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Lithium intercalation of WO2Cl2
Mat. Res. B u l l . , Vol. 23, pp. 165-169, 1988. Printed in the USA. 0025-5408/88 $3.00 + .09 Copyright ( c ) 1987 Pergamon Journals Ltd.
L I T H I U M INTERCALATION OF WO2CI 2
J.F. A c k e r m a n General Electric Company Corporate Research and Development P.O. Box 8 Schenectady, NY 12301
Center
(Received August 31, 1987; Communicated b y R . C . DeVries)
ABSTRACT The layered solid WO~CI~ was intercalated with lithium via chemical techz z niques. The electronic properties of the solid change during reaction from an insulator to a n a r r o w b a n d semiconductor. MATERIALS
INDEX:
chlorides,
tungsten,
lithium
Introduction Recent investigations of layered solids have d e m o n s t r a t e d the intercalating ability of g u ~ s ~ @toms or molecules into the v a n der Waals regions b e t w e e n the layers.--'--'However, unquestionable interpretation of electronic, magnetic, and optical measurements is rare since m a s k i n g effects from rapid e l e c t r o n exchange are present in these intrinsic semiconductors and metals. We b e l i e v e that an ionic diamagnetic insulator with a layered structure such as WO^CI^ w o u l d provide an ideal host for further investigations. ' z z' We d e m o n s t r a t e ~ere the ability of W02CI 2 to undergo intercalation by treatment with active lithium. Experimental WO2CI 2 was p r e p a r e d by the direct combination of 2W02 + IWCI 6 in an evacuated silica tube w i t h i n a thermal gradient of 300-270°C. A mixture of 4.0g ~CI 6 and 5o0g WO^ was w e i g h e d under N^ and transferred to a 10cm x 3 cm silica 3 tube. After e v a c u a t i n g to i# the tu~e was sealed and placed in a 3 zone tube furnace. The charge was h e a t e d to 300°C, the growth zone to 270°C and the neck of the tube to 300°C. After 3 days the furnace was allowed to air quench to 25°C; then the tube was extracted and opened under N 2. I n t e r c a l a t i o n with lithium took place by WO^CI 2 (0.1g) was p l a c e d in an argon purged toluene. Five m i l l i l i t e r s of 1.6M n-butyl dropwise at room temperature over a period flask was o p e n e d and the solid separated by place under an a r g o n atmosphere. 165
the n-butyl lithium technique. 4 hermetic flask with 25cc of dry lithium (in hexane) were added of 2 days. After one week the filtration. All operations took
J.F.
166
ACKERMAN
Vol. 23, No. 2
Lattice constants were obtained from least squares refinements of Guinier-Hagg data calibrated with pure Si. Electrical resistivities were measured by the standard 4 probe method using silver paste for the initial ohmic contact to the samples on the (010) and (010) faces. Results and Discussion Large (15xl5x3mm) micaceous single crystals of W02CI 2 could be grown by transport of WO 3 and WCI 6. When free from WCIr they are transparent, ~ l o r less, diamagnetlc and electrically insulating; Raving resistivities ~I0 ohmcm. X-ray diffraction peaks are compatible with the monoclinic cell previously reported; with a=14.42A bz3.89A c=7.68A and ~=i05.4 °. As atomic lithium, generated from the reaction 2n-BuLi ~ 2Li+n-octane, is brought into contact with WO~CI9 it diffuses into the van der Waals region. The WO~CI 2 rapidly darkens-t~ become blue with transmitted light. With further n-~uL1 exposure the blue color is replaced by a copper colored metallic reflectivity. Upon completing the reaction the stoichiometry of the product was Li 2 0W02CI 2 by chemical analysis and Lil.98WO2CI 2 by weight gain.
TABLE i Crystallographic data for Li2WO2CI 20rthorhombic a=7.674A b=30.180A c=3.924A ( ±.002A)
d(A)
I
hkl
d(A)
I
10.297 7.521 3.924 3.769 3.663 3.192 3.017 2.715 2.630 2.557 2.392 2.215 1.888 1.831 1.706 1.666 1.601 1.533 1.473 1.350 1.328 1.275 1.254
35 30 5 60 95 30 20 55 5 20 25 5 75 50 50 15 i0 i0 20 8 I0 5 20
030 040 001 080 031 141 0,I0,0 171 231 300;091 0,I0,i 281 0,16,0 062 242 1,16,1 0,19,0 510 1,13,2 442 1,21,1 1,22,1 0,24,0
7.657 6.056 3.837 3 728 3 331 3 068 2 751 2 670 2 576 2 516 2 354 1.954 1.862 1.714 1.678 1.627 1.564 1.509 1.357 1.334 1.314 1.259
25 2 20 i00 5 15 5 80 5 35 35 i0 45 i0 80 i0 5 i0 20 25 I0 i0
hkl i00 050 200 220 090 260 0,i0,0 280 181 0,12,0 350 022 440 480 0,18,0 4,10,0 312 0,20,0 2 452 0,23,0 640
Vol. 23, No. 2
WO2CI2
167
X-ray diffraction patterns varied as a function of lithium (x in Li WO~CI~). No changes in peak positions was seen up to x=0.3. When 0.3~x_~1.2~ t~e ~k0 peaks were attenuated and 00~ diffraction demonstrated a new phase with layered-axis dimension 20.7A. Higher lithium concentration produced a biphasic product consisting of a phase with the layered-axis dimension 30.18A, mixed with the 20.7A phase. Only as x approaches the limiting value of 2.0 can the 30.18A phase be obtained pure, Table i. Further lithiation degrades this product.
Figure i - Crystal structure of WO2CI 2 The crystal structure of W02C12, Figure i, consists of layers of WO~CI 2 octahedra which share corners vla oxygen; leaving the apices o c c u p i e ~ by chlorine. The layers are separated from one another by a 3.7A van der Waals region. Within this region there are 2 different sites compatible with metal atom occupation. These are indicited as sites A and B. Site A is 5 coordinate with square pyramidal symmetry. Site B is 4 coordinate with tetrahedral symmetry and lies in the center of the van der Waals region. Whereas the type A sites are found to be occupied in the related oxyhalide FeOCI , we believe they are not occupied here. With A-site to chlorine distances of 2.7A and 2.9A the A-sites are large enough to accommodate the small lithium atoms without any expansion of the lattice. However, B-site to chlorine distances
168
J.F.
ACKERMAN
Vol. 23, No. 2
are 2.25A which are shorter than the sums of the ionic radii and Li and CI. Occupation of these sites would result in a lengthening of the B-site to chlorine distance by a least .2A with a subsequent increase in the layer axis dimension; such as is observed. The interlayer expansion of .53A increases the Li-CI distances to 2.42A which compares very favorably with the ionic radii sum. The 20.7A interlayer phase is most likely the 3rd stage material having a stoichiometry of Li.66WO2CI 2. The resistivity of Li2WO2Cli.as a function of temperature is shown in Figure 2. The activation energy is .05eV and the thermoelectric coefficient is 240pV/°C at 300°K, suggesting that this material is a narrow band-gap ntype semiconductor.
1.0
E
O
O.1
•
1:0
1/T
x 10 3
12.O
Figure 2 - Resistivity of Li2W02CI 2 as a function of temperature The tungsten and oxygen atoms in WO^CI^ have similar geometry to the • z z tungsten and oxygen atoms in the (001) plane of WOR. We may therefore expect W02CI 9 to have a similar band structure to WO~; differing only by the distortion ~rom octahedral symmetry and width of the W-CI bands. The electron configuration would be aW-0(4) oW-CI(2) ~W-0(0). Upon lithiation 2 electrons are removed from lithium and added to the ~ bands, aW-O(4) aW-CI(2) ~W-O(2). Such free electrons in the ~ filled bands are expected to produce metallic conductivity. Its absence is possibly due to the orientation of the electrical contacts on the crystal by which we are trying to pass current through the van der Waals gap.
Vol. 23, No. 2
WO2CI2
169
Conclusions Dielectric diamagnetic WO_CI_ has been intercalated by Li. The extent of 2 intercalation has been determlne~ by chemical and weighing methods to be 2 lithium per W02CI 2. There appears to be a site preference for Li occupation which gives rlse to a lattice expansion. The electronic properties changed markedly upon intercalation from insulating to conducting. Preliminary experiments have been performed with pyridine which indicate the molecular intercalation occurs without the loss of insulating behavior.
References
i.
Palvadeau, (1978).
L.
Coic,
Rouxel,
2.
F. Kanamura, M. Shimada, M. Koizumi, M. Pakanok, State Chem. R , I (1973).
3.
F.R. Gamble, J. Osiecki, M. Cais, Geballe, Science 174, 493 (1971).
4.
M. Armand and W. van Gool (ed.), "Fast Ion Transport Holland, Amsterdam 1973 p. 666.
5.
O. Jarchow, (1968).
6.
J.B. Goodenough,
F. Schroder,
and J.
Portier,
R.
Mat.
Bull.
13,
221
and T. Pakada, J. Solid
Pishaiody,
and H. Schultz,
Res.
Z. Anorg.
F.
DiSalvo,
and T.H.
in Solids."
Allg.
Bull. Soc. Chim. France 1965, 1200 (1965).
Chem.
North
36__~3, 58
L I T H I U M INTERCALATION OF WO2CI 2
J.F. A c k e r m a n General Electric Company Corporate Research and Development P.O. Box 8 Schenectady, NY 12301
Center
(Received August 31, 1987; Communicated b y R . C . DeVries)
ABSTRACT The layered solid WO~CI~ was intercalated with lithium via chemical techz z niques. The electronic properties of the solid change during reaction from an insulator to a n a r r o w b a n d semiconductor. MATERIALS
INDEX:
chlorides,
tungsten,
lithium
Introduction Recent investigations of layered solids have d e m o n s t r a t e d the intercalating ability of g u ~ s ~ @toms or molecules into the v a n der Waals regions b e t w e e n the layers.--'--'However, unquestionable interpretation of electronic, magnetic, and optical measurements is rare since m a s k i n g effects from rapid e l e c t r o n exchange are present in these intrinsic semiconductors and metals. We b e l i e v e that an ionic diamagnetic insulator with a layered structure such as WO^CI^ w o u l d provide an ideal host for further investigations. ' z z' We d e m o n s t r a t e ~ere the ability of W02CI 2 to undergo intercalation by treatment with active lithium. Experimental WO2CI 2 was p r e p a r e d by the direct combination of 2W02 + IWCI 6 in an evacuated silica tube w i t h i n a thermal gradient of 300-270°C. A mixture of 4.0g ~CI 6 and 5o0g WO^ was w e i g h e d under N^ and transferred to a 10cm x 3 cm silica 3 tube. After e v a c u a t i n g to i# the tu~e was sealed and placed in a 3 zone tube furnace. The charge was h e a t e d to 300°C, the growth zone to 270°C and the neck of the tube to 300°C. After 3 days the furnace was allowed to air quench to 25°C; then the tube was extracted and opened under N 2. I n t e r c a l a t i o n with lithium took place by WO^CI 2 (0.1g) was p l a c e d in an argon purged toluene. Five m i l l i l i t e r s of 1.6M n-butyl dropwise at room temperature over a period flask was o p e n e d and the solid separated by place under an a r g o n atmosphere. 165
the n-butyl lithium technique. 4 hermetic flask with 25cc of dry lithium (in hexane) were added of 2 days. After one week the filtration. All operations took
J.F.
166
ACKERMAN
Vol. 23, No. 2
Lattice constants were obtained from least squares refinements of Guinier-Hagg data calibrated with pure Si. Electrical resistivities were measured by the standard 4 probe method using silver paste for the initial ohmic contact to the samples on the (010) and (010) faces. Results and Discussion Large (15xl5x3mm) micaceous single crystals of W02CI 2 could be grown by transport of WO 3 and WCI 6. When free from WCIr they are transparent, ~ l o r less, diamagnetlc and electrically insulating; Raving resistivities ~I0 ohmcm. X-ray diffraction peaks are compatible with the monoclinic cell previously reported; with a=14.42A bz3.89A c=7.68A and ~=i05.4 °. As atomic lithium, generated from the reaction 2n-BuLi ~ 2Li+n-octane, is brought into contact with WO~CI9 it diffuses into the van der Waals region. The WO~CI 2 rapidly darkens-t~ become blue with transmitted light. With further n-~uL1 exposure the blue color is replaced by a copper colored metallic reflectivity. Upon completing the reaction the stoichiometry of the product was Li 2 0W02CI 2 by chemical analysis and Lil.98WO2CI 2 by weight gain.
TABLE i Crystallographic data for Li2WO2CI 20rthorhombic a=7.674A b=30.180A c=3.924A ( ±.002A)
d(A)
I
hkl
d(A)
I
10.297 7.521 3.924 3.769 3.663 3.192 3.017 2.715 2.630 2.557 2.392 2.215 1.888 1.831 1.706 1.666 1.601 1.533 1.473 1.350 1.328 1.275 1.254
35 30 5 60 95 30 20 55 5 20 25 5 75 50 50 15 i0 i0 20 8 I0 5 20
030 040 001 080 031 141 0,I0,0 171 231 300;091 0,I0,i 281 0,16,0 062 242 1,16,1 0,19,0 510 1,13,2 442 1,21,1 1,22,1 0,24,0
7.657 6.056 3.837 3 728 3 331 3 068 2 751 2 670 2 576 2 516 2 354 1.954 1.862 1.714 1.678 1.627 1.564 1.509 1.357 1.334 1.314 1.259
25 2 20 i00 5 15 5 80 5 35 35 i0 45 i0 80 i0 5 i0 20 25 I0 i0
hkl i00 050 200 220 090 260 0,i0,0 280 181 0,12,0 350 022 440 480 0,18,0 4,10,0 312 0,20,0 2 452 0,23,0 640
Vol. 23, No. 2
WO2CI2
167
X-ray diffraction patterns varied as a function of lithium (x in Li WO~CI~). No changes in peak positions was seen up to x=0.3. When 0.3~x_~1.2~ t~e ~k0 peaks were attenuated and 00~ diffraction demonstrated a new phase with layered-axis dimension 20.7A. Higher lithium concentration produced a biphasic product consisting of a phase with the layered-axis dimension 30.18A, mixed with the 20.7A phase. Only as x approaches the limiting value of 2.0 can the 30.18A phase be obtained pure, Table i. Further lithiation degrades this product.
Figure i - Crystal structure of WO2CI 2 The crystal structure of W02C12, Figure i, consists of layers of WO~CI 2 octahedra which share corners vla oxygen; leaving the apices o c c u p i e ~ by chlorine. The layers are separated from one another by a 3.7A van der Waals region. Within this region there are 2 different sites compatible with metal atom occupation. These are indicited as sites A and B. Site A is 5 coordinate with square pyramidal symmetry. Site B is 4 coordinate with tetrahedral symmetry and lies in the center of the van der Waals region. Whereas the type A sites are found to be occupied in the related oxyhalide FeOCI , we believe they are not occupied here. With A-site to chlorine distances of 2.7A and 2.9A the A-sites are large enough to accommodate the small lithium atoms without any expansion of the lattice. However, B-site to chlorine distances
168
J.F.
ACKERMAN
Vol. 23, No. 2
are 2.25A which are shorter than the sums of the ionic radii and Li and CI. Occupation of these sites would result in a lengthening of the B-site to chlorine distance by a least .2A with a subsequent increase in the layer axis dimension; such as is observed. The interlayer expansion of .53A increases the Li-CI distances to 2.42A which compares very favorably with the ionic radii sum. The 20.7A interlayer phase is most likely the 3rd stage material having a stoichiometry of Li.66WO2CI 2. The resistivity of Li2WO2Cli.as a function of temperature is shown in Figure 2. The activation energy is .05eV and the thermoelectric coefficient is 240pV/°C at 300°K, suggesting that this material is a narrow band-gap ntype semiconductor.
1.0
E
O
O.1
•
1:0
1/T
x 10 3
12.O
Figure 2 - Resistivity of Li2W02CI 2 as a function of temperature The tungsten and oxygen atoms in WO^CI^ have similar geometry to the • z z tungsten and oxygen atoms in the (001) plane of WOR. We may therefore expect W02CI 9 to have a similar band structure to WO~; differing only by the distortion ~rom octahedral symmetry and width of the W-CI bands. The electron configuration would be aW-0(4) oW-CI(2) ~W-0(0). Upon lithiation 2 electrons are removed from lithium and added to the ~ bands, aW-O(4) aW-CI(2) ~W-O(2). Such free electrons in the ~ filled bands are expected to produce metallic conductivity. Its absence is possibly due to the orientation of the electrical contacts on the crystal by which we are trying to pass current through the van der Waals gap.
Vol. 23, No. 2
WO2CI2
169
Conclusions Dielectric diamagnetic WO_CI_ has been intercalated by Li. The extent of 2 intercalation has been determlne~ by chemical and weighing methods to be 2 lithium per W02CI 2. There appears to be a site preference for Li occupation which gives rlse to a lattice expansion. The electronic properties changed markedly upon intercalation from insulating to conducting. Preliminary experiments have been performed with pyridine which indicate the molecular intercalation occurs without the loss of insulating behavior.
References
i.
Palvadeau, (1978).
L.
Coic,
Rouxel,
2.
F. Kanamura, M. Shimada, M. Koizumi, M. Pakanok, State Chem. R , I (1973).
3.
F.R. Gamble, J. Osiecki, M. Cais, Geballe, Science 174, 493 (1971).
4.
M. Armand and W. van Gool (ed.), "Fast Ion Transport Holland, Amsterdam 1973 p. 666.
5.
O. Jarchow, (1968).
6.
J.B. Goodenough,
F. Schroder,
and J.
Portier,
R.
Mat.
Bull.
13,
221
and T. Pakada, J. Solid
Pishaiody,
and H. Schultz,
Res.
Z. Anorg.
F.
DiSalvo,
and T.H.
in Solids."
Allg.
Bull. Soc. Chim. France 1965, 1200 (1965).
Chem.
North
36__~3, 58