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Neutron diffraction study of NaNO2 ferroelectric nanowires
ARTICLE IN PRESS
Physica B 350 (2004) e1119–e1121
Neutron diffraction study of NaNO2 ferroelectric nanowires S. Borisova, T. Hansenb, Yu. Kumzerova, A. Naberezhnova,*, V. Simkinc, O. Smirnovd, A. Sotnikova, M. Tovare, S. Vakhrusheva a
Ioffe Physico-Technical Institute, 26 Polytechnicheskaya, S.-Petersburg 194021, Russia b Institute Laue-Langevin, F-38042 Grenoble Cedex 9, France c Joint Institute of Nuclear Research, Moscow district, Dubna 141980, Russia d Petersburg Nuclear Physics Institute, Leningrad district, Gatchina 188300, Russia e Hahn–Meitner-Institut, Glinicker Strabe 100, D-14 109 Berlin, Germany
Abstract For the first time the temperature evolution of the structure of ferroelectric nanowires of NaNO2 was studied by neutron diffraction from room temperature up to melting, i.e. in ferro- and paraelectric phases. Samples were produced in natural chrysotile asbestos with average channel diameter 671.5 nm. It is demonstrated that in the ferroelectric phase the structure is consistent with the bulk but is strongly textured. The temperature dependence of order parameter in the ferroelectric phase is determined for the confined sodium nitrite. It is shown that this dependence follows a power law with Tc=413.072.5 K and b=0.3470.05, and differs from the same for the bulk material. r 2004 Elsevier B.V. All rights reserved. PACS: 61.12.q; 61.46.w; 77.80.e Keywords: Neutron diffraction; Nanocomposite materials; Structure; Ferroelectrics
1. Introduction In recent years nanostructured materials attracted a steadfast attention because their properties are essentially different from those of conventional bulk materials. It is shown that the reduction of physical size from the microscopic scale down to the meso- and nanoscopic scales results in a change of the majority of physical *Corresponding author. E-mail address: [email protected] (A. Naberezhnov).
properties of confined materials (CM), such as temperature and type of phase transitions (PT) [1–6], dielectric permittivity [7,8], atomic mobility of constituent ions [9–11], flowing of liquids in a confined geometry [11,12] and so on. One of the important aspects of CM is phase stability as a function of spatial dimension, geometry and topology of nanoparticles. Ferroelectric nanocomposites have been studied intensively since the beginning of 1950s [13], but the majority of experimental results have been obtained for thin films or granular materials. At the same time there is another method of preparation of such dispersed
0921-4526/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2004.03.304
ARTICLE IN PRESS S. Borisov et al. / Physica B 350 (2004) e1119–e1121
substances—an intrusion of materials into artificial or natural porous matrices such as porous glasses, chrysotile asbestos, zeolites, opals and so on [14]. We have attempted to study the temperature evolution of the structure of confined NaNO2 in chrysotile asbestos with average channel diameter 671.5 nm at temperatures below and above TC by neutron diffraction, to clarify the peculiarities of ferroelectric phase transition in a system of quasi one-dimensional nanotubes.
2. Sample and experiment Sodium nitrite is an order–disorder ferroelectric and undergoes the first-order phase transition at TCE437 K. At room temperature its space group ( b=5.578 A, ( c=5.39 A) ( with is Im2m (a=3.57 A, two molecules per unit cell. The spontaneous polarization is oriented along the b-axis and appears due to partially ordered alignment of NO2 groups along this axis, accompanied by the displacement of sodium ions. Above Tc a mirror plane perpendicular to the b-axis appears and the space group changes to Immm. Bulk sodium nitrite melts at 554.1 K. Natural chrysotile asbestos (Mg3Si2O5(OH)4) is a regular set of closely packed parallel ultrathin dielectric tubes with external channel diameters of B30 nm and with internal diameters of 671.5 nm, the length of these tubes being about 25 mm (in our samples). The parallelism of nanochannels is better than 2 . Due to high wetting ability molten NaNO2 penetrates into these channels and forms a quasi onedimensional structure. The volume amount of linear nanostructured materials reaches 5%. The study of structure evolution of nanocomposite NaNO2 was performed from room temperature (RT) up to 543 K, i.e. below and above TC, on the TOF diffractometer HRFD (JINR, FLNP, Dubna, Russia) and powder diffractometers (PNPI, ( Gatchina, Russia, l=1.3841 A; E9, HMI, ( and D20, ILL, l=2.41 A). ( The saml=1.796 A ples were mounted as vertically as possible on the scattering plane and total deviation of the channels from the vertical axis did not exceed 8 . The temperature instability was better by 0.5% in Gatchina and does not exceed 71 K for the
others. The chrysotile asbestos has been measured at RT and at 543 K. Experimental results were treated by a FullProf program [15].
3. Results and discussion Typical diffraction patterns (without asbestos peaks) are presented in Fig. 1. We have described the structure of asbestos using the so-called ‘‘matching-mode’’ and later on we considered it as an additional background. The first unexpected experimental result is the high intensities of Bragg peaks from NaNO2 when compared to previous results [16]. This is surprising as the volume amount of salt is essentially less than in the case of porous glass with average pore diameter 7 nm. Furthermore, the ratios of intensities visibly differ from the ones observed for the bulk material. This fact could be explained by texture effect and indeed, the introduction of preferred orientation in data treatment procedure has essentially improved the description of diffraction patterns. Upon heating the intensities of Bragg peaks at large Q decrease faster than in the bulk and nanocomposite 7 nm glass samples, demonstrating the strong ‘‘softening’’ of lattice. It has been shown [17,18] that in NaNO2 the intensity of diffraction peaks is proportional to
100
(c) 50
Intensity, arb. un.
e1120
0
(b)
200 0 400
(a)
200 0 -200 40
50
60
70
80
90
100
2θ, degrees
( (a) the bulk at Fig. 1. Diffraction patterns at l=1.3841 A: 287 K, vertical bars indicate the Bragg peaks; (b) NaNO2 within asbestos at 287 K; (c) as (b) but at 422 K. The arrows indicate the positions of (0 2 2), (1 3 2) and (1 2 3) Bragg peaks. The asbestos is subtracted.
ARTICLE IN PRESS S. Borisov et al. / Physica B 350 (2004) e1119–e1121
Acknowledgements
1.2 1.0
This work was supported by the RFBR (Grants 00-02-16883, 01-02-17739 and 03-02-16545), INTAS-2001-0826 CRDF RP1-2361-ST02 and Program of Division of Physical Sciences of Russian Academy of Sciences. A.N. and A.S. would like to thank Berlin Neutron Scattering Center (BENSC) and Hahn–Meitner-Institut for financial support.
0.8
η
e1121
0.6 0.4 0.2 0.0
270
300
330
360
390
420
450
T, K Fig. 2. Temperature dependences of order parameter for the bulk (black circles) [17], NaNO2 within 771 nm porous glass (open triangles, [16]) and asbestos (black squares). Solid line is a result of fitting by a power law (see text); dashed line is drawn by eye.
2 2 jF j2 ¼ Freal þ Z2 ðTÞ Fim ; where Freal and Fim are the real and imaginary parts of the structure factor F ; and Z is the order parameter in the ferroelectric phase. The value of Z was determined from intensities of (0 2 2), (1 2 3) and (1 3 2) reflections, 2 2 for which Fim bFreal (Fig. 2). It is easy to see that this dependence does not correspond either to that observed for the bulk material or to the one obtained for NaNO2 in 7 nm porous glass [16] (TC=425.672.1 K). Above 413 K, the intensities of Bragg peaks depending on order parameters are very small and correspond to the value expected for the paraelectric phase. This fact is an evidence for a further decrease of TC for NaNO2 in asbestos, relative to the values observed for the bulk and nanocomposite glass samples. Temperature dependence of order parameter follows a power law (1–T/TC)b with b=0.34(5). This value b corresponds to that observed for NaNO2 within porous glass [16] and is close to the critical exponents for 3D-Ising (0.324770.001) and 3D-Heisenberg (0.364770.0012) models [19]. Above 543 K we did not observe any diffraction picture from sodium nitrite. On cooling, diffraction patterns began to be restored below 508 K, giving evidence for essential temperature hysteresis of the melting– freezing phase transition.
References [1] W.L. Zhong, Y.G. Wang, P.L. Zhang, Ferroelectric Lett. 1 (1998) 131 and references therein. [2] W. Neubeck, L. Ranno, M. Hunt, C. Vettier, D. Givord, Appl. Surf. Sci. 138–139 (1999) 195. [3] Shaoping Li, J.A. Eastman, Z. Li, C.M. Foster, R.E. Newnham, L.E. Cross, Phys. Lett. A 212 (1996) 341. [4] I.V. Golosovsky, I. Mirebeau, G. Andr!e, D.A. Kurdyukov, Yu.A. Kumzerov, S.B. Vakhrushev, Phys. Rev. Lett. 86 (2001) 5783. [5] Ping Sheng, R.W. Cohen, J.R. Schrieffer, J. Phys. C: Solid State Phys. 14 (1981) L565. [6] Yu.A. Kumzerov, A.A. Nabereznov, S.B. Vakhrushev, B.N. Savenko, Phys. Rev. B 52 (1995) 4772. [7] S.V. Pan‘kova, V.V. Poborchii, V.G. Solov‘ev, J. Phys.: Condens. Matter 8 (1996) L203. [8] E.V. Colla, A.V. Fokin, Yu.A. Kumzerov, Solid State Commun. 103 (1997) 127. [9] A. Beskrovny, I. Golosovsky, A. Fokin, Yu. Kumzerov, A. Kurbakov, A. Naberezhnov, S. Vakhrushev, Appl. Phys. A 74 (2002) S1001. [10] A.V. Fokin, Yu.A. Kumzerov, N.M. Okuneva, A.A. Naberezhnov, S.B. Vakhrushev, I.V. Golosovsky, A.I. Kurbakov, Phys. Rev. Lett. 89 (2002) 175503-1. [11] E.V. Charnaya, T. Loeser, D. Michel, C. Tien, D. Yaskov, Yu.A. Kumzerov, Phys. Rev. Lett. 88 (2001) 097602-1. [12] J.M. Drake, G.S. Grest, J. Klafter, R. Kopelman (Eds.), Dynamics in Small Confining Systems, MRS, Warrendale, PA, 1999. [13] K. Anliker, H.R. Brugger, W. K.anzig, Helv. Phys. Acta 27 (1954) 99. [14] Yu.A. Kumzerov, in: G.M. Chow, et al. (Eds.), Nanostructured Films and Coating, Kluwer Academic Publishers, Dordrecht, 2000, pp. 63–76. [15] J. Rodrigues-Carvajal, Program FULLPROF, version 2000, LLB CEA, Saclay. [16] A. Naberezhnov, A. Fokin, Yu. Kumzerov, S. Vakhrushev, B. Dorner, Eur. Phys. J. E 12 (2003) s21. [17] A. da Costa Lamas, S.-L. Chang, S. Caticha-Ellis, Phys. Stat. Sol. A 68 (1981) 173. [18] S. Tanisaki, J. Phys. Soc. Japan 18 (1963) 1181. [19] J.C. Le Guillou, J. Zinn-Justin, Phys. Rev. Lett. 39 (1977) 95.
Physica B 350 (2004) e1119–e1121
Neutron diffraction study of NaNO2 ferroelectric nanowires S. Borisova, T. Hansenb, Yu. Kumzerova, A. Naberezhnova,*, V. Simkinc, O. Smirnovd, A. Sotnikova, M. Tovare, S. Vakhrusheva a
Ioffe Physico-Technical Institute, 26 Polytechnicheskaya, S.-Petersburg 194021, Russia b Institute Laue-Langevin, F-38042 Grenoble Cedex 9, France c Joint Institute of Nuclear Research, Moscow district, Dubna 141980, Russia d Petersburg Nuclear Physics Institute, Leningrad district, Gatchina 188300, Russia e Hahn–Meitner-Institut, Glinicker Strabe 100, D-14 109 Berlin, Germany
Abstract For the first time the temperature evolution of the structure of ferroelectric nanowires of NaNO2 was studied by neutron diffraction from room temperature up to melting, i.e. in ferro- and paraelectric phases. Samples were produced in natural chrysotile asbestos with average channel diameter 671.5 nm. It is demonstrated that in the ferroelectric phase the structure is consistent with the bulk but is strongly textured. The temperature dependence of order parameter in the ferroelectric phase is determined for the confined sodium nitrite. It is shown that this dependence follows a power law with Tc=413.072.5 K and b=0.3470.05, and differs from the same for the bulk material. r 2004 Elsevier B.V. All rights reserved. PACS: 61.12.q; 61.46.w; 77.80.e Keywords: Neutron diffraction; Nanocomposite materials; Structure; Ferroelectrics
1. Introduction In recent years nanostructured materials attracted a steadfast attention because their properties are essentially different from those of conventional bulk materials. It is shown that the reduction of physical size from the microscopic scale down to the meso- and nanoscopic scales results in a change of the majority of physical *Corresponding author. E-mail address: [email protected] (A. Naberezhnov).
properties of confined materials (CM), such as temperature and type of phase transitions (PT) [1–6], dielectric permittivity [7,8], atomic mobility of constituent ions [9–11], flowing of liquids in a confined geometry [11,12] and so on. One of the important aspects of CM is phase stability as a function of spatial dimension, geometry and topology of nanoparticles. Ferroelectric nanocomposites have been studied intensively since the beginning of 1950s [13], but the majority of experimental results have been obtained for thin films or granular materials. At the same time there is another method of preparation of such dispersed
0921-4526/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2004.03.304
ARTICLE IN PRESS S. Borisov et al. / Physica B 350 (2004) e1119–e1121
substances—an intrusion of materials into artificial or natural porous matrices such as porous glasses, chrysotile asbestos, zeolites, opals and so on [14]. We have attempted to study the temperature evolution of the structure of confined NaNO2 in chrysotile asbestos with average channel diameter 671.5 nm at temperatures below and above TC by neutron diffraction, to clarify the peculiarities of ferroelectric phase transition in a system of quasi one-dimensional nanotubes.
2. Sample and experiment Sodium nitrite is an order–disorder ferroelectric and undergoes the first-order phase transition at TCE437 K. At room temperature its space group ( b=5.578 A, ( c=5.39 A) ( with is Im2m (a=3.57 A, two molecules per unit cell. The spontaneous polarization is oriented along the b-axis and appears due to partially ordered alignment of NO2 groups along this axis, accompanied by the displacement of sodium ions. Above Tc a mirror plane perpendicular to the b-axis appears and the space group changes to Immm. Bulk sodium nitrite melts at 554.1 K. Natural chrysotile asbestos (Mg3Si2O5(OH)4) is a regular set of closely packed parallel ultrathin dielectric tubes with external channel diameters of B30 nm and with internal diameters of 671.5 nm, the length of these tubes being about 25 mm (in our samples). The parallelism of nanochannels is better than 2 . Due to high wetting ability molten NaNO2 penetrates into these channels and forms a quasi onedimensional structure. The volume amount of linear nanostructured materials reaches 5%. The study of structure evolution of nanocomposite NaNO2 was performed from room temperature (RT) up to 543 K, i.e. below and above TC, on the TOF diffractometer HRFD (JINR, FLNP, Dubna, Russia) and powder diffractometers (PNPI, ( Gatchina, Russia, l=1.3841 A; E9, HMI, ( and D20, ILL, l=2.41 A). ( The saml=1.796 A ples were mounted as vertically as possible on the scattering plane and total deviation of the channels from the vertical axis did not exceed 8 . The temperature instability was better by 0.5% in Gatchina and does not exceed 71 K for the
others. The chrysotile asbestos has been measured at RT and at 543 K. Experimental results were treated by a FullProf program [15].
3. Results and discussion Typical diffraction patterns (without asbestos peaks) are presented in Fig. 1. We have described the structure of asbestos using the so-called ‘‘matching-mode’’ and later on we considered it as an additional background. The first unexpected experimental result is the high intensities of Bragg peaks from NaNO2 when compared to previous results [16]. This is surprising as the volume amount of salt is essentially less than in the case of porous glass with average pore diameter 7 nm. Furthermore, the ratios of intensities visibly differ from the ones observed for the bulk material. This fact could be explained by texture effect and indeed, the introduction of preferred orientation in data treatment procedure has essentially improved the description of diffraction patterns. Upon heating the intensities of Bragg peaks at large Q decrease faster than in the bulk and nanocomposite 7 nm glass samples, demonstrating the strong ‘‘softening’’ of lattice. It has been shown [17,18] that in NaNO2 the intensity of diffraction peaks is proportional to
100
(c) 50
Intensity, arb. un.
e1120
0
(b)
200 0 400
(a)
200 0 -200 40
50
60
70
80
90
100
2θ, degrees
( (a) the bulk at Fig. 1. Diffraction patterns at l=1.3841 A: 287 K, vertical bars indicate the Bragg peaks; (b) NaNO2 within asbestos at 287 K; (c) as (b) but at 422 K. The arrows indicate the positions of (0 2 2), (1 3 2) and (1 2 3) Bragg peaks. The asbestos is subtracted.
ARTICLE IN PRESS S. Borisov et al. / Physica B 350 (2004) e1119–e1121
Acknowledgements
1.2 1.0
This work was supported by the RFBR (Grants 00-02-16883, 01-02-17739 and 03-02-16545), INTAS-2001-0826 CRDF RP1-2361-ST02 and Program of Division of Physical Sciences of Russian Academy of Sciences. A.N. and A.S. would like to thank Berlin Neutron Scattering Center (BENSC) and Hahn–Meitner-Institut for financial support.
0.8
η
e1121
0.6 0.4 0.2 0.0
270
300
330
360
390
420
450
T, K Fig. 2. Temperature dependences of order parameter for the bulk (black circles) [17], NaNO2 within 771 nm porous glass (open triangles, [16]) and asbestos (black squares). Solid line is a result of fitting by a power law (see text); dashed line is drawn by eye.
2 2 jF j2 ¼ Freal þ Z2 ðTÞ Fim ; where Freal and Fim are the real and imaginary parts of the structure factor F ; and Z is the order parameter in the ferroelectric phase. The value of Z was determined from intensities of (0 2 2), (1 2 3) and (1 3 2) reflections, 2 2 for which Fim bFreal (Fig. 2). It is easy to see that this dependence does not correspond either to that observed for the bulk material or to the one obtained for NaNO2 in 7 nm porous glass [16] (TC=425.672.1 K). Above 413 K, the intensities of Bragg peaks depending on order parameters are very small and correspond to the value expected for the paraelectric phase. This fact is an evidence for a further decrease of TC for NaNO2 in asbestos, relative to the values observed for the bulk and nanocomposite glass samples. Temperature dependence of order parameter follows a power law (1–T/TC)b with b=0.34(5). This value b corresponds to that observed for NaNO2 within porous glass [16] and is close to the critical exponents for 3D-Ising (0.324770.001) and 3D-Heisenberg (0.364770.0012) models [19]. Above 543 K we did not observe any diffraction picture from sodium nitrite. On cooling, diffraction patterns began to be restored below 508 K, giving evidence for essential temperature hysteresis of the melting– freezing phase transition.
References [1] W.L. Zhong, Y.G. Wang, P.L. Zhang, Ferroelectric Lett. 1 (1998) 131 and references therein. [2] W. Neubeck, L. Ranno, M. Hunt, C. Vettier, D. Givord, Appl. Surf. Sci. 138–139 (1999) 195. [3] Shaoping Li, J.A. Eastman, Z. Li, C.M. Foster, R.E. Newnham, L.E. Cross, Phys. Lett. A 212 (1996) 341. [4] I.V. Golosovsky, I. Mirebeau, G. Andr!e, D.A. Kurdyukov, Yu.A. Kumzerov, S.B. Vakhrushev, Phys. Rev. Lett. 86 (2001) 5783. [5] Ping Sheng, R.W. Cohen, J.R. Schrieffer, J. Phys. C: Solid State Phys. 14 (1981) L565. [6] Yu.A. Kumzerov, A.A. Nabereznov, S.B. Vakhrushev, B.N. Savenko, Phys. Rev. B 52 (1995) 4772. [7] S.V. Pan‘kova, V.V. Poborchii, V.G. Solov‘ev, J. Phys.: Condens. Matter 8 (1996) L203. [8] E.V. Colla, A.V. Fokin, Yu.A. Kumzerov, Solid State Commun. 103 (1997) 127. [9] A. Beskrovny, I. Golosovsky, A. Fokin, Yu. Kumzerov, A. Kurbakov, A. Naberezhnov, S. Vakhrushev, Appl. Phys. A 74 (2002) S1001. [10] A.V. Fokin, Yu.A. Kumzerov, N.M. Okuneva, A.A. Naberezhnov, S.B. Vakhrushev, I.V. Golosovsky, A.I. Kurbakov, Phys. Rev. Lett. 89 (2002) 175503-1. [11] E.V. Charnaya, T. Loeser, D. Michel, C. Tien, D. Yaskov, Yu.A. Kumzerov, Phys. Rev. Lett. 88 (2001) 097602-1. [12] J.M. Drake, G.S. Grest, J. Klafter, R. Kopelman (Eds.), Dynamics in Small Confining Systems, MRS, Warrendale, PA, 1999. [13] K. Anliker, H.R. Brugger, W. K.anzig, Helv. Phys. Acta 27 (1954) 99. [14] Yu.A. Kumzerov, in: G.M. Chow, et al. (Eds.), Nanostructured Films and Coating, Kluwer Academic Publishers, Dordrecht, 2000, pp. 63–76. [15] J. Rodrigues-Carvajal, Program FULLPROF, version 2000, LLB CEA, Saclay. [16] A. Naberezhnov, A. Fokin, Yu. Kumzerov, S. Vakhrushev, B. Dorner, Eur. Phys. J. E 12 (2003) s21. [17] A. da Costa Lamas, S.-L. Chang, S. Caticha-Ellis, Phys. Stat. Sol. A 68 (1981) 173. [18] S. Tanisaki, J. Phys. Soc. Japan 18 (1963) 1181. [19] J.C. Le Guillou, J. Zinn-Justin, Phys. Rev. Lett. 39 (1977) 95.