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Reactivity of hydrogen and ternary nitrides containing lithium and 13 group elements
Journal of Alloys and Compounds 402 (2005) L1–L3
Letter
Reactivity of hydrogen and ternary nitrides containing lithium and 13 group elements Hisanori Yamane a,∗ , Tomomi Kano a , Atsunori Kamegawa b , Masatoshi Shibata c , Takahiro Yamada d , Masuo Okada b , Masahiko Shimada e a Center for Interdisciplinary Research, Tohoku University, 6-3 Aramaki, Aoba, Aoba-ku, Sendai 980-8578, Japan Department of Materials Science, Graduate School of Engineering, 6-2 Aramaki, Aoba, Aoba-ku, Sendai 980-8579, Japan Functional Materials Laboratory, Central Research Laboratories, Idemitsu Kosan Co. Ltd., 1280 Kami-Izumi, Sodegaura, Chiba 299-0293, Japan d Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan e Akita National College of Technology, 1-1 Bunkyo-cho Iijima, Akita 011-8511, Japan b
c
Received 14 January 2005; accepted 20 January 2005 Available online 31 May 2005
Abstract Ternary nitrides, Li3 XN2 (X = B, Al, Ga), were prepared at 973–1073 K in N2 by solid state reaction of Li3 N and XN. Among these three compounds, Li3 GaN2 reacted with H2 gas at 573 K and changed into a mixture of LiNH2 , LiH, and GaN. The amount of hydrogen reacted was 3.4 mass% to the amount of Li3 GaN2 , and 1.7 mass% of hydrogen was released under a reduced pressure. © 2005 Elsevier B.V. All rights reserved. Keywords: Hydrogen storage materials; Chemical synthesis; X-ray diffraction; Pressure-composition isotherm
1. Introduction Safe and effective hydrogen storage is indispensable for the hydrogen energy system. Various kinds of intermetallics and chemical hydrides have been investigated as hydrogen storage materials. After the recent report on the hydrogen storage properties of lithium nitride and lithium amide by Chen et al. [1,2], additives to lithium nitride and amide were tested to improve the reaction rate and to lower the reaction temperature [3]. Some groups have searched compounds containing lithium and nitrogen for new hydrogen storage materials [4–6]. It has been known that lithium nitride reacts with many binary nitrides of main-group and transition-metal elements, forming ternary nitrides [7]. Ternary nitrides of Li3 XN2 were prepared for 13 group elements of X = B, Al, Ga [8–10]. In the structures of the low-temperature phase (␣, tetragonal) and high-temperature phase (, monoclinic) of Li3 BN2 [8,9], ∗
Corresponding author. Tel.: +81 22 795 4402; fax: +81 22 795 4402. E-mail address: [email protected] (H. Yamane).
0925-8388/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2005.01.064
the boron atom is linearly coordinated by two nitrogen atoms and the lithium atoms are in the distorted nitrogen tetrahedra. Li3 AlN2 and Li3 GaN2 crystallize in isotypic cubic structures which are superstructures of the anti-fluorite-type structure. Li and Al or Ga atoms orderly occupy the four-fold coordination sites in the face-centered cubic arrangement of the N atoms. Li3 AlN2 was investigated as a lithium ion conductor and the materials for nitrogen potential measurement [11,12]. In the present paper, we prepared the ternary nitrides Li3 XN2 (X = B, Al, Ga) by the solid state reaction and studied their reactivity in H2 gas.
2. Experimental All manipulations were carried out in an Ar-filled glove box (O2 , H2 O <1 ppm). Lithium nitride was prepared by reaction of N2 gas (Nippon Sanso, >99.9999%) with lithium metal (Rare Metallic, 99.95%) at 300–500 K in a molybdenum boat. Li3 N and other binary nitrides of BN (Mitsuwa Chemical, 99.5%), AlN (Toyo Aluminum, Grate UF), and
L2
H. Yamane et al. / Journal of Alloys and Compounds 402 (2005) L1–L3
GaN (Cerac, 99.9%) were weighed, mixed with an agate mortar and then pressed into pellets. The pellets were placed in a molybdenum boat and set into a stainless steel container. The reactor was heated at 973–1073 K and 0.1–0.2 MPa of N2 for 3–12 h using an electric heater. After heating, the samples were cooled to room temperature in the furnace and ground into powder with an agate mortar. The samples were sealed in thin-wall glass capillaries and characterized by X-ray powder diffraction (XRD) in an imaging plate Guinier camera with Cu K␣1 radiation (Huber 670). A stainless steel cell in which a sample of 0.25–0.35 g was loaded was evacuated with a rotary vacuum pump, and then filled with H2 gas and heated with an electric heater in order to obtain pressure–composition (P–C) isotherm curves. In our experiment, the equilibrium hydrogen pressure plotted on the curve was determined when the pressure change in the cell became less than 0.001 MPa for 45 min. After the P–C isotherm measurement, X-ray powder diffraction pattern was taken to clarify the phase change and reaction products.
3. Results and discussion ␣-Li3 BN2 was prepared at 973 K for 12 h by the solid state reaction of a Li3 N and BN mixture with the stoichiometric composition Li:B = 3:1. The formation of Li3 AlN2 and Li3 GaN2 was not accomplished at 873–973 K for 12 h and unreacted Li3 N and AlN or GaN remained in the samples. Li3 N vaporization was observed by heating at higher temperatures. We used starting mixtures with a Li3 N excess composition Li:Al/Ga = 1:3.15, as reported in the previous study [11], and obtained the single phase of Li3 AlN2 at 1073 K for 6 h and Li3 GaN2 at 1023 K for 3 h. The hydrogen absorption was not recognized up to 573 K under 10 MPa of H2 for Li3 BN2 and Li3 AlN2 . After this experiment, no change was observed in the XRD patterns and we did not see any reaction of these two nitrides to H2 gas. The sample of Li3 GaN2 also did not absorb hydrogen at 493 and 523 K. However, as shown in Fig. 1, absorption was observed at 573 K and around 3 MPa of H2 . 2.9 mass% of hydrogen against the initial amount of Li3 GaN2 reacted around this pressure, and the reaction continued to 3.3 mass% at 10 MPa. In the desorption isotherm, H2 was released and the concentration of hydrogen in the sample reached to 2.4 mass% at 0.3 MPa and to 1.9 mass% at 4.0 × 10−3 MPa. The second cycle was also measured at 573 K. A plateau was observed above 2.4 mass% at 1 MPa which was lower than that of 3 MPa in the first cycle. The maximum amount of hydrogen absorbed at 10 MPa was 3.4 mass%. A plateau in the hydrogen release of the second cycle was also observed at 0.3 MPa. 1.7 mass% of hydrogen was released at 1.7 × 10−3 MPa. The P–C isotherm measurement of the third cycle was performed at 523 K at which the reaction did not start at the first cycle. The concentration of hydrogen increased gradually from 2.0 to 3.3 mass% with increasing H2 pressure from 0.25 to
Fig. 1. P–C isotherm curves of Li3 GaN2 .
2.5 MPa. In the desorption isotherm, H2 pressure decreased gradually from 0.08 to 2.4 × 10−3 MPa with decreasing hydrogen concentration from 3.25 to 2.0 mass%. All peaks in the X-ray powder diffraction pattern of Li3 GaN2 prepared in the present study were indexed with a ˚ with space group Ia-3 cubic lattice parameter a = 9.6175(2) A (Fig. 2(a)). Fig. 2(b) shows the XRD pattern from the sam-
Fig. 2. X-ray powder diffraction patterns of Li3 GaN2 (a), the sample hydrated at 573 K and 10 MPa of H2 (b), and the sample dehydrated at 573 K and 1.7 × 10−3 MPa (c).
H. Yamane et al. / Journal of Alloys and Compounds 402 (2005) L1–L3
ple hydrogenated at 573 K and 10 MPa of H2 and quenched at room temperature under H2 pressure. This pattern consists of the peaks from GaN, LiNH2 , and LiH, and very small peaks of Li3 GaN2 . The peak positions and relative intensities of LiNH2 and LiH agreed with the reported values [13,14]. The XRD pattern shown in Fig. 2(c) is from the sample dehydrogenated at 573 K and 2 × 10−3 MPa of H2 after hydrogenation at 573 K and 10 MPa of H2 . Two broad peaks were observed at 2θ = 31◦ and 52.5◦ in addition to the peaks of GaN and LiH and very small peaks of Li3 GaN2 . These two peaks were probably related to the 1 1 1 and 0 2 2 of Li2 NH ˚ Fm-3m) [15], but they were shifted at (cubic, a = 5.047 A, higher diffraction angles. The lattice parameter calculated ˚ from the peak positions was 4.96 A. The crystal structure of Li2 NH could be explained with the anti-fluorite-type structure if the H atoms distributed statistically around the N atoms. Li3 GaN2 crystallizes in an anti-fluorite superstructure and the basic unit length ˚ The partial of the anti-fluorite-type structure is 4.809 A. substitution of Ga for Li, introducing defects, may cause the smaller lattice parameter and the broader diffraction peaks of the Li2 NH related phase. The crystal structure of GaN formed in the present study ˚ P63 mc). was wurtzite type (hexagonal, a = 3.188, c = 5.185 A, However, we occasionally observed a broad peak at around 2θ = 40◦ (see Fig. 2(c)). This might be attributed to the 2 0 0 diffraction peak of GaN with the zinc-blende-type structure ˚ F-43m). The formation of cubic GaN was (cubic, a = 4.502 A, reported in the low temperature synthesis of fine powder, thin film and single crystals [16]. The process of GaN formation in the present study was also carried out at a low temperature of 573 K. From the results of the P–C isotherm measurement and X-ray diffraction, the reaction of Li3 GaN2 and H2 , and hydrogen absorption and desorption processes can be expressed as follows: Li3 GaN2 + 2H2 → LiNH2 + 2LiH + GaN ↔ Li2 NH + LiH + GaN + H2
(1)
The first reaction shows that the amount of hydrogen reacted with Li3 GaN2 is 3.4 mass%. The concentration of hydrogen measured at the first cycle was up to 3.3 mass% and the very small amount of residual Li3 GaN2 was observed in the sample. At the second cycle, the value of 3.4 mass% agree with that expected from the above formula. Hydrogen desorption was stopped at 1.7 mass% after the second cycle, which also coincided with the reversible part of the reaction (1). Thus, the reaction after the first cycle is identical with the following reversible reaction after the reaction of Li3 N and H2 . Li3 N + 2H2 → LiNH2 + 2LiH ↔ Li2 NH + LiH + H2 (2) The reaction of Li3 GaN2 with H2 needed temperature of 573 K and H2 pressure of 3 MPa as observed in the first cycle,
L3
but the mixture of Li2 NH, LiH and GaN absorbed hydrogen at a lower pressure of 1 MPa in the second cycle. This means that Li3 GaN2 is more stable than the mixture, and than Li3 N which reacted with H2 above 373 K [1]. The H2 pressure of about 0.3 MPa measured in the process of H2 desorption at 573 K was close to that reported for the mixture started from Li3 N. The difference of H2 pressures between absorption and desorption was small in the case of the mixture from Li3 N. By contrast, a large hysteresis was observed for the mixture from Li3 GaN2 , in particular, in the third cycle at a lower temperature of 523 K. The hysteresis may be caused by the presence of GaN that hinders the reaction kinetically. The formation of the Li2 NH related phase having the smaller lattice parameter might also contribute to this large hysteresis. Further study is needed to clear this point. To summarize, ternary nitrides of Li3 BN2 , Li3 AlN2 and Li3 GaN2 were prepared and their reactivity to hydrogen was investigated. The nitride containing Ga whose covalency is smallest among the three 13 group elements, reacted with 3.4 mass% of hydrogen at 573 K, and produced LiNH2 , LiH and GaN. After this reaction, 1.7 mass% of hydrogen was released in the desorption process. The doping of Ga into the Li2 NH phase was suggested by the X-ray diffraction analysis. The large hysteresis was observed between the absorption and desorption.
Acknowledgement This work was partially supported by The Collaborative Research in Center for Interdisciplinary Research, Tohoku University.
References [1] P. Chen, Z. Xiong, J. Luo, J. Lin, K.L. Tan, Nature 420 (2002) 302. [2] P. Chen, Z. Xiong, J. Luo, J. Lin, K.L. Tan, J. Phys. Chem. B 107 (2003) 10967. [3] T. Ichikawa, S. Isobe, N. Hanada, H. Fujii, J. Alloys Compd. 365 (2004) 271. [4] H.Y. Leng, T. Ichikawa, S. Hino, N. Hanada, S. Isobe, H. Fujii, J. Phys. Chem. B 108 (2004) 8763. [5] Y. Nakamori, S. Orimo, Mater. Sci. Eng. B 108 (2004) 48. [6] Y. Nakamori, G. Kitahara, K. Miwa, S. Towata, S. Orimo, Appl. Phys. A 80 (2005) 1. [7] R. Juza, K. Langer, K. Benda, Angew. Chem. 80 (1968) 373. [8] R. Juza, F. Hund, Z. Anorg. Allg. Chem. 257 (1948) 13. [9] H. Yamane, S. Kikkawa, M. Koizumi, J. Solid State Chem. 71 (1987) 1. [10] H. Yamane, S. Kikkawa, H. Horiuchi, M. Koizumi, J. Solid State Chem. 65 (1986) 6. [11] H. Yamane, S. Kikkawa, M. Koizumi, Solid State Ionics 15 (1985) 51. [12] M.S. Bhamra, D.J. Fray, J. Mater. Sci. 30 (1995) 5381. [13] H. Jacobs, R. Juza, Z. Anorg. Allg. Chem. 391 (1972) 271. [14] J.P. Vidal, G. Vidal-Valat, Acta Cryst. B 42 (1986) 131. [15] R. Juza, K. Opp, Z. Anorg. Allg. Chem. 266 (1951) 325. [16] H. Yamane, M. Shimada, F.J. DiSalvo, Mater. Lett. 42 (2000) 66.
Letter
Reactivity of hydrogen and ternary nitrides containing lithium and 13 group elements Hisanori Yamane a,∗ , Tomomi Kano a , Atsunori Kamegawa b , Masatoshi Shibata c , Takahiro Yamada d , Masuo Okada b , Masahiko Shimada e a Center for Interdisciplinary Research, Tohoku University, 6-3 Aramaki, Aoba, Aoba-ku, Sendai 980-8578, Japan Department of Materials Science, Graduate School of Engineering, 6-2 Aramaki, Aoba, Aoba-ku, Sendai 980-8579, Japan Functional Materials Laboratory, Central Research Laboratories, Idemitsu Kosan Co. Ltd., 1280 Kami-Izumi, Sodegaura, Chiba 299-0293, Japan d Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan e Akita National College of Technology, 1-1 Bunkyo-cho Iijima, Akita 011-8511, Japan b
c
Received 14 January 2005; accepted 20 January 2005 Available online 31 May 2005
Abstract Ternary nitrides, Li3 XN2 (X = B, Al, Ga), were prepared at 973–1073 K in N2 by solid state reaction of Li3 N and XN. Among these three compounds, Li3 GaN2 reacted with H2 gas at 573 K and changed into a mixture of LiNH2 , LiH, and GaN. The amount of hydrogen reacted was 3.4 mass% to the amount of Li3 GaN2 , and 1.7 mass% of hydrogen was released under a reduced pressure. © 2005 Elsevier B.V. All rights reserved. Keywords: Hydrogen storage materials; Chemical synthesis; X-ray diffraction; Pressure-composition isotherm
1. Introduction Safe and effective hydrogen storage is indispensable for the hydrogen energy system. Various kinds of intermetallics and chemical hydrides have been investigated as hydrogen storage materials. After the recent report on the hydrogen storage properties of lithium nitride and lithium amide by Chen et al. [1,2], additives to lithium nitride and amide were tested to improve the reaction rate and to lower the reaction temperature [3]. Some groups have searched compounds containing lithium and nitrogen for new hydrogen storage materials [4–6]. It has been known that lithium nitride reacts with many binary nitrides of main-group and transition-metal elements, forming ternary nitrides [7]. Ternary nitrides of Li3 XN2 were prepared for 13 group elements of X = B, Al, Ga [8–10]. In the structures of the low-temperature phase (␣, tetragonal) and high-temperature phase (, monoclinic) of Li3 BN2 [8,9], ∗
Corresponding author. Tel.: +81 22 795 4402; fax: +81 22 795 4402. E-mail address: [email protected] (H. Yamane).
0925-8388/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2005.01.064
the boron atom is linearly coordinated by two nitrogen atoms and the lithium atoms are in the distorted nitrogen tetrahedra. Li3 AlN2 and Li3 GaN2 crystallize in isotypic cubic structures which are superstructures of the anti-fluorite-type structure. Li and Al or Ga atoms orderly occupy the four-fold coordination sites in the face-centered cubic arrangement of the N atoms. Li3 AlN2 was investigated as a lithium ion conductor and the materials for nitrogen potential measurement [11,12]. In the present paper, we prepared the ternary nitrides Li3 XN2 (X = B, Al, Ga) by the solid state reaction and studied their reactivity in H2 gas.
2. Experimental All manipulations were carried out in an Ar-filled glove box (O2 , H2 O <1 ppm). Lithium nitride was prepared by reaction of N2 gas (Nippon Sanso, >99.9999%) with lithium metal (Rare Metallic, 99.95%) at 300–500 K in a molybdenum boat. Li3 N and other binary nitrides of BN (Mitsuwa Chemical, 99.5%), AlN (Toyo Aluminum, Grate UF), and
L2
H. Yamane et al. / Journal of Alloys and Compounds 402 (2005) L1–L3
GaN (Cerac, 99.9%) were weighed, mixed with an agate mortar and then pressed into pellets. The pellets were placed in a molybdenum boat and set into a stainless steel container. The reactor was heated at 973–1073 K and 0.1–0.2 MPa of N2 for 3–12 h using an electric heater. After heating, the samples were cooled to room temperature in the furnace and ground into powder with an agate mortar. The samples were sealed in thin-wall glass capillaries and characterized by X-ray powder diffraction (XRD) in an imaging plate Guinier camera with Cu K␣1 radiation (Huber 670). A stainless steel cell in which a sample of 0.25–0.35 g was loaded was evacuated with a rotary vacuum pump, and then filled with H2 gas and heated with an electric heater in order to obtain pressure–composition (P–C) isotherm curves. In our experiment, the equilibrium hydrogen pressure plotted on the curve was determined when the pressure change in the cell became less than 0.001 MPa for 45 min. After the P–C isotherm measurement, X-ray powder diffraction pattern was taken to clarify the phase change and reaction products.
3. Results and discussion ␣-Li3 BN2 was prepared at 973 K for 12 h by the solid state reaction of a Li3 N and BN mixture with the stoichiometric composition Li:B = 3:1. The formation of Li3 AlN2 and Li3 GaN2 was not accomplished at 873–973 K for 12 h and unreacted Li3 N and AlN or GaN remained in the samples. Li3 N vaporization was observed by heating at higher temperatures. We used starting mixtures with a Li3 N excess composition Li:Al/Ga = 1:3.15, as reported in the previous study [11], and obtained the single phase of Li3 AlN2 at 1073 K for 6 h and Li3 GaN2 at 1023 K for 3 h. The hydrogen absorption was not recognized up to 573 K under 10 MPa of H2 for Li3 BN2 and Li3 AlN2 . After this experiment, no change was observed in the XRD patterns and we did not see any reaction of these two nitrides to H2 gas. The sample of Li3 GaN2 also did not absorb hydrogen at 493 and 523 K. However, as shown in Fig. 1, absorption was observed at 573 K and around 3 MPa of H2 . 2.9 mass% of hydrogen against the initial amount of Li3 GaN2 reacted around this pressure, and the reaction continued to 3.3 mass% at 10 MPa. In the desorption isotherm, H2 was released and the concentration of hydrogen in the sample reached to 2.4 mass% at 0.3 MPa and to 1.9 mass% at 4.0 × 10−3 MPa. The second cycle was also measured at 573 K. A plateau was observed above 2.4 mass% at 1 MPa which was lower than that of 3 MPa in the first cycle. The maximum amount of hydrogen absorbed at 10 MPa was 3.4 mass%. A plateau in the hydrogen release of the second cycle was also observed at 0.3 MPa. 1.7 mass% of hydrogen was released at 1.7 × 10−3 MPa. The P–C isotherm measurement of the third cycle was performed at 523 K at which the reaction did not start at the first cycle. The concentration of hydrogen increased gradually from 2.0 to 3.3 mass% with increasing H2 pressure from 0.25 to
Fig. 1. P–C isotherm curves of Li3 GaN2 .
2.5 MPa. In the desorption isotherm, H2 pressure decreased gradually from 0.08 to 2.4 × 10−3 MPa with decreasing hydrogen concentration from 3.25 to 2.0 mass%. All peaks in the X-ray powder diffraction pattern of Li3 GaN2 prepared in the present study were indexed with a ˚ with space group Ia-3 cubic lattice parameter a = 9.6175(2) A (Fig. 2(a)). Fig. 2(b) shows the XRD pattern from the sam-
Fig. 2. X-ray powder diffraction patterns of Li3 GaN2 (a), the sample hydrated at 573 K and 10 MPa of H2 (b), and the sample dehydrated at 573 K and 1.7 × 10−3 MPa (c).
H. Yamane et al. / Journal of Alloys and Compounds 402 (2005) L1–L3
ple hydrogenated at 573 K and 10 MPa of H2 and quenched at room temperature under H2 pressure. This pattern consists of the peaks from GaN, LiNH2 , and LiH, and very small peaks of Li3 GaN2 . The peak positions and relative intensities of LiNH2 and LiH agreed with the reported values [13,14]. The XRD pattern shown in Fig. 2(c) is from the sample dehydrogenated at 573 K and 2 × 10−3 MPa of H2 after hydrogenation at 573 K and 10 MPa of H2 . Two broad peaks were observed at 2θ = 31◦ and 52.5◦ in addition to the peaks of GaN and LiH and very small peaks of Li3 GaN2 . These two peaks were probably related to the 1 1 1 and 0 2 2 of Li2 NH ˚ Fm-3m) [15], but they were shifted at (cubic, a = 5.047 A, higher diffraction angles. The lattice parameter calculated ˚ from the peak positions was 4.96 A. The crystal structure of Li2 NH could be explained with the anti-fluorite-type structure if the H atoms distributed statistically around the N atoms. Li3 GaN2 crystallizes in an anti-fluorite superstructure and the basic unit length ˚ The partial of the anti-fluorite-type structure is 4.809 A. substitution of Ga for Li, introducing defects, may cause the smaller lattice parameter and the broader diffraction peaks of the Li2 NH related phase. The crystal structure of GaN formed in the present study ˚ P63 mc). was wurtzite type (hexagonal, a = 3.188, c = 5.185 A, However, we occasionally observed a broad peak at around 2θ = 40◦ (see Fig. 2(c)). This might be attributed to the 2 0 0 diffraction peak of GaN with the zinc-blende-type structure ˚ F-43m). The formation of cubic GaN was (cubic, a = 4.502 A, reported in the low temperature synthesis of fine powder, thin film and single crystals [16]. The process of GaN formation in the present study was also carried out at a low temperature of 573 K. From the results of the P–C isotherm measurement and X-ray diffraction, the reaction of Li3 GaN2 and H2 , and hydrogen absorption and desorption processes can be expressed as follows: Li3 GaN2 + 2H2 → LiNH2 + 2LiH + GaN ↔ Li2 NH + LiH + GaN + H2
(1)
The first reaction shows that the amount of hydrogen reacted with Li3 GaN2 is 3.4 mass%. The concentration of hydrogen measured at the first cycle was up to 3.3 mass% and the very small amount of residual Li3 GaN2 was observed in the sample. At the second cycle, the value of 3.4 mass% agree with that expected from the above formula. Hydrogen desorption was stopped at 1.7 mass% after the second cycle, which also coincided with the reversible part of the reaction (1). Thus, the reaction after the first cycle is identical with the following reversible reaction after the reaction of Li3 N and H2 . Li3 N + 2H2 → LiNH2 + 2LiH ↔ Li2 NH + LiH + H2 (2) The reaction of Li3 GaN2 with H2 needed temperature of 573 K and H2 pressure of 3 MPa as observed in the first cycle,
L3
but the mixture of Li2 NH, LiH and GaN absorbed hydrogen at a lower pressure of 1 MPa in the second cycle. This means that Li3 GaN2 is more stable than the mixture, and than Li3 N which reacted with H2 above 373 K [1]. The H2 pressure of about 0.3 MPa measured in the process of H2 desorption at 573 K was close to that reported for the mixture started from Li3 N. The difference of H2 pressures between absorption and desorption was small in the case of the mixture from Li3 N. By contrast, a large hysteresis was observed for the mixture from Li3 GaN2 , in particular, in the third cycle at a lower temperature of 523 K. The hysteresis may be caused by the presence of GaN that hinders the reaction kinetically. The formation of the Li2 NH related phase having the smaller lattice parameter might also contribute to this large hysteresis. Further study is needed to clear this point. To summarize, ternary nitrides of Li3 BN2 , Li3 AlN2 and Li3 GaN2 were prepared and their reactivity to hydrogen was investigated. The nitride containing Ga whose covalency is smallest among the three 13 group elements, reacted with 3.4 mass% of hydrogen at 573 K, and produced LiNH2 , LiH and GaN. After this reaction, 1.7 mass% of hydrogen was released in the desorption process. The doping of Ga into the Li2 NH phase was suggested by the X-ray diffraction analysis. The large hysteresis was observed between the absorption and desorption.
Acknowledgement This work was partially supported by The Collaborative Research in Center for Interdisciplinary Research, Tohoku University.
References [1] P. Chen, Z. Xiong, J. Luo, J. Lin, K.L. Tan, Nature 420 (2002) 302. [2] P. Chen, Z. Xiong, J. Luo, J. Lin, K.L. Tan, J. Phys. Chem. B 107 (2003) 10967. [3] T. Ichikawa, S. Isobe, N. Hanada, H. Fujii, J. Alloys Compd. 365 (2004) 271. [4] H.Y. Leng, T. Ichikawa, S. Hino, N. Hanada, S. Isobe, H. Fujii, J. Phys. Chem. B 108 (2004) 8763. [5] Y. Nakamori, S. Orimo, Mater. Sci. Eng. B 108 (2004) 48. [6] Y. Nakamori, G. Kitahara, K. Miwa, S. Towata, S. Orimo, Appl. Phys. A 80 (2005) 1. [7] R. Juza, K. Langer, K. Benda, Angew. Chem. 80 (1968) 373. [8] R. Juza, F. Hund, Z. Anorg. Allg. Chem. 257 (1948) 13. [9] H. Yamane, S. Kikkawa, M. Koizumi, J. Solid State Chem. 71 (1987) 1. [10] H. Yamane, S. Kikkawa, H. Horiuchi, M. Koizumi, J. Solid State Chem. 65 (1986) 6. [11] H. Yamane, S. Kikkawa, M. Koizumi, Solid State Ionics 15 (1985) 51. [12] M.S. Bhamra, D.J. Fray, J. Mater. Sci. 30 (1995) 5381. [13] H. Jacobs, R. Juza, Z. Anorg. Allg. Chem. 391 (1972) 271. [14] J.P. Vidal, G. Vidal-Valat, Acta Cryst. B 42 (1986) 131. [15] R. Juza, K. Opp, Z. Anorg. Allg. Chem. 266 (1951) 325. [16] H. Yamane, M. Shimada, F.J. DiSalvo, Mater. Lett. 42 (2000) 66.