Geoscience Reference
In-Depth Information
8.11.4 Hydrothermal Synthesis of Chalcohalides
The chalcohalides include very complex inorganic compounds in which the sulfide
and halogenides simultaneously go as anions in their composition. The interest in
these compounds is connected to the photosemiconductor and piezoelectric proper-
ties. Hydrothermal synthesis of chalcohalides of type ABC, where A
Sb, Bi;
5
B
113]
. The
principal experimental difficulty arising while studying the conditions of synthesis
of the ternary chalcohalides A
v
B
vi
C
vii
under hydrothermal conditions lies in creat-
ing conditions that would eliminate the possibility of oxidation or, in other words,
it is essential that the original components would have the valence state A
3
1
B
2
2
C
1
2
in the solution. However, a specific value of the redox potential is merely nec-
essary, not a sufficient condition for the synthesis of A
v
B
vi
C
vii
. The probability of
the formation of any of these compounds will be determined by the concentration
of the original components as well as the pH of the medium and the presence of a
halogen.
S, Se, Te; C
Br, I, have been carried out by several authors
[109
5
5
9
=
;
SbI
4
1
Sb
4HI
!½
2H
2
m
1
4
2
4
1
SbI
4
1
2
½
4
½
H
2
S
!½
Sb
2
I
2
ð
H
2
S
Þ
6I
pH
6
ð
8
:
33
8
:
35
Þ
,
4
2
4
!
½
Sb
2
I
2
ð
H
2
S
Þ
2SbSI
2H
2
S
2H
2
m
1
1
=
!½
SbI
4
1
2H
2
m
Sb
1
4HI
½
SbI
4
1
2
½
HS
2
!½
SbS
2
1
2I
2HI
1
pH
5
7
2
10
ð
8
:
36
8
:
39
Þ
Sb
H
2
m
2
½
SbS
2
1
4
½
HS
2
!
2Sb
2
S
3
1
2H
2
S
m
2
½
HS
2
!½
SbS
2
1
1
;
9
=
;
HS
2
!½
SbS
2
1
Sb
2
½
H
2
m
1
SbS
2
1
HS
2
!
2
½
4
½
2Sb
2
S
3
1
2H
2
S
m
pH
10
ð
8
:
40
8
:
42
Þ
.
S
2
2
!
2
½
SbS
2
1
½
Sb
2
S
3
1
2S
7. The range of
formation of SbSI in solutions with low pH values may be associated with the
stability of a hypothetical complex of the
Hence, SbSI will chiefly be formed in solutions with pH
,
4
4
type, which may be
formed as a result of an interaction between the two genuinely existing complexes.
The
½
Sb
2
I
2
ð
H
2
S
Þ
SbS
2
is well known to be a stable ion interacting with other sulfide com-
plexes; it necessarily leads to the formation of Sb
2
S
3
. Popolitov and Litvin
[111]
have synthesized Pb
5
S
2
I
6
½
a
a
a
a
single crystals
in the system Pb
S
I
R
H
2
O
(R
solvent) under hydrothermal conditions. The experiments were carried out in
Teflon-lined autoclaves at 200
5
1.8
C/
cm.
Figure 8.30
shows a photograph of Pb
5
S
2
I
6
single crystals
[113]
. Note that
Pb
5
S
2
I
6
belongs to the monoclinic system and the phase transition occurs at
290
300
C with a temperature gradient of 0.6
5
C. Rabenau and Rau
[113]
have reported the growth of Pb
7
S
2
Br
10
single
crystals. The typical experimental conditions are T
6
450
C, liquid S pressure
300
5
1.6
/cm. Elemental Pb and S, liquid Br
2
, PbBr
2
,
and PbS, in various molar ratios were used as starting materials.
(2.02
20.2) 107 Pa,
Δ
T
0.4
5
