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Organic intercalation on layered compound KTiNbO5
Physica 105B (1981) 234-237 North-Holland Publishing Company
O R G A N I C I N T E R C A L A T I O N ON LAYERED C O M P O U N D KTiNbO5 S. K I K K A W A and M. K O I Z U M I The Institute of Scientific and Industrial Research, Osaka University, Suita, Osaka 565, Japan
Organic intercalations are investigated on KTiNbO5with a layer structure through its cation exchanged form HTiNbOs. The compound intercalates various kinds of amine (B) forming (H+)l ~/,,(BH*)l/m (TiNbOg). When aliphatic amines of the type CH3(CHz)n-INH2 are used as intercalants, m is estimated to be 2 and the chain axes of the double layered intercalants are almost perpendicular to the host layer.
1. Introduction Some layered inorganic compounds intercalate organic molecules as well as inorganic and/or organic ions. Many investigations have been made on intercalation of layered non-oxide materials. However, further studies on oxides are inevitably required to obtain the stable intercalation compounds. A t t e m p t s are being made at our laboratory to explore the layered oxides for intercalation. T h e present report will describe part of those investigations with KTiNbO5 as an example.
The crystal structure of layered c o m p o u n d KTiNbOS was investigated by Wadsley [1]. As shown in fig. 1, two octahedra have an edge in common, and by additional edge sharing to similar pairs above and below they extend as double zigzag strings elongated in the direction of the b-axis. The Ti and Nb atoms are presented at r a n d o m in two sets of central positions of octahedra with a little displacement from the octahedral centers. The double strings are joined by sharing octahedral corners to form puckered infinite sheets parallel to (001) with the composition (TiNbO5)~ n. These sheets are held together by the interlayer potassium ions. This p a p e r deals with the reversible exchange of potassium ion in KTiNbO5 with H ÷ at first, and then follows the studies of organic intercalation to HTiNbOs.
2. Experimental
t:l Fig. 1. Structure of KTiNbO5 drawn as octahedra, with potassium ions indicated by circles. Ti and Nb atoms are present at random in two sets of central position of the oetahedra.
KTiNbO5 was p r e p a r e d as a white solid by heating a mixture of K2CO3, TiO2 and Nb205 in the molar ratio 1 : 2 : 1 at 1100°C overnight. X-ray diffraction pattern of the product was indexed using the lattice p a r a m e t e r s obtained by Wadsley [1]. The KTiNbO5 obtained was treated in 2M HCI at 60°C for 1 h, and was washed with distilled water. The flame analysis showed no existence of potassium in the acid-treated material. The ability of organic intercalation was investigated on the original KTiNbO5 as well as on the HCl-treated sample. These materials were
0378-4363/81/0000-0000/$2.50 O North-Holland Publishing C o m p a n y and Y a m a d a Science Foundation
S. Kikkawa and M. Koizumi/lntercalation on layered KTINb05
sealed in glass tubes with organic compound and reacted at 600C for several hours.
235
1600 1400 1200 1000 800 I'-
3. Results and discussion
X-ray diffraction patterns of KTiNbO5 and its acid-treated material, depicted in fig. 2a, b, were indexed as orthorhombic. These two materials showed very similar lattice parameters: a = 6.44, b = 3.80, c = 18.24 A for KTiNbO5 and a -- 6.54, b = 3.78, c - - 1 7 . 5 2 A for the HCl-treated one. Qualitative chemical analysis of the acid-treated sample indicated the complete removal of potassium from KTiNbOs, and an infrared spectrum represented in fig. 3b, showed the presence of proton in the treated sample. The spectrum had an absorption at around 1100 cm -~ assigned to bending vibration of M - O - H , where M was Ti or Nb [2]. KTiNbO5 showed a spectrum, shown in fig. 3a, similar to that shown in fig. 3b, except for the 1100cm -1 absorption. The chemical analysis and IR spectrum implied that the product was HTiNbOs. HTiNbO5 returned to KTiNbO5 when it was dipped in 1 M K O H aqueous solution for 5 h at 60°C. These results
,00 I
.
AO02
II
020
a
I
/
2ool
b
c
i
,o
i
20 2e
3b
20
5o
(Cu-Ko~)
Fig. 2. X-ray diffraction diagrams of: (a) KTiNbOs; (b) HTiNbO5 (HCl-treated KTiNbOs); and (c) HTiNbO5reacted with ethylamine.
C
1600 1400 1200 1000 800 Wovenumber (cm")
Fig. 3. Infrared spectra of: (a) KTiNbOs; (b) HTiN-bOs; (c) tri-n-butylamine intercalated HTiNbO5 (m = 8); (d) di-npropylamine intercalated HTiNbO5 (m = 3); (e) tri-n-butylamine; and (f) di-n-propylamine, respectively. The shaded absorptions are assigned to the bending vibration of M-O-H [21. suggested that the potassium ion in KTiNbO5 was exchanged with proton without the reconstruction of the host (TiNbO~) layer during the acid treatment. Hydrazine intercalations were tried on both KTiNbO5 and HTiNbOs. These solid materials were soaked in hydrazine at 60°C for 5 h. The intercalation of hydrazine was completed on HTiNbOs. However, in the system KTiNbOshydrazine, no change was observed on X-ray diffraction. Secondly, organic amine intercalations were investigated on HTiNbOs. It reacted with the organic bases listed in table I. Excess amounts of organic bases were removed and the remaining products were washed with acetone and dried in air. X-ray diffraction lines assigned to h00 and 0k0 did not shift drastically on reaction with organic bases (e.g. fig. 2c). Lattice parameters were calculated using the reflections 200, 020 and 002 based on an orthorhombic lattice. U p o n reaction large expansions were observed on the c-lattice
236
S. Kikkawa and M. Koizumi/lntercalation on layered KTiNb05
Table I Lattice parameters, in A, of intercalation c o m p o u n d s prepared from HTiNbO5
20
Lattice parameters a Intercalated organic base
a
b
c
Ammonia Methylamine Ethylamine n-Propylamine n-Butylamine Hydrazine Di-n-propylamine Tri-n-butylamine
6.46 6.44 6.46 6.46 6.44 6.50 6.50 6.54
3.80 3.81 3.78 3.80 3.80 3.80 . 3.80 3.78
19.02 22.96 26.78 35.34 36.82 21.30 33.34 39.28
5
O
15
y0
O
I
I
I
I
I
2
3
4
Number of cat'bon : n
a These parameters are calculated using 200, 020 and 002 X-ray diffractions in Cu-K~. Deviations are ±0.05, ±0.01 and ---0.2 ~ respectively, for a, b and c.
Fig. 4. Interlayer distances (c/2) of the intercalation compounds (H+)H/,, (BH+)v~, (TiNbO~) as a function of carbon n u m b e r in CH3(CH2),-INH2.
parameter with only small changes in the a and b parameters. These changes of lattice parameters suggest that organic bases are intercalated into the interlayer region of (TiNbO~). HTiNbO5 probably behaves as a Br6nsted acid and reacts with organic B r f n s t e d base denoted as B, forming intercalation compound (H+)H/m (BH+)1/m (TiNbO~). The chemical analyses for C, H and N showed that m = 2 when B was an aliphatic amine of the type CH3(CH2),-1NH2 and that m = 3 and 8, respectively, for di-n-proplyamine and for tri-n-butylamine. The amount of H ÷ in the interlayer decreased with an increasing amount of intercalated amines. Infrared spectra illustrated in fig. 3c, d showed that the intercalation compounds have characteristic absorptions of the intercalated amines in addition to those of host material. The intensity of the absorption of M O - H appeared in the region around 1100 cm -~ decreased with intercalation and also with the decrease of m value. c-Lattice parameters of the intercalation compounds are plotted against the numbers of carbon in the series of the intercalated compounds CH3(CH2),-1NH2, as shown in fig. 4. One-half of the c-parameter corresponds to the interlayer distance. The distance of c/2 almost linearly increases with the number of carbon having a gradient value of 2.40. Molecular
orientations can be estimated by using this gradient. The i n c r e a s e in the length of an aliphatic chain per carbon is 1.27 ~ . The observed gradient suggests that the intercalated amines form a double layer with their terminal NH~ groups pointing to the host (TiNbO~) layers. The angle of inclination of the chain length to the basal plane is sin -t (2.40/2.54) which is equivalent to 71 °. This angle cannot be accurate, but the axes of the long carbon chains are almost perpendicular to the host layer, as schematically shown in fig. 5. This kind of estimate has been widely applied to intercalation compounds containing alkyl chains and flat basal planes [3]. The inclination angle of alkyl chain to the host layer is usually 56 ° in intercalation compounds of transition metal dichalcogenides [4]. However, the host (TiNbO~) layer is fairly puckered. The corrugation of the host layer might affect the inclination of the intercalated alkyl chain especially in the case of a short alkyl chain. Since the van der Waals radius of the methyl group is 2.0 ~ , an intercalated molecule occupies the area of about 12/~2 (,r x 2 2/~k2) in the basal plane in this case. One formula unit of (FiNbO~) has an area of about 6 A 2 (a. b/z) projected to (001) because a = 6.44 A, b = 3.80/~, and z = 4. Thus, one amine molecule can be accommodated in the area of two units of (TiNbO~). This calculation agrees well
S. Kikkawa and M. Koizumi/Intercalation on layered KT'tNb05
( Ti Nb0 5 )
layer
. . . . 7~- -
237
vestigate cation transport in the interlayer region [5]. We investigated the intercalations of alkylamines into KTiTaO5 as well as KTiNbOs. These two compounds showed similar results in X-ray study. It is considered that both HTiNbO5 and HTiTaO5 behave as Br6nsted acids to intercalate aliphatic amines working as Br6nsted bases into the acidic host materials. However, the alkyl amines also work as alkyl ammonium ions in the presence of water. They may substitute the p r o tons previously exchanged. Acknowledgment
(TiNb0 5 )
layer
---
Fig. 5. Schematically represented structure of the intercalation
compound
(I-V) H/m
(CH3(CH2)n-INH~)t/m
(TiNbO~). with the experimental results of m = 2. Hydrogen atoms occupy the vacant sites in the basal plane balancing the total charge. Recently Rebbah et al. reported the interlayer cation exchange on KTiNbO5 and on the isostructural compound KTiTaO5 in order to in-
We are indebted to the Ministry of Education for Grant-in-Aid for Scientific Research who supported this research. References
[1] A . D Wadsley, Acta Cryst. 17 (1964) 623. [2] K. Nakamoto, Infrared Spectra of Inorganic and Coordination Compounds, 2nd ed. (John Wiley, New York, 1970) p. 169. [3] G.W. Brindley and S. Ray, Amer. Mineralogist 49 (1964) 106. [4] A. Weiss and R. Ruthardt, Z. Naturforsch. 28b (1973) 249. [5] H. Rebbah, G. Desgardin and B. Raveau, Mater. Res. Bull. 14 (1979) 1125.
O R G A N I C I N T E R C A L A T I O N ON LAYERED C O M P O U N D KTiNbO5 S. K I K K A W A and M. K O I Z U M I The Institute of Scientific and Industrial Research, Osaka University, Suita, Osaka 565, Japan
Organic intercalations are investigated on KTiNbO5with a layer structure through its cation exchanged form HTiNbOs. The compound intercalates various kinds of amine (B) forming (H+)l ~/,,(BH*)l/m (TiNbOg). When aliphatic amines of the type CH3(CHz)n-INH2 are used as intercalants, m is estimated to be 2 and the chain axes of the double layered intercalants are almost perpendicular to the host layer.
1. Introduction Some layered inorganic compounds intercalate organic molecules as well as inorganic and/or organic ions. Many investigations have been made on intercalation of layered non-oxide materials. However, further studies on oxides are inevitably required to obtain the stable intercalation compounds. A t t e m p t s are being made at our laboratory to explore the layered oxides for intercalation. T h e present report will describe part of those investigations with KTiNbO5 as an example.
The crystal structure of layered c o m p o u n d KTiNbOS was investigated by Wadsley [1]. As shown in fig. 1, two octahedra have an edge in common, and by additional edge sharing to similar pairs above and below they extend as double zigzag strings elongated in the direction of the b-axis. The Ti and Nb atoms are presented at r a n d o m in two sets of central positions of octahedra with a little displacement from the octahedral centers. The double strings are joined by sharing octahedral corners to form puckered infinite sheets parallel to (001) with the composition (TiNbO5)~ n. These sheets are held together by the interlayer potassium ions. This p a p e r deals with the reversible exchange of potassium ion in KTiNbO5 with H ÷ at first, and then follows the studies of organic intercalation to HTiNbOs.
2. Experimental
t:l Fig. 1. Structure of KTiNbO5 drawn as octahedra, with potassium ions indicated by circles. Ti and Nb atoms are present at random in two sets of central position of the oetahedra.
KTiNbO5 was p r e p a r e d as a white solid by heating a mixture of K2CO3, TiO2 and Nb205 in the molar ratio 1 : 2 : 1 at 1100°C overnight. X-ray diffraction pattern of the product was indexed using the lattice p a r a m e t e r s obtained by Wadsley [1]. The KTiNbO5 obtained was treated in 2M HCI at 60°C for 1 h, and was washed with distilled water. The flame analysis showed no existence of potassium in the acid-treated material. The ability of organic intercalation was investigated on the original KTiNbO5 as well as on the HCl-treated sample. These materials were
0378-4363/81/0000-0000/$2.50 O North-Holland Publishing C o m p a n y and Y a m a d a Science Foundation
S. Kikkawa and M. Koizumi/lntercalation on layered KTINb05
sealed in glass tubes with organic compound and reacted at 600C for several hours.
235
1600 1400 1200 1000 800 I'-
3. Results and discussion
X-ray diffraction patterns of KTiNbO5 and its acid-treated material, depicted in fig. 2a, b, were indexed as orthorhombic. These two materials showed very similar lattice parameters: a = 6.44, b = 3.80, c = 18.24 A for KTiNbO5 and a -- 6.54, b = 3.78, c - - 1 7 . 5 2 A for the HCl-treated one. Qualitative chemical analysis of the acid-treated sample indicated the complete removal of potassium from KTiNbOs, and an infrared spectrum represented in fig. 3b, showed the presence of proton in the treated sample. The spectrum had an absorption at around 1100 cm -~ assigned to bending vibration of M - O - H , where M was Ti or Nb [2]. KTiNbO5 showed a spectrum, shown in fig. 3a, similar to that shown in fig. 3b, except for the 1100cm -1 absorption. The chemical analysis and IR spectrum implied that the product was HTiNbOs. HTiNbO5 returned to KTiNbO5 when it was dipped in 1 M K O H aqueous solution for 5 h at 60°C. These results
,00 I
.
AO02
II
020
a
I
/
2ool
b
c
i
,o
i
20 2e
3b
20
5o
(Cu-Ko~)
Fig. 2. X-ray diffraction diagrams of: (a) KTiNbOs; (b) HTiNbO5 (HCl-treated KTiNbOs); and (c) HTiNbO5reacted with ethylamine.
C
1600 1400 1200 1000 800 Wovenumber (cm")
Fig. 3. Infrared spectra of: (a) KTiNbOs; (b) HTiN-bOs; (c) tri-n-butylamine intercalated HTiNbO5 (m = 8); (d) di-npropylamine intercalated HTiNbO5 (m = 3); (e) tri-n-butylamine; and (f) di-n-propylamine, respectively. The shaded absorptions are assigned to the bending vibration of M-O-H [21. suggested that the potassium ion in KTiNbO5 was exchanged with proton without the reconstruction of the host (TiNbO~) layer during the acid treatment. Hydrazine intercalations were tried on both KTiNbO5 and HTiNbOs. These solid materials were soaked in hydrazine at 60°C for 5 h. The intercalation of hydrazine was completed on HTiNbOs. However, in the system KTiNbOshydrazine, no change was observed on X-ray diffraction. Secondly, organic amine intercalations were investigated on HTiNbOs. It reacted with the organic bases listed in table I. Excess amounts of organic bases were removed and the remaining products were washed with acetone and dried in air. X-ray diffraction lines assigned to h00 and 0k0 did not shift drastically on reaction with organic bases (e.g. fig. 2c). Lattice parameters were calculated using the reflections 200, 020 and 002 based on an orthorhombic lattice. U p o n reaction large expansions were observed on the c-lattice
236
S. Kikkawa and M. Koizumi/lntercalation on layered KTiNb05
Table I Lattice parameters, in A, of intercalation c o m p o u n d s prepared from HTiNbO5
20
Lattice parameters a Intercalated organic base
a
b
c
Ammonia Methylamine Ethylamine n-Propylamine n-Butylamine Hydrazine Di-n-propylamine Tri-n-butylamine
6.46 6.44 6.46 6.46 6.44 6.50 6.50 6.54
3.80 3.81 3.78 3.80 3.80 3.80 . 3.80 3.78
19.02 22.96 26.78 35.34 36.82 21.30 33.34 39.28
5
O
15
y0
O
I
I
I
I
I
2
3
4
Number of cat'bon : n
a These parameters are calculated using 200, 020 and 002 X-ray diffractions in Cu-K~. Deviations are ±0.05, ±0.01 and ---0.2 ~ respectively, for a, b and c.
Fig. 4. Interlayer distances (c/2) of the intercalation compounds (H+)H/,, (BH+)v~, (TiNbO~) as a function of carbon n u m b e r in CH3(CH2),-INH2.
parameter with only small changes in the a and b parameters. These changes of lattice parameters suggest that organic bases are intercalated into the interlayer region of (TiNbO~). HTiNbO5 probably behaves as a Br6nsted acid and reacts with organic B r f n s t e d base denoted as B, forming intercalation compound (H+)H/m (BH+)1/m (TiNbO~). The chemical analyses for C, H and N showed that m = 2 when B was an aliphatic amine of the type CH3(CH2),-1NH2 and that m = 3 and 8, respectively, for di-n-proplyamine and for tri-n-butylamine. The amount of H ÷ in the interlayer decreased with an increasing amount of intercalated amines. Infrared spectra illustrated in fig. 3c, d showed that the intercalation compounds have characteristic absorptions of the intercalated amines in addition to those of host material. The intensity of the absorption of M O - H appeared in the region around 1100 cm -~ decreased with intercalation and also with the decrease of m value. c-Lattice parameters of the intercalation compounds are plotted against the numbers of carbon in the series of the intercalated compounds CH3(CH2),-1NH2, as shown in fig. 4. One-half of the c-parameter corresponds to the interlayer distance. The distance of c/2 almost linearly increases with the number of carbon having a gradient value of 2.40. Molecular
orientations can be estimated by using this gradient. The i n c r e a s e in the length of an aliphatic chain per carbon is 1.27 ~ . The observed gradient suggests that the intercalated amines form a double layer with their terminal NH~ groups pointing to the host (TiNbO~) layers. The angle of inclination of the chain length to the basal plane is sin -t (2.40/2.54) which is equivalent to 71 °. This angle cannot be accurate, but the axes of the long carbon chains are almost perpendicular to the host layer, as schematically shown in fig. 5. This kind of estimate has been widely applied to intercalation compounds containing alkyl chains and flat basal planes [3]. The inclination angle of alkyl chain to the host layer is usually 56 ° in intercalation compounds of transition metal dichalcogenides [4]. However, the host (TiNbO~) layer is fairly puckered. The corrugation of the host layer might affect the inclination of the intercalated alkyl chain especially in the case of a short alkyl chain. Since the van der Waals radius of the methyl group is 2.0 ~ , an intercalated molecule occupies the area of about 12/~2 (,r x 2 2/~k2) in the basal plane in this case. One formula unit of (FiNbO~) has an area of about 6 A 2 (a. b/z) projected to (001) because a = 6.44 A, b = 3.80/~, and z = 4. Thus, one amine molecule can be accommodated in the area of two units of (TiNbO~). This calculation agrees well
S. Kikkawa and M. Koizumi/Intercalation on layered KT'tNb05
( Ti Nb0 5 )
layer
. . . . 7~- -
237
vestigate cation transport in the interlayer region [5]. We investigated the intercalations of alkylamines into KTiTaO5 as well as KTiNbOs. These two compounds showed similar results in X-ray study. It is considered that both HTiNbO5 and HTiTaO5 behave as Br6nsted acids to intercalate aliphatic amines working as Br6nsted bases into the acidic host materials. However, the alkyl amines also work as alkyl ammonium ions in the presence of water. They may substitute the p r o tons previously exchanged. Acknowledgment
(TiNb0 5 )
layer
---
Fig. 5. Schematically represented structure of the intercalation
compound
(I-V) H/m
(CH3(CH2)n-INH~)t/m
(TiNbO~). with the experimental results of m = 2. Hydrogen atoms occupy the vacant sites in the basal plane balancing the total charge. Recently Rebbah et al. reported the interlayer cation exchange on KTiNbO5 and on the isostructural compound KTiTaO5 in order to in-
We are indebted to the Ministry of Education for Grant-in-Aid for Scientific Research who supported this research. References
[1] A . D Wadsley, Acta Cryst. 17 (1964) 623. [2] K. Nakamoto, Infrared Spectra of Inorganic and Coordination Compounds, 2nd ed. (John Wiley, New York, 1970) p. 169. [3] G.W. Brindley and S. Ray, Amer. Mineralogist 49 (1964) 106. [4] A. Weiss and R. Ruthardt, Z. Naturforsch. 28b (1973) 249. [5] H. Rebbah, G. Desgardin and B. Raveau, Mater. Res. Bull. 14 (1979) 1125.