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Electron microscope observations of the defect structure of pyrrhotite
Mat. Res. Bull. Vol. 7, pp. 71-80, 1972. the United States.
ELECTRON MICROSCOPE
Pergamon P r e s s , Inc.
OBSERVATIONS
OF THE DEFECT
Printed in
STRUCTURE
OF PYRRHOTITE::
J . V a n L a n d u y t and S . A m e l i n c k x xx RUCA-Antwerpen, Belgium
(Received November 1, 1971; Communicated by S. Ameltnckx)
ABSTRACT The d e f e c t s t r u c t u r e of the m o n o c l i n i c (4C) p y r r h o t i t e phase is analysed. The d e s c r i p t i o n of the s t r u c t u r e w i t h r e s p e c t to the nickel a r s e n i d e structure allows to p r e d i c t a v a r i e t y of d e f e c t s such as a n t i - p h a s e boundaries, stacking faults and twin b o u n d a r i e s assoc i a t e d w i t h the o r d e r i n g of vacancies. E l e c t r o n m i c r o s c o p y o b s e r v a t i o n s on n a t u r a l p y r r h o t i t e c r y s t a l s are shown. They c o n f i r m the p r e d i c t i o n s from the s t r u c t u r e model.
Introduction In r e c e n t years covers
All of these
structures
cancies;
charge
to b e c o m e
compounds
that the name p y r r h o t i t e
w h i c h have the c o m p o s i t i o n
have
so called
"defective"
(Fig.l).
The n o n - s t o i c h i o m e t r y
is c a u s e d by the p r e s e n c e
compensation
trivalent
t h e n requires
for every vacancy.
m e a n s of X-ray d i f f r a c t i o n
of iron va-
two d i v a l e n t
Berthaut
that the v a c a n c i e s
also shown that the a r r a n g e m e n t Coulomb
clear
in fact a n u m b e r of structures
Fen_iSn[l]. NiAs
it has b e c o m e
iron ions
[2] has shown by
are ordered.
found in this way m i n i m i z e s
He has the
energy.
::Work p e r f o r m e d under the a u s p i c e s of the a s s o c i a t i o n XgAlso at S . C . K . - C . E . N . , Mol (Belgium) 71
RUCA-SCK
72
D E F E C T STRUCTURE OF PYRRHOTITE
In view of the possible
Vol. 7, No. 1
interaction between lattice defects
and magnetic defects and also because of the potential use of pyrrho£ite as a geological while to examine tron microscopy.
thermometer,
its defect structure
it was considered worth-
in detail by means of elec-
We present here some preliminary results.
Defect structures due to ordering of vacancies have been studied previously
for instance in ~-In2S 3 [3] and in VC The structure of pyrrhotite
The NiAs structure
is hexagonal;
[4].
(Fe7S8)
it is shown in ~ig.l;
can be considered as a stacking of close-packed
it
layers parallel
to the c-plane described by means of the letter sequence aBayaBay...
The latin letters represent cations,
whereas the
greek letters represent anions. Since Fe7S 8 is the only compound for which the structure has been determined
in detail the discussion will be limited to this case.
In Fe7S 8 th sulfur lattice is complete, of iron ions are full and defective. tain vacancies defective
but alternating
layers
The defective
layers con-
according to the pattern of Fig.2,b.
Successive
layers are shifted one with respect to the next in such
a way that an arbitrary chosen origin in the defective planes
~
a -
a
A
o,~01S
C
• FIG.I The NiAs structure of FeS
Fe
Vol. 7, No. 1
D E F E C T S T R U C T U R E OF PYRRHOTITE
73 m
s _
_
0
0
•
0
•
Fe
--S ]~'-
_ _
Fe+vae S _Fe S sFe+vac
!II . . . . . . . . . . .
Q
•
•
o
• , 0~[
•
~
•
~[~
R.~W. ~ //~ ~ •
11.0
•
H
•
m
., ',,~
•
C:4c
(c) s
11 _ _
I
Fe+vac S
• S I
.
.
.
.
.
.
.
.
.
.
Fe .vac
s
•
~
O
•
•
proj~ctlon of C-axis
(a)
(d)
(b) FIG.2
(a)Schematic r e p r e s e n t a t i o n of the p y r r h o t i t e s t r u c t u r e . A l t e r n a t i n g layers of Fe are full or d e f e c t i v e (Fe+vac.). (b)The o r d e r i n g of v a c a n c i e s (open circles) in an F e - l a y e r of p y r r h o t i t e F e 7 S 8. The p o s i t i o n s of s u c c e s s i v e layers are i n d i c a t e d by I, II, III and IV. The unit cell is o u t l i n e d by m e a n s of a d o u b l e line. The p r o j e c t i o n of the c-axis is i n d i c a t e d for the stacking sequence I, II, III, IV (or the e q u i v a l e n t I, II, III, IV'). (c)The sense of the p r o j e c t i o n of the c-axis d e p e n d s on the sense in w h i c h the lozenge I, II, III, IV' is described. (d)The six p o s s i b l e o r i e n t a t i o n s for the p r o j e c t i o n of the c-axis (and t h e r e f o r e also for the structure). occupies
successively
alternatively
I, II,
the p o s i t i o n s III and IV'
are in fact c r y s t a l l o g r a p h i c a l l y in the c - d i r e c t i o n NiAs;
now b e c o m e s
also the lattice
(~ = 89,63°); Fig.2(c).
the p r o j e c t i o n
Within
stacking
sequence
II; this
changes
projection
the same
since
III,
equivalent.
four times
The d e f e c t On p u r e l y
sulfur III,
lattice IV into
than that of
(c')
is indicated
one can change its r e v e r s e
in
the
I, IV',
of the c-axis.
III
The
is shown by m e a n s
in Fig.2,b. structure
geometrical
: two d i m e n s i o n a l
grounds
on cooling.
interfaces
one can p r e d i c t
of a number of i n t e r f a c e s
of v a c a n c i e s
IV and IV'
in fact s l i g h t l y m o n o c l i n i c
the sense of the p r o j e c t i o n
line
Fig.2,b or
The r e p e a t d i s t a n c e
larger
of the c-axis
from I, II,
IV of
the p o s i t i o n s
of the unit cell on the basal plane
of the d o u b l e
occurrence
becomes
I, II,
the p o s s i b l e
as a r e s u l t of the o r d e r i n g
74
DEFECT
Assuming
STRUCTURE
OF PYRRHOTITE
the lattice of sulphur
build the pyrrhotite
structure
Vol. 7, No. I
ions to be continuous
in a number of different
ding to a large number of possible
interfaces
i) Assuming
layers
the full and defective
in the whole crystal, the same,
different
and assuming
parallel marked
leads to the possible
occurrence
vectors
(b) are related
different
vector
lea-
types.
to be
are possible,
correspon-
I, II, III and IV in Fig.2,a. of antiphase
boundaries
schematically
situations
by a rotation.
with displacement
of different
the layer sequence
RI' R2 and R3 as shown
Only two essentially
ways
to be at the same level
orientations
ding to the positions
placement
one can
occur,
Presumably
R3 have the smallest
with dis-
in Fig.3.
since
antiphase
This
(a) and
boundaries
energy and are t h e r e
for preferred.
/ •
• 0
,
• .
•
• 0
•
•
o
o • (a)
•
• •
•
0/0
• •
o/%
•
o/o~I o/o
o/o
o •
• •
o
o/ / O
o
•
(b)•
•
0/•
o
o
•
o/•
•
O/O
•
/
Y
•
0
• o
O
•
• @
•
o
o
•
@~ • 0/0
•
o
•
•
• O
•
O/O /
•
• 0
• •
0
• O
o •
•
• •
0
O
•
•
O
o/o oi.
O O
/APB O/O •
• •
O
•
•
o •
O
•
• •
•
•
o •
O
•
/ O
• •
O
•
•
O
•
O
o
•
O •
O
O •
•
•
o/ /
/
o/ o/
o/
•
,
0 •
•
•
O
•
•
•
•
•
O •
•
•
•
•
• •
•
0 / ~
o
• 0
o/0
o/O o,o
O
•
•
•
•
•
(c) o
•
O
•
•
O
•
•
•
FIG.3 Possible antiphase boundaries : only two are essentially different e.G.(a) and (c); (a) and (b) are more conservative; (c) is conservative.
Vol. 7, No. 1 i i) Also
D E F E C T S T R U C T U R E OF P Y R R H O T I T E
stacking
IV. This w o u l d
faults may occur
lead to i n t e r f a c e s
tors RI' R2 or R3 but w h e r e a s nes,
stacking
pecially iii)
those g e n e r a t e d
two m o r e
the APB w o u l d
(00
The crystal
under
The m o n o c l i n i c
deformation layers.
out of six p o s s i b l e along the d i a g o n a l ting p o s i t i o n s
which
vector
leads to
are still p a r a l l e l again an anti-
is now of the type
possible
essentially projection
is described.
c-axis
the two c r y s t a l (i/8)c,
ferent
parts
in the two parts.
schematically
situations,
enclose
t a t i o n of the p r o j e c t i o n Fig.2,d.
Coherent
the p r i s m planes, the c-axis, boundary.
to the sense
it is from IV'
depending
finds
ortho-,
meta-
to c o n s i d e r
Boundaries
on w h e t h e r
the
and p a r a - b o u n d a r i e s combinations of the type
deformation
i.e.
may be dif-
cypher d e n o t e s
can e i t h e r
or it can be the c - p l a n e
(iv)
in the c - d i r e c t i o n
of the x - a x i s w i t h r e s p e c t
the angle
of anti-
of this type are r e p r e s e n t e d
the arabic
twin p l a n e s
mo-
an angle of 60 ° , 120 ° , or 180 ° .
the m o n o c l i n i c
bisecting
to
One can d i s t i n g u i s h
(iii) w i t h d e f e c t s
in Fig.4 w h e r e
represen-
in any one out of six
are not only s h i f t e d
but m o r e o v e r
is
regions w h i c h have a d i f f e r e n t
also p o s s i b l e
of type
in one
1 ..... 6 in Fig.2,d.
We shall call these b o u n d a r i e s
phase b o u n d a r i e s
can
of the c-axis
for the lozenge one
is of the twin type.
of the c-axes
of the c-axis
In Fig.2
choices
numbered
sequences
it is r e l a t e d
can be o r i e n t e d
three d i f f e r e n t
[5]. It is c l e a r l y
vec-
w i t h the
formed by the p o i n t s
layers;
all p o s s i b l e
deformation
stacking
The p r o j e c t i o n
of the lozenge
directions,
associated
w i t h the p r o j e c t i o n
The contact plane b e t w e e n noclinic
is c l e a r l y
directions.
in w h i c h the lozenge
that the p r o j e c t e d
es-
join a
This
is t h e r e f o r e
The d i f f e r e n t
of s u c c e s s i v e
Considering
pla-
(i) or zero.
give rise to structures
over
structures
This d i s p l a c e m e n t
shift of s u c c e s s i v e
II.
to c-planes,
~I c) + Ri' w h e r e R.l is either one of the d i s p l a c e m e n t
tors d i s c u s s e d iv)
confined
in one part of the crystal may
on both sides of the interface, phase boundary.
vec-
lie in a r b i t r a r y
in a second part of the crystal.
"variants".
III and
by glide.
iron plane
iron plane
I, II,
w i t h the same d i s p l a c e m e n t
faults w o u l d be largely
A "full"
defect
in the sequence
75
the o r i e n -
to the key of
be p a r a l l e l
to one of
formed by the p r o j e c t i o n in the case of the para-
of
76
D E F E C T S T R U C T U R E OF P Y R R H O T I T E
Whereas sed in
the antiphase
(i),
(ii) and
faces mentionned over regions
(iii)
periments;
under
(iv) should be visible
It is possible antiphase
type
(i) boundaries which
ries.
Also the diffraction
tify the phases present, (iv) and
the inter-
as 6-fringes;
to distinguish
boundaries
reflections;
i.e.
faults discus-
(iii) will be imaged as e-fringes,
(OOOZ)
twinning
and stacking
on both sides will have a different
this last case. and type
boundaries
Vol. 7, No. 1
intensity
between
morein
type
(i)
on the basis of contrast
ex-
will always be out of contrast
is not the case for type pattern will allow,
but also to establish
for
(iii) bounda-
not only to iaenthe presence
of
(v) type boundaries. Observations
Specimens
were prepared
by sawing thin slices
termined
crystallographic
thinning
these by ion bombardment
have examined
crystals
of these crystals
®~
~
~
crystals
and We
and from Yougoslavia.
Some
than one pyrrhotite
identification
since a wide variety
from natural
to the final thickness.
from Mexico
contained more
made an unambigeous especially
directions
along prede-
of planar
of interfaces
.._~ortho
meta para
phase which
interfaces
difficult,
is possible
even
.1~ortho ®~@meta "~para
m" [] . . . . .
1" . . . . . . . .
.......
11I
!-V/~6 ---n
I ....... . . . . . . .
][
(a)
b) fulllayerof
........ d e f e c t i v e
(c)
Fe l a y e r of
Fe FIG.4
Schematic representation of interfaces; only iron layers are shown. (a) Anti-phase boundary with a displacement vector i/8c. (b) Twin boundaries; ortho- meta or para depending on the relative orientation of the c-axis in the two parts. (c) Combination of (a) and (b).
Vol.
7, No.
1
DEFECT
within one phase.
STRUCTURE
PYRRHOTITE
We can therefore only present
results which do indicate however, faces occur
OF
77
some preliminary
that different types of inter-
in Fe7S 8 and that they are due to ordering of the
vacancies.
Anti-phase boundaries 4C-pyrrhotite.
(APB)
FIG.5 and twin type boundaries
(T) in
OlP FIG.6
Intersecting set of stacking faults in natural pyrrhotite crystals. Notice the complex dislocation arrangements.
78
D E F E C T STRUCTURE OF PYRRHOTITE Fig.5
represents
bly associated
The intersecting
are attached
systems of e-fringes
with anti-phase
times wavy character are presumably
e.g.
boundaries,
and the occurrence
planar
fringe
associated
Vol. 7, No. 1
because
of angular
of their
some-
arrangements.
systems of Fig.6 on the other hand
with stacking
to dislocations
which are proba-
faults.
Also since they
they are presumably
deformation
ge-
nerated. Fig.7
shows further
6-type
are expected
for the interfaces
Their planar
nature
are situated
in the c-plane,
boundaries.
An orientation
nearly parallel
suggests
beam;
had become
fragmented
disordering
followed
systems(marked
T)such as
of the type discussed
in
(iv).
that they should be coherent. and are therefore
presumably
They para-
where both types of boundaries
with the electron
Some of the specimens of the electron
fringe
beam is shown in Fig.8.
were heated
in the microscope
it was found that after cooling into very wavy domains, by partial
are
reordering
which
by means
the crystals
shows that
had taken place. W
0
T Q
APB
FIG. 7 Twin type boundaries showing typical 6-contrast. The antiphase boundaries present in this micrograph have only a very faint contrast.
Vol. 7, No. 1
D E F E C T STRUCTURE OF PYRRHOTITE
79
FIG.8 Twin and anti-phase pyrrhotite phase. Also a different of sulphur From a complex
boundaries
in the c-plane
phase had been formed,
of the 4C-
presumably
as a result
loss. Fig.6 we can also conclude
that the dislocations
structure;
consist
some apparently
have
of four components.
References i. N. Morimoto, H.Nakazawa, 168, 964 (1970)
K.Nishiguchi
2. E.F.Bertaut,
~,
Acta Cryst.
3. J.Van Landuyt 4. J.Venables,
557
and S.Amelinckx,
D.Kahn and R.Lye,
5. J.Van Landuyt, (1970)
G.Remaut
and M.Tokonami,
Science
(1953) phys.stat.sol.3_~l,
Phil.Mag.18,
and S.Amelinckx,
77,
589
(1969)
(1968)
phys.stat.sol.4_~l,
271
ELECTRON MICROSCOPE
Pergamon P r e s s , Inc.
OBSERVATIONS
OF THE DEFECT
Printed in
STRUCTURE
OF PYRRHOTITE::
J . V a n L a n d u y t and S . A m e l i n c k x xx RUCA-Antwerpen, Belgium
(Received November 1, 1971; Communicated by S. Ameltnckx)
ABSTRACT The d e f e c t s t r u c t u r e of the m o n o c l i n i c (4C) p y r r h o t i t e phase is analysed. The d e s c r i p t i o n of the s t r u c t u r e w i t h r e s p e c t to the nickel a r s e n i d e structure allows to p r e d i c t a v a r i e t y of d e f e c t s such as a n t i - p h a s e boundaries, stacking faults and twin b o u n d a r i e s assoc i a t e d w i t h the o r d e r i n g of vacancies. E l e c t r o n m i c r o s c o p y o b s e r v a t i o n s on n a t u r a l p y r r h o t i t e c r y s t a l s are shown. They c o n f i r m the p r e d i c t i o n s from the s t r u c t u r e model.
Introduction In r e c e n t years covers
All of these
structures
cancies;
charge
to b e c o m e
compounds
that the name p y r r h o t i t e
w h i c h have the c o m p o s i t i o n
have
so called
"defective"
(Fig.l).
The n o n - s t o i c h i o m e t r y
is c a u s e d by the p r e s e n c e
compensation
trivalent
t h e n requires
for every vacancy.
m e a n s of X-ray d i f f r a c t i o n
of iron va-
two d i v a l e n t
Berthaut
that the v a c a n c i e s
also shown that the a r r a n g e m e n t Coulomb
clear
in fact a n u m b e r of structures
Fen_iSn[l]. NiAs
it has b e c o m e
iron ions
[2] has shown by
are ordered.
found in this way m i n i m i z e s
He has the
energy.
::Work p e r f o r m e d under the a u s p i c e s of the a s s o c i a t i o n XgAlso at S . C . K . - C . E . N . , Mol (Belgium) 71
RUCA-SCK
72
D E F E C T STRUCTURE OF PYRRHOTITE
In view of the possible
Vol. 7, No. 1
interaction between lattice defects
and magnetic defects and also because of the potential use of pyrrho£ite as a geological while to examine tron microscopy.
thermometer,
its defect structure
it was considered worth-
in detail by means of elec-
We present here some preliminary results.
Defect structures due to ordering of vacancies have been studied previously
for instance in ~-In2S 3 [3] and in VC The structure of pyrrhotite
The NiAs structure
is hexagonal;
[4].
(Fe7S8)
it is shown in ~ig.l;
can be considered as a stacking of close-packed
it
layers parallel
to the c-plane described by means of the letter sequence aBayaBay...
The latin letters represent cations,
whereas the
greek letters represent anions. Since Fe7S 8 is the only compound for which the structure has been determined
in detail the discussion will be limited to this case.
In Fe7S 8 th sulfur lattice is complete, of iron ions are full and defective. tain vacancies defective
but alternating
layers
The defective
layers con-
according to the pattern of Fig.2,b.
Successive
layers are shifted one with respect to the next in such
a way that an arbitrary chosen origin in the defective planes
~
a -
a
A
o,~01S
C
• FIG.I The NiAs structure of FeS
Fe
Vol. 7, No. 1
D E F E C T S T R U C T U R E OF PYRRHOTITE
73 m
s _
_
0
0
•
0
•
Fe
--S ]~'-
_ _
Fe+vae S _Fe S sFe+vac
!II . . . . . . . . . . .
Q
•
•
o
• , 0~[
•
~
•
~[~
R.~W. ~ //~ ~ •
11.0
•
H
•
m
., ',,~
•
C:4c
(c) s
11 _ _
I
Fe+vac S
• S I
.
.
.
.
.
.
.
.
.
.
Fe .vac
s
•
~
O
•
•
proj~ctlon of C-axis
(a)
(d)
(b) FIG.2
(a)Schematic r e p r e s e n t a t i o n of the p y r r h o t i t e s t r u c t u r e . A l t e r n a t i n g layers of Fe are full or d e f e c t i v e (Fe+vac.). (b)The o r d e r i n g of v a c a n c i e s (open circles) in an F e - l a y e r of p y r r h o t i t e F e 7 S 8. The p o s i t i o n s of s u c c e s s i v e layers are i n d i c a t e d by I, II, III and IV. The unit cell is o u t l i n e d by m e a n s of a d o u b l e line. The p r o j e c t i o n of the c-axis is i n d i c a t e d for the stacking sequence I, II, III, IV (or the e q u i v a l e n t I, II, III, IV'). (c)The sense of the p r o j e c t i o n of the c-axis d e p e n d s on the sense in w h i c h the lozenge I, II, III, IV' is described. (d)The six p o s s i b l e o r i e n t a t i o n s for the p r o j e c t i o n of the c-axis (and t h e r e f o r e also for the structure). occupies
successively
alternatively
I, II,
the p o s i t i o n s III and IV'
are in fact c r y s t a l l o g r a p h i c a l l y in the c - d i r e c t i o n NiAs;
now b e c o m e s
also the lattice
(~ = 89,63°); Fig.2(c).
the p r o j e c t i o n
Within
stacking
sequence
II; this
changes
projection
the same
since
III,
equivalent.
four times
The d e f e c t On p u r e l y
sulfur III,
lattice IV into
than that of
(c')
is indicated
one can change its r e v e r s e
in
the
I, IV',
of the c-axis.
III
The
is shown by m e a n s
in Fig.2,b. structure
geometrical
: two d i m e n s i o n a l
grounds
on cooling.
interfaces
one can p r e d i c t
of a number of i n t e r f a c e s
of v a c a n c i e s
IV and IV'
in fact s l i g h t l y m o n o c l i n i c
the sense of the p r o j e c t i o n
line
Fig.2,b or
The r e p e a t d i s t a n c e
larger
of the c-axis
from I, II,
IV of
the p o s i t i o n s
of the unit cell on the basal plane
of the d o u b l e
occurrence
becomes
I, II,
the p o s s i b l e
as a r e s u l t of the o r d e r i n g
74
DEFECT
Assuming
STRUCTURE
OF PYRRHOTITE
the lattice of sulphur
build the pyrrhotite
structure
Vol. 7, No. I
ions to be continuous
in a number of different
ding to a large number of possible
interfaces
i) Assuming
layers
the full and defective
in the whole crystal, the same,
different
and assuming
parallel marked
leads to the possible
occurrence
vectors
(b) are related
different
vector
lea-
types.
to be
are possible,
correspon-
I, II, III and IV in Fig.2,a. of antiphase
boundaries
schematically
situations
by a rotation.
with displacement
of different
the layer sequence
RI' R2 and R3 as shown
Only two essentially
ways
to be at the same level
orientations
ding to the positions
placement
one can
occur,
Presumably
R3 have the smallest
with dis-
in Fig.3.
since
antiphase
This
(a) and
boundaries
energy and are t h e r e
for preferred.
/ •
• 0
,
• .
•
• 0
•
•
o
o • (a)
•
• •
•
0/0
• •
o/%
•
o/o~I o/o
o/o
o •
• •
o
o/ / O
o
•
(b)•
•
0/•
o
o
•
o/•
•
O/O
•
/
Y
•
0
• o
O
•
• @
•
o
o
•
@~ • 0/0
•
o
•
•
• O
•
O/O /
•
• 0
• •
0
• O
o •
•
• •
0
O
•
•
O
o/o oi.
O O
/APB O/O •
• •
O
•
•
o •
O
•
• •
•
•
o •
O
•
/ O
• •
O
•
•
O
•
O
o
•
O •
O
O •
•
•
o/ /
/
o/ o/
o/
•
,
0 •
•
•
O
•
•
•
•
•
O •
•
•
•
•
• •
•
0 / ~
o
• 0
o/0
o/O o,o
O
•
•
•
•
•
(c) o
•
O
•
•
O
•
•
•
FIG.3 Possible antiphase boundaries : only two are essentially different e.G.(a) and (c); (a) and (b) are more conservative; (c) is conservative.
Vol. 7, No. 1 i i) Also
D E F E C T S T R U C T U R E OF P Y R R H O T I T E
stacking
IV. This w o u l d
faults may occur
lead to i n t e r f a c e s
tors RI' R2 or R3 but w h e r e a s nes,
stacking
pecially iii)
those g e n e r a t e d
two m o r e
the APB w o u l d
(00
The crystal
under
The m o n o c l i n i c
deformation layers.
out of six p o s s i b l e along the d i a g o n a l ting p o s i t i o n s
which
vector
leads to
are still p a r a l l e l again an anti-
is now of the type
possible
essentially projection
is described.
c-axis
the two c r y s t a l (i/8)c,
ferent
parts
in the two parts.
schematically
situations,
enclose
t a t i o n of the p r o j e c t i o n Fig.2,d.
Coherent
the p r i s m planes, the c-axis, boundary.
to the sense
it is from IV'
depending
finds
ortho-,
meta-
to c o n s i d e r
Boundaries
on w h e t h e r
the
and p a r a - b o u n d a r i e s combinations of the type
deformation
i.e.
may be dif-
cypher d e n o t e s
can e i t h e r
or it can be the c - p l a n e
(iv)
in the c - d i r e c t i o n
of the x - a x i s w i t h r e s p e c t
the angle
of anti-
of this type are r e p r e s e n t e d
the arabic
twin p l a n e s
mo-
an angle of 60 ° , 120 ° , or 180 ° .
the m o n o c l i n i c
bisecting
to
One can d i s t i n g u i s h
(iii) w i t h d e f e c t s
in Fig.4 w h e r e
represen-
in any one out of six
are not only s h i f t e d
but m o r e o v e r
is
regions w h i c h have a d i f f e r e n t
also p o s s i b l e
of type
in one
1 ..... 6 in Fig.2,d.
We shall call these b o u n d a r i e s
phase b o u n d a r i e s
can
of the c-axis
for the lozenge one
is of the twin type.
of the c-axes
of the c-axis
In Fig.2
choices
numbered
sequences
it is r e l a t e d
can be o r i e n t e d
three d i f f e r e n t
[5]. It is c l e a r l y
vec-
w i t h the
formed by the p o i n t s
layers;
all p o s s i b l e
deformation
stacking
The p r o j e c t i o n
of the lozenge
directions,
associated
w i t h the p r o j e c t i o n
The contact plane b e t w e e n noclinic
is c l e a r l y
directions.
in w h i c h the lozenge
that the p r o j e c t e d
es-
join a
This
is t h e r e f o r e
The d i f f e r e n t
of s u c c e s s i v e
Considering
pla-
(i) or zero.
give rise to structures
over
structures
This d i s p l a c e m e n t
shift of s u c c e s s i v e
II.
to c-planes,
~I c) + Ri' w h e r e R.l is either one of the d i s p l a c e m e n t
tors d i s c u s s e d iv)
confined
in one part of the crystal may
on both sides of the interface, phase boundary.
vec-
lie in a r b i t r a r y
in a second part of the crystal.
"variants".
III and
by glide.
iron plane
iron plane
I, II,
w i t h the same d i s p l a c e m e n t
faults w o u l d be largely
A "full"
defect
in the sequence
75
the o r i e n -
to the key of
be p a r a l l e l
to one of
formed by the p r o j e c t i o n in the case of the para-
of
76
D E F E C T S T R U C T U R E OF P Y R R H O T I T E
Whereas sed in
the antiphase
(i),
(ii) and
faces mentionned over regions
(iii)
periments;
under
(iv) should be visible
It is possible antiphase
type
(i) boundaries which
ries.
Also the diffraction
tify the phases present, (iv) and
the inter-
as 6-fringes;
to distinguish
boundaries
reflections;
i.e.
faults discus-
(iii) will be imaged as e-fringes,
(OOOZ)
twinning
and stacking
on both sides will have a different
this last case. and type
boundaries
Vol. 7, No. 1
intensity
between
morein
type
(i)
on the basis of contrast
ex-
will always be out of contrast
is not the case for type pattern will allow,
but also to establish
for
(iii) bounda-
not only to iaenthe presence
of
(v) type boundaries. Observations
Specimens
were prepared
by sawing thin slices
termined
crystallographic
thinning
these by ion bombardment
have examined
crystals
of these crystals
®~
~
~
crystals
and We
and from Yougoslavia.
Some
than one pyrrhotite
identification
since a wide variety
from natural
to the final thickness.
from Mexico
contained more
made an unambigeous especially
directions
along prede-
of planar
of interfaces
.._~ortho
meta para
phase which
interfaces
difficult,
is possible
even
.1~ortho ®~@meta "~para
m" [] . . . . .
1" . . . . . . . .
.......
11I
!-V/~6 ---n
I ....... . . . . . . .
][
(a)
b) fulllayerof
........ d e f e c t i v e
(c)
Fe l a y e r of
Fe FIG.4
Schematic representation of interfaces; only iron layers are shown. (a) Anti-phase boundary with a displacement vector i/8c. (b) Twin boundaries; ortho- meta or para depending on the relative orientation of the c-axis in the two parts. (c) Combination of (a) and (b).
Vol.
7, No.
1
DEFECT
within one phase.
STRUCTURE
PYRRHOTITE
We can therefore only present
results which do indicate however, faces occur
OF
77
some preliminary
that different types of inter-
in Fe7S 8 and that they are due to ordering of the
vacancies.
Anti-phase boundaries 4C-pyrrhotite.
(APB)
FIG.5 and twin type boundaries
(T) in
OlP FIG.6
Intersecting set of stacking faults in natural pyrrhotite crystals. Notice the complex dislocation arrangements.
78
D E F E C T STRUCTURE OF PYRRHOTITE Fig.5
represents
bly associated
The intersecting
are attached
systems of e-fringes
with anti-phase
times wavy character are presumably
e.g.
boundaries,
and the occurrence
planar
fringe
associated
Vol. 7, No. 1
because
of angular
of their
some-
arrangements.
systems of Fig.6 on the other hand
with stacking
to dislocations
which are proba-
faults.
Also since they
they are presumably
deformation
ge-
nerated. Fig.7
shows further
6-type
are expected
for the interfaces
Their planar
nature
are situated
in the c-plane,
boundaries.
An orientation
nearly parallel
suggests
beam;
had become
fragmented
disordering
followed
systems(marked
T)such as
of the type discussed
in
(iv).
that they should be coherent. and are therefore
presumably
They para-
where both types of boundaries
with the electron
Some of the specimens of the electron
fringe
beam is shown in Fig.8.
were heated
in the microscope
it was found that after cooling into very wavy domains, by partial
are
reordering
which
by means
the crystals
shows that
had taken place. W
0
T Q
APB
FIG. 7 Twin type boundaries showing typical 6-contrast. The antiphase boundaries present in this micrograph have only a very faint contrast.
Vol. 7, No. 1
D E F E C T STRUCTURE OF PYRRHOTITE
79
FIG.8 Twin and anti-phase pyrrhotite phase. Also a different of sulphur From a complex
boundaries
in the c-plane
phase had been formed,
of the 4C-
presumably
as a result
loss. Fig.6 we can also conclude
that the dislocations
structure;
consist
some apparently
have
of four components.
References i. N. Morimoto, H.Nakazawa, 168, 964 (1970)
K.Nishiguchi
2. E.F.Bertaut,
~,
Acta Cryst.
3. J.Van Landuyt 4. J.Venables,
557
and S.Amelinckx,
D.Kahn and R.Lye,
5. J.Van Landuyt, (1970)
G.Remaut
and M.Tokonami,
Science
(1953) phys.stat.sol.3_~l,
Phil.Mag.18,
and S.Amelinckx,
77,
589
(1969)
(1968)
phys.stat.sol.4_~l,
271