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Lattice parameter and superconductivity in Nax(H3O)zCoO2 · yH2O
Physica C 463–465 (2007) 68–70 www.elsevier.com/locate/physc
Lattice parameter and superconductivity in Nax(H3O)zCoO2 Æ yH2O Hiroya Sakurai *, Satoshi Takenouchi, Kazunori Takada, Takayoshi Sasaki, Eiji Takayama-Muromachi National Institute for Materials Science, Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan Accepted 6 February 2007 Available online 17 May 2007
Abstract We synthesized Nax(H3O)zCoO2 Æ yH2O samples with various chemical compositions, and measured their magnetic properties to draw the superconducting phase diagram. Although the superconductivity is very sensitive to both the Na content and the Co valence, the c-axis length seems to be a good parameter governing the phase diagram. The relation between the c-axis length and superconductivity is discussed. Ó 2007 Elsevier B.V. All rights reserved. PACS: 74.62. c; 74.62.Bf Keywords: NaxCoO2 Æ yH2O; Superconductivity; Phase diagram
1. Introduction Sodium cobalt oxhydrate, Nax(H3O)zCoO2 Æ yH2O, has been intensively studied since the discovery of its superconductivity with Tc = 4.6 K [1–3]. Recently, we succeeded in controlling the chemical composition and reported the x– s–T phase diagram (s: Co valence) [4–8]. On the s = +3.40 section, magnetically ordered phase (M phase) appears in the range of 0.33 < x < 0.35, segmentalizing the superconducting region into two parts [4]. On the other hand, a dome-shaped superconducting region appears in the range of 0.33 < x < 0.38 [5] on the s = +3.48 section. The x = 0.350 sample on the s = +3.40 section and the x = 0.332 sample on the s = +3.48 section undergo transformation from the superconducting state to the magnetically ordered state by applying magnetic field (transition fields are 5.3 T [6] and 4.5 T [7] at 1.8 K, respectively) suggesting that the M phase shifts slightly to the lower x direction with increasing s [7]. Both the Na content and the Co
*
Corresponding author. Tel.: +81 29 860 4771; fax: +81 29 860 4674. E-mail address: [email protected] (H. Sakurai).
0921-4534/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2007.05.005
valence are thereby crucial parameters of the phase diagram. On the other hand, it was pointed out that the phase diagram can be satisfactorily drawn using a single parameter of nuclear quadrupole resonance (NQR) frequency [9]. This result suggests strongly that thickness of the CoO2 layer (along the c-axis) is a hidden key parameter governing superconductivity and the magnetic ordering, and the NQR frequency scales it. It is natural to assume a certain correlation between thickness of the CoO2 layer and the c-axis length and this is our main motif of the present study. In this short paper, we discuss relationship between superconductivity and the c-axis length for various superconducting phases with different compositions. 2. Experimental The samples were synthesized from Na0.70CoO2 precursor, which was made by conventional solid-state reaction for a mixture of Na2CO3 and Co3O4 [10]. The precursor (1 g) was immersed in 5 vol.% Br2 acetonitrile solution (35 ml) for 5 days and filtrated, then was immersed in 400 ml distilled water for 3 days. To control Na content keeping the Co valence constant, a certain volume (v ml)
H. Sakurai et al. / Physica C 463–465 (2007) 68–70 Table 1 Na content, Co valence, and c-axis length, and Tc of the samples HCl series 0 2 4 6 8 10 NaOH series 0 10 20 30 40 100 500
Na content
Co valence
8
˚) c (A 7
0.350 0.346 0.346 0.336 0.322 0.302 0.332 0.346 0.354 0.357 0.358 0.368 0.380
3.41 3.40 3.41 3.40 3.40 3.36 3.48 3.48 3.49 3.50 3.47 3.47 3.49
19.717 19.724 19.752 19.775 19.820 19.810 19.736 19.691 19.685 19.664 19.662 19.614 19.588
Temperature, T (K)
v (ml)
69
6
5
M 4
SC
3
SC
2 19.60
19.70
19.80
Lattice parameter, c (A)
of 0.1 M HCl or 0.1 M NaOH aqueous solution was added to the solution (10 or 50 ml 1 M NaOH solution was added for vNaOH = 100 or 500 ml, respectively). The sample was filtrated and dried in the air after being kept in the solution for three more days. It was proved by X-ray powder diffraction patterns that all samples were single phase except for the vNaOH = 500 ml sample with a trace amount of secondary phase. The Na content and the Co valence were determined by inductively coupled plasma atomic emission spectroscopy and redox titration as shown in Table 1. The superconducting and magnetic transition temperatures (Tc and Tm, respectively) were determined by magnetic susceptibility measurements [4,5]. The magnetic susceptibility has a small anomaly at Tm, below which the internal field was observed by NQR measurements [11]. 3. Results and discussion Fig. 1 shows c-axis length variations of Tc and Tm. The magnetically ordered phase appears in the range of ˚ < c < 19.80 A ˚ , segmentalizing the superconduc19.725 A ting region. It is notable that the transition temperatures determined for two series of the samples with different Co valences characterize the phase diagram together, which means that the c-axis length is an effective single parameter to represent the phase diagram. Furthermore, this phase diagram is quite similar to that drawn for the NQR frequency as the parameter, where the M phase also segmentalizes the superconducting region [12]. Since the NQR frequency increases with the compression of the CoO2 layer [9], our result suggests that enlarging the c-axis length causes the compression. This correlation between the c-axis length and the thickness of the CoO2 layer looks quite natural because the Coulomb attraction between oxygen ion in the CoO2 layer and Na+/H3O+ ion becomes weaker with increasing the c-axis length. Indeed, it has been reported that the layer becomes thicker when the clength becomes shorter under a pressure [13].
Fig. 1. The c–T phase diagram. The circles and squares were from the samples made using HCl and NaOH aqueous solutions, respectively. The full and open makers represent Tc and Tm, respectively.
Our results imply that the band structure which governs the superconductivity depends strongly on the CoO2 layer thickness, and thereby on the c-axis length. This supports an idea that the superconductivity is induced closely related to pocket-like Fermi surface appearance of which depends on the CoO2 layer thickness [14,15]. It is worth noting here that the CoO2 layer thickness of the monolayered hydrate ˚ [16]) or the anhydrate (1.93–1.98 A ˚ [2,17–19]) is (1.84 A ˚ much thicker than that of the bilayered hydrate (1.78 A [2]), and pocket-like Fermi surface has never been observed for them [20–22]. Considering this fact, the above idea can well account for why the superconductivity does not appear in the monolayered hydrate [16] nor the anhydrate, and why the monolayered and bilayered hydrates show very different magnetic behaviors [8,23]. 4. Summary For Nax(H3O)zCoO2 Æ yH2O samples with various compositions, we investigated the phase diagram with the c-axis length as a parameter. It was proved that the c-axis length is a good parameter governing the physical nature of the system. The c–T phase diagram is topologically the same as the m–T phase diagram (m: NQR frequency), suggesting that increasing the c-axis causes the compression of the CoO2 layer. These results strongly suggest that the superconductivity is induced closely related to the appearance of pocket-like Fermi surface. Acknowledgements This work is partially supported by Grants-in-Aid from JSPS and MEXT (16340111, 16076209) and by CREST, JST.
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H. Sakurai et al. / Physica C 463–465 (2007) 68–70
References [1] K. Takada, H. Sakurai, E. Takayama-Muromachi, F. Izumi, R.A. Dilanian, T. Sasaki, Nature (London) 422 (2003) 53. [2] H. Sakurai, K. Takada, S. Yoshii, T. Sasaki, K. Kindo, E. Takayama-Muromachi, Phys. Rev. B 68 (2003) 132507. [3] K. Takada, K. Fukuda, M. Osada, I. Nakai, F. Izumi, R.A. Dilanian, K. Kato, M. Takata, H. Sakurai, E. Takayama-Muromachi, T. Sasaki, J. Mater. Chem. 14 (2004) 1448. [4] H. Sakurai, K. Takada, T. Sasaki, E. Takayama-Muromachi, J. Phys. Soc. Jpn. 74 (2005) 2909. [5] H. Sakurai, N. Tsujii, O. Suzuki, H. Kitazawa, G. Kido, K. Takada, T. Sasaki, Phys. Rev. B 74 (2006) 092502. [6] H. Sakurai, K. Takada, T. Sasaki, E. Takayama-Muromachi, Physica C 445–448 (2006) 31. [7] H. Sakurai, K. Takada, T. Sasaki, E. Takayama-Muromachi, J. Magn. Magn. Mater. 310 (2007) e136. [8] H. Sakurai, K. Takada, T. Sasaki, E. Takayama-Muromachi, Physica C, in press, doi:10.1016/j.physc.2007.03.042. [9] Y. Ihara, H. Takeya, K. Ishida, H. Ikeda, C. Michioka, K. Yoshimura, K. Takada, T. Sasaki, H. Sakurai, E. TakayamaMuromachi, J. Phys. Soc. Jpn. 75 (2006) 124714. [10] H. Sakurai, S. Takenouchi, N. Tsujii, E. Takayama-Muromachi, J. Phys. Soc. Jpn. 73 (2004) 2081. [11] Y. Ihara, K. Ishida, C. Michioka, M. Kato, K. Yoshimura, K. Takada, T. Sasaki, H. Sakurai, E. Takayama-Muromachi, J. Phys. Soc. Jpn. 74 (2005) 867.
[12] Y. Kobayashi, M. Yokoi, T. Moyoshi, M. Sato, presented at 2006 Autumn Meeting of the Physical Society of Japan. [13] J.D. Jorgensen, M. Avdeev, D.G. Hinks, P.W. Barnes, S. Short, Phys. Rev. B 72 (2005) 224515. [14] D.J. Singh, Phys. Rev. B 61 (2000) 13397. [15] K. Kuroki, S. Onari, Y. Tanaka, R. Arita, T. Nojima, Phys. Rev. B 73 (2006) 184503. [16] K. Takada, H. Sakurai, E. Takayama-Muromachi, F. Izumi, R.A. Dilanian, T. Sasaki, J. Solid State Chem. 177 (2004) 372. [17] R.J. Balsys, R.L. Davis, Solid State Ionics 93 (1997) 279. [18] Y. Ono, N. Kato, Y. Ishii, Y. Miyazaki, T. Kajitani, J. Jpn. Soc. Powder Powder Metall. 50 (2003) 469. [19] H. Nakatsugawa, K. Nagasawa, J. Solid State Chem. 177 (2004) 1137. [20] M.Z. Hasan, Y.-D. Chuang, D. Qian, Y.W. Li, Y. Kong, A. Kuprin, A.V. Fedorov, R. Kimmerling, E. Rotenberg, K. Rossnagel, Z. Hussain, H. Koh, N.S. Rogado, M.L. Foo, R.J. Cava, Phys. Rev. Lett. 92 (2004) 246402. [21] H.-B. Yang, S.-C. Wang, A.K.P. Sekharan, H. Matsui, S. Souma, T. Sato, T. Takahashi, T. Takeuchi, J.C. Campuzano, R. Jin, B.S. Sales, D. Mandrus, Z. Wang, H. Ding, Phys. Rev. Lett. 92 (2004) 246403. [22] H.-B. Yang, Z.-H. Pan, A.K.P. Sekharan, T. Sato, S. Souma, T. Takahashi, R. Jin, B.C. Sales, D. Mandrus, A.V. Fedorov, Z. Wang, H. Ding, Phys. Rev. Lett. 95 (2005) 146401. [23] H. Sakurai, K. Takada, F. Izumi, R.A. Dilanian, T. Sasaki, E. Takayama-Muromachi, Physica C 412–414 (2004) 182.
Lattice parameter and superconductivity in Nax(H3O)zCoO2 Æ yH2O Hiroya Sakurai *, Satoshi Takenouchi, Kazunori Takada, Takayoshi Sasaki, Eiji Takayama-Muromachi National Institute for Materials Science, Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan Accepted 6 February 2007 Available online 17 May 2007
Abstract We synthesized Nax(H3O)zCoO2 Æ yH2O samples with various chemical compositions, and measured their magnetic properties to draw the superconducting phase diagram. Although the superconductivity is very sensitive to both the Na content and the Co valence, the c-axis length seems to be a good parameter governing the phase diagram. The relation between the c-axis length and superconductivity is discussed. Ó 2007 Elsevier B.V. All rights reserved. PACS: 74.62. c; 74.62.Bf Keywords: NaxCoO2 Æ yH2O; Superconductivity; Phase diagram
1. Introduction Sodium cobalt oxhydrate, Nax(H3O)zCoO2 Æ yH2O, has been intensively studied since the discovery of its superconductivity with Tc = 4.6 K [1–3]. Recently, we succeeded in controlling the chemical composition and reported the x– s–T phase diagram (s: Co valence) [4–8]. On the s = +3.40 section, magnetically ordered phase (M phase) appears in the range of 0.33 < x < 0.35, segmentalizing the superconducting region into two parts [4]. On the other hand, a dome-shaped superconducting region appears in the range of 0.33 < x < 0.38 [5] on the s = +3.48 section. The x = 0.350 sample on the s = +3.40 section and the x = 0.332 sample on the s = +3.48 section undergo transformation from the superconducting state to the magnetically ordered state by applying magnetic field (transition fields are 5.3 T [6] and 4.5 T [7] at 1.8 K, respectively) suggesting that the M phase shifts slightly to the lower x direction with increasing s [7]. Both the Na content and the Co
*
Corresponding author. Tel.: +81 29 860 4771; fax: +81 29 860 4674. E-mail address: [email protected] (H. Sakurai).
0921-4534/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2007.05.005
valence are thereby crucial parameters of the phase diagram. On the other hand, it was pointed out that the phase diagram can be satisfactorily drawn using a single parameter of nuclear quadrupole resonance (NQR) frequency [9]. This result suggests strongly that thickness of the CoO2 layer (along the c-axis) is a hidden key parameter governing superconductivity and the magnetic ordering, and the NQR frequency scales it. It is natural to assume a certain correlation between thickness of the CoO2 layer and the c-axis length and this is our main motif of the present study. In this short paper, we discuss relationship between superconductivity and the c-axis length for various superconducting phases with different compositions. 2. Experimental The samples were synthesized from Na0.70CoO2 precursor, which was made by conventional solid-state reaction for a mixture of Na2CO3 and Co3O4 [10]. The precursor (1 g) was immersed in 5 vol.% Br2 acetonitrile solution (35 ml) for 5 days and filtrated, then was immersed in 400 ml distilled water for 3 days. To control Na content keeping the Co valence constant, a certain volume (v ml)
H. Sakurai et al. / Physica C 463–465 (2007) 68–70 Table 1 Na content, Co valence, and c-axis length, and Tc of the samples HCl series 0 2 4 6 8 10 NaOH series 0 10 20 30 40 100 500
Na content
Co valence
8
˚) c (A 7
0.350 0.346 0.346 0.336 0.322 0.302 0.332 0.346 0.354 0.357 0.358 0.368 0.380
3.41 3.40 3.41 3.40 3.40 3.36 3.48 3.48 3.49 3.50 3.47 3.47 3.49
19.717 19.724 19.752 19.775 19.820 19.810 19.736 19.691 19.685 19.664 19.662 19.614 19.588
Temperature, T (K)
v (ml)
69
6
5
M 4
SC
3
SC
2 19.60
19.70
19.80
Lattice parameter, c (A)
of 0.1 M HCl or 0.1 M NaOH aqueous solution was added to the solution (10 or 50 ml 1 M NaOH solution was added for vNaOH = 100 or 500 ml, respectively). The sample was filtrated and dried in the air after being kept in the solution for three more days. It was proved by X-ray powder diffraction patterns that all samples were single phase except for the vNaOH = 500 ml sample with a trace amount of secondary phase. The Na content and the Co valence were determined by inductively coupled plasma atomic emission spectroscopy and redox titration as shown in Table 1. The superconducting and magnetic transition temperatures (Tc and Tm, respectively) were determined by magnetic susceptibility measurements [4,5]. The magnetic susceptibility has a small anomaly at Tm, below which the internal field was observed by NQR measurements [11]. 3. Results and discussion Fig. 1 shows c-axis length variations of Tc and Tm. The magnetically ordered phase appears in the range of ˚ < c < 19.80 A ˚ , segmentalizing the superconduc19.725 A ting region. It is notable that the transition temperatures determined for two series of the samples with different Co valences characterize the phase diagram together, which means that the c-axis length is an effective single parameter to represent the phase diagram. Furthermore, this phase diagram is quite similar to that drawn for the NQR frequency as the parameter, where the M phase also segmentalizes the superconducting region [12]. Since the NQR frequency increases with the compression of the CoO2 layer [9], our result suggests that enlarging the c-axis length causes the compression. This correlation between the c-axis length and the thickness of the CoO2 layer looks quite natural because the Coulomb attraction between oxygen ion in the CoO2 layer and Na+/H3O+ ion becomes weaker with increasing the c-axis length. Indeed, it has been reported that the layer becomes thicker when the clength becomes shorter under a pressure [13].
Fig. 1. The c–T phase diagram. The circles and squares were from the samples made using HCl and NaOH aqueous solutions, respectively. The full and open makers represent Tc and Tm, respectively.
Our results imply that the band structure which governs the superconductivity depends strongly on the CoO2 layer thickness, and thereby on the c-axis length. This supports an idea that the superconductivity is induced closely related to pocket-like Fermi surface appearance of which depends on the CoO2 layer thickness [14,15]. It is worth noting here that the CoO2 layer thickness of the monolayered hydrate ˚ [16]) or the anhydrate (1.93–1.98 A ˚ [2,17–19]) is (1.84 A ˚ much thicker than that of the bilayered hydrate (1.78 A [2]), and pocket-like Fermi surface has never been observed for them [20–22]. Considering this fact, the above idea can well account for why the superconductivity does not appear in the monolayered hydrate [16] nor the anhydrate, and why the monolayered and bilayered hydrates show very different magnetic behaviors [8,23]. 4. Summary For Nax(H3O)zCoO2 Æ yH2O samples with various compositions, we investigated the phase diagram with the c-axis length as a parameter. It was proved that the c-axis length is a good parameter governing the physical nature of the system. The c–T phase diagram is topologically the same as the m–T phase diagram (m: NQR frequency), suggesting that increasing the c-axis causes the compression of the CoO2 layer. These results strongly suggest that the superconductivity is induced closely related to the appearance of pocket-like Fermi surface. Acknowledgements This work is partially supported by Grants-in-Aid from JSPS and MEXT (16340111, 16076209) and by CREST, JST.
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H. Sakurai et al. / Physica C 463–465 (2007) 68–70
References [1] K. Takada, H. Sakurai, E. Takayama-Muromachi, F. Izumi, R.A. Dilanian, T. Sasaki, Nature (London) 422 (2003) 53. [2] H. Sakurai, K. Takada, S. Yoshii, T. Sasaki, K. Kindo, E. Takayama-Muromachi, Phys. Rev. B 68 (2003) 132507. [3] K. Takada, K. Fukuda, M. Osada, I. Nakai, F. Izumi, R.A. Dilanian, K. Kato, M. Takata, H. Sakurai, E. Takayama-Muromachi, T. Sasaki, J. Mater. Chem. 14 (2004) 1448. [4] H. Sakurai, K. Takada, T. Sasaki, E. Takayama-Muromachi, J. Phys. Soc. Jpn. 74 (2005) 2909. [5] H. Sakurai, N. Tsujii, O. Suzuki, H. Kitazawa, G. Kido, K. Takada, T. Sasaki, Phys. Rev. B 74 (2006) 092502. [6] H. Sakurai, K. Takada, T. Sasaki, E. Takayama-Muromachi, Physica C 445–448 (2006) 31. [7] H. Sakurai, K. Takada, T. Sasaki, E. Takayama-Muromachi, J. Magn. Magn. Mater. 310 (2007) e136. [8] H. Sakurai, K. Takada, T. Sasaki, E. Takayama-Muromachi, Physica C, in press, doi:10.1016/j.physc.2007.03.042. [9] Y. Ihara, H. Takeya, K. Ishida, H. Ikeda, C. Michioka, K. Yoshimura, K. Takada, T. Sasaki, H. Sakurai, E. TakayamaMuromachi, J. Phys. Soc. Jpn. 75 (2006) 124714. [10] H. Sakurai, S. Takenouchi, N. Tsujii, E. Takayama-Muromachi, J. Phys. Soc. Jpn. 73 (2004) 2081. [11] Y. Ihara, K. Ishida, C. Michioka, M. Kato, K. Yoshimura, K. Takada, T. Sasaki, H. Sakurai, E. Takayama-Muromachi, J. Phys. Soc. Jpn. 74 (2005) 867.
[12] Y. Kobayashi, M. Yokoi, T. Moyoshi, M. Sato, presented at 2006 Autumn Meeting of the Physical Society of Japan. [13] J.D. Jorgensen, M. Avdeev, D.G. Hinks, P.W. Barnes, S. Short, Phys. Rev. B 72 (2005) 224515. [14] D.J. Singh, Phys. Rev. B 61 (2000) 13397. [15] K. Kuroki, S. Onari, Y. Tanaka, R. Arita, T. Nojima, Phys. Rev. B 73 (2006) 184503. [16] K. Takada, H. Sakurai, E. Takayama-Muromachi, F. Izumi, R.A. Dilanian, T. Sasaki, J. Solid State Chem. 177 (2004) 372. [17] R.J. Balsys, R.L. Davis, Solid State Ionics 93 (1997) 279. [18] Y. Ono, N. Kato, Y. Ishii, Y. Miyazaki, T. Kajitani, J. Jpn. Soc. Powder Powder Metall. 50 (2003) 469. [19] H. Nakatsugawa, K. Nagasawa, J. Solid State Chem. 177 (2004) 1137. [20] M.Z. Hasan, Y.-D. Chuang, D. Qian, Y.W. Li, Y. Kong, A. Kuprin, A.V. Fedorov, R. Kimmerling, E. Rotenberg, K. Rossnagel, Z. Hussain, H. Koh, N.S. Rogado, M.L. Foo, R.J. Cava, Phys. Rev. Lett. 92 (2004) 246402. [21] H.-B. Yang, S.-C. Wang, A.K.P. Sekharan, H. Matsui, S. Souma, T. Sato, T. Takahashi, T. Takeuchi, J.C. Campuzano, R. Jin, B.S. Sales, D. Mandrus, Z. Wang, H. Ding, Phys. Rev. Lett. 92 (2004) 246403. [22] H.-B. Yang, Z.-H. Pan, A.K.P. Sekharan, T. Sato, S. Souma, T. Takahashi, R. Jin, B.C. Sales, D. Mandrus, A.V. Fedorov, Z. Wang, H. Ding, Phys. Rev. Lett. 95 (2005) 146401. [23] H. Sakurai, K. Takada, F. Izumi, R.A. Dilanian, T. Sasaki, E. Takayama-Muromachi, Physica C 412–414 (2004) 182.