- Email: [email protected]
Deuteron ordering in ice containing impurities: A neutron diffraction study
ARTICLE IN PRESS
Physica B 385–386 (2006) 113–115 www.elsevier.com/locate/physb
Deuteron ordering in ice containing impurities: A neutron diffraction study Hiroshi Fukazawaa,, Akinori Hoshikawab, Hiroki Yamauchib, Yasuo Yamaguchic, Naoki Igawab, Yoshinobu Ishiib a
Department of Materials Sciences, Japan Atomic Energy Research Institute, Tokai-mura, Ibaraki 319-1195, Japan Neutron Science Research Center, Japan Atomic Energy Research Institute, Tokai-mura, Ibaraki 319-1195, Japan c Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
b
Abstract We measured neutron powder diffraction of 0.13-M KOD-doped D2O ice at temperatures in the range of 52–80 K to investigate the growth mechanism of ice XI, a deuteron-ordered phase of ice Ih. We observed that the diffraction profiles of the doped ice change with time in the temperature range of 67–74 K. To obtain the mass fraction f (the ratio of mass of ice XI to that of the doped ice), we carried out Rietveld analysis using a two-phase model. The results show that the growth rate of ice XI increases and approaches the transition temperature Tc ¼ 76 K. The f value reaches 0.125 in about 3 days of measurement at a temperature just below Tc. Further, we found that the growth rate is accelerated by annealing the ice at temperatures lower than 64 K for sufficient time in advance to produce ice XI. We conclude that the temperature history of an ice sample is important for understanding the growth mechanisms of ice XI. r 2006 Elsevier B.V. All rights reserved. Keywords: Neutron diffraction; Rietveld analysis; Crystal growth; Ice
1. Introduction The arrangement of protons in ice Ih (ordinary ice) is disordered at temperatures from 273 K down to about 0 K. The structure of ice Ih is described by the fixed position of oxygen with a hexagonal arrangement (space group P63/ mmc) and the proton (or deuteron for D2O ice) equally distributed among two possible sites on each O–O bond according to the ice rule. This model, proposed by Pauling [1] has been confirmed by neutron diffraction measurement [2]. The structure with an ordered arrangement of protons, which must have lower energy than ice Ih, is likely to become a thermodynamically stable structure at very low temperatures. But the equilibrium state is not attainable within limited time frames because the mobility of the protons in ice is very low at low temperatures. Therefore, ice has disordered protons even at very low temperatures. Corresponding author. Tel.: +81 29 284 3908; fax: +81 29 284 3909.
E-mail address: [email protected] (H. Fukazawa). 0921-4526/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2006.05.177
The doping of KOH speeds the transition from ice Ih to a proton-ordered structure, because the mobility of the protons increases due to defects in the lattice [3,4]. At the Institute Laue Langevin, Leadbetter et al. [5] measured neutron diffraction of 0.1-M KOD-doped D2O ice that was annealed at 65 K. They found part or partial ordering of deuterons. The profile-refinement with a reliability factor Rp ( ¼ S|yoiyci|/Syoi, where yoi and yci are observed and calculated intensities at the ith step angle) of 23.7% is consistent with the model in which some deuterons occupy ordered positions in the space group Cmc21. Fig. 1(a) shows the ordered structure, named ice XI. Neutron diffraction of the doped ice kept at about 60 K for 12 days was measured using the high-resolution powder diffractometer (HRPD) at the pulsed neutron source, ISIS [6]. The result provided the splitting of the 004 diffraction peak, which showed the existence of two phases in the annealed ice. Line and Whitworth [7] measured 0.08-M KOD-doped ice annealed at 72 K for 3 days using HRPD, and confirmed the existence of the 131 diffraction peak that is forbidden in ice Ih and the difference of lattice constants
ARTICLE IN PRESS H. Fukazawa et al. / Physica B 385–386 (2006) 113–115
114
Fig. 1.
between ice Ih and XI. Neutron diffraction from single crystal of the doped ice also has the 131 peak [8,9]. Based on Rietveld analysis of neutron diffraction data of 0.1-M KOD-doped ice, Fukazawa et al. [10] investigated the formation process of ice XI. The analysis, under an assumption of a mixture of ice Ih and XI with a better value of Rp ¼ 5.7%, provided the mass fraction f (the ratio of mass of ice XI to that of the doped ice) as a function of time t. The values of f increased with t at 68 K, but f could not exceed a small value (0.06), even though t ¼ N. A quantitative understanding of the growth of ice XI in doped ice is useful for making ice samples with higher values of f, which should provide reliable information about the structure. To understand the formation and growth conditions of ice XI, we measured neutron powder diffraction of 0.13-M KOD-doped D2O ice at 52–80 K.
to collect neutron diffraction data when temperature T reached 56.5 K. Each diffraction pattern needed about 0.25 h exposure to the neutron beam. Fig. 1(b) shows the diffraction profiles in the range of 2y ¼ 48.0–51.81 for the 131 peak position of ice XI. The profiles at 56.5 K do not have the 131 Bragg peak; therefore, the sample is completely ice Ih. The ice was kept until t ¼ 3.45 h, where t is the time elapsed since neutron measurement started. Then the ice was warmed and kept at 70 K for t ¼ 40.93 h. Tiny peaks (yellow color) appeared at 2y ¼ 49.91 after t ¼ 8 h. Since no clear increase in the peak intensity was observed, we changed T to 65 K and waited until t ¼ 65.4 h. However, ice XI did not grow. We mounted sample 2 inside a cryostat and cooled it down as described above. The ice was then warmed to 52 K, and we started to measure diffraction. As shown in Fig. 1(c) we changed T from 52 to 64 K with steps of 2 K. The 131 peak was not observed at those temperatures. To produce ice XI, the ice was warmed to 67 K. The 131 peak (yellow color) appeared and grew at 2y ¼ 49.91 when t414 h. The peak intensity successfully increased at T ¼ 70 K until t ¼ 44.96 h, as shown by the blue color. We changed T from 70 to 80 K with steps of 2 K. The peak grew with t and T, and then the peak intensity decreased at 76 K. Fig. 2 shows a diffraction pattern from sample 2 at T ¼ 74 K (t ¼ 62.40–63.27 h). The diffraction peak at 2y ¼ 78.11 is spread out from 77.5 to 79.81, due to the 151, 241, 311, and 134 peaks of ice XI. The diffraction peak at 2y ¼ 102.31 (the 045 and 225 peaks of ice XI) is also broader. Those features are consistent with a previous study [10].
2. Experiment 4. Discussion To make a sample with a homogeneous concentration of KOD in ice lattice, we produced KOD-doped D2O powder by rapid solidification of a mist of 0.13-M-KOD solution (deuterium oxide; Merck, 99.75% D and potassium deuteroxide; Isotec 99% D) in a vessel with a shallow pool of liquid nitrogen. The powder was passed through a sieve at about 223 K in gaseous helium to remove particles with diameters exceeding 600 mm In vanadium cans (60 mm ong, 10 mm diameter, 0.2 mm thick) with helium gas 1.66 and 1.37 g of doped ices (samples 1 and 2) were sealed. The cans were stored at about 77 K. Diffraction was measured using the neutron diffractometer HERMES installed in the research reactor, JRR3 M, at the Japan Atomic Energy Research Institute [11]. Data were collected with a step angle of 0.11 in the range of 2y ¼ 20–1401 (2y is the scattering angle) using a wavelength of 1.8196 A˚.
To obtain a temporal variation of f, we carried out Rietveld analysis for all diffraction profiles from sample 2 under the assumption of the existence of two phases
3. Results We mounted sample 1 inside a cryostat, which was cooled down to 9.5 K. We then warmed the ice and started
Fig. 2.
ARTICLE IN PRESS H. Fukazawa et al. / Physica B 385–386 (2006) 113–115
115
5. Conclusion
Fig. 3.
(P63/mmc for ice Ih and Cmc21 for XI) in the doped ice. As shown in Fig. 3, values of f were approximate zero at 52–62 K. But, f increases with t and T at 64–74 K (12.08–63.27 h). Finally, f reached 0.125 at 74 K, which is about 2 times higher than that obtained from an experiment with similar period of 68 K [10]. The growth rates are 1.6 103 and 2.2 103 h1 at 64–67 K (12.08–19.97 h) and 70–74 K (20.41–63.27 h), respectively. We warmed the ice to obtain the structural evidence of disordering. f went back to zero at 76 K. Thus the transition temperature, Tc, is about 76 K. It is between two temperatures (75.3 and 76.3 K) at which heat capacity peaks occurred [12]. These results provide the quantitative information that ice XI grows well at temperatures close to Tc after doped ice has been annealed for sufficient time below 64 K. The solid line in Fig. 2 is the calculated pattern from the Rietveld refinement. The atomic coordinates and the isotropic displacement parameters in ice XI were fixed as being those obtained in Ref. [5], and the other parameters for ice Ih were refined. Since the values of Rwp (reliability factor based on the weighted profile) and S ( ¼ Rwp/Re, where Re is an expected value of Rwp), which reflect the progress of the refinement [13], are sufficiently small (e.g., 6.3% and 1.6), the analyses provide reliable values of f. However, a significant difference of intensities between the observed and calculated profiles exists at around 2y ¼ 49.91 for the 131 peak, which is the most characteristic peak caused by the deuteron ordering. Furthermore, the calculation cannot produce the broad features of the peak around 2y ¼ 78.11. A more developed structure model may be needed to reveal details of the structure parameters in ice XI.
We measured neutron powder diffraction of 0.13-M KOD-doped D2O ice at temperatures in the range of 5280 K to investigate the growth of ice XI. The diffraction profiles for doped ice at 6774 K obviously changed with time to the transition if the doped ice was sufficiently annealed below 64 K in advance. The values of f were approximate zero at 52–62 K, and increased with t and T at 64–74 K. f reached 0.125 at 74 K, which was about 2 times higher than that obtained from a similar experiment of 68 K. The results show that the temperature history of ice sample has large effects on formation and growth processes of ice XI. The f of 0.125 is still small, which indicates that the observed phenomenon is the first stage of growth of ice XI. Future studies to determine whether or not f reaches 1.0 at t ¼ N are important for an understanding of the lowtemperature properties of ice. If f achieved by an enough annealing time is small, there is a possibility that the KOD molecules simply cause the growth of small ordered regions around each impurity site, rather than a new stable phase. Structural study in respect to the effects of impurities (species and density) on the growth mechanism is being undertaken. We thank Mr. K. Nemoto for his assistance during the neutron scattering experiments. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]
L. Pauling, J. Am. Chem. Soc. 57 (1935) 2680. S.W. Peterson, H.A. Levy, Acta Crystallogr 10 (1957) 70. S. Kawada, J. Phys. Soc. Japan 32 (1972) 1442. Y. Tajima, T. Matsuo, H. Suga, Nature 299 (1982) 810. A.J. Leadbetter, R.C. Ward, J.W. Clark, P.A. Tucker, T. Matsuo, H. Suga, J. Chem. Phys. 82 (1985) 424. R. Howe, R.W. Whitworth, J. Chem. Phys. 90 (1989) 4450. C.M.B. Line, R.W. Whitworth, J. Chem. Phys. 104 (1996) 10008. S.M. Jackson, V.M. Nield, R.W. Whitworth, M. Oguro, C.C. Wilson, J. Phys. Chem. B 101 (1997) 6142. H. Fukazawa, S. Ikeda, M. Oguro, T. Fukumura, S. Mae, J. Phys. Chem. B 106 (2002) 6021. H. Fukazawa, A. Hoshikawa, H. Yamauchi, Y. Yamaguchi, Y. Ishii, J. Crystal Growth 282 (2005) 251. K. Ohoyama, T. Kanouchi, K. Nemoto, M. Ohashi, T. Kajitani, Y. Yamaguchi, Jpn. J. Appl. Phys. 37 (1998) 3319. T. Matsuo, Y. Tajima, H. Suga, J. Phys. Chem. Solids 47 (1986) 165. R.A. Young, The Rietveld Method, Oxford University Press, Oxford, 1993, p. 22.
Physica B 385–386 (2006) 113–115 www.elsevier.com/locate/physb
Deuteron ordering in ice containing impurities: A neutron diffraction study Hiroshi Fukazawaa,, Akinori Hoshikawab, Hiroki Yamauchib, Yasuo Yamaguchic, Naoki Igawab, Yoshinobu Ishiib a
Department of Materials Sciences, Japan Atomic Energy Research Institute, Tokai-mura, Ibaraki 319-1195, Japan Neutron Science Research Center, Japan Atomic Energy Research Institute, Tokai-mura, Ibaraki 319-1195, Japan c Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
b
Abstract We measured neutron powder diffraction of 0.13-M KOD-doped D2O ice at temperatures in the range of 52–80 K to investigate the growth mechanism of ice XI, a deuteron-ordered phase of ice Ih. We observed that the diffraction profiles of the doped ice change with time in the temperature range of 67–74 K. To obtain the mass fraction f (the ratio of mass of ice XI to that of the doped ice), we carried out Rietveld analysis using a two-phase model. The results show that the growth rate of ice XI increases and approaches the transition temperature Tc ¼ 76 K. The f value reaches 0.125 in about 3 days of measurement at a temperature just below Tc. Further, we found that the growth rate is accelerated by annealing the ice at temperatures lower than 64 K for sufficient time in advance to produce ice XI. We conclude that the temperature history of an ice sample is important for understanding the growth mechanisms of ice XI. r 2006 Elsevier B.V. All rights reserved. Keywords: Neutron diffraction; Rietveld analysis; Crystal growth; Ice
1. Introduction The arrangement of protons in ice Ih (ordinary ice) is disordered at temperatures from 273 K down to about 0 K. The structure of ice Ih is described by the fixed position of oxygen with a hexagonal arrangement (space group P63/ mmc) and the proton (or deuteron for D2O ice) equally distributed among two possible sites on each O–O bond according to the ice rule. This model, proposed by Pauling [1] has been confirmed by neutron diffraction measurement [2]. The structure with an ordered arrangement of protons, which must have lower energy than ice Ih, is likely to become a thermodynamically stable structure at very low temperatures. But the equilibrium state is not attainable within limited time frames because the mobility of the protons in ice is very low at low temperatures. Therefore, ice has disordered protons even at very low temperatures. Corresponding author. Tel.: +81 29 284 3908; fax: +81 29 284 3909.
E-mail address: [email protected] (H. Fukazawa). 0921-4526/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2006.05.177
The doping of KOH speeds the transition from ice Ih to a proton-ordered structure, because the mobility of the protons increases due to defects in the lattice [3,4]. At the Institute Laue Langevin, Leadbetter et al. [5] measured neutron diffraction of 0.1-M KOD-doped D2O ice that was annealed at 65 K. They found part or partial ordering of deuterons. The profile-refinement with a reliability factor Rp ( ¼ S|yoiyci|/Syoi, where yoi and yci are observed and calculated intensities at the ith step angle) of 23.7% is consistent with the model in which some deuterons occupy ordered positions in the space group Cmc21. Fig. 1(a) shows the ordered structure, named ice XI. Neutron diffraction of the doped ice kept at about 60 K for 12 days was measured using the high-resolution powder diffractometer (HRPD) at the pulsed neutron source, ISIS [6]. The result provided the splitting of the 004 diffraction peak, which showed the existence of two phases in the annealed ice. Line and Whitworth [7] measured 0.08-M KOD-doped ice annealed at 72 K for 3 days using HRPD, and confirmed the existence of the 131 diffraction peak that is forbidden in ice Ih and the difference of lattice constants
ARTICLE IN PRESS H. Fukazawa et al. / Physica B 385–386 (2006) 113–115
114
Fig. 1.
between ice Ih and XI. Neutron diffraction from single crystal of the doped ice also has the 131 peak [8,9]. Based on Rietveld analysis of neutron diffraction data of 0.1-M KOD-doped ice, Fukazawa et al. [10] investigated the formation process of ice XI. The analysis, under an assumption of a mixture of ice Ih and XI with a better value of Rp ¼ 5.7%, provided the mass fraction f (the ratio of mass of ice XI to that of the doped ice) as a function of time t. The values of f increased with t at 68 K, but f could not exceed a small value (0.06), even though t ¼ N. A quantitative understanding of the growth of ice XI in doped ice is useful for making ice samples with higher values of f, which should provide reliable information about the structure. To understand the formation and growth conditions of ice XI, we measured neutron powder diffraction of 0.13-M KOD-doped D2O ice at 52–80 K.
to collect neutron diffraction data when temperature T reached 56.5 K. Each diffraction pattern needed about 0.25 h exposure to the neutron beam. Fig. 1(b) shows the diffraction profiles in the range of 2y ¼ 48.0–51.81 for the 131 peak position of ice XI. The profiles at 56.5 K do not have the 131 Bragg peak; therefore, the sample is completely ice Ih. The ice was kept until t ¼ 3.45 h, where t is the time elapsed since neutron measurement started. Then the ice was warmed and kept at 70 K for t ¼ 40.93 h. Tiny peaks (yellow color) appeared at 2y ¼ 49.91 after t ¼ 8 h. Since no clear increase in the peak intensity was observed, we changed T to 65 K and waited until t ¼ 65.4 h. However, ice XI did not grow. We mounted sample 2 inside a cryostat and cooled it down as described above. The ice was then warmed to 52 K, and we started to measure diffraction. As shown in Fig. 1(c) we changed T from 52 to 64 K with steps of 2 K. The 131 peak was not observed at those temperatures. To produce ice XI, the ice was warmed to 67 K. The 131 peak (yellow color) appeared and grew at 2y ¼ 49.91 when t414 h. The peak intensity successfully increased at T ¼ 70 K until t ¼ 44.96 h, as shown by the blue color. We changed T from 70 to 80 K with steps of 2 K. The peak grew with t and T, and then the peak intensity decreased at 76 K. Fig. 2 shows a diffraction pattern from sample 2 at T ¼ 74 K (t ¼ 62.40–63.27 h). The diffraction peak at 2y ¼ 78.11 is spread out from 77.5 to 79.81, due to the 151, 241, 311, and 134 peaks of ice XI. The diffraction peak at 2y ¼ 102.31 (the 045 and 225 peaks of ice XI) is also broader. Those features are consistent with a previous study [10].
2. Experiment 4. Discussion To make a sample with a homogeneous concentration of KOD in ice lattice, we produced KOD-doped D2O powder by rapid solidification of a mist of 0.13-M-KOD solution (deuterium oxide; Merck, 99.75% D and potassium deuteroxide; Isotec 99% D) in a vessel with a shallow pool of liquid nitrogen. The powder was passed through a sieve at about 223 K in gaseous helium to remove particles with diameters exceeding 600 mm In vanadium cans (60 mm ong, 10 mm diameter, 0.2 mm thick) with helium gas 1.66 and 1.37 g of doped ices (samples 1 and 2) were sealed. The cans were stored at about 77 K. Diffraction was measured using the neutron diffractometer HERMES installed in the research reactor, JRR3 M, at the Japan Atomic Energy Research Institute [11]. Data were collected with a step angle of 0.11 in the range of 2y ¼ 20–1401 (2y is the scattering angle) using a wavelength of 1.8196 A˚.
To obtain a temporal variation of f, we carried out Rietveld analysis for all diffraction profiles from sample 2 under the assumption of the existence of two phases
3. Results We mounted sample 1 inside a cryostat, which was cooled down to 9.5 K. We then warmed the ice and started
Fig. 2.
ARTICLE IN PRESS H. Fukazawa et al. / Physica B 385–386 (2006) 113–115
115
5. Conclusion
Fig. 3.
(P63/mmc for ice Ih and Cmc21 for XI) in the doped ice. As shown in Fig. 3, values of f were approximate zero at 52–62 K. But, f increases with t and T at 64–74 K (12.08–63.27 h). Finally, f reached 0.125 at 74 K, which is about 2 times higher than that obtained from an experiment with similar period of 68 K [10]. The growth rates are 1.6 103 and 2.2 103 h1 at 64–67 K (12.08–19.97 h) and 70–74 K (20.41–63.27 h), respectively. We warmed the ice to obtain the structural evidence of disordering. f went back to zero at 76 K. Thus the transition temperature, Tc, is about 76 K. It is between two temperatures (75.3 and 76.3 K) at which heat capacity peaks occurred [12]. These results provide the quantitative information that ice XI grows well at temperatures close to Tc after doped ice has been annealed for sufficient time below 64 K. The solid line in Fig. 2 is the calculated pattern from the Rietveld refinement. The atomic coordinates and the isotropic displacement parameters in ice XI were fixed as being those obtained in Ref. [5], and the other parameters for ice Ih were refined. Since the values of Rwp (reliability factor based on the weighted profile) and S ( ¼ Rwp/Re, where Re is an expected value of Rwp), which reflect the progress of the refinement [13], are sufficiently small (e.g., 6.3% and 1.6), the analyses provide reliable values of f. However, a significant difference of intensities between the observed and calculated profiles exists at around 2y ¼ 49.91 for the 131 peak, which is the most characteristic peak caused by the deuteron ordering. Furthermore, the calculation cannot produce the broad features of the peak around 2y ¼ 78.11. A more developed structure model may be needed to reveal details of the structure parameters in ice XI.
We measured neutron powder diffraction of 0.13-M KOD-doped D2O ice at temperatures in the range of 5280 K to investigate the growth of ice XI. The diffraction profiles for doped ice at 6774 K obviously changed with time to the transition if the doped ice was sufficiently annealed below 64 K in advance. The values of f were approximate zero at 52–62 K, and increased with t and T at 64–74 K. f reached 0.125 at 74 K, which was about 2 times higher than that obtained from a similar experiment of 68 K. The results show that the temperature history of ice sample has large effects on formation and growth processes of ice XI. The f of 0.125 is still small, which indicates that the observed phenomenon is the first stage of growth of ice XI. Future studies to determine whether or not f reaches 1.0 at t ¼ N are important for an understanding of the lowtemperature properties of ice. If f achieved by an enough annealing time is small, there is a possibility that the KOD molecules simply cause the growth of small ordered regions around each impurity site, rather than a new stable phase. Structural study in respect to the effects of impurities (species and density) on the growth mechanism is being undertaken. We thank Mr. K. Nemoto for his assistance during the neutron scattering experiments. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]
L. Pauling, J. Am. Chem. Soc. 57 (1935) 2680. S.W. Peterson, H.A. Levy, Acta Crystallogr 10 (1957) 70. S. Kawada, J. Phys. Soc. Japan 32 (1972) 1442. Y. Tajima, T. Matsuo, H. Suga, Nature 299 (1982) 810. A.J. Leadbetter, R.C. Ward, J.W. Clark, P.A. Tucker, T. Matsuo, H. Suga, J. Chem. Phys. 82 (1985) 424. R. Howe, R.W. Whitworth, J. Chem. Phys. 90 (1989) 4450. C.M.B. Line, R.W. Whitworth, J. Chem. Phys. 104 (1996) 10008. S.M. Jackson, V.M. Nield, R.W. Whitworth, M. Oguro, C.C. Wilson, J. Phys. Chem. B 101 (1997) 6142. H. Fukazawa, S. Ikeda, M. Oguro, T. Fukumura, S. Mae, J. Phys. Chem. B 106 (2002) 6021. H. Fukazawa, A. Hoshikawa, H. Yamauchi, Y. Yamaguchi, Y. Ishii, J. Crystal Growth 282 (2005) 251. K. Ohoyama, T. Kanouchi, K. Nemoto, M. Ohashi, T. Kajitani, Y. Yamaguchi, Jpn. J. Appl. Phys. 37 (1998) 3319. T. Matsuo, Y. Tajima, H. Suga, J. Phys. Chem. Solids 47 (1986) 165. R.A. Young, The Rietveld Method, Oxford University Press, Oxford, 1993, p. 22.