- Email: [email protected]
Superprotonic conducting phosphate glasses containing water
Journal of Non-Crystalline Solids 351 (2005) 2138–2141 www.elsevier.com/locate/jnoncrysol
Rapid Communication
Superprotonic conducting phosphate glasses containing water Yoshihiro Abe
a,*
, Mitsuhiko Hayashi b, Takashi Iwamoto b, Hirofumi Sumi c, L.L. Hench d
a
d
College of Engineering, Chubu University, Matsumoto-cho, Kasugai-city, Aichi 487-8501, Japan b R&D Center, TYK Corporation, Ohbata-cho, Tajimi-city, Gifu 507-8607, Japan c Department of Fundamental Research, Toho Gas Co. Ltd., Shinpo-machi, Tokai-city, Aichi 476-8501, Japan Department of Materials, Imperial College of Science, Technology and Medicine, Prince Consort Road, London, UK Received 7 February 2005; received in revised form 11 May 2005 Available online 21 June 2005
Abstract Fuel cells using H2–O2 offer the potential to minimize atmospheric pollution. Newly developed baria-phosphate glasses containing an appreciable amount of mobile hydrogen ions (protons) as well as molecular water exhibit super proton-conductivity. The new BaO–La2O3–Al2O3–P2O5 glasses exhibit high proton conductivities of 102 S/cm at 200 C and 103 S/cm at 25 C with a low activation energy of 0.17 eV. A H2–O2 fuel cell using this superprotonic glass electrolyte is operable at temperatures from 25 C to 200 C even under non-humidified conditions. The protons in oxide glasses have been often considered for a long time to be almost immobile. However, here we show that these superprotonic conductors of phosphate glasses are a good candidate material for viable electrolytes of fuel cells. 2005 Elsevier B.V. All rights reserved.
Solid electrolytes for fuel cells are preferable to liquids, but at present the temperature ranges of operation for solid electrolytes are limited to either very high (above 600 C) or rather low (below 100 C) [1–3]. Stable superprotonic conducting membranes working at the medium temperature region of 100–300 C are needed to obtain high H2–O2 fuel cell efficiencies. Conventional organic polymer membranes of perfluoropolymer electrolytes do not operate at temperatures higher than 100 C and require humid operating conditions [3]. Superprotonic conductors of hydrated inorganic oxides reported so far [4–6] do not function at medium temperatures owing to their dehydration. Only a few reports on high proton-conducting amorphous materials have been reported so far [7,8]. Among the superprotonic conductors of which room temperature conductivity is
*
Corresponding author. Tel.: +81 568 51 1111; fax: +81 561 74 1515. E-mail address: [email protected] (Y. Abe).
0022-3093/$ - see front matter 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2005.05.010
higher than 105 S/cm and activation energy is lower than 0.4 eV, we can not find any bulk glasses. The aim of the present study was to develop superprotonic conductors of inorganic solid oxide glasses, and to demonstrate their potential application to fuel cells. In contrast to powder compacts, glasses have the advantage of easy processing of gas-impermeable membranes. Our new processing method of low temperature liquid phase condensation–polymerization of modified baria-phosphate compositions produces membranes composed of superprotonic conducting glasses that contain an appreciable amount of molecular water [9], a key component for the glasses to exhibit high values of superprotonic conductivity. We reported earlier that the hydrogen-bonded protons in calcium phosphate-based glasses are mobile, and suggested that glass membranes made from proton conducting glasses might be used in fuel cells [10,11]. However, the conductivities of the first generation of proton conducting glasses were too low for use as viable
Y. Abe et al. / Journal of Non-Crystalline Solids 351 (2005) 2138–2141
H3 PO4 ! H2 O þ –P–O–H þ –P–O–P–
ð1Þ
Previous reports describe the superprotonic conductors of sol–gel derived phosphate-based glasses such as the ZrO2–P2O5 and ZrO2–P2O5–SiO2 systems containing molecular water [16–18]. However, sol–gel processing of the glasses is time-consuming and the large shrinkage makes it difficult to prepare a large area membranes or plates. In contrast, glass membranes of the present study are easily prepared with a large area (7 cm · 7 cm) at temperatures (<800 C) much lower than those of conventional melt-quenched glasses. The glasses developed here contain an appreciable amount of molecular water and no interconnected pores. The charge carriers are anhydrous protons. Fig. 1 shows plots of protonic conductivity versus temperature for various compositions of glasses obtained by the present processing method. The conductivity of a specific composition depends on the amount of mobile protons per cm2 and also on the amount of molecular water present in the glass. Thus, conductivity depends on glass composition, processing temperature, time at temperature, and ambient atmosphere, all of which control the resultant amount of molecular water retained in the glass. As seen in the Fig. 1, the conductivities of the glasses prepared in a similar way depend considerably on the base compositions; introduction of alumina into glass results in the drastic increase in chemical durability and decrease in protonic conductivity. Infrared spectra of the thin plates show deep absorption bands at around 2900 cm1 and at around 3400 cm1; the former band is due to hydroxyl groups of which protons are mobile [9], and the latter one due to molecular water [13,19]. Among these specimens of Fig. 1, sample 1 gives the highest proton-conductivity (102 S/cm at 200 C and 103 at 25 C), and sample 2 exhibits the lowest conductivity (105 S/cm at 200 C). The activation energies (0.11–0.24 eV) are very small for all the glasses. It is interesting that the content of molecular water is the highest for sample 1 (5.3 wt%), and the lowest for the sample 2 (3.9 wt%), where the
o
Temperature ( C) 300
-1
200
100
50 sample1 sample2 sample3 sample4 sample5
E=0.17eV
-2 Log [ σ (S. cm-1)]
electrolytes. Recently, a second generation of glasses containing mobile protons as well as molecular water were developed and shown to have substantially higher protonic conductivities [12,13]. The new glass compositions are also based on the phosphate system which exhibits unique characteristics from silicate glasses, such as molecular structure, crystallization behavior [14] and high proton conductivities due to hydrogen-bonded protons in the 3-D glass network being very mobile [15]. Liquid phosphoric acids were used as the network forming precursors for the formation of the high proton-conducting glasses. The liquid phosphoric acids change on heating from a monomeric state to a viscous polymer network by condensation–polymerization accompanied with dehydration as given in Eq. (1).
2139
-3
E=0.20eV E=0.17eV E=0.24eV
-4 E=0.11eV
-5
-6 1.5
2
2.5 1000 / T (K-1)
3
3.5
Fig. 1. Protonic conductivity versus 1/T plots for the glasses obtained by the present processing (in ambient atmosphere, Au-electrode, at 10 kHz). Sample 1: 22BaO–2.5La2O3–0.5Al2O3–75P2O5 (700 C). Sample 2: 5SrO–15BaO–10PbO–1Al2O3–69P2O5 (600 C). Sample 3: 6SrO–18BaO–12PbO–64P2O5 (600 C). Sample 4: 12SrO–12BaO– 12PbO–64P2O5 (700 C). Sample 5: 18SrO–6BaO–12PbO–64P2O5 (800 C). Sample glasses (in mole ratio) were prepared by heating a mixture of raw materials such as H3PO4 and metal carbonates at the temperatures given in parenthesis for 30 min, and subsequently by quenching.
water content was determined by a gravimetric method [20]. It is important to note that the room temperature conductivity of sample 1 is nearly equal to that of one of the highest proton conducting materials known, HUO2PO4 4H2O [21]. Fig. 1 indicates that the selection of starting phosphate glass compositions is very important. In contrast to the results shown in Fig. 1, the proton-conducting glasses in binary alkaline-earth phosphates prepared by a conventional melt-quenching gave very low proton conductivities of 108–1015 S/cm at 150 C and high activation energies of 1.0–1.5 eV, respectively [9]. It is surprising that the protonic conductivities of sample 1 are nearly 5 orders of magnitude higher than those of binary phosphate glasses prepared by a conventional melt-quenching processing. The structural features and transport mechanisms responsible for these large differences are still under investigation. Fig. 2 shows the plots of EMF as a function of logðPH2 =P0H2 Þ for a hydrogen gas concentration cell using sample 2 of Fig. 1. The plots agree well with the theoretical line (solid line), which suggests for the transport number of proton of the glass to be nearly unity. It is also suggested that the electrical charge carrier is anhydrous hydrogen ion (proton) but not a hydrous ion, such as H3O+ ion, since the currents remain unchanged during operation of the concentration cell under dry H2-gas conditions. Protons are considered
2140
Y. Abe et al. / Journal of Non-Crystalline Solids 351 (2005) 2138–2141 80 sample 2 60
200 o C 15mm dia., 1mm thick
EMF (mV)
40 20 0 -20 -40 -60 -80 0.01
0.1
1
10
100
Hydrogen partial pressure ratio, P H2 / PH2, standard
Fig. 2. Electrical motive force of hydrogen gas concentration cell where dry H2-gases were used at anode and cathode. (Sample 2, Ptblacks electrodes).
to be transported by hopping via molecular water to next site [12]. Fig. 3 shows H2–O2 fuel cell performance. The fuel cell is operable at 200 C for sample 2 (Fig. 3(a)) but
the current density and power density are not sufficient owing to the low proton-conductivity of the glass membrane (sample 2 in Fig. 1). An example of improved performance characteristics of a H2–O2 fuel cell using the high proton conductivity of sample 1 is shown in Fig. 3(b) in which a large area of 7 cm · 7 cm with 1 mm thick plate glass specimen was used. It is noteworthy that the cell is operable under dry H2 and at room temperature. It can be expected for a similar fuel cell based upon a membrane made from the glass of sample 1 of a thickness reduced to 0.2 mm and an operating temperature of 200 C that the maximum power will reach 250 mW (=5 mW cm2). These superprotonic conductors of solid oxide glasses of anhydrous proton transport, unlike polymer electrolytes, will not require cumbersome humidification systems for the operation of H2–O2 fuel cells. Moreover, they are operable at medium temperatures around 200 C to room temperature, depending on composition and proton conductivity of the glass membrane.
Acknowledgement 1
10 200 oC 15mm dia., 1mm thick
8
0.6
6
0.4
4
0.2
2
0
0 0
20
40
30
50
Current density (µA.cm-2)
a
Cell potential (V)
10
1.0
5
0.8
4
0.6
3
0.4
2
0.2
Power (mW)
Cell potential (V)
0.8
Power density ( µ W• cm-2)
sample 2
1 sample 1, 7cm x 7cm, 1mm thick, 25 oC
0 0
5
0
0.1
10
15
20
25
Current (mA) b
0.2
0.3
0.4
0.5
Current density (mA.cm-2)
Fig. 3. Cell performance for hydrogen–oxygen fuel cell (Pt-blacks electrodes). (a) Sample 2: 1 atm (10% dry H2 + Ar)/1 atm (air, at 200 C). (b) Sample 1: 1 atm (dry H2)/1 atm (air, at 25 C).
This work was partly supported by a grant of the Business-Academia Collaboration Promotion Project from Ministry of Education, Culture, Sports, Science and Technology, Japan.
References [1] A. Weber, E. Ivers-Tiffee, J. Power Sour. 127 (2004) 273. [2] H. Iwahara, in: Ph. Colomban (Ed.), Proton Conductors, Cambridge University, Cambridge, 1992, p. 122. [3] Ph. Colomban, Ann. Chim. Sci. Mater. 24 (1999) 1. [4] A.L. Lasker, S. Chandra (Eds.), Superionic Solids and Solid Electrolytes Recent Trends, Academic press, 1989. [5] Ph. Colomban (Ed.), Proton Conductors, Cambridge University, Cambridge, 1992. [6] K.D. Kreuer, Chem. Mater. 8 (1996) 610. [7] M. Shilton, A. Howe, in: P. Vashishta, J. Mundy, G. Shenoy (Eds.), Fast Ion Tansport in Solids, North-Holland, 1978, p. 727. [8] J. Garbarczyk, Mater. Sci. Forum 76 (1991) 87. [9] Y. Abe, M. Hayashi, T. Iwamoto, Jpn Patent, Appl. No. 2001316962 (2001). [10] Y. Abe, H. Shimakawa, L.L. Hench, J. Non-Cryst. Solids 51 (1982) 357. [11] Y. Abe, H. Hosono, Y. Ohta, L.L. Hench, Phys. Rev. B 38 (1988) 10166. [12] Y. Abe, Proceedings of 17th International Congress on Glass, vol. 1, Chinese Ceramic Society, 1995, p. 105. [13] H. Hosono, K. Kawamura, H. Kawazoe, N. Matsunami, Y. Abe, J. Appl. Phys. 81 (1997) 1296. [14] Y. Abe, Nature 282 (1979) 55. [15] Y. Abe, H. Hosono, O. Akita, L.L. Hench, J. Electrochem. Soc. 14 (1994) L64. [16] Y. Abe, G. Li, M. Nogami, T. Kasuga, L.L. Hench, J. Electrochem. Soc. 143 (1996) 144.
Y. Abe et al. / Journal of Non-Crystalline Solids 351 (2005) 2138–2141 [17] M. Nogami, R. Nagao, K. Makita, Y. Abe, Appl. Phys. Lett. 77 (1997) 1. [18] M. Nogami, K. Miyamura, Y. Abe, J. Electrochem. Soc. 144 (1997) 2175.
2141
[19] H. Li, M. Tomozawa, J. Non-Cryst. Solids 168 (1994) 287. [20] E.J. Grifith, C.F. Callis, J. Am. Chem. Soc. 81 (1956) 833. [21] M.G. Shilton, A.T. Howe, Mater. Res. Bull. 12 (1977) 701.
Rapid Communication
Superprotonic conducting phosphate glasses containing water Yoshihiro Abe
a,*
, Mitsuhiko Hayashi b, Takashi Iwamoto b, Hirofumi Sumi c, L.L. Hench d
a
d
College of Engineering, Chubu University, Matsumoto-cho, Kasugai-city, Aichi 487-8501, Japan b R&D Center, TYK Corporation, Ohbata-cho, Tajimi-city, Gifu 507-8607, Japan c Department of Fundamental Research, Toho Gas Co. Ltd., Shinpo-machi, Tokai-city, Aichi 476-8501, Japan Department of Materials, Imperial College of Science, Technology and Medicine, Prince Consort Road, London, UK Received 7 February 2005; received in revised form 11 May 2005 Available online 21 June 2005
Abstract Fuel cells using H2–O2 offer the potential to minimize atmospheric pollution. Newly developed baria-phosphate glasses containing an appreciable amount of mobile hydrogen ions (protons) as well as molecular water exhibit super proton-conductivity. The new BaO–La2O3–Al2O3–P2O5 glasses exhibit high proton conductivities of 102 S/cm at 200 C and 103 S/cm at 25 C with a low activation energy of 0.17 eV. A H2–O2 fuel cell using this superprotonic glass electrolyte is operable at temperatures from 25 C to 200 C even under non-humidified conditions. The protons in oxide glasses have been often considered for a long time to be almost immobile. However, here we show that these superprotonic conductors of phosphate glasses are a good candidate material for viable electrolytes of fuel cells. 2005 Elsevier B.V. All rights reserved.
Solid electrolytes for fuel cells are preferable to liquids, but at present the temperature ranges of operation for solid electrolytes are limited to either very high (above 600 C) or rather low (below 100 C) [1–3]. Stable superprotonic conducting membranes working at the medium temperature region of 100–300 C are needed to obtain high H2–O2 fuel cell efficiencies. Conventional organic polymer membranes of perfluoropolymer electrolytes do not operate at temperatures higher than 100 C and require humid operating conditions [3]. Superprotonic conductors of hydrated inorganic oxides reported so far [4–6] do not function at medium temperatures owing to their dehydration. Only a few reports on high proton-conducting amorphous materials have been reported so far [7,8]. Among the superprotonic conductors of which room temperature conductivity is
*
Corresponding author. Tel.: +81 568 51 1111; fax: +81 561 74 1515. E-mail address: [email protected] (Y. Abe).
0022-3093/$ - see front matter 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2005.05.010
higher than 105 S/cm and activation energy is lower than 0.4 eV, we can not find any bulk glasses. The aim of the present study was to develop superprotonic conductors of inorganic solid oxide glasses, and to demonstrate their potential application to fuel cells. In contrast to powder compacts, glasses have the advantage of easy processing of gas-impermeable membranes. Our new processing method of low temperature liquid phase condensation–polymerization of modified baria-phosphate compositions produces membranes composed of superprotonic conducting glasses that contain an appreciable amount of molecular water [9], a key component for the glasses to exhibit high values of superprotonic conductivity. We reported earlier that the hydrogen-bonded protons in calcium phosphate-based glasses are mobile, and suggested that glass membranes made from proton conducting glasses might be used in fuel cells [10,11]. However, the conductivities of the first generation of proton conducting glasses were too low for use as viable
Y. Abe et al. / Journal of Non-Crystalline Solids 351 (2005) 2138–2141
H3 PO4 ! H2 O þ –P–O–H þ –P–O–P–
ð1Þ
Previous reports describe the superprotonic conductors of sol–gel derived phosphate-based glasses such as the ZrO2–P2O5 and ZrO2–P2O5–SiO2 systems containing molecular water [16–18]. However, sol–gel processing of the glasses is time-consuming and the large shrinkage makes it difficult to prepare a large area membranes or plates. In contrast, glass membranes of the present study are easily prepared with a large area (7 cm · 7 cm) at temperatures (<800 C) much lower than those of conventional melt-quenched glasses. The glasses developed here contain an appreciable amount of molecular water and no interconnected pores. The charge carriers are anhydrous protons. Fig. 1 shows plots of protonic conductivity versus temperature for various compositions of glasses obtained by the present processing method. The conductivity of a specific composition depends on the amount of mobile protons per cm2 and also on the amount of molecular water present in the glass. Thus, conductivity depends on glass composition, processing temperature, time at temperature, and ambient atmosphere, all of which control the resultant amount of molecular water retained in the glass. As seen in the Fig. 1, the conductivities of the glasses prepared in a similar way depend considerably on the base compositions; introduction of alumina into glass results in the drastic increase in chemical durability and decrease in protonic conductivity. Infrared spectra of the thin plates show deep absorption bands at around 2900 cm1 and at around 3400 cm1; the former band is due to hydroxyl groups of which protons are mobile [9], and the latter one due to molecular water [13,19]. Among these specimens of Fig. 1, sample 1 gives the highest proton-conductivity (102 S/cm at 200 C and 103 at 25 C), and sample 2 exhibits the lowest conductivity (105 S/cm at 200 C). The activation energies (0.11–0.24 eV) are very small for all the glasses. It is interesting that the content of molecular water is the highest for sample 1 (5.3 wt%), and the lowest for the sample 2 (3.9 wt%), where the
o
Temperature ( C) 300
-1
200
100
50 sample1 sample2 sample3 sample4 sample5
E=0.17eV
-2 Log [ σ (S. cm-1)]
electrolytes. Recently, a second generation of glasses containing mobile protons as well as molecular water were developed and shown to have substantially higher protonic conductivities [12,13]. The new glass compositions are also based on the phosphate system which exhibits unique characteristics from silicate glasses, such as molecular structure, crystallization behavior [14] and high proton conductivities due to hydrogen-bonded protons in the 3-D glass network being very mobile [15]. Liquid phosphoric acids were used as the network forming precursors for the formation of the high proton-conducting glasses. The liquid phosphoric acids change on heating from a monomeric state to a viscous polymer network by condensation–polymerization accompanied with dehydration as given in Eq. (1).
2139
-3
E=0.20eV E=0.17eV E=0.24eV
-4 E=0.11eV
-5
-6 1.5
2
2.5 1000 / T (K-1)
3
3.5
Fig. 1. Protonic conductivity versus 1/T plots for the glasses obtained by the present processing (in ambient atmosphere, Au-electrode, at 10 kHz). Sample 1: 22BaO–2.5La2O3–0.5Al2O3–75P2O5 (700 C). Sample 2: 5SrO–15BaO–10PbO–1Al2O3–69P2O5 (600 C). Sample 3: 6SrO–18BaO–12PbO–64P2O5 (600 C). Sample 4: 12SrO–12BaO– 12PbO–64P2O5 (700 C). Sample 5: 18SrO–6BaO–12PbO–64P2O5 (800 C). Sample glasses (in mole ratio) were prepared by heating a mixture of raw materials such as H3PO4 and metal carbonates at the temperatures given in parenthesis for 30 min, and subsequently by quenching.
water content was determined by a gravimetric method [20]. It is important to note that the room temperature conductivity of sample 1 is nearly equal to that of one of the highest proton conducting materials known, HUO2PO4 4H2O [21]. Fig. 1 indicates that the selection of starting phosphate glass compositions is very important. In contrast to the results shown in Fig. 1, the proton-conducting glasses in binary alkaline-earth phosphates prepared by a conventional melt-quenching gave very low proton conductivities of 108–1015 S/cm at 150 C and high activation energies of 1.0–1.5 eV, respectively [9]. It is surprising that the protonic conductivities of sample 1 are nearly 5 orders of magnitude higher than those of binary phosphate glasses prepared by a conventional melt-quenching processing. The structural features and transport mechanisms responsible for these large differences are still under investigation. Fig. 2 shows the plots of EMF as a function of logðPH2 =P0H2 Þ for a hydrogen gas concentration cell using sample 2 of Fig. 1. The plots agree well with the theoretical line (solid line), which suggests for the transport number of proton of the glass to be nearly unity. It is also suggested that the electrical charge carrier is anhydrous hydrogen ion (proton) but not a hydrous ion, such as H3O+ ion, since the currents remain unchanged during operation of the concentration cell under dry H2-gas conditions. Protons are considered
2140
Y. Abe et al. / Journal of Non-Crystalline Solids 351 (2005) 2138–2141 80 sample 2 60
200 o C 15mm dia., 1mm thick
EMF (mV)
40 20 0 -20 -40 -60 -80 0.01
0.1
1
10
100
Hydrogen partial pressure ratio, P H2 / PH2, standard
Fig. 2. Electrical motive force of hydrogen gas concentration cell where dry H2-gases were used at anode and cathode. (Sample 2, Ptblacks electrodes).
to be transported by hopping via molecular water to next site [12]. Fig. 3 shows H2–O2 fuel cell performance. The fuel cell is operable at 200 C for sample 2 (Fig. 3(a)) but
the current density and power density are not sufficient owing to the low proton-conductivity of the glass membrane (sample 2 in Fig. 1). An example of improved performance characteristics of a H2–O2 fuel cell using the high proton conductivity of sample 1 is shown in Fig. 3(b) in which a large area of 7 cm · 7 cm with 1 mm thick plate glass specimen was used. It is noteworthy that the cell is operable under dry H2 and at room temperature. It can be expected for a similar fuel cell based upon a membrane made from the glass of sample 1 of a thickness reduced to 0.2 mm and an operating temperature of 200 C that the maximum power will reach 250 mW (=5 mW cm2). These superprotonic conductors of solid oxide glasses of anhydrous proton transport, unlike polymer electrolytes, will not require cumbersome humidification systems for the operation of H2–O2 fuel cells. Moreover, they are operable at medium temperatures around 200 C to room temperature, depending on composition and proton conductivity of the glass membrane.
Acknowledgement 1
10 200 oC 15mm dia., 1mm thick
8
0.6
6
0.4
4
0.2
2
0
0 0
20
40
30
50
Current density (µA.cm-2)
a
Cell potential (V)
10
1.0
5
0.8
4
0.6
3
0.4
2
0.2
Power (mW)
Cell potential (V)
0.8
Power density ( µ W• cm-2)
sample 2
1 sample 1, 7cm x 7cm, 1mm thick, 25 oC
0 0
5
0
0.1
10
15
20
25
Current (mA) b
0.2
0.3
0.4
0.5
Current density (mA.cm-2)
Fig. 3. Cell performance for hydrogen–oxygen fuel cell (Pt-blacks electrodes). (a) Sample 2: 1 atm (10% dry H2 + Ar)/1 atm (air, at 200 C). (b) Sample 1: 1 atm (dry H2)/1 atm (air, at 25 C).
This work was partly supported by a grant of the Business-Academia Collaboration Promotion Project from Ministry of Education, Culture, Sports, Science and Technology, Japan.
References [1] A. Weber, E. Ivers-Tiffee, J. Power Sour. 127 (2004) 273. [2] H. Iwahara, in: Ph. Colomban (Ed.), Proton Conductors, Cambridge University, Cambridge, 1992, p. 122. [3] Ph. Colomban, Ann. Chim. Sci. Mater. 24 (1999) 1. [4] A.L. Lasker, S. Chandra (Eds.), Superionic Solids and Solid Electrolytes Recent Trends, Academic press, 1989. [5] Ph. Colomban (Ed.), Proton Conductors, Cambridge University, Cambridge, 1992. [6] K.D. Kreuer, Chem. Mater. 8 (1996) 610. [7] M. Shilton, A. Howe, in: P. Vashishta, J. Mundy, G. Shenoy (Eds.), Fast Ion Tansport in Solids, North-Holland, 1978, p. 727. [8] J. Garbarczyk, Mater. Sci. Forum 76 (1991) 87. [9] Y. Abe, M. Hayashi, T. Iwamoto, Jpn Patent, Appl. No. 2001316962 (2001). [10] Y. Abe, H. Shimakawa, L.L. Hench, J. Non-Cryst. Solids 51 (1982) 357. [11] Y. Abe, H. Hosono, Y. Ohta, L.L. Hench, Phys. Rev. B 38 (1988) 10166. [12] Y. Abe, Proceedings of 17th International Congress on Glass, vol. 1, Chinese Ceramic Society, 1995, p. 105. [13] H. Hosono, K. Kawamura, H. Kawazoe, N. Matsunami, Y. Abe, J. Appl. Phys. 81 (1997) 1296. [14] Y. Abe, Nature 282 (1979) 55. [15] Y. Abe, H. Hosono, O. Akita, L.L. Hench, J. Electrochem. Soc. 14 (1994) L64. [16] Y. Abe, G. Li, M. Nogami, T. Kasuga, L.L. Hench, J. Electrochem. Soc. 143 (1996) 144.
Y. Abe et al. / Journal of Non-Crystalline Solids 351 (2005) 2138–2141 [17] M. Nogami, R. Nagao, K. Makita, Y. Abe, Appl. Phys. Lett. 77 (1997) 1. [18] M. Nogami, K. Miyamura, Y. Abe, J. Electrochem. Soc. 144 (1997) 2175.
2141
[19] H. Li, M. Tomozawa, J. Non-Cryst. Solids 168 (1994) 287. [20] E.J. Grifith, C.F. Callis, J. Am. Chem. Soc. 81 (1956) 833. [21] M.G. Shilton, A.T. Howe, Mater. Res. Bull. 12 (1977) 701.