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The sodium intercalates of vanadium disulfide and their hydrolysis products
Mat. Res. Bull. Vol. 9, pp. 1261-1266, Printed in the United States.
THE SODIUM
INTERCALATES
1974
Pergamon
Press,
OF VANADI0;.I DISULFIOZ
THEIR HYDROLYSIS
Inc
AND
PRODUCTS
G.A.
Wiegers, R. van der Meet, H. van nein±~g~n, H.J. Kloosterboer and A.J.A. Alberink Laboratorium voor Anorganische Chemie, Rijksuniversitei%, Zernikelaan, Groningen, The Netherlands
(Received June 27, 1974; C o m m u n i c a t e d
by G. H. Jonker)
ABSTRACT Nonstoichiometric phases Na VS~ were prepared from the elements. x T h ey have VS 2 layers with vanadium in octahedral coordination; the layers are separated by sodium. Three different structures were found; they differ in the coordination of sodium (trigonal-prismatic and octahedral) and the packing of the sulfur atoms. Hydrolysis of Na VS. proceeds in two steps, the d Istance ~etween vanadium planes x changing from 7.10 via 8.57 to 11.72 ~.
Introduction Intercalation compounds of layered transition-metal dichalcogenides have aroused great interest recently. The alkali-metal intercalates usually are prepared from the transition-metal dichalcogenides by reaction with alkali metal dissolved in liquid ammonia (intercalation), or by reaction of the transition-metal dichalcogenides in salt melts of the corresponding alkali halides under H2S/CS 2 atmosphere. Results Since VS_ does not exist, we prepared compounds Na VS 2 (x = O.I, 0.2 etc.) from~the elements in evacuated quartz tubes. T~e samples were first slowly heated to about 200°C, the temperature interval in which the reaction with sulfur proceeds. Then, they were heated to 6OO°C, left at that temperature for four days and quenched. X-ray data (DehyeScherrer camera with CuK~ radiation) were obtained in the absence of air, because the samples are hygroscopic. For x = 0.1 and 0.2 the diffraction pattern agreed with that of V~S&. For 0 . 3 ~ x - ~ I a rhombohedral cell was found. The cell constants (Wa-= 3.311, c = 21.21 ~ for ia O 6VS2 ) and the intensity sequence roughly agreed with those of " Na O ~=TiS o (a = 3.433, c = 20.94 ~) reported by Rouxel et al. (I), i n d i c a t i n g ' ~ e t~o compounds to have the same structure. The intensities calculated with Rouxel's coordinates 1261
1262
INTERCALATES
OF
(all atoms in positions
VANADIUM
DISULFIDE
Vol. 9, No.
9
3 a of space group R3m):
(O00, 3x Na 3 V 3 S 3 S were in good agreement
2/3 1/3 I/3, in OOz with " " " " " " " " "
z z z z
I/3 2/3 2/3) + = 0.83 = 0 = 0.40 = 0.61
wit~ the estimated
intensities.
The structure is shown in Fig. 2a. In Na VS~ ( O . 3 ~ x ~ 1 ) and the isostructural phases Na TiS~ ( 0 . 3 8 ~ x < O . 7 2 ) , X K ~iS~(O.28~x~1), Rb TiS~ ( 0 . 4 2 < x ~ 1 ) an~ CsLTiS~ ( 0 . 5 6 < x ~ 1 ) (~,2,~), the coordination X ~ d . . . X ~ . . . . of the alkall metal is trlgona!-prlsmatlc, that of the transition metal is octahedral. The variation o9 the lenEths of the a- and c axes with the alkali-metal content, given in Fig. 1 shows the same 21.5 behaviour as found for Na TiS 2 3.3/, (0.38
J
i
21,1
i
i
i
i
i
The sodium-rich rhombohedral samples (x~0.8) were often contaminated by a form isomorphous with NaCrS~ (6). Occasionally, this form was obtained in a pure state. The cell c~nstants, a = 3.566, c = 19.68 ~, are almost identical with those reported by R~dorff (7) and Elstermann (8). a = 3.57, c = 19.65 ~ for NaVS 2 prepared from Na^S and V_S_ at 900°C. The sodium and vanadium atoms are in octahedra~ holes ~fDa cubic close packing of sulfur atoms (Fig. 2c). The intensities of the powder lines calculated with the atoms in the following positions of space group R3m: (000, 3 Na 3 V 6 S
2/3 in 3 in 3 in 6
1/3 1/3, 1/3 2/3 2/3) + b: O01/2 a: 000 c: ± OOz with z = .267
were in good agreement with the observed intensities. The same structure has been reported for NaCrS 2 (6) and NaxTiS 2 ( O . 7 9 - ~ x ~ 1 ) (1,2,3,4).
Vol. 9, No.
9
INTERCALATES
OF
VANADIUM
DISULFIDE
1263
0 @
) 0
a~
)
)
0 ( ©
<
©
@
© (a)
Q
0 @
o<
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@ ©
©
0
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()
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( ) )
@
0 0
< (c)
(b)
FIG.
©
)
(d)
2
Sections through the (11}0) planes of (a) Na VS~ ( 0 . 3 ~ x ~ I ) (b) lowtemperature form of Na VS~ (c) Na VS^ with N ~ C r ~ structure X L X ~ (d) Na n ~(H90)~ ~xVSo . Large open clrcles are sulfur atoms, small open circle~'~re~va~um~atoms, hatched circles are sodium atoms or hydrated sodium atoms (d). Discussion The unit cell dimensions and cell volumes of the compounds Na MS~ with M = Ti, V and Cr are collected in Table I. These compounds X L + -X . . . . may be formulated as Na [MS^] . The coordlnatlon of the transltlon metal • . X " ~ . . . . Is octahedral in all cases ~ut the coordlnatlon of sodlum can be elther trigonal-prismatic ( type I, Fig. 2a) or octahedral (type II, Fig. 2c and type III, Fig. 2b). These two kinds of coordination of alkali metal have been discussed by Huisman et al. (9). In type III compounds every sodium atom has two transition metal neighbours at rather short distances (I/2 c), in type I compounds it has one such neighbour, in type II compounds none. It is understandable, therefore, that the repeat distance (c for type III, I/3 c for types I and II) decreases in the sequence III>I>II. It can also be understood that I compounds usually are obtained for smaller sodium contents than type II compounds, and that
1264
INTERCALATES
OF VANADIUM
DISULFIDE
Vol. 9, No. 9
TABLE I Cell dimensions and cell volumes of compounds NaxMS 2 (M = Ti,V,Cr) structure type
compound
I ( Fig. 2a)
II (Fig. 2c)
III (Fig. 2b)
a (~)
c (~)
V (~3)
ref.
Na~ _~TiS^ 3.411 ma^ ~^'z'l,~^ 3.446 l~a_ 3.288 o.J_ v ~ Na 1o0VS2 3.346
21.O0 20.82 21.46 21.O2
423.2 425.2 401.8 407.5
1,2 I ,2 this work " "
Na^ _^TiS^ NaU./~iS z Na~O 2 NaCr~ 2
3.55 3.47 3.566 3.5=4
20.04 20.58 19.68 19.49
437.4 429.2 436.1 426.4
1,2 1,2 this work " 6
NaxVS 2
3.22
7.30
392.7/3
this work **
" Exact composition not known but probably close to NaVS 2 **Cell constants almost independent of sodium content. structures of type III are found for LixMS2. The a-axes of Na MS~ show a behaviour opposite to the c-axes, although the unit-cel~ volumes are not quite independent of the structure type (Table I). Since the closest approaches between transition metals M are equal to the a-axes, a type II structure will be favored if the bondlng withln the [MS_I sandwlches Is more 1onlc. Indeed, NaCrS_ which may be expected Go be the most Ionic compound zn the series, exists only with a type II structure: this compound is stable in air, has localized magnetic moments and a high electrical resistivity (6,7,8). •
.
~
--X
.
.
.
.
Hydrolysis The rhombohedral compounds Na VS. ( 0 . 3 ~ < x < I ) are hygroscopic. A sample of composmtlon Na_ ~VSA mounte~ in a sample holder of a powder diffractometer was h y d r o ~ e d Z i n moist air and the powder pattern was recorded several times during hydrolysis. The composition of the final product deduced from a~alysis of the Na, V and S contents and the amount of water absorbed (obtained by weighing a sample during hydrolysis) was Na 0 6(H90)~ K.VS~. It was found that the hydrolysis proceeds in two ste~s. Flr~£, " ~ h strong reflections with d values of 8.55, 4.27 and 2.85 ~, together with a number of weak reflections, appeared. We did not succeed in indexing this pattern with a hexagonal cell with an a-axis about 3.3-3.6 ~ and c = n × 8.57 ~ or a simple supercell based on such a hexagonal cell. It is, however, reasonable to assume that the repeat distance in the c-axis direction is 8.57 ~ or a multiple. Afterwards, the diffraction lines of the final hydrate appeared, while those of the first hydrate disappeared. They could be indexed on basis of a rhombohedral cell with a = 3.271, c = 35.15 ~. The distance between vanadium planes changed also from 21.21/3 = 7.07 (for Na n ~VS)) via 8.57 to 11.72 ~ ( = 35.15/3) for the final form. Similag"Sbs~rvations have been reported recently (10) for Nao.~TiS~ and Na n zTiS~ (8.93 - 8.61 ~ for the first hydration step and 11.5~ ~ 11~39 ~ fo~'~he ~econd step). The composition of the last step was Nao.5(H20)2TiS 2. •
.
X
The structure of Na~ r(H~O), r~VS~, given in Fig. 2d is essential~:y the same as that of Na X V~[°wi~h ~&~#S~Lstructure (Fig.2c). The VS~ ~ . layers have the same dlmenslons in bo~h structures, they are separated, however, by a much larger distance (an increase of(35.15 - 19.68)/3 = 5.16 ~) in the hydrate. The intensities of the powder lines, calculated
Vol. 9, No. 9
INTERCALATES
OF VANADIUM
DISULFIDE
1265
with 3 x 0.6 Na in OO1/2, 3 V in OOO and 6 S in ± OOz with z = .292 in space group R3m (the water molecules were not taken into account) were in reasonable good agreement with the observed intensities (Table 2). TABLE 2 X-ray powder diffraction data (diffractometer) h k 00 0 O 0 0 0 0 fl 0 I 0 0 1 I O 0 1 0 0 I 0 0 1
i 3 6 9 12 1 4 5 7 8 15 10 11
dobs(~) dcalc(~) Iobs Icalc 11.70 11.72 100 100 5.86 5.86 50 18 3.910 3.906 2 I 2.933 2.929 flO O 2.824 2.824 8 0 2.7000 2.696 12 29 2.625 2.627 5 4 2.468 2.467 32 15 2.382 2.381 4 3 2.346 2.341 2 0 2.207 2.206 18 23 2.120 2.120 2 2
h k 1 I O 0 0 0 1 I 0 00 0 1 1 1 1 1 1 1 I 0 0 1 O 0
13 18 14 16 21 17 0 3 6 19 20 24
of Nao.6(H20)3.63VS 2
dobs(~) dcalc(~) Iobs 1.956 1.881 1.735 1.670 1.636 1.620 1.574 1.553 1.492 1.465
1.956 1.953 1.879 1.736 1.674 1.670 1.636 1.620 1.570 1.549 1.493 1.465
4 9 2 8 flO 5 2 I 3 4
Icalc 2 I 12 I O 4 4 2 2 I 4 1
The a-axis is short (3.271 ~) and about equal to that found in NaxVS 2 of type I; this may indicate that the d-electrons in the VS 2 layers are delocalized. Indeed, preliminary experiments showed that the hydrate has a low resistivity. Hydrolysis of NaA ~VS_ in water gave a black precipitate; there Ob 2 was no evolution of hydrogen during hydrolysis. The powder pattern of the precipitate agreed with that of the final product of hydrolysis in moist air. Hydrolysis in moist air of a sample of composition Na n VS did not lead to a homogeneous product. The powder pattern showed i~'~o ~e a mixture of phases with powder pattern identical to those of the two hydratation steps of Nao.6VS 2 and probably of V3S 4. References I. J. Rouxel, M. Danot and J. Bichon, Bull. Soc. Chim. Fr. 1971, 3930. 2. A. Leblanc-Soreau, 2' 191 (1974).
M. Danot, L. Trichet and J. Rouxel, Mat. Res. Bull.
3- G. Grams, Dissertation,
T~bingen 1961.
4. J. Bichon, M. Danot and J. Rouxel, C.R. Acad. Sc. 276, 1283 (1973). 5. B. van Laar and D.J.W. Ydo, J. S o l d State Chem. ~, 590 (1971). 6. F.M.R. Engelsman, G.A. Wiegers, F. Jellinek and B. van Laar, J.Solid State Chem. 6, 574 (1973). 7. W. R~dorff, Chimia 19, 489 (1965). 8. C.H. Elstermann,
Dissertation, T~bingen 1965.
9. R. Huisman, R. de Jonge, C. Haas and F. Jellinek, J. Solid State Chem. ~, 56 (1971). 10. R. Schollhorn and A. Weiss, Z. Naturforsch.
28b, 711 (1974).
THE SODIUM
INTERCALATES
1974
Pergamon
Press,
OF VANADI0;.I DISULFIOZ
THEIR HYDROLYSIS
Inc
AND
PRODUCTS
G.A.
Wiegers, R. van der Meet, H. van nein±~g~n, H.J. Kloosterboer and A.J.A. Alberink Laboratorium voor Anorganische Chemie, Rijksuniversitei%, Zernikelaan, Groningen, The Netherlands
(Received June 27, 1974; C o m m u n i c a t e d
by G. H. Jonker)
ABSTRACT Nonstoichiometric phases Na VS~ were prepared from the elements. x T h ey have VS 2 layers with vanadium in octahedral coordination; the layers are separated by sodium. Three different structures were found; they differ in the coordination of sodium (trigonal-prismatic and octahedral) and the packing of the sulfur atoms. Hydrolysis of Na VS. proceeds in two steps, the d Istance ~etween vanadium planes x changing from 7.10 via 8.57 to 11.72 ~.
Introduction Intercalation compounds of layered transition-metal dichalcogenides have aroused great interest recently. The alkali-metal intercalates usually are prepared from the transition-metal dichalcogenides by reaction with alkali metal dissolved in liquid ammonia (intercalation), or by reaction of the transition-metal dichalcogenides in salt melts of the corresponding alkali halides under H2S/CS 2 atmosphere. Results Since VS_ does not exist, we prepared compounds Na VS 2 (x = O.I, 0.2 etc.) from~the elements in evacuated quartz tubes. T~e samples were first slowly heated to about 200°C, the temperature interval in which the reaction with sulfur proceeds. Then, they were heated to 6OO°C, left at that temperature for four days and quenched. X-ray data (DehyeScherrer camera with CuK~ radiation) were obtained in the absence of air, because the samples are hygroscopic. For x = 0.1 and 0.2 the diffraction pattern agreed with that of V~S&. For 0 . 3 ~ x - ~ I a rhombohedral cell was found. The cell constants (Wa-= 3.311, c = 21.21 ~ for ia O 6VS2 ) and the intensity sequence roughly agreed with those of " Na O ~=TiS o (a = 3.433, c = 20.94 ~) reported by Rouxel et al. (I), i n d i c a t i n g ' ~ e t~o compounds to have the same structure. The intensities calculated with Rouxel's coordinates 1261
1262
INTERCALATES
OF
(all atoms in positions
VANADIUM
DISULFIDE
Vol. 9, No.
9
3 a of space group R3m):
(O00, 3x Na 3 V 3 S 3 S were in good agreement
2/3 1/3 I/3, in OOz with " " " " " " " " "
z z z z
I/3 2/3 2/3) + = 0.83 = 0 = 0.40 = 0.61
wit~ the estimated
intensities.
The structure is shown in Fig. 2a. In Na VS~ ( O . 3 ~ x ~ 1 ) and the isostructural phases Na TiS~ ( 0 . 3 8 ~ x < O . 7 2 ) , X K ~iS~(O.28~x~1), Rb TiS~ ( 0 . 4 2 < x ~ 1 ) an~ CsLTiS~ ( 0 . 5 6 < x ~ 1 ) (~,2,~), the coordination X ~ d . . . X ~ . . . . of the alkall metal is trlgona!-prlsmatlc, that of the transition metal is octahedral. The variation o9 the lenEths of the a- and c axes with the alkali-metal content, given in Fig. 1 shows the same 21.5 behaviour as found for Na TiS 2 3.3/, (0.38
J
i
21,1
i
i
i
i
i
The sodium-rich rhombohedral samples (x~0.8) were often contaminated by a form isomorphous with NaCrS~ (6). Occasionally, this form was obtained in a pure state. The cell c~nstants, a = 3.566, c = 19.68 ~, are almost identical with those reported by R~dorff (7) and Elstermann (8). a = 3.57, c = 19.65 ~ for NaVS 2 prepared from Na^S and V_S_ at 900°C. The sodium and vanadium atoms are in octahedra~ holes ~fDa cubic close packing of sulfur atoms (Fig. 2c). The intensities of the powder lines calculated with the atoms in the following positions of space group R3m: (000, 3 Na 3 V 6 S
2/3 in 3 in 3 in 6
1/3 1/3, 1/3 2/3 2/3) + b: O01/2 a: 000 c: ± OOz with z = .267
were in good agreement with the observed intensities. The same structure has been reported for NaCrS 2 (6) and NaxTiS 2 ( O . 7 9 - ~ x ~ 1 ) (1,2,3,4).
Vol. 9, No.
9
INTERCALATES
OF
VANADIUM
DISULFIDE
1263
0 @
) 0
a~
)
)
0 ( ©
<
©
@
© (a)
Q
0 @
o<
<
@ ©
©
0
©
()
<
( ) )
@
0 0
< (c)
(b)
FIG.
©
)
(d)
2
Sections through the (11}0) planes of (a) Na VS~ ( 0 . 3 ~ x ~ I ) (b) lowtemperature form of Na VS~ (c) Na VS^ with N ~ C r ~ structure X L X ~ (d) Na n ~(H90)~ ~xVSo . Large open clrcles are sulfur atoms, small open circle~'~re~va~um~atoms, hatched circles are sodium atoms or hydrated sodium atoms (d). Discussion The unit cell dimensions and cell volumes of the compounds Na MS~ with M = Ti, V and Cr are collected in Table I. These compounds X L + -X . . . . may be formulated as Na [MS^] . The coordlnatlon of the transltlon metal • . X " ~ . . . . Is octahedral in all cases ~ut the coordlnatlon of sodlum can be elther trigonal-prismatic ( type I, Fig. 2a) or octahedral (type II, Fig. 2c and type III, Fig. 2b). These two kinds of coordination of alkali metal have been discussed by Huisman et al. (9). In type III compounds every sodium atom has two transition metal neighbours at rather short distances (I/2 c), in type I compounds it has one such neighbour, in type II compounds none. It is understandable, therefore, that the repeat distance (c for type III, I/3 c for types I and II) decreases in the sequence III>I>II. It can also be understood that I compounds usually are obtained for smaller sodium contents than type II compounds, and that
1264
INTERCALATES
OF VANADIUM
DISULFIDE
Vol. 9, No. 9
TABLE I Cell dimensions and cell volumes of compounds NaxMS 2 (M = Ti,V,Cr) structure type
compound
I ( Fig. 2a)
II (Fig. 2c)
III (Fig. 2b)
a (~)
c (~)
V (~3)
ref.
Na~ _~TiS^ 3.411 ma^ ~^'z'l,~^ 3.446 l~a_ 3.288 o.J_ v ~ Na 1o0VS2 3.346
21.O0 20.82 21.46 21.O2
423.2 425.2 401.8 407.5
1,2 I ,2 this work " "
Na^ _^TiS^ NaU./~iS z Na~O 2 NaCr~ 2
3.55 3.47 3.566 3.5=4
20.04 20.58 19.68 19.49
437.4 429.2 436.1 426.4
1,2 1,2 this work " 6
NaxVS 2
3.22
7.30
392.7/3
this work **
" Exact composition not known but probably close to NaVS 2 **Cell constants almost independent of sodium content. structures of type III are found for LixMS2. The a-axes of Na MS~ show a behaviour opposite to the c-axes, although the unit-cel~ volumes are not quite independent of the structure type (Table I). Since the closest approaches between transition metals M are equal to the a-axes, a type II structure will be favored if the bondlng withln the [MS_I sandwlches Is more 1onlc. Indeed, NaCrS_ which may be expected Go be the most Ionic compound zn the series, exists only with a type II structure: this compound is stable in air, has localized magnetic moments and a high electrical resistivity (6,7,8). •
.
~
--X
.
.
.
.
Hydrolysis The rhombohedral compounds Na VS. ( 0 . 3 ~ < x < I ) are hygroscopic. A sample of composmtlon Na_ ~VSA mounte~ in a sample holder of a powder diffractometer was h y d r o ~ e d Z i n moist air and the powder pattern was recorded several times during hydrolysis. The composition of the final product deduced from a~alysis of the Na, V and S contents and the amount of water absorbed (obtained by weighing a sample during hydrolysis) was Na 0 6(H90)~ K.VS~. It was found that the hydrolysis proceeds in two ste~s. Flr~£, " ~ h strong reflections with d values of 8.55, 4.27 and 2.85 ~, together with a number of weak reflections, appeared. We did not succeed in indexing this pattern with a hexagonal cell with an a-axis about 3.3-3.6 ~ and c = n × 8.57 ~ or a simple supercell based on such a hexagonal cell. It is, however, reasonable to assume that the repeat distance in the c-axis direction is 8.57 ~ or a multiple. Afterwards, the diffraction lines of the final hydrate appeared, while those of the first hydrate disappeared. They could be indexed on basis of a rhombohedral cell with a = 3.271, c = 35.15 ~. The distance between vanadium planes changed also from 21.21/3 = 7.07 (for Na n ~VS)) via 8.57 to 11.72 ~ ( = 35.15/3) for the final form. Similag"Sbs~rvations have been reported recently (10) for Nao.~TiS~ and Na n zTiS~ (8.93 - 8.61 ~ for the first hydration step and 11.5~ ~ 11~39 ~ fo~'~he ~econd step). The composition of the last step was Nao.5(H20)2TiS 2. •
.
X
The structure of Na~ r(H~O), r~VS~, given in Fig. 2d is essential~:y the same as that of Na X V~[°wi~h ~&~#S~Lstructure (Fig.2c). The VS~ ~ . layers have the same dlmenslons in bo~h structures, they are separated, however, by a much larger distance (an increase of(35.15 - 19.68)/3 = 5.16 ~) in the hydrate. The intensities of the powder lines, calculated
Vol. 9, No. 9
INTERCALATES
OF VANADIUM
DISULFIDE
1265
with 3 x 0.6 Na in OO1/2, 3 V in OOO and 6 S in ± OOz with z = .292 in space group R3m (the water molecules were not taken into account) were in reasonable good agreement with the observed intensities (Table 2). TABLE 2 X-ray powder diffraction data (diffractometer) h k 00 0 O 0 0 0 0 fl 0 I 0 0 1 I O 0 1 0 0 I 0 0 1
i 3 6 9 12 1 4 5 7 8 15 10 11
dobs(~) dcalc(~) Iobs Icalc 11.70 11.72 100 100 5.86 5.86 50 18 3.910 3.906 2 I 2.933 2.929 flO O 2.824 2.824 8 0 2.7000 2.696 12 29 2.625 2.627 5 4 2.468 2.467 32 15 2.382 2.381 4 3 2.346 2.341 2 0 2.207 2.206 18 23 2.120 2.120 2 2
h k 1 I O 0 0 0 1 I 0 00 0 1 1 1 1 1 1 1 I 0 0 1 O 0
13 18 14 16 21 17 0 3 6 19 20 24
of Nao.6(H20)3.63VS 2
dobs(~) dcalc(~) Iobs 1.956 1.881 1.735 1.670 1.636 1.620 1.574 1.553 1.492 1.465
1.956 1.953 1.879 1.736 1.674 1.670 1.636 1.620 1.570 1.549 1.493 1.465
4 9 2 8 flO 5 2 I 3 4
Icalc 2 I 12 I O 4 4 2 2 I 4 1
The a-axis is short (3.271 ~) and about equal to that found in NaxVS 2 of type I; this may indicate that the d-electrons in the VS 2 layers are delocalized. Indeed, preliminary experiments showed that the hydrate has a low resistivity. Hydrolysis of NaA ~VS_ in water gave a black precipitate; there Ob 2 was no evolution of hydrogen during hydrolysis. The powder pattern of the precipitate agreed with that of the final product of hydrolysis in moist air. Hydrolysis in moist air of a sample of composition Na n VS did not lead to a homogeneous product. The powder pattern showed i~'~o ~e a mixture of phases with powder pattern identical to those of the two hydratation steps of Nao.6VS 2 and probably of V3S 4. References I. J. Rouxel, M. Danot and J. Bichon, Bull. Soc. Chim. Fr. 1971, 3930. 2. A. Leblanc-Soreau, 2' 191 (1974).
M. Danot, L. Trichet and J. Rouxel, Mat. Res. Bull.
3- G. Grams, Dissertation,
T~bingen 1961.
4. J. Bichon, M. Danot and J. Rouxel, C.R. Acad. Sc. 276, 1283 (1973). 5. B. van Laar and D.J.W. Ydo, J. S o l d State Chem. ~, 590 (1971). 6. F.M.R. Engelsman, G.A. Wiegers, F. Jellinek and B. van Laar, J.Solid State Chem. 6, 574 (1973). 7. W. R~dorff, Chimia 19, 489 (1965). 8. C.H. Elstermann,
Dissertation, T~bingen 1965.
9. R. Huisman, R. de Jonge, C. Haas and F. Jellinek, J. Solid State Chem. ~, 56 (1971). 10. R. Schollhorn and A. Weiss, Z. Naturforsch.
28b, 711 (1974).