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Growth of Li3N crystals doped with deuterium and hydrogen
644
Journal of Crystal Growth 58 (1982) 644—646 North-Holland Publishing Cornpan~
LETTER TO THE EDITORS GROWTH OF LI1N CRYSTALS DOPED WITH DEUTERIUM AND HYDROGEN Steen SKAARUP Phi’s,cs Laboratory Ill, Technical University of Denmark, DK-2800 Lrnghi. Denmark Received 16 April 1982
Crystals of lithium nitride doped with deuterium or hydrogen have been grown by the C~ochralski method. Ehe hydrogen wa.s incorporated by adding weighed amounts of solid lithium amide to the lithium before reaction and crystal growth. This method of doping is shown to have advantages compared to the one previously used of having gaseous hydrogen present in the growth chamber.
Lithium nitride has attracted interest as a potential material for use in high energy density batteries because of its lithium ionic conductivity [l—3]. The substance is also interesting from a purely scientific viewpoint because of its unique hexagonal structure [4]. It has been shown that the highest ionic conductivities are obtained when the material is doped with hydrogen ions [5,61.The latest results indicate that the hydrogen ions also are mobile when a current of lithium ions is passed through the crystal [7]. It therefore becomes of interest to study crystals doped with deuterium because of thethe large relative difference in masses, Furthermore, measurement of the small (~-~ I
method of hydrogen doping [II]: Solid lithium amide, LiNH, is added to the lithium metal (CERAC, 99.9%) in the tungsten crucible before melting the metal in a pure (99.9992%) N atmosphere to produce Li~N. The amide seems to dissolve completely in the L11N melt (M0 813°C’) which is then used for pulling a crystalline boule by the Czochralski method at a rate of 3-4 mm/h. A piece of molybdenum metal sheet (0.4>< 10 X 50 mm) is used for nucleating Li3N crystals. Because of growth of parasitic grains [9] the boule always contatned several the maximum size was being 3. The grains crystal—pulling apparatus a about 1 cm NRC crystal furnace with PID terncommercial
at%) concentration of H~ has proven difficult, and deuterium doped crystals would be useful for measuring the concentration by methods more sensitive to deuterium than to hydrogen, e.g. nuclear reaction analysis and neutron diffraction
perature regulation evacuated to l0~ Torr hefore introducing N-, to avoid traces of H0 and
[8]. Crystals of lithium nitride without any intentional doping were first grown by Schonherr et al. using the Czochralski method [9]. Later results showed, however, that the crystals nearly always contained some hydrogen as an unavoidable impurity. When the beneficial effect of hydrogen on the ionic conductivity became known. intentionally doped crystals were grown by adding 5—25% H2 to the N2 atmosphere in the growth chamber [5,101. D2 has also been used [5]. The present work has employed an alternative 0022-0248/82/0000--0000/$02.75
©
02.
The present method of adding hydrogen via solid LiNH 2 is believed to have advantages cornpared to introducing gaseous H, to the reaction and growth chamber for the following reasons: — It is easier to control the amount of hydrogen added by simply weighing the LiNH than to control the partial pressure of H2 above the melt. — The method avoids working with hydrogen gas at about 0.25 atm and 800°C which is preferable from a safety viewpoint. -The amount of hydrogen added can become larger thereby increasing the maximum obtainable ionic conductivity [12]. The amount of H2 in the gas-phase method is limited by the requirements
1982 North- Holland
S. Skaarup
/
Li
3N crystals doped with deuteriurn and hydrogen
645
that the N2 pressure cannot be much lower than I atm in order to avoid Li3N decomposition [2], and that the total pressure should not exceed I atm for safety reasons. The solid addition method would probably work with Li2NH and possibly also with LiH. The amounts of LiNH2 added varied from 0.3 to 3 g per 25 g lithium. It turns out that the maximum incorporation of hydrogen is reached at about 1.5 g of LiNH2. Further addition leads to no observed increase in H~concentration and seems to make the growth of well-formed grains more difficult. perhaps because of higher impurity levels. The deuterated crystals were grown by adding LiND2 to the lithium before the reaction with N2. The lithiumdeuteroamide was prepared in the following way: ND4C1 was made by dissolving NH4C1 in excess D20 and evaporating the water in vacuo. This process was repeated 4 times to get rid of all the hydrogen. LiOD was made by reacting Li metal with D20. The LiND2 was then synthesized according to:
room temperature, LiND2 is produced. Fig. 1 shows the infrared absorption of a slice of crystal parallel to the c-axis. The absorption at 2315 cm~ corresponds to the N—D stretching vibration [5]. The corresponding N—H vibration has a frequency of 3120 cm~[5,6]. The frequency ratio is 0.74 which is close to the 0.71 (y’~/2) expected from the mass ratio of 2. Some hydrogen is present as impurity from the intensity of the infrared absorption and the expected intensity ratio [14], the amount of hydrogen seems to be approximately equal to the amount of deuterium. The deuterated crystals have been used for measuring the deuterium concentration by nuclear reaction analysis and by neutron diffraction [8]. The D~content has been estimated to be 0.25 at% by the former method and 0.5 at% by the latter. These values are in reasonable agreement with the lithium deficiency of about I at% found by X-ray structure work [15].
ND 3 + Li
11 /
Max Planck in Stuttgart K.F. Nielsen of theInstitute Technical Universityand of Dr. Denmark
A mixture of ND4CL and excess LiOD is heated in vacuum. ND3 is produced at 190—195°C[13], is dried through a filter with LiOD and is condensed on top of the lithium pieces cooled by liquid nitrogen. As the reaction vessel is slowly heated to
are thanked for aiding in the first phase of the crystal growing work. Dr. A. Hooper of AERE Harwell is thanked for helping with the infrared work.
—
LiND 2 + 1 //2 D2~
—~
—
Dr. E. Schonherr and Fräulein G. MUller of the
References 100
-
-
0
2500 2000 WAVENUMBER lcm~l
Fig. 1. Infrared spectrum of a deuterated Li3N crystal in the frequency region of N—D stretching vibrations.
[1] BA. Boukamp and R.A. Huggins, Phys. Letters 58A(1976) 231. [21 A. Rabenau, Festkorperprobleme 18 (1978) 77. [3] U.V. Alpen, J. Solid State Chem. 29 (1979) 379. [4] A. Rabenau and H. Schulz, J. Less-Common Metals 50 (1976) 155. [5] J. Wahi, Solid State Commun. 29 (1979) 485. [61 A. Hooper, T. Lapp and S. Skaarup, Mater. Res. Bull. 14 (1979) 1617. [7] M.F. Bell and R.D. Armstrong, J. Electroanal. Chem. 129 (1981) 321. [8] JO. Thomas and R. Teligren, Solid State lonics 5 (1981) 407. [9] E. Schonherr, G. Muller and E. Winckler, J. Crystal 43 and (1978) 469. [10] Growth E. Gmelin K. Guckelsberger, J. Phys. C (Solid State Phys.) 14(1981) L21. [11] 5. Skaarup, Danish Patent AppI. No. 171/80 (1980). [121 T. Lapp, S. Skaarup and A. Hooper, to be published.
646
S. Skaarup
/ I.i~I5’crystal., doped with deuteriu,n and In’drogi’n
[13] G. Brauer, Handbuch der Praparativen Anorganischen Chemie (Enke. Stuttgart, 1954).
[141 Eli. Wilson, iC. Decius and P.C. Cross, Molecular Vibralions (McGraw-Hill. New York. 1955). [IS)
H. Schultz and K. Schwarz, Acta Cryst. A34 (1978)
~
Journal of Crystal Growth 58 (1982) 644—646 North-Holland Publishing Cornpan~
LETTER TO THE EDITORS GROWTH OF LI1N CRYSTALS DOPED WITH DEUTERIUM AND HYDROGEN Steen SKAARUP Phi’s,cs Laboratory Ill, Technical University of Denmark, DK-2800 Lrnghi. Denmark Received 16 April 1982
Crystals of lithium nitride doped with deuterium or hydrogen have been grown by the C~ochralski method. Ehe hydrogen wa.s incorporated by adding weighed amounts of solid lithium amide to the lithium before reaction and crystal growth. This method of doping is shown to have advantages compared to the one previously used of having gaseous hydrogen present in the growth chamber.
Lithium nitride has attracted interest as a potential material for use in high energy density batteries because of its lithium ionic conductivity [l—3]. The substance is also interesting from a purely scientific viewpoint because of its unique hexagonal structure [4]. It has been shown that the highest ionic conductivities are obtained when the material is doped with hydrogen ions [5,61.The latest results indicate that the hydrogen ions also are mobile when a current of lithium ions is passed through the crystal [7]. It therefore becomes of interest to study crystals doped with deuterium because of thethe large relative difference in masses, Furthermore, measurement of the small (~-~ I
method of hydrogen doping [II]: Solid lithium amide, LiNH, is added to the lithium metal (CERAC, 99.9%) in the tungsten crucible before melting the metal in a pure (99.9992%) N atmosphere to produce Li~N. The amide seems to dissolve completely in the L11N melt (M0 813°C’) which is then used for pulling a crystalline boule by the Czochralski method at a rate of 3-4 mm/h. A piece of molybdenum metal sheet (0.4>< 10 X 50 mm) is used for nucleating Li3N crystals. Because of growth of parasitic grains [9] the boule always contatned several the maximum size was being 3. The grains crystal—pulling apparatus a about 1 cm NRC crystal furnace with PID terncommercial
at%) concentration of H~ has proven difficult, and deuterium doped crystals would be useful for measuring the concentration by methods more sensitive to deuterium than to hydrogen, e.g. nuclear reaction analysis and neutron diffraction
perature regulation evacuated to l0~ Torr hefore introducing N-, to avoid traces of H0 and
[8]. Crystals of lithium nitride without any intentional doping were first grown by Schonherr et al. using the Czochralski method [9]. Later results showed, however, that the crystals nearly always contained some hydrogen as an unavoidable impurity. When the beneficial effect of hydrogen on the ionic conductivity became known. intentionally doped crystals were grown by adding 5—25% H2 to the N2 atmosphere in the growth chamber [5,101. D2 has also been used [5]. The present work has employed an alternative 0022-0248/82/0000--0000/$02.75
©
02.
The present method of adding hydrogen via solid LiNH 2 is believed to have advantages cornpared to introducing gaseous H, to the reaction and growth chamber for the following reasons: — It is easier to control the amount of hydrogen added by simply weighing the LiNH than to control the partial pressure of H2 above the melt. — The method avoids working with hydrogen gas at about 0.25 atm and 800°C which is preferable from a safety viewpoint. -The amount of hydrogen added can become larger thereby increasing the maximum obtainable ionic conductivity [12]. The amount of H2 in the gas-phase method is limited by the requirements
1982 North- Holland
S. Skaarup
/
Li
3N crystals doped with deuteriurn and hydrogen
645
that the N2 pressure cannot be much lower than I atm in order to avoid Li3N decomposition [2], and that the total pressure should not exceed I atm for safety reasons. The solid addition method would probably work with Li2NH and possibly also with LiH. The amounts of LiNH2 added varied from 0.3 to 3 g per 25 g lithium. It turns out that the maximum incorporation of hydrogen is reached at about 1.5 g of LiNH2. Further addition leads to no observed increase in H~concentration and seems to make the growth of well-formed grains more difficult. perhaps because of higher impurity levels. The deuterated crystals were grown by adding LiND2 to the lithium before the reaction with N2. The lithiumdeuteroamide was prepared in the following way: ND4C1 was made by dissolving NH4C1 in excess D20 and evaporating the water in vacuo. This process was repeated 4 times to get rid of all the hydrogen. LiOD was made by reacting Li metal with D20. The LiND2 was then synthesized according to:
room temperature, LiND2 is produced. Fig. 1 shows the infrared absorption of a slice of crystal parallel to the c-axis. The absorption at 2315 cm~ corresponds to the N—D stretching vibration [5]. The corresponding N—H vibration has a frequency of 3120 cm~[5,6]. The frequency ratio is 0.74 which is close to the 0.71 (y’~/2) expected from the mass ratio of 2. Some hydrogen is present as impurity from the intensity of the infrared absorption and the expected intensity ratio [14], the amount of hydrogen seems to be approximately equal to the amount of deuterium. The deuterated crystals have been used for measuring the deuterium concentration by nuclear reaction analysis and by neutron diffraction [8]. The D~content has been estimated to be 0.25 at% by the former method and 0.5 at% by the latter. These values are in reasonable agreement with the lithium deficiency of about I at% found by X-ray structure work [15].
ND 3 + Li
11 /
Max Planck in Stuttgart K.F. Nielsen of theInstitute Technical Universityand of Dr. Denmark
A mixture of ND4CL and excess LiOD is heated in vacuum. ND3 is produced at 190—195°C[13], is dried through a filter with LiOD and is condensed on top of the lithium pieces cooled by liquid nitrogen. As the reaction vessel is slowly heated to
are thanked for aiding in the first phase of the crystal growing work. Dr. A. Hooper of AERE Harwell is thanked for helping with the infrared work.
—
LiND 2 + 1 //2 D2~
—~
—
Dr. E. Schonherr and Fräulein G. MUller of the
References 100
-
-
0
2500 2000 WAVENUMBER lcm~l
Fig. 1. Infrared spectrum of a deuterated Li3N crystal in the frequency region of N—D stretching vibrations.
[1] BA. Boukamp and R.A. Huggins, Phys. Letters 58A(1976) 231. [21 A. Rabenau, Festkorperprobleme 18 (1978) 77. [3] U.V. Alpen, J. Solid State Chem. 29 (1979) 379. [4] A. Rabenau and H. Schulz, J. Less-Common Metals 50 (1976) 155. [5] J. Wahi, Solid State Commun. 29 (1979) 485. [61 A. Hooper, T. Lapp and S. Skaarup, Mater. Res. Bull. 14 (1979) 1617. [7] M.F. Bell and R.D. Armstrong, J. Electroanal. Chem. 129 (1981) 321. [8] JO. Thomas and R. Teligren, Solid State lonics 5 (1981) 407. [9] E. Schonherr, G. Muller and E. Winckler, J. Crystal 43 and (1978) 469. [10] Growth E. Gmelin K. Guckelsberger, J. Phys. C (Solid State Phys.) 14(1981) L21. [11] 5. Skaarup, Danish Patent AppI. No. 171/80 (1980). [121 T. Lapp, S. Skaarup and A. Hooper, to be published.
646
S. Skaarup
/ I.i~I5’crystal., doped with deuteriu,n and In’drogi’n
[13] G. Brauer, Handbuch der Praparativen Anorganischen Chemie (Enke. Stuttgart, 1954).
[141 Eli. Wilson, iC. Decius and P.C. Cross, Molecular Vibralions (McGraw-Hill. New York. 1955). [IS)
H. Schultz and K. Schwarz, Acta Cryst. A34 (1978)
~