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Synthesis of superconducting cobalt oxyhydrates using a novel method: Electrolyzed and oxidized water
Physica C 460–462 (2007) 493–494 www.elsevier.com/locate/physc
Synthesis of superconducting cobalt oxyhydrates using a novel method: Electrolyzed and oxidized water Chia-Jyi Liu *, Tsung-Hsien Wu, Lin-Li Hsu, Jung-Sheng Wang, Shu-Yo Chen Department of Physics, National Changhua University of Education, Changhua 50007, Taiwan Available online 28 March 2007
Abstract By deintercalation of Na+ followed by inserting bilayers of water molecules into the host lattice, the layered cobalt oxide of c-Na0.7CoO2 undergoes a topotactic transformation to a layered cobalt oxyhydrate of Na0.35(H2O)1.3CoO2 d with the c-axis expanded ˚ to c 19.6 A ˚ . In this paper, we demonstrate that the superconducting phase of c 19.6 A ˚ can be directly obtained by from c 10.9 A simply immersing c-Na0.7CoO2 powders in electrolyzed/oxidized (EO) water, which is readily available from a commercial electrolyzed water generator. We found that high oxidation–reduction potential of EO water drives the oxidation of the cobalt ions accompanying by ˚ phase. Our results demonstrate how EO water can be used to oxidize the cobalt ions and the formation of the superconductive c 19.6 A hence form superconducting cobalt oxyhydrates in a clean and simple way and may provide an economic and environment-friendly route to oxidize the transition metal of complex metal oxides. 2007 Elsevier B.V. All rights reserved. Keywords: Superconductors; Sodium cobalt oxyhydrates; Electrolyzed and oxidized water
Transforming thermoelectric material c-Na0.7CoO2 into superconductive cobalt oxyhydrate Na0.35(H2O)1.3CoO2 [1] can be viewed as a topotactic process by intercalating water molecules between the CoO2 layers and the Na ion layers of the host lattice with the c-axis elongation from ˚ to 19.6 A ˚ . The procedure of preparing supercon10.9 A ductive cobalt oxyhydrate can be accomplished either by immersing c-Na0.7CoO2 in an oxidizing solution such as Br2 in CH3CN, [1] Na2S2O8(aq), [2] KMnO4(aq), [3] and NaMnO4(aq), [4] or anodically polarizing c-Na0.7CoO2 [5] with a constant voltage of 0.6–1.2 V at room temperature. There are two distinct crystallographic sites, i.e., 2b and 2d, for the Na ions in the hexagonal unit cell of c-Na0.7CoO2. The Na+ in the 2b site tends to disassociate from the crystal lattice when immersed in aqueous or acetonitrile solution [6]. Formation of the sodium cobalt oxyhydrates involves
*
Corresponding author. Tel.: +886 4 7232105x3337; fax: +886 4 7211153. E-mail address: [email protected] (C.-J. Liu). 0921-4534/$ - see front matter 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2007.03.171
de-intercalation, oxidation and hydration reaction. Whether the cobalt ions can be oxidized seems to play a ˚ significant role in forming the superconducting c 19.6 A phase [7]. Electrolyzed/oxidized (EO) water features a high oxidation–reduction potential (ORP) and a low pH value. We find that the high ORP of EO water could drive the oxidation of the cobalt ions accompanying by the formation ˚ phase. In this paper, of the superconductive c 19.6 A we demonstrate that the EO water can be used to oxidize the cobalt ions and hence form superconducting cobalt oxyhydrates in a clean and simple way. Polycrystalline c-Na0.7CoO2 powders (100 mg) were immersed in the 250 ml EO water followed by filtration. The EO water with ORP of 880 mV was obtained directly from a commercial electrolyzed water generator. Powder X-ray diffraction (XRD) patterns were obtained using a Shimadzu XRD-6000 diffractometer equipped with Fe Ka radiation. The data were collected in the range 5 6 2h 6 50 with 0.02 2h steps. The magnetization data were obtained using a SQUID magnetometer (Quantum Design).
494
C.-J. Liu et al. / Physica C 460–462 (2007) 493–494
(004)
(100) (102)
(006)
(002)
Intensity (arb. units)
Fe Kα (a)
(b)
10
20
30 2θ (degree)
40
50
Fig. 1. The powder XRD patterns of (a) Na0.417(H2O)1.33CoO2 d obtained by aqueous NaMnO4 solution and (b) EO-treated Nax(H2O)yCoO2 d.
The powder X-ray diffraction pattern for the EO watertreated sample is shown in Fig. 1. All the reflection peaks of the EO water-treated sample are identical to those of Na0.417(H2O)1.33CoO2 d obtained by immersing c-Na0.7CoO2 in aqueous NaMnO4 solution [4] and are indexable based on the unit cell having space group P63/ ˚ and c 19.6 A ˚ . The c 19.6 A ˚ phase mmc with a 2.82 A is sensitive to the surrounding humidity. Insufficient ˚ phase. The humidity would lead to the c 13.9 A ˚ has bilayers of water molecules in the hexagonal c 19.6 A lattice with one layer residing between the CoO2 layers and Na+ ions layers, and the other residing within the Na+ layers. The water molecules sitting between the CoO2 layers and Na+ ions layers tend to escape in an insufficient humidity environment, under pressure, or subject to evacuation, ˚ which would result in the formation of the c 13.9 A phase with monolayer water molecules residing within the Na+ layers [8]. Fig. 2 shows the zero-field-cooled magnetization data of the EO water-treated sample measured in a field of 10 Oe down to 2 K. One can clearly see a diamagnetic signal of magnetization and a rapid decrease at 4.2 K, where the superconducting transition begins to occur. The mass magnetization at 2 K is 7.49 · 10 3 emu/g zero-field-cooled mode. Sufficient ORP of the EO water seems to be essential for ˚ phase. We the formation of superconducting c 19.6 A find that EO water with insufficient ORP would lead to products with similar XRD patterns for the powders obtained by immersing c-Na0.7CoO2 in the tap water, which results in de-intercalation of Na+ and large oxygen deficiency but would not oxidize the Co ions. The ORP of the tap water is 600 mV. Before measuring the ORP of EO water or tap water, we have used the Hanna 7022 ORP solution with ORP = 470 mV at 25 C to calibrate the ORP sensor of platinum electrode. According to the composition analysis using inductively coupled plasma atomic-emission spectrometry, water content determina-
Magnetization (emu/g)
0.002 0 -0.002 -0.004 H = 10 Oe
-0.006 -0.008
0
5
10 15 Temperature (K)
20
25
Fig. 2. The mass magnetization of the EO-treated sodium cobalt oxyhydrate with the onset Tc = 4.2 K.
tion using thermogravimetric analyzer, and oxygen content determination using iodometric titration, the tap watertreated product has the chemical formula of Na0.29(H2O)0.41CoO1.78. The oxidation number of Co is ˚ phase +3.48 and +3.27 for the superconducting c 19.6 A and the tap water-treated sample, respectively. In summary, we are able to use the electrolyzed and oxidized water to make superconducting sodium cobalt oxyhydrates with onset Tc = 4.2 K. Like high-Tc copper oxide superconductor, the cobalt oxyhydrates require an appropriate oxidation number of the Co ions in order to undergo superconducting transition. Therefore, the key ˚ phase factor of forming the superconducting c 19.6 A relies on whether the oxidizing solution has the ability to abstract electrons from the cobalt ions. Deintercalation of Na+ for c-Na0.7CoO2 is spontaneous and would not necessarily bring about oxidation of the cobalt ions. Acknowledgment This work is supported by the National Science Council of Taiwan, ROC, Grant No. NSC 94-2112-M-018-001. References [1] K. Takada, H. Sakurai, E. Takayama-Muromachi, F. Izumi, R.A. Dilanian, T. Sasaki, Nature 422 (2003) 53. [2] S. Park, Y. Lee, A. Moodenbaugh, T. Vogt, Phys. Rev. B 68 (2003) 180505. [3] C.-J. Liu, C.-Y. Liao, L.-C. Huang, C.-H. Su, S. Neeleshwar, Y.-Y. Chen, C.-J.C. Liu, Physica C 416 (2004) 43. [4] C.-J. Liu, W.-C. Hung, J.-S. Wang, C.-J.C. Liu, J. Am. Chem. Soc. 127 (2005) 830. [5] F.C. Chou, J.H. Cho, P.A. Lee, E.T. Abel, K. Matan, Y.S. Lee, Phys. Rev. Lett. 92 (2004) 157004. [6] J.D. Jorgensen, M. Avdeev, D.G. Hinks, J.C. Burley, S. Short, Phys. Rev. B 68 (2003) 214517. [7] C.-J. Liu, W.-C. Hung, C.-Y. Liao, J.-S. Wang, H.-S. Sheu, cond-mat/ 0603701. [8] C.-J. Liu, C.-Y. Liao, L.-C. Huang, C.-H. Su, W.-C. Hung, S. Neeleshwar, Y.-Y. Chen, C.-J.C. Liu, Chin. J. Phys. 43 (2005) 547.
Synthesis of superconducting cobalt oxyhydrates using a novel method: Electrolyzed and oxidized water Chia-Jyi Liu *, Tsung-Hsien Wu, Lin-Li Hsu, Jung-Sheng Wang, Shu-Yo Chen Department of Physics, National Changhua University of Education, Changhua 50007, Taiwan Available online 28 March 2007
Abstract By deintercalation of Na+ followed by inserting bilayers of water molecules into the host lattice, the layered cobalt oxide of c-Na0.7CoO2 undergoes a topotactic transformation to a layered cobalt oxyhydrate of Na0.35(H2O)1.3CoO2 d with the c-axis expanded ˚ to c 19.6 A ˚ . In this paper, we demonstrate that the superconducting phase of c 19.6 A ˚ can be directly obtained by from c 10.9 A simply immersing c-Na0.7CoO2 powders in electrolyzed/oxidized (EO) water, which is readily available from a commercial electrolyzed water generator. We found that high oxidation–reduction potential of EO water drives the oxidation of the cobalt ions accompanying by ˚ phase. Our results demonstrate how EO water can be used to oxidize the cobalt ions and the formation of the superconductive c 19.6 A hence form superconducting cobalt oxyhydrates in a clean and simple way and may provide an economic and environment-friendly route to oxidize the transition metal of complex metal oxides. 2007 Elsevier B.V. All rights reserved. Keywords: Superconductors; Sodium cobalt oxyhydrates; Electrolyzed and oxidized water
Transforming thermoelectric material c-Na0.7CoO2 into superconductive cobalt oxyhydrate Na0.35(H2O)1.3CoO2 [1] can be viewed as a topotactic process by intercalating water molecules between the CoO2 layers and the Na ion layers of the host lattice with the c-axis elongation from ˚ to 19.6 A ˚ . The procedure of preparing supercon10.9 A ductive cobalt oxyhydrate can be accomplished either by immersing c-Na0.7CoO2 in an oxidizing solution such as Br2 in CH3CN, [1] Na2S2O8(aq), [2] KMnO4(aq), [3] and NaMnO4(aq), [4] or anodically polarizing c-Na0.7CoO2 [5] with a constant voltage of 0.6–1.2 V at room temperature. There are two distinct crystallographic sites, i.e., 2b and 2d, for the Na ions in the hexagonal unit cell of c-Na0.7CoO2. The Na+ in the 2b site tends to disassociate from the crystal lattice when immersed in aqueous or acetonitrile solution [6]. Formation of the sodium cobalt oxyhydrates involves
*
Corresponding author. Tel.: +886 4 7232105x3337; fax: +886 4 7211153. E-mail address: [email protected] (C.-J. Liu). 0921-4534/$ - see front matter 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2007.03.171
de-intercalation, oxidation and hydration reaction. Whether the cobalt ions can be oxidized seems to play a ˚ significant role in forming the superconducting c 19.6 A phase [7]. Electrolyzed/oxidized (EO) water features a high oxidation–reduction potential (ORP) and a low pH value. We find that the high ORP of EO water could drive the oxidation of the cobalt ions accompanying by the formation ˚ phase. In this paper, of the superconductive c 19.6 A we demonstrate that the EO water can be used to oxidize the cobalt ions and hence form superconducting cobalt oxyhydrates in a clean and simple way. Polycrystalline c-Na0.7CoO2 powders (100 mg) were immersed in the 250 ml EO water followed by filtration. The EO water with ORP of 880 mV was obtained directly from a commercial electrolyzed water generator. Powder X-ray diffraction (XRD) patterns were obtained using a Shimadzu XRD-6000 diffractometer equipped with Fe Ka radiation. The data were collected in the range 5 6 2h 6 50 with 0.02 2h steps. The magnetization data were obtained using a SQUID magnetometer (Quantum Design).
494
C.-J. Liu et al. / Physica C 460–462 (2007) 493–494
(004)
(100) (102)
(006)
(002)
Intensity (arb. units)
Fe Kα (a)
(b)
10
20
30 2θ (degree)
40
50
Fig. 1. The powder XRD patterns of (a) Na0.417(H2O)1.33CoO2 d obtained by aqueous NaMnO4 solution and (b) EO-treated Nax(H2O)yCoO2 d.
The powder X-ray diffraction pattern for the EO watertreated sample is shown in Fig. 1. All the reflection peaks of the EO water-treated sample are identical to those of Na0.417(H2O)1.33CoO2 d obtained by immersing c-Na0.7CoO2 in aqueous NaMnO4 solution [4] and are indexable based on the unit cell having space group P63/ ˚ and c 19.6 A ˚ . The c 19.6 A ˚ phase mmc with a 2.82 A is sensitive to the surrounding humidity. Insufficient ˚ phase. The humidity would lead to the c 13.9 A ˚ has bilayers of water molecules in the hexagonal c 19.6 A lattice with one layer residing between the CoO2 layers and Na+ ions layers, and the other residing within the Na+ layers. The water molecules sitting between the CoO2 layers and Na+ ions layers tend to escape in an insufficient humidity environment, under pressure, or subject to evacuation, ˚ which would result in the formation of the c 13.9 A phase with monolayer water molecules residing within the Na+ layers [8]. Fig. 2 shows the zero-field-cooled magnetization data of the EO water-treated sample measured in a field of 10 Oe down to 2 K. One can clearly see a diamagnetic signal of magnetization and a rapid decrease at 4.2 K, where the superconducting transition begins to occur. The mass magnetization at 2 K is 7.49 · 10 3 emu/g zero-field-cooled mode. Sufficient ORP of the EO water seems to be essential for ˚ phase. We the formation of superconducting c 19.6 A find that EO water with insufficient ORP would lead to products with similar XRD patterns for the powders obtained by immersing c-Na0.7CoO2 in the tap water, which results in de-intercalation of Na+ and large oxygen deficiency but would not oxidize the Co ions. The ORP of the tap water is 600 mV. Before measuring the ORP of EO water or tap water, we have used the Hanna 7022 ORP solution with ORP = 470 mV at 25 C to calibrate the ORP sensor of platinum electrode. According to the composition analysis using inductively coupled plasma atomic-emission spectrometry, water content determina-
Magnetization (emu/g)
0.002 0 -0.002 -0.004 H = 10 Oe
-0.006 -0.008
0
5
10 15 Temperature (K)
20
25
Fig. 2. The mass magnetization of the EO-treated sodium cobalt oxyhydrate with the onset Tc = 4.2 K.
tion using thermogravimetric analyzer, and oxygen content determination using iodometric titration, the tap watertreated product has the chemical formula of Na0.29(H2O)0.41CoO1.78. The oxidation number of Co is ˚ phase +3.48 and +3.27 for the superconducting c 19.6 A and the tap water-treated sample, respectively. In summary, we are able to use the electrolyzed and oxidized water to make superconducting sodium cobalt oxyhydrates with onset Tc = 4.2 K. Like high-Tc copper oxide superconductor, the cobalt oxyhydrates require an appropriate oxidation number of the Co ions in order to undergo superconducting transition. Therefore, the key ˚ phase factor of forming the superconducting c 19.6 A relies on whether the oxidizing solution has the ability to abstract electrons from the cobalt ions. Deintercalation of Na+ for c-Na0.7CoO2 is spontaneous and would not necessarily bring about oxidation of the cobalt ions. Acknowledgment This work is supported by the National Science Council of Taiwan, ROC, Grant No. NSC 94-2112-M-018-001. References [1] K. Takada, H. Sakurai, E. Takayama-Muromachi, F. Izumi, R.A. Dilanian, T. Sasaki, Nature 422 (2003) 53. [2] S. Park, Y. Lee, A. Moodenbaugh, T. Vogt, Phys. Rev. B 68 (2003) 180505. [3] C.-J. Liu, C.-Y. Liao, L.-C. Huang, C.-H. Su, S. Neeleshwar, Y.-Y. Chen, C.-J.C. Liu, Physica C 416 (2004) 43. [4] C.-J. Liu, W.-C. Hung, J.-S. Wang, C.-J.C. Liu, J. Am. Chem. Soc. 127 (2005) 830. [5] F.C. Chou, J.H. Cho, P.A. Lee, E.T. Abel, K. Matan, Y.S. Lee, Phys. Rev. Lett. 92 (2004) 157004. [6] J.D. Jorgensen, M. Avdeev, D.G. Hinks, J.C. Burley, S. Short, Phys. Rev. B 68 (2003) 214517. [7] C.-J. Liu, W.-C. Hung, C.-Y. Liao, J.-S. Wang, H.-S. Sheu, cond-mat/ 0603701. [8] C.-J. Liu, C.-Y. Liao, L.-C. Huang, C.-H. Su, W.-C. Hung, S. Neeleshwar, Y.-Y. Chen, C.-J.C. Liu, Chin. J. Phys. 43 (2005) 547.