiferro-ferrimagnetic transition,
comparable to the transition in hematite [
143
,
144
]. The Mössbauer spectra are
usually complex and mainly consist of three to four overlapping sextets with
subsequent hyperfine fields within ranges 22.0-23.5, 25.5-26.5 and 27.5-31.5 T
which can be attributed to the various sites in the ordered structure [
145
,
146
].
Pyrrhotite Fe
7
S
8
(x = 0.125) is normally monoclinic and exhibits a ferrimag-
netic behavior. The Mössbauer spectrum consists apparently of three overlapping
sextets at RT, but at 80 K four sextets could be well resolved (see Table
3.9
)with
intensity ratio 2:1:2:2 according to the occupation in the structural model of
Bertaut [
139
]. Similar hyperfine parameter values are obtained for a synthetic and
a natural sample by Jeandey et al. [
147
].
