- Email: [email protected]
Electrical properties of the solid solution Li4 − 3xInxSiO4
cm .
SOLID STATE
mm
k!i@ __
ELXWIER
Solid State Ionics 83 (1996) 245-248
IONICS
Electrical properties of the solid solution Li,_,,In,SiO, J.B. Chavarria a, P. Quintana b, A. Huanosta a a Instituto de Investigation en Materiales, Universidad National Autonama de Mexico, 04.510 Coyoacan, D.F., Mexico b Departamento de Fisica Aplicada, Centro de Investigation y de Estudios Avanzados de1 Instituto Politecnico National Unidad Merida, A.P. Cordemex, 97310 Merida, Yucatan, Mexico Received 21 May 1995; accepted 28 October 1995
Abstract Polycrystalline solid solutions with formula Li,_ 3XIn,SiO, : 0 I x I 0.15 were prepared by solid state synthesis. These materials were found to exhibit lithium ion vacancies. From ac impedance measurements conductivities with values around 1 x low5 K ’ cm- ’ at 25O”C, are found. Keywords: Lithium indium silicates; Lithium ion conductor; Ionic conductivity - lithium
1. Introduction In the search for a variety of batteries and solid state devices with Li+ ion conductors, considerable interest has been shown in systems based on Li,SiO, [l-4]. A group of closely related structure types, based on Li,SiO, have formed the basis of a large number of lithium ion conducting materials, some of which have been used as secondary cells that are operable at almost near room temperature. These electrolytes containing Li,PO, and L13V04, can be fabricated in thin film configuration using deposition techniques, such as rf-sputtering, vacuum evaporation or chemical vapor deposition [5-71. Li,SiO, has a versatile host structure and forms nonstoichiometric materials with different cations including, P, As, V [8-lo], Al, Ga [ll-131 and Zn, Mg [14]. The aluminium and gallium containing materials are particularly interesting because the host Li,SiO, strnctnre can be substituted in two ways, giving the series, Li,+,(M,Si,_,)O, and Li,_,,M,SiO,: M = Al, Ga. For Al, the solid solution limits are x = 0.40,
y = 0.60 [12], for Ga, they are x = 0.30 and y = 0.25 [13]. The first series leads to the creation of interstitial lithium ions, while the second leads to vacancies; in both series, dramatic increases in conductivity occur. Highest conductivities were found in the first series, M = Al, e.g. 3 X lop5 iR_’ cm-’ at 100°C for y = 0.20-0.25. The work hereby described was carried out with the aim of synthesizing new solid electrolytes to improve the ionic conductivity of the lithium ion, by introducing In ions in the structure of Li,SiO, to promote the formation of structural defects (i.e. creating Li vacancies or introducing Li interstially).
2. Experimental Polycrystalline samples were prepared by the solid state reaction technique from mixtures of Li,CO,, In,O,, SiO, (J.T. Baker and Koch-Ligth). The resulting powder materials were cold pressed into pellets of 12 mm in diameter and l-2 mm thickness,
0167-2738/%/$15.00 0 1996 Elsevier Science B.V. All rights reserved SSDI 0167-2738(95)00230-S
246
J.B. Chauarria et al./ Solid State Ionics 83 (1996) 245-248
they were sintered at 1020°C for 22 h in a lab atmosphere. Gold painted electrodes were applied to the surface of sintered pellets to register electrical response data arising from the sample. Experimental impedance measurements were obtained with a Hewlett-Packard 4192A Impedance Analyser controlled by a HP85 microcomputer. The investigated frequency range was from 5 Hz to 13 MHz, with an applied voltage of 1 V. Experimental data were recorded from room temperature up to 350°C. All measurements were made in air. Products were analyzed before and after the conductivity measurements by X-ray diffraction, using a Hagg-Guinier camera, Philips, with Cu K 011 radiation (A = 1.5405 A).
0
I.06
1.02
2.16
1000
7
3. Results and discussion Several compositions near Li,SiO, and LiInO, were prepared and reacted in order to look for the ocurrence of solid solutions. A well constituted solid solution based on Li,SiO, was found on the join, Li,SiO,-LiInSiO,, and there was no evidence for the formation of solid solutions on the join, LiInO,Li,SiO,. The results on the solid solution showed that the solid solubility range for In in the structure extends over a quite short range of compositions, creating Li vacancies with a solid solution mechanism: 3Lif * In3+. The corresponding compositions in the solid solution will be described as Li,_,,In,SiO, where OIXlO.15. In an Arrhenius scheme, the calculated conductivities for three compositions, x= 0.05, 0.1 and 0.15, of the solid solutions have been plotted. Additionally data from the LiInO, compound have been included. First, the results for the solid solution Li,_ &,SiO, will be discussed. The solution bulk conductivity data are shown in Fig. 1. Two linear regions can be appreciated in the temperature dependence of their electric properties. There is a small change in slope around 234°C for all three exhibited compositions. Below 234°C the associated activation energy is 0.73 eV (+0.02) whereas above that it is 0.79 eV ( f 0.05). Experimental conductivity data can be analyzed using two equivalent formalisms, admittances or
2.7
K-’
Fig. 1. Temperature dependence of conductivity for the studied compounds in the system Li,_ ,,In,SiO, and LiInO,. Compositional dependence of conductivity is shown in the inset for the solid solution at 3 13°C. Key symbols: (A > x = 0.05; (0) x = 0.1; (0) x = 0.15.
impedances, which in any case depend on the experimental frequency. The impedance formalism to analyze the experimental results has been chosen. At the lowest experimental temperatures, all the data obtained were distributed in the region of high frequencies. At higher temperatures data distribution becomes a well defined shape in the impedance plane. Below 200°C a semicircle was observed in the complex impedance plane. At higher temperatures and relatively low frequencies an inclined spike appears. A typical impedance plot is shown in Fig. 2. The equivalent circuit from the impedance plane is a parallel RC circuit followed by a capacitive, C’, element in series with the parallel arrangement. R is a discrete resistive element. C’ has been used to study the electrode phenomena, in that sense it describes the phenomenological behaviour at low frequencies. These capacitances were calculated using the aproximation C’ = 1/(2rfl), Z” and f being at the inclined spike. The capacitance associated with the spike at the lowest experimental frequencies, C’, was of the order of PF which is typical of electrical double layer phenomena, and it is characteristic for ionic ceramic conductors. In this case the natural candidate to be considered as a mobile ionic species
J.B. Chuuarria et al./Solid
is Li+ [ 12,131. The experimental information in the full semicircle was assigned to the bulk, crystal response of the sample. It was due to the capacitance (C) associated with it, which is - 15 pF. The calculations were made using the relationship 2~flC = 1, f being the experimental frequency at the semicircle maximum. The C values obtained can be used to calculate the dielectric constant by E’ = (gf)C/&,, where (gf) is a geometrical factor and E,, = 0.08854 pF/cm. Changes of dielectric constant with temperature were observed, an average value of this parameter is 40. Incidentally, the impedance data have revealed in any case no grain boundary effects. From Fig. 1 it can be recognized that there is no strong compositional dependence of the conductivity for the solid solution found. The distribution of the data in the Arrhenius plot suggests a very similar electric behaviour for all compounds. With regard to the compositional dependence of the conductivity in similar silicate systems like Li,SiO,-Li(A1, Ga)SiO,, it has been found that (+ passes through a maximum at intermediate x values, 0.22 and 0.25, for Al and Ga respectively, associated to a maximum concentration of mobile Li ions [12,15,16]. In the case of In, the conductivity has a limited range of solid solutions close to the end phase member Li,SiO,, and the compositional behaviour can suggest a dome shaped dependence (see inset Fig. l>, with a smooth maximum at x = 0.1, due to a lower concentration of the mobile species.
3.6
Li 4_3x 2.4 -
1.2 -
w
8
o”
In,
Si 0,
x=0.15
moxR C= 1 o
’
. ~~Ooo 106Hz
0
T= 314OC
0
1.2
2.4
3.6
z’(Kn
Rt 4.6
6
1
Fig. 2. Typical impedance plot corresponding to the solid solution Li +_ ,,In,SiO,. For x = 0.15 at 314°C. It also shows the capacitance value at a low frequency region for the double layer phenomena.
State Ionics 83 (1996) 245-248
. -41
Fig. 3. General ac conductive behaviour in terms of the admitance.
The frequency dependent complex electrical conductivity (T(O) = o’(w) + j,“(u), where o= 2rrf, can be analyzed in a similar way using complex admittance y(w) = y’(o) + j y”( 01. We will concentrate on the real part of the conductivity y’(w) just to show the experimental behaviour. The shape of log y’(o) versus log o plots is often diagnostic for hopping mechanism [17,18]. Fig. 3 shows the general trend exhibited for all compounds studied in Li ,_,,In,SiO,. This means that, if the real part of the admittance behaves as an exponential function of frequency, a hopping mechanism will be involved in the process of charge movement. Thus Lif may be participating in a transport mechanism which is a thermally activated hopping process across an energy barrier. The arrow in Fig. 3 shows the point where the conductive response from low to high frequency dispersion occurs. This change of slope shifts to higher frequencies as the temperature increases. The conductivity of LiInO, as a function of temperature is shown in Fig. 1. This compound was obtained following similar techniques as in the solid solution case. Experimental impedance measurements were made from 200°C to 750°C. A couple of observations will be made now. In the case of Li ,_,,In,SiO, the conductive response was registered at relatively low temperatures, whereas in the case of LiInO, only a poor response was obtained under 250°C. The experimental data describe a good semicircular data distribution in the complex impedance plane, Fig. 4. Impedance plots from LiInO, do not show the typical spike for ionic conductivity. Around 250°C the difference in conductivity values is more than three decades between this com-
248
J.B. Chauarria et al./ Solid State Ionics 83 (1996) 245-248 C=13pF
20
Fig. 4. Corresponding
40
60
experimental
100
60
impedance
In Fig. 5, the conductivity for the series Li,_ ,,M,SiO, (M = Al, Ga, In) at a selected composition around x = 0.1 is shown. Evidently, the change in the cation substitution of Lif, in Li,SiO,, for M3+ = Al, Ga and with In improves the conductivity. Therefore, at higher atomic radius the conductivity decreases.
plot for LiInO, .
Acknowledgements -4
We thank DGAPA-UNAM (IN101893) for financial support and E. Amano for technical support. _
-6
T
E 0 i E r -a
References
0
X 3
-7
-0 2.1
2.3
2.5
2.7 1000 T
2.9
3.1
3.3
K-1
Fig. 5. Schematic plots for the solid solution series Li,_ ,,M,SiO, where M = Al, Ga, In, around x = 0.1, showing how the experimental trend of conductivity compare with the host Li,SiO, structure.
pound and the solid solutions studied as can be appreciated in Fig. 1. There is also a change in slope around 450°C on the linear behaviour; it is more pronounced than in the solid solution Li,_ ,,In,SiO, case. The pronounced increase in conductivity above 450°C reflects a greater concentration of thermally activated charge carriers, i.e., the electrons from inner shells can be promoted to the conduction level. The associated activation energies in the two linear regions are 0.6 eV ( &-0.02) below 450°C and 1.26 eV ( + 0.02) above that.
[l] T. Takahashi and A. Kozawa, eds, in: Applications of Solid Electrolytes (JEC Press, Cleveland, OH 19801 p. 201. [2] R.G. Linford, Solid State Ionics 28/30 (1988) 831. [3] C. Julien, Mater. Sci. Eng. B 6 (1990) 9. [4] 0. Tillement, Solid State Ionics 68 (1994) 9. [5] K. Kanehori, K. Matsumoto, K. Miyauchi and T. Kudo, Solid State Ionics 9/10 (1983) 1445. 161 H. Ohtsuka, S. Okada and J-I. Yamaki, Solid State Ionics 40/41 (1990) 964. [7] J.B. Bates, N.J. Dudney, G.R. Gruzalski, R.A. Zuhr, A. Choudhury, CF. Luck and J.D. Robertson, Solid State Ionics 53-56 (1992) 647. [8] R.A. Huggins, Electrochim. Acta 22 (19771 773. [9] R.D. Shannon, B.E. Taylor, A.D. English and T. Bernins, Electrochim. Acta 22 (1977) 783. [lo] A. Khorassani and A.R. West, J. Solid State Chem. 53 (1984) 369. [ 111 K. Jackowska and A.R. West, J. Mater. Sci. 18 (1983) 2380. [12] A. Garcia, G. Torres-Trevino and A.R. West, Solid State Ionics 40/41 (1990) 13. [13] P. Quintana, F. Velasco and A.R. West, Solid State Ionics 34 (1989) 149. [14] A.R. West and F.P. Glasscr, J. Mater. Sci. 6 (1971) 1100. [15] P. Quintana, PhD Thesis, Equilibria de fases, formaciQ de compuestos y conductit-idad i6nica de nuevos galosilicatos de litio @NAM, Mexico, 1992). [16] A.R. Rodger, J. Kuwano and A.R. West, Solid State Ionics 15 (1985) 185. [17] D.P. Almond, CC. Hunter and A.R. West, J. Mater. Sci. 19 (1984) 3236. [lS] K. Funke, Z. Phys. Chem. (NF) 154 (1987) 251.
SOLID STATE
mm
k!i@ __
ELXWIER
Solid State Ionics 83 (1996) 245-248
IONICS
Electrical properties of the solid solution Li,_,,In,SiO, J.B. Chavarria a, P. Quintana b, A. Huanosta a a Instituto de Investigation en Materiales, Universidad National Autonama de Mexico, 04.510 Coyoacan, D.F., Mexico b Departamento de Fisica Aplicada, Centro de Investigation y de Estudios Avanzados de1 Instituto Politecnico National Unidad Merida, A.P. Cordemex, 97310 Merida, Yucatan, Mexico Received 21 May 1995; accepted 28 October 1995
Abstract Polycrystalline solid solutions with formula Li,_ 3XIn,SiO, : 0 I x I 0.15 were prepared by solid state synthesis. These materials were found to exhibit lithium ion vacancies. From ac impedance measurements conductivities with values around 1 x low5 K ’ cm- ’ at 25O”C, are found. Keywords: Lithium indium silicates; Lithium ion conductor; Ionic conductivity - lithium
1. Introduction In the search for a variety of batteries and solid state devices with Li+ ion conductors, considerable interest has been shown in systems based on Li,SiO, [l-4]. A group of closely related structure types, based on Li,SiO, have formed the basis of a large number of lithium ion conducting materials, some of which have been used as secondary cells that are operable at almost near room temperature. These electrolytes containing Li,PO, and L13V04, can be fabricated in thin film configuration using deposition techniques, such as rf-sputtering, vacuum evaporation or chemical vapor deposition [5-71. Li,SiO, has a versatile host structure and forms nonstoichiometric materials with different cations including, P, As, V [8-lo], Al, Ga [ll-131 and Zn, Mg [14]. The aluminium and gallium containing materials are particularly interesting because the host Li,SiO, strnctnre can be substituted in two ways, giving the series, Li,+,(M,Si,_,)O, and Li,_,,M,SiO,: M = Al, Ga. For Al, the solid solution limits are x = 0.40,
y = 0.60 [12], for Ga, they are x = 0.30 and y = 0.25 [13]. The first series leads to the creation of interstitial lithium ions, while the second leads to vacancies; in both series, dramatic increases in conductivity occur. Highest conductivities were found in the first series, M = Al, e.g. 3 X lop5 iR_’ cm-’ at 100°C for y = 0.20-0.25. The work hereby described was carried out with the aim of synthesizing new solid electrolytes to improve the ionic conductivity of the lithium ion, by introducing In ions in the structure of Li,SiO, to promote the formation of structural defects (i.e. creating Li vacancies or introducing Li interstially).
2. Experimental Polycrystalline samples were prepared by the solid state reaction technique from mixtures of Li,CO,, In,O,, SiO, (J.T. Baker and Koch-Ligth). The resulting powder materials were cold pressed into pellets of 12 mm in diameter and l-2 mm thickness,
0167-2738/%/$15.00 0 1996 Elsevier Science B.V. All rights reserved SSDI 0167-2738(95)00230-S
246
J.B. Chauarria et al./ Solid State Ionics 83 (1996) 245-248
they were sintered at 1020°C for 22 h in a lab atmosphere. Gold painted electrodes were applied to the surface of sintered pellets to register electrical response data arising from the sample. Experimental impedance measurements were obtained with a Hewlett-Packard 4192A Impedance Analyser controlled by a HP85 microcomputer. The investigated frequency range was from 5 Hz to 13 MHz, with an applied voltage of 1 V. Experimental data were recorded from room temperature up to 350°C. All measurements were made in air. Products were analyzed before and after the conductivity measurements by X-ray diffraction, using a Hagg-Guinier camera, Philips, with Cu K 011 radiation (A = 1.5405 A).
0
I.06
1.02
2.16
1000
7
3. Results and discussion Several compositions near Li,SiO, and LiInO, were prepared and reacted in order to look for the ocurrence of solid solutions. A well constituted solid solution based on Li,SiO, was found on the join, Li,SiO,-LiInSiO,, and there was no evidence for the formation of solid solutions on the join, LiInO,Li,SiO,. The results on the solid solution showed that the solid solubility range for In in the structure extends over a quite short range of compositions, creating Li vacancies with a solid solution mechanism: 3Lif * In3+. The corresponding compositions in the solid solution will be described as Li,_,,In,SiO, where OIXlO.15. In an Arrhenius scheme, the calculated conductivities for three compositions, x= 0.05, 0.1 and 0.15, of the solid solutions have been plotted. Additionally data from the LiInO, compound have been included. First, the results for the solid solution Li,_ &,SiO, will be discussed. The solution bulk conductivity data are shown in Fig. 1. Two linear regions can be appreciated in the temperature dependence of their electric properties. There is a small change in slope around 234°C for all three exhibited compositions. Below 234°C the associated activation energy is 0.73 eV (+0.02) whereas above that it is 0.79 eV ( f 0.05). Experimental conductivity data can be analyzed using two equivalent formalisms, admittances or
2.7
K-’
Fig. 1. Temperature dependence of conductivity for the studied compounds in the system Li,_ ,,In,SiO, and LiInO,. Compositional dependence of conductivity is shown in the inset for the solid solution at 3 13°C. Key symbols: (A > x = 0.05; (0) x = 0.1; (0) x = 0.15.
impedances, which in any case depend on the experimental frequency. The impedance formalism to analyze the experimental results has been chosen. At the lowest experimental temperatures, all the data obtained were distributed in the region of high frequencies. At higher temperatures data distribution becomes a well defined shape in the impedance plane. Below 200°C a semicircle was observed in the complex impedance plane. At higher temperatures and relatively low frequencies an inclined spike appears. A typical impedance plot is shown in Fig. 2. The equivalent circuit from the impedance plane is a parallel RC circuit followed by a capacitive, C’, element in series with the parallel arrangement. R is a discrete resistive element. C’ has been used to study the electrode phenomena, in that sense it describes the phenomenological behaviour at low frequencies. These capacitances were calculated using the aproximation C’ = 1/(2rfl), Z” and f being at the inclined spike. The capacitance associated with the spike at the lowest experimental frequencies, C’, was of the order of PF which is typical of electrical double layer phenomena, and it is characteristic for ionic ceramic conductors. In this case the natural candidate to be considered as a mobile ionic species
J.B. Chuuarria et al./Solid
is Li+ [ 12,131. The experimental information in the full semicircle was assigned to the bulk, crystal response of the sample. It was due to the capacitance (C) associated with it, which is - 15 pF. The calculations were made using the relationship 2~flC = 1, f being the experimental frequency at the semicircle maximum. The C values obtained can be used to calculate the dielectric constant by E’ = (gf)C/&,, where (gf) is a geometrical factor and E,, = 0.08854 pF/cm. Changes of dielectric constant with temperature were observed, an average value of this parameter is 40. Incidentally, the impedance data have revealed in any case no grain boundary effects. From Fig. 1 it can be recognized that there is no strong compositional dependence of the conductivity for the solid solution found. The distribution of the data in the Arrhenius plot suggests a very similar electric behaviour for all compounds. With regard to the compositional dependence of the conductivity in similar silicate systems like Li,SiO,-Li(A1, Ga)SiO,, it has been found that (+ passes through a maximum at intermediate x values, 0.22 and 0.25, for Al and Ga respectively, associated to a maximum concentration of mobile Li ions [12,15,16]. In the case of In, the conductivity has a limited range of solid solutions close to the end phase member Li,SiO,, and the compositional behaviour can suggest a dome shaped dependence (see inset Fig. l>, with a smooth maximum at x = 0.1, due to a lower concentration of the mobile species.
3.6
Li 4_3x 2.4 -
1.2 -
w
8
o”
In,
Si 0,
x=0.15
moxR C= 1 o
’
. ~~Ooo 106Hz
0
T= 314OC
0
1.2
2.4
3.6
z’(Kn
Rt 4.6
6
1
Fig. 2. Typical impedance plot corresponding to the solid solution Li +_ ,,In,SiO,. For x = 0.15 at 314°C. It also shows the capacitance value at a low frequency region for the double layer phenomena.
State Ionics 83 (1996) 245-248
. -41
Fig. 3. General ac conductive behaviour in terms of the admitance.
The frequency dependent complex electrical conductivity (T(O) = o’(w) + j,“(u), where o= 2rrf, can be analyzed in a similar way using complex admittance y(w) = y’(o) + j y”( 01. We will concentrate on the real part of the conductivity y’(w) just to show the experimental behaviour. The shape of log y’(o) versus log o plots is often diagnostic for hopping mechanism [17,18]. Fig. 3 shows the general trend exhibited for all compounds studied in Li ,_,,In,SiO,. This means that, if the real part of the admittance behaves as an exponential function of frequency, a hopping mechanism will be involved in the process of charge movement. Thus Lif may be participating in a transport mechanism which is a thermally activated hopping process across an energy barrier. The arrow in Fig. 3 shows the point where the conductive response from low to high frequency dispersion occurs. This change of slope shifts to higher frequencies as the temperature increases. The conductivity of LiInO, as a function of temperature is shown in Fig. 1. This compound was obtained following similar techniques as in the solid solution case. Experimental impedance measurements were made from 200°C to 750°C. A couple of observations will be made now. In the case of Li ,_,,In,SiO, the conductive response was registered at relatively low temperatures, whereas in the case of LiInO, only a poor response was obtained under 250°C. The experimental data describe a good semicircular data distribution in the complex impedance plane, Fig. 4. Impedance plots from LiInO, do not show the typical spike for ionic conductivity. Around 250°C the difference in conductivity values is more than three decades between this com-
248
J.B. Chauarria et al./ Solid State Ionics 83 (1996) 245-248 C=13pF
20
Fig. 4. Corresponding
40
60
experimental
100
60
impedance
In Fig. 5, the conductivity for the series Li,_ ,,M,SiO, (M = Al, Ga, In) at a selected composition around x = 0.1 is shown. Evidently, the change in the cation substitution of Lif, in Li,SiO,, for M3+ = Al, Ga and with In improves the conductivity. Therefore, at higher atomic radius the conductivity decreases.
plot for LiInO, .
Acknowledgements -4
We thank DGAPA-UNAM (IN101893) for financial support and E. Amano for technical support. _
-6
T
E 0 i E r -a
References
0
X 3
-7
-0 2.1
2.3
2.5
2.7 1000 T
2.9
3.1
3.3
K-1
Fig. 5. Schematic plots for the solid solution series Li,_ ,,M,SiO, where M = Al, Ga, In, around x = 0.1, showing how the experimental trend of conductivity compare with the host Li,SiO, structure.
pound and the solid solutions studied as can be appreciated in Fig. 1. There is also a change in slope around 450°C on the linear behaviour; it is more pronounced than in the solid solution Li,_ ,,In,SiO, case. The pronounced increase in conductivity above 450°C reflects a greater concentration of thermally activated charge carriers, i.e., the electrons from inner shells can be promoted to the conduction level. The associated activation energies in the two linear regions are 0.6 eV ( &-0.02) below 450°C and 1.26 eV ( + 0.02) above that.
[l] T. Takahashi and A. Kozawa, eds, in: Applications of Solid Electrolytes (JEC Press, Cleveland, OH 19801 p. 201. [2] R.G. Linford, Solid State Ionics 28/30 (1988) 831. [3] C. Julien, Mater. Sci. Eng. B 6 (1990) 9. [4] 0. Tillement, Solid State Ionics 68 (1994) 9. [5] K. Kanehori, K. Matsumoto, K. Miyauchi and T. Kudo, Solid State Ionics 9/10 (1983) 1445. 161 H. Ohtsuka, S. Okada and J-I. Yamaki, Solid State Ionics 40/41 (1990) 964. [7] J.B. Bates, N.J. Dudney, G.R. Gruzalski, R.A. Zuhr, A. Choudhury, CF. Luck and J.D. Robertson, Solid State Ionics 53-56 (1992) 647. [8] R.A. Huggins, Electrochim. Acta 22 (19771 773. [9] R.D. Shannon, B.E. Taylor, A.D. English and T. Bernins, Electrochim. Acta 22 (1977) 783. [lo] A. Khorassani and A.R. West, J. Solid State Chem. 53 (1984) 369. [ 111 K. Jackowska and A.R. West, J. Mater. Sci. 18 (1983) 2380. [12] A. Garcia, G. Torres-Trevino and A.R. West, Solid State Ionics 40/41 (1990) 13. [13] P. Quintana, F. Velasco and A.R. West, Solid State Ionics 34 (1989) 149. [14] A.R. West and F.P. Glasscr, J. Mater. Sci. 6 (1971) 1100. [15] P. Quintana, PhD Thesis, Equilibria de fases, formaciQ de compuestos y conductit-idad i6nica de nuevos galosilicatos de litio @NAM, Mexico, 1992). [16] A.R. Rodger, J. Kuwano and A.R. West, Solid State Ionics 15 (1985) 185. [17] D.P. Almond, CC. Hunter and A.R. West, J. Mater. Sci. 19 (1984) 3236. [lS] K. Funke, Z. Phys. Chem. (NF) 154 (1987) 251.