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Initial description of a bulk crystalline carbon-nitride phase
SSC 4776
PERGAMON
Solid State Communications 111 (1999) 443–446
Initial description of a bulk crystalline carbon-nitride phase V.P. Dymont*, E.M. Nekrashevich, I.M. Starchenko Institute of Solid State and Semiconductor Physics, Academy of Sciences of Belarus, P. Brovky Str., 17, Minsk 220072, Belarus Received 2 October 1998; received in revised form 29 December 1998; accepted 29 April 1999 by J. Kuhl
Abstract The crystalline carbon-nitride phase has been synthesized by high-pressure techniques from precursor containing carbon, nitrogen and hydrogen. This material has been analyzed by X-ray diffraction, IR and Raman microprobe analyzed, and Auger electron spectroscopy. The carbon-nitride phase has an X-ray diffraction pattern compatible with the hexagonal symmetry. The best agreement between the experimental and calculated values of d-spacings is revealed with the unit cell parameters: a 0.665 nm and c 0.482 nm. q 1999 Elsevier Science Ltd. All rights reserved. Keywords: A. Disordered systems; B. Crystal growth; C. Crystal structure and symmetry; C. X-ray scattering
Since Liu and Cohen [1,2] reported a theoretical calculation of a compound b-C3N4, whose bulk modulus should be at least as high as that of diamond, much effort has been put in order to synthesize these new super hard materials. In almost all the experiments reported to date, solid films of carbon-nitride have been produced [3–6]. As the known high-pressure and high-temperature techniques are commonly used to probe dense and hard solid phases, although their use in the synthesizing of crystalline carbon-nitride materials has been relatively unexplored. Wixom [7] used the shock wave compression technology starting from a nitrogen content precursor. The main result of this work is that, under typical conditions of diamond and boron nitride synthesis, the material produced has quite a low overall nitrogen content and it contains some well ordered diamond. Recently Nguyen and Jeanloz [8] have reported a synthesis of a new crystalline phase synthesized from a mixture of carbon and nitro* Corresponding author. E-mail address: [email protected] (V.P. Dymont)
gen heated to 2000–2500 K at 30 ^ 5 GPa. This phase has an X-ray diffraction pattern compatible with cubic symmetry, but it is not compatible with the theoretically expected patterns for carbon-nitride phases [9]. These results suggest that the optimum processing conditions for crystalline carbon-nitride have not been obtained. In this article we report the successful synthesis of a bulk crystalline carbon-nitride phase from a precursor containing carbon, nitrogen, and hydrogen. The precursor synthetic route was based on an electrochemical process [10]. A solution of acetylene in liquid ammonia was used as an electrolyte. The electrolysis voltage and current density were varied in the 15–20 V and 10 21 –10 22 A/cm 2 ranges, respectively. The reaction product was repeatedly washed with distilled water, and dried in vacuum at an ambient temperature. A bulk brownish-black powder has been obtained by this way. The samples prepared in the present conditions showed no distinct X-ray peak; indicating that they are amorphous (Fig. 1(a)). Fig. 2(a) shows the IR spectra of this powder. The absorption band at 3600–3100, 3000–2800, 1700, 1630,
0038-1098/99/$ - see front matter q 1999 Elsevier Science Ltd. All rights reserved. PII: S0038-109 8(99)00222-7
444
V.P. Dymont et al. / Solid State Communications 111 (1999) 443–446
Fig. 1. Powder X-ray diffraction data from precursor (a) and sample produced by high pressure (b).
1550, and 1380 cm 21 are seen. The absorption band at 3600–3100 cm 21 can be attributed to N–H bonds. The absorption band at 3000–2800 cm 21 indicates the presence of the C–H bonds. We assigned the
absorption band at 1700 cm 21 to the CyN stretch. Usually the CyN stretching frequency occurs in the range 1650–1680 cm 21. When one or more N–H groups are attached to the carbon atom of the CyN
Fig. 2. The infrared transmission spectra of precursor (a) and sample produced by high pressure (b).
V.P. Dymont et al. / Solid State Communications 111 (1999) 443–446 Table 1 Comparison of the d-spacings determined experimentally from the X-ray diffraction pattern with the calculated one (a 0.665 nm; c 0.482 nm) Measured d (nm)
Calculated d (nm)
(hkl)
0.334 0.288 0.241 0.219 0.202 0.182 0.179 0.162 0.139 0.l20 0.118 0.111
0.332 0.288 0.241 0.219 – – 0.178 0.160 0.139 0.120 0.118 0.110
(110) (200) (002) (120) – – (301) (003) (222) (004) (104) (330)
link, the frequencies appear to be slightly higher than usual [11]. The absorption band at 1630 cm 21 can be attributed to the olefinic CyC stretch. This band becomes IR active because of the symmetry breaking by nitrogen doping [12]. The absorption band at 1550 cm 21 can be attributed to the NH2 symmetric bending mode, and the absorption band at 1380 cm 21, to the CH3C groups. The syntheses of a carbon-nitride phase from this precursor were carried out on the toroid type apparatus under quasi-hydrostatic conditions. The syntheses were performed at pressures up to 7 GPa and temperature was varied between 300 and 600 K. The black powder has been produced by this way. The X-ray diffraction spectra were measured by using the Cu Ka-radiation at room temperature. Preliminary X-ray diffraction studies of our samples show that precursor is successively changed from completely amorphous carbon-nitride to the crystalline carbon-nitride. Fig. 1(b) shows the X-ray diffraction pattern for samples produced by high pressure at 7 GPa and ambient temperature. Two broad peaks at 2Q 25.58 (d 0.349 nm) and 438 (d 0.210 nm) are visible in the spectrum. These peaks can be attributed to the (002) and (101) crystalline planes of graphite. In addition, 12 narrow peaks are visible in the spectrum. The observed d-spacings (with the exception of two peaks) can be indexed with a hexagonal unit cell. The best agreement between the experimental and calculated values of d-spacings was revealed with the unit cell parameters: a
445
0.665 nm, c 0.482 nm. Table 1 lists all the observed interplanar spacing data and possible matching data. The rest of the peaks at 0.202 and 0.182 nm can correspond to carbyne—a linear chainlike carbon allotrope. Room temperature Raman spectra of our high-pressure samples were recorded using an argon laser as a light source operating at 514.5 nm. The Raman spectrum showed two weak and very broad bands around 1350 and 1600 cm 21 only. These bands can be attributed to highly disordered carbons. There is no sign of a peak in the 1212–1265 cm 21 region in which the carbon–nitrogen (C3N4) peak is expected [7]. The vibration modes in the crystalline C–N structures may be not significantly active for Raman scattering at room temperature. Auger spectra has been used to analyze the composition of the sample produced by high pressure. The results show that the crystalline phase is composed primarily of C and N with some amount of O. However, the semi-quantitative results are not accurate enough for absolutely analyzing the stoichiometry of this hexagonal carbon-nitride phase. It is probable that the powder obtained by the highpressure technique consists of more than one phase. Three phases may exist. These are a highly disordered carbon, carbyne—a linear chainlike carbon allotrope, and a new hexagonal carbon-nitride phase. The lattice constants of this hexagonal phase are: a 0.665 nm and c 0.482 nm, which are in sufficient agreement with the theoretically predicted lattice constants for aC3N4: a 0.64665 nm and c 0.47097 nm [9]. However, the semi-quantitative results of Auger electron spectroscopy study allow us to maintain that the average amount of nitrogen is less than expected for C3N4 (57%). That is why the structure proposed by Hughbanks and Tian [13] seems more suitable in our case. Hughbanks and Tian have proposed the carbonnitride structure which was constructed by replacing one-quarter nitrogen atoms with carbon atoms in the b-C3N4 structure (hexagonal, a 0.653 nm, c 0.240 nm). A more carbon-rich composition (C4N3) retains most of the structural features of b-C3N4, but a doubling of the c-axis is observed. The C4N3 composition has the lattice constants a 0.653 nm, c 0.480 nm. Of course, powder X-ray diffraction data, which conveys information about the cell dimensions only, are not sufficient to distinguish between a-C3N4
446
V.P. Dymont et al. / Solid State Communications 111 (1999) 443–446
and the more carbon-rich variants—b-C4N3. Undoubtedly, further work is required to determine the exact structure and composition of this carbonnitride phase. References [1] A.Y. Liu, M.L. Cohen, Science 245 (1989) 841. [2] A.Y. Liu, M.L. Cohen, Phys. Rev. 41 (1990) 10 727. [3] M.M. Lacerda, D.F. Franceshini, F.L. Freire, C.A. Achete, G. Mariotto, J. Vac. Sci. Technol. A15 (1997) 1970. [4] A. Bousetta, M. Lu, A. Bensaoula, A. Schultz, Appl. Phys. Lett. 65 (1994) 696.
[5] M.B. Guseva, V.G. Babaev, V.M. Babina, V.V. Khvostov, A.Z. Zhunk, A.A. Lash, I.A. Fedorinin, Diam. Relat. Mater. 6 (1997) 640. [6] Y. Chen, L. Guo, F. Chen, E.G. Wang, J. Phys.: Condens. Matter 73 (1996) 1973. [7] M.R. Wixom, J. Am. Ceram. Soc. 73 (1990) 1973. [8] J.H. Nguyen, R. Jeanloz, Mater. Sci. Engng A209 (1996) 23. [9] D.M. Teter, R.J. Hemley, Science 271 (1996) 53. [10] V.P. Novikov, V.P. Dymont, Appl. Phys. Lett. 70 (1997) 200. [11] S. Liu, S. Gangopadhyay, G. Sreenivas, S.S. Ang, H.A. Naseem, Phys. Rev. B55 (1997) 13020. [12] J.H. Kaufman, S. Metin, D.D. Saperstein, Phys. Rev. B39 (1989) 13053. [13] T. Hughbanks, Y. Tian, Solid State Commun. 96 (1995) 321.
PERGAMON
Solid State Communications 111 (1999) 443–446
Initial description of a bulk crystalline carbon-nitride phase V.P. Dymont*, E.M. Nekrashevich, I.M. Starchenko Institute of Solid State and Semiconductor Physics, Academy of Sciences of Belarus, P. Brovky Str., 17, Minsk 220072, Belarus Received 2 October 1998; received in revised form 29 December 1998; accepted 29 April 1999 by J. Kuhl
Abstract The crystalline carbon-nitride phase has been synthesized by high-pressure techniques from precursor containing carbon, nitrogen and hydrogen. This material has been analyzed by X-ray diffraction, IR and Raman microprobe analyzed, and Auger electron spectroscopy. The carbon-nitride phase has an X-ray diffraction pattern compatible with the hexagonal symmetry. The best agreement between the experimental and calculated values of d-spacings is revealed with the unit cell parameters: a 0.665 nm and c 0.482 nm. q 1999 Elsevier Science Ltd. All rights reserved. Keywords: A. Disordered systems; B. Crystal growth; C. Crystal structure and symmetry; C. X-ray scattering
Since Liu and Cohen [1,2] reported a theoretical calculation of a compound b-C3N4, whose bulk modulus should be at least as high as that of diamond, much effort has been put in order to synthesize these new super hard materials. In almost all the experiments reported to date, solid films of carbon-nitride have been produced [3–6]. As the known high-pressure and high-temperature techniques are commonly used to probe dense and hard solid phases, although their use in the synthesizing of crystalline carbon-nitride materials has been relatively unexplored. Wixom [7] used the shock wave compression technology starting from a nitrogen content precursor. The main result of this work is that, under typical conditions of diamond and boron nitride synthesis, the material produced has quite a low overall nitrogen content and it contains some well ordered diamond. Recently Nguyen and Jeanloz [8] have reported a synthesis of a new crystalline phase synthesized from a mixture of carbon and nitro* Corresponding author. E-mail address: [email protected] (V.P. Dymont)
gen heated to 2000–2500 K at 30 ^ 5 GPa. This phase has an X-ray diffraction pattern compatible with cubic symmetry, but it is not compatible with the theoretically expected patterns for carbon-nitride phases [9]. These results suggest that the optimum processing conditions for crystalline carbon-nitride have not been obtained. In this article we report the successful synthesis of a bulk crystalline carbon-nitride phase from a precursor containing carbon, nitrogen, and hydrogen. The precursor synthetic route was based on an electrochemical process [10]. A solution of acetylene in liquid ammonia was used as an electrolyte. The electrolysis voltage and current density were varied in the 15–20 V and 10 21 –10 22 A/cm 2 ranges, respectively. The reaction product was repeatedly washed with distilled water, and dried in vacuum at an ambient temperature. A bulk brownish-black powder has been obtained by this way. The samples prepared in the present conditions showed no distinct X-ray peak; indicating that they are amorphous (Fig. 1(a)). Fig. 2(a) shows the IR spectra of this powder. The absorption band at 3600–3100, 3000–2800, 1700, 1630,
0038-1098/99/$ - see front matter q 1999 Elsevier Science Ltd. All rights reserved. PII: S0038-109 8(99)00222-7
444
V.P. Dymont et al. / Solid State Communications 111 (1999) 443–446
Fig. 1. Powder X-ray diffraction data from precursor (a) and sample produced by high pressure (b).
1550, and 1380 cm 21 are seen. The absorption band at 3600–3100 cm 21 can be attributed to N–H bonds. The absorption band at 3000–2800 cm 21 indicates the presence of the C–H bonds. We assigned the
absorption band at 1700 cm 21 to the CyN stretch. Usually the CyN stretching frequency occurs in the range 1650–1680 cm 21. When one or more N–H groups are attached to the carbon atom of the CyN
Fig. 2. The infrared transmission spectra of precursor (a) and sample produced by high pressure (b).
V.P. Dymont et al. / Solid State Communications 111 (1999) 443–446 Table 1 Comparison of the d-spacings determined experimentally from the X-ray diffraction pattern with the calculated one (a 0.665 nm; c 0.482 nm) Measured d (nm)
Calculated d (nm)
(hkl)
0.334 0.288 0.241 0.219 0.202 0.182 0.179 0.162 0.139 0.l20 0.118 0.111
0.332 0.288 0.241 0.219 – – 0.178 0.160 0.139 0.120 0.118 0.110
(110) (200) (002) (120) – – (301) (003) (222) (004) (104) (330)
link, the frequencies appear to be slightly higher than usual [11]. The absorption band at 1630 cm 21 can be attributed to the olefinic CyC stretch. This band becomes IR active because of the symmetry breaking by nitrogen doping [12]. The absorption band at 1550 cm 21 can be attributed to the NH2 symmetric bending mode, and the absorption band at 1380 cm 21, to the CH3C groups. The syntheses of a carbon-nitride phase from this precursor were carried out on the toroid type apparatus under quasi-hydrostatic conditions. The syntheses were performed at pressures up to 7 GPa and temperature was varied between 300 and 600 K. The black powder has been produced by this way. The X-ray diffraction spectra were measured by using the Cu Ka-radiation at room temperature. Preliminary X-ray diffraction studies of our samples show that precursor is successively changed from completely amorphous carbon-nitride to the crystalline carbon-nitride. Fig. 1(b) shows the X-ray diffraction pattern for samples produced by high pressure at 7 GPa and ambient temperature. Two broad peaks at 2Q 25.58 (d 0.349 nm) and 438 (d 0.210 nm) are visible in the spectrum. These peaks can be attributed to the (002) and (101) crystalline planes of graphite. In addition, 12 narrow peaks are visible in the spectrum. The observed d-spacings (with the exception of two peaks) can be indexed with a hexagonal unit cell. The best agreement between the experimental and calculated values of d-spacings was revealed with the unit cell parameters: a
445
0.665 nm, c 0.482 nm. Table 1 lists all the observed interplanar spacing data and possible matching data. The rest of the peaks at 0.202 and 0.182 nm can correspond to carbyne—a linear chainlike carbon allotrope. Room temperature Raman spectra of our high-pressure samples were recorded using an argon laser as a light source operating at 514.5 nm. The Raman spectrum showed two weak and very broad bands around 1350 and 1600 cm 21 only. These bands can be attributed to highly disordered carbons. There is no sign of a peak in the 1212–1265 cm 21 region in which the carbon–nitrogen (C3N4) peak is expected [7]. The vibration modes in the crystalline C–N structures may be not significantly active for Raman scattering at room temperature. Auger spectra has been used to analyze the composition of the sample produced by high pressure. The results show that the crystalline phase is composed primarily of C and N with some amount of O. However, the semi-quantitative results are not accurate enough for absolutely analyzing the stoichiometry of this hexagonal carbon-nitride phase. It is probable that the powder obtained by the highpressure technique consists of more than one phase. Three phases may exist. These are a highly disordered carbon, carbyne—a linear chainlike carbon allotrope, and a new hexagonal carbon-nitride phase. The lattice constants of this hexagonal phase are: a 0.665 nm and c 0.482 nm, which are in sufficient agreement with the theoretically predicted lattice constants for aC3N4: a 0.64665 nm and c 0.47097 nm [9]. However, the semi-quantitative results of Auger electron spectroscopy study allow us to maintain that the average amount of nitrogen is less than expected for C3N4 (57%). That is why the structure proposed by Hughbanks and Tian [13] seems more suitable in our case. Hughbanks and Tian have proposed the carbonnitride structure which was constructed by replacing one-quarter nitrogen atoms with carbon atoms in the b-C3N4 structure (hexagonal, a 0.653 nm, c 0.240 nm). A more carbon-rich composition (C4N3) retains most of the structural features of b-C3N4, but a doubling of the c-axis is observed. The C4N3 composition has the lattice constants a 0.653 nm, c 0.480 nm. Of course, powder X-ray diffraction data, which conveys information about the cell dimensions only, are not sufficient to distinguish between a-C3N4
446
V.P. Dymont et al. / Solid State Communications 111 (1999) 443–446
and the more carbon-rich variants—b-C4N3. Undoubtedly, further work is required to determine the exact structure and composition of this carbonnitride phase. References [1] A.Y. Liu, M.L. Cohen, Science 245 (1989) 841. [2] A.Y. Liu, M.L. Cohen, Phys. Rev. 41 (1990) 10 727. [3] M.M. Lacerda, D.F. Franceshini, F.L. Freire, C.A. Achete, G. Mariotto, J. Vac. Sci. Technol. A15 (1997) 1970. [4] A. Bousetta, M. Lu, A. Bensaoula, A. Schultz, Appl. Phys. Lett. 65 (1994) 696.
[5] M.B. Guseva, V.G. Babaev, V.M. Babina, V.V. Khvostov, A.Z. Zhunk, A.A. Lash, I.A. Fedorinin, Diam. Relat. Mater. 6 (1997) 640. [6] Y. Chen, L. Guo, F. Chen, E.G. Wang, J. Phys.: Condens. Matter 73 (1996) 1973. [7] M.R. Wixom, J. Am. Ceram. Soc. 73 (1990) 1973. [8] J.H. Nguyen, R. Jeanloz, Mater. Sci. Engng A209 (1996) 23. [9] D.M. Teter, R.J. Hemley, Science 271 (1996) 53. [10] V.P. Novikov, V.P. Dymont, Appl. Phys. Lett. 70 (1997) 200. [11] S. Liu, S. Gangopadhyay, G. Sreenivas, S.S. Ang, H.A. Naseem, Phys. Rev. B55 (1997) 13020. [12] J.H. Kaufman, S. Metin, D.D. Saperstein, Phys. Rev. B39 (1989) 13053. [13] T. Hughbanks, Y. Tian, Solid State Commun. 96 (1995) 321.