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High-pressure and high-temperature electrical resistivity studies on Nd-123
Materials Letters 59 (2005) 1764 – 1766 www.elsevier.com/locate/matlet
High-pressure and high-temperature electrical resistivity studies on Nd-123 R. Selva VennilaT, N. Victor Jaya, S. Natarajan Department of Physics, Anna University, Chennai-600 025, India Received 7 April 2004; accepted 26 January 2005 Available online 19 March 2005
Abstract High-pressure, high-temperature electrical resistivity measurements are carried out on NdBa2Cu3O7 d high Tc superconductor (HTSC). The electrical resistivity is measured by four-probe method using Bridgmann Opposed Anvil High-Pressure Device (OAHPD). The hightemperature measurement is done using heating coil arrangement in OAHPD. The electrical resistivity is found to decrease with the increase of pressure up to 8 GPa. The sample shows a decrease in the resistivity up to the maximum pressure and temperature of 8 GPa and 523 K, respectively. D 2005 Elsevier B.V. All rights reserved. Keywords: Electrical properties; Perovskites; Superconductors; Crystal structure; X-ray techniques
1. Introduction Neodymium is the first element in the rare earth series forming the proper 123-structure. Other substitutions, such as Ba for Nd, lead to a suppression of superconductivity [1]. The substitution of Nd totally in place of Y showed a raise in critical temperature, which is even higher than all other 123-compounds [2]. A stabilization of the RE-123 stoichiometry was done by melt processing under reduced oxygen partial pressure, which plays an important role for change in the Tc of the high-temperature superconductors [3,4] and a maximum Tc of 96 K was obtained for Nd/Ba ratio of 0.5 concentration. Superconductivity is achieved in NdBa2 Cu3O7 d for dN0.64–0.69 in which the holes are mobile [5]. The NdBa2Cu3O7 d based superconductor receives greater attention because of (a) the increase in critical current density in external magnetic field as compared to its value in self-field, (b) the high irreversible fields greater than that of YBa2Cu3O7 d and (c) the possibility to achieve high rates of melt texturing about 50 times faster than YBa2Cu3O7 d because of the higher solubility of the Nd in T Corresponding author. E-mail address: [email protected] (R.S. Vennila). 0167-577X/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2005.01.062
the melt when compared with Y [1]. The maximum critical temperature and maximum current density for this compound is greater than the YBCO [3,6], hence it can well replace the YBCO in the technological application. Highpressure experiments constitute a sensitive probe of the superconducting state because of the change in electronic and phonic properties [7]. The present investigation gives the high-pressure high-temperature electrical resistivity behaviour of these samples up to 8 GPa and a maximum temperature of 523 K.
2. Experimental The NdBa2Cu3O7 d sample is synthesised by solid state method [2]. High purity Nd2O3, BaCO3, CuO, CaCO3 of stoichiometric composition were taken and ground finely. The pellets of the mixture was calcined at 1173 K, 1193 K and at 1193 K with intermediate grindings. The sample was annealed in flowing oxygen at 733 K for 3 days and the temperature was finally decreased to room temperature at the rate of 12 K/h. Energy-dispersive X-ray powder diffraction (EDXRD) study is carried out on Nd-123 system using white X-rays
R.S. Vennila et al. / Materials Letters 59 (2005) 1764–1766
1765
1.0 (110)
0.9 523 K
0.8
(arb. units)
473 K
0.7
0
10
(014)
0.3 GPa (116)
(214)
(016) (007)
(101)
20
373 K
0.5 323 K
0.4
RT
0.3 0.2
0
(002)
(113)
ρ/ρ
(020)
Intensity
423 K
0.6
30
40
50
Energy (keV) Fig. 1. EDXRD pattern of the NdBa2Cu3O7
0.1 0
d.
from copper target produced by rotating anode X-ray generator, Rigaku. An X-ray diffraction measurement confirms the formation of single phase. The system was indexed with orthorhombic structure using XRD analysis software [9]. The EDXRD pattern obtained for the Nd-123 is shown in Fig. 1. High-pressure electrical resistivity study was carried out by four-probe method using Bridgmann Opposed Anvil High-Pressure Device (OAHPD). High-pressure, hightemperature electrical resistivity measurements are carried out using OAHPD along with a heating coil attachment, which is shown in Fig. 2. Annular heating coil is placed in between the opposed anvils. The temperature stability obtained was F2 K. The power to the coil is controlled by a variac and the temperature has been maintained using
1
2
3
4
6
7
8
9
10
Fig. 3. Variation of electrical resistivity of NdBa2Cu3O7 d studied up to a maximum pressure of 8 GPa for temperatures up to 523 K.
a temperature controller [8]. In this arrangement a chromel– alumel thermocouple connected together by spot welding is used as a temperature sensor. The spot welded junction was hammered and made very thin and flat. The sample of thickness 0.1 mm has been used for the resistivity measurements. The temperature was determined from the thermo emf versus temperature chart. The pressure cell assembly, thermocouples, sample and the annular heating coil were assembled for good thermal contact. Mica sheets and tapes were used for insulating purposes. The position of the sample and the thermocouple in the high-pressure, high-
Thermocouple
Temperature controller
Voltmeter
5
Pressure (GPa)
Anvil
Heating coil
Constant current source Fig. 2. High-pressure, high-temperature setup for electrical resistivity measurements.
1766
R.S. Vennila et al. / Materials Letters 59 (2005) 1764–1766 -3.20
log (ρ) Ohm cm
-3.40
-3.60
-3.80
-4.00
-4.20 0
1
2
3
4
5
6
7
8
9
10
Pressure (GPa) Fig. 4. Variation of log(q) versus pressure of NdBa2Cu3O7
to the pressure and temperature is found to be reversible with hysteresis. Variation of log(q) versus pressure is plotted and shown in Fig. 4, which confirms the layered structure of the sample. The q behaviour at the two regions (i.e., low- and high-pressure regions) corresponds to inter- and intralayer changes, which may be attributed from Fig. 4. The initial rapid decrease in q is caused by the changes in the interlayer spacing, and beyond which, the interlayer is not affected much, which is shown by a nearly constant curve at higher pressures. The intralayer bonds are very much stronger and require pressure higher than 8 GPa to produce changes in it. From the study of the behaviour it can be understood that the application of even a small pressure in the layered copper oxides increases the carrier concentration between the CuO layers, thereby improving the metallic behaviour in the Nd-123 superconductor. Alternatively, temperature opposes the interlayer bond breaking effects caused by the pressure.
d.
temperature arrangement using heating coil setup is shown in Fig. 2.
3. Results and discussion NdBa2Cu3O7 d system is found to be crystallised in orthorhombic structure with lattice parameters a=3.87F0.01 2, b=3.92F0.01 2 and c=11.74F0.01 2 and v=177.3 23, and the results are found to be in good agreement with the literature [2]. The variation of high-pressure electrical resistivity observed at different temperatures, 323 K, 373 K, 423 K, 473 K and 523 K (maximum temperature studied), is shown in Fig. 3. Initially, the electrical resistivity of the sample decreases rapidly with pressure. At higher pressures, the decrease in q is very small and can be assumed to be a constant when compared with the initial drop. A systematic upward shift in resistivity with temperature is observed up to 523 K with the same trend as observed at room temperature. The sample shows metallic behaviour up to a maximum pressure and temperature of 8 GPa and 523 K, respectively. The absence of phase transitions up to 8 GPa and 523 K is reported. The behaviour confirms the metallic nature of sample up to 523 K and a maximum pressure of 8 GPa. Also, the effect due
Acknowledgement We thank Dr. S. Reza Ghorbani, Iran and Prof. ¨ . Rapp, Sweden for providing the samples for the Dr. O studies. We also thank the University Grants Commission, Government of India, for financial support.
References ¨ . Rapp, R. Tellgren, Z. Hegedu¨s, Physica. [1] P. Lundqvist, C. Tengroth, O C 229 (1996) 231 – 241. ¨ . Rapp, [2] S.R. Ghorbani, M. Anderson, P. Lundquist, M. Vallodor, O Physica. C 339 (2000) 245 – 247. [3] M. Murakami, S.I. Yoo, T. Higuchi, N. Sakai, J. Weltz, N. Koshizuka, S. Tanaka, Jpn. J. Appl. Phys. 33 (1994) L715. [4] G. Krabbes, P. Schatzle, W. Bieger, G. Fuchs, Appl. Supercond. 6 (1998) 61. [5] G. Flor, G. Chiodelli, G. Spinolo, P. Ghigna, Physica. C 316 (1999) 13 – 20. [6] T. Egi, J.G. Wen, K. Kuroda, H. Unoki, N. Koshizuka, Appl. Phys. Lett. 67 (1995) 2404. [7] J.S. Schilling, J. Phys. Chem. Solids 59 (1998) 553 – 568. [8] T.K. Jaya Arun, N. Victor Jaya, Published in the Second International Conference on High Pressure Science and Technology Conducted at National Physical Laboratory, New Delhi During Nov. 28–30, 2001. [9] S. Desgreniers, K. Lagarec, J. Appl. Crystallogr. 27 (1994) 432 – 440.
High-pressure and high-temperature electrical resistivity studies on Nd-123 R. Selva VennilaT, N. Victor Jaya, S. Natarajan Department of Physics, Anna University, Chennai-600 025, India Received 7 April 2004; accepted 26 January 2005 Available online 19 March 2005
Abstract High-pressure, high-temperature electrical resistivity measurements are carried out on NdBa2Cu3O7 d high Tc superconductor (HTSC). The electrical resistivity is measured by four-probe method using Bridgmann Opposed Anvil High-Pressure Device (OAHPD). The hightemperature measurement is done using heating coil arrangement in OAHPD. The electrical resistivity is found to decrease with the increase of pressure up to 8 GPa. The sample shows a decrease in the resistivity up to the maximum pressure and temperature of 8 GPa and 523 K, respectively. D 2005 Elsevier B.V. All rights reserved. Keywords: Electrical properties; Perovskites; Superconductors; Crystal structure; X-ray techniques
1. Introduction Neodymium is the first element in the rare earth series forming the proper 123-structure. Other substitutions, such as Ba for Nd, lead to a suppression of superconductivity [1]. The substitution of Nd totally in place of Y showed a raise in critical temperature, which is even higher than all other 123-compounds [2]. A stabilization of the RE-123 stoichiometry was done by melt processing under reduced oxygen partial pressure, which plays an important role for change in the Tc of the high-temperature superconductors [3,4] and a maximum Tc of 96 K was obtained for Nd/Ba ratio of 0.5 concentration. Superconductivity is achieved in NdBa2 Cu3O7 d for dN0.64–0.69 in which the holes are mobile [5]. The NdBa2Cu3O7 d based superconductor receives greater attention because of (a) the increase in critical current density in external magnetic field as compared to its value in self-field, (b) the high irreversible fields greater than that of YBa2Cu3O7 d and (c) the possibility to achieve high rates of melt texturing about 50 times faster than YBa2Cu3O7 d because of the higher solubility of the Nd in T Corresponding author. E-mail address: [email protected] (R.S. Vennila). 0167-577X/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2005.01.062
the melt when compared with Y [1]. The maximum critical temperature and maximum current density for this compound is greater than the YBCO [3,6], hence it can well replace the YBCO in the technological application. Highpressure experiments constitute a sensitive probe of the superconducting state because of the change in electronic and phonic properties [7]. The present investigation gives the high-pressure high-temperature electrical resistivity behaviour of these samples up to 8 GPa and a maximum temperature of 523 K.
2. Experimental The NdBa2Cu3O7 d sample is synthesised by solid state method [2]. High purity Nd2O3, BaCO3, CuO, CaCO3 of stoichiometric composition were taken and ground finely. The pellets of the mixture was calcined at 1173 K, 1193 K and at 1193 K with intermediate grindings. The sample was annealed in flowing oxygen at 733 K for 3 days and the temperature was finally decreased to room temperature at the rate of 12 K/h. Energy-dispersive X-ray powder diffraction (EDXRD) study is carried out on Nd-123 system using white X-rays
R.S. Vennila et al. / Materials Letters 59 (2005) 1764–1766
1765
1.0 (110)
0.9 523 K
0.8
(arb. units)
473 K
0.7
0
10
(014)
0.3 GPa (116)
(214)
(016) (007)
(101)
20
373 K
0.5 323 K
0.4
RT
0.3 0.2
0
(002)
(113)
ρ/ρ
(020)
Intensity
423 K
0.6
30
40
50
Energy (keV) Fig. 1. EDXRD pattern of the NdBa2Cu3O7
0.1 0
d.
from copper target produced by rotating anode X-ray generator, Rigaku. An X-ray diffraction measurement confirms the formation of single phase. The system was indexed with orthorhombic structure using XRD analysis software [9]. The EDXRD pattern obtained for the Nd-123 is shown in Fig. 1. High-pressure electrical resistivity study was carried out by four-probe method using Bridgmann Opposed Anvil High-Pressure Device (OAHPD). High-pressure, hightemperature electrical resistivity measurements are carried out using OAHPD along with a heating coil attachment, which is shown in Fig. 2. Annular heating coil is placed in between the opposed anvils. The temperature stability obtained was F2 K. The power to the coil is controlled by a variac and the temperature has been maintained using
1
2
3
4
6
7
8
9
10
Fig. 3. Variation of electrical resistivity of NdBa2Cu3O7 d studied up to a maximum pressure of 8 GPa for temperatures up to 523 K.
a temperature controller [8]. In this arrangement a chromel– alumel thermocouple connected together by spot welding is used as a temperature sensor. The spot welded junction was hammered and made very thin and flat. The sample of thickness 0.1 mm has been used for the resistivity measurements. The temperature was determined from the thermo emf versus temperature chart. The pressure cell assembly, thermocouples, sample and the annular heating coil were assembled for good thermal contact. Mica sheets and tapes were used for insulating purposes. The position of the sample and the thermocouple in the high-pressure, high-
Thermocouple
Temperature controller
Voltmeter
5
Pressure (GPa)
Anvil
Heating coil
Constant current source Fig. 2. High-pressure, high-temperature setup for electrical resistivity measurements.
1766
R.S. Vennila et al. / Materials Letters 59 (2005) 1764–1766 -3.20
log (ρ) Ohm cm
-3.40
-3.60
-3.80
-4.00
-4.20 0
1
2
3
4
5
6
7
8
9
10
Pressure (GPa) Fig. 4. Variation of log(q) versus pressure of NdBa2Cu3O7
to the pressure and temperature is found to be reversible with hysteresis. Variation of log(q) versus pressure is plotted and shown in Fig. 4, which confirms the layered structure of the sample. The q behaviour at the two regions (i.e., low- and high-pressure regions) corresponds to inter- and intralayer changes, which may be attributed from Fig. 4. The initial rapid decrease in q is caused by the changes in the interlayer spacing, and beyond which, the interlayer is not affected much, which is shown by a nearly constant curve at higher pressures. The intralayer bonds are very much stronger and require pressure higher than 8 GPa to produce changes in it. From the study of the behaviour it can be understood that the application of even a small pressure in the layered copper oxides increases the carrier concentration between the CuO layers, thereby improving the metallic behaviour in the Nd-123 superconductor. Alternatively, temperature opposes the interlayer bond breaking effects caused by the pressure.
d.
temperature arrangement using heating coil setup is shown in Fig. 2.
3. Results and discussion NdBa2Cu3O7 d system is found to be crystallised in orthorhombic structure with lattice parameters a=3.87F0.01 2, b=3.92F0.01 2 and c=11.74F0.01 2 and v=177.3 23, and the results are found to be in good agreement with the literature [2]. The variation of high-pressure electrical resistivity observed at different temperatures, 323 K, 373 K, 423 K, 473 K and 523 K (maximum temperature studied), is shown in Fig. 3. Initially, the electrical resistivity of the sample decreases rapidly with pressure. At higher pressures, the decrease in q is very small and can be assumed to be a constant when compared with the initial drop. A systematic upward shift in resistivity with temperature is observed up to 523 K with the same trend as observed at room temperature. The sample shows metallic behaviour up to a maximum pressure and temperature of 8 GPa and 523 K, respectively. The absence of phase transitions up to 8 GPa and 523 K is reported. The behaviour confirms the metallic nature of sample up to 523 K and a maximum pressure of 8 GPa. Also, the effect due
Acknowledgement We thank Dr. S. Reza Ghorbani, Iran and Prof. ¨ . Rapp, Sweden for providing the samples for the Dr. O studies. We also thank the University Grants Commission, Government of India, for financial support.
References ¨ . Rapp, R. Tellgren, Z. Hegedu¨s, Physica. [1] P. Lundqvist, C. Tengroth, O C 229 (1996) 231 – 241. ¨ . Rapp, [2] S.R. Ghorbani, M. Anderson, P. Lundquist, M. Vallodor, O Physica. C 339 (2000) 245 – 247. [3] M. Murakami, S.I. Yoo, T. Higuchi, N. Sakai, J. Weltz, N. Koshizuka, S. Tanaka, Jpn. J. Appl. Phys. 33 (1994) L715. [4] G. Krabbes, P. Schatzle, W. Bieger, G. Fuchs, Appl. Supercond. 6 (1998) 61. [5] G. Flor, G. Chiodelli, G. Spinolo, P. Ghigna, Physica. C 316 (1999) 13 – 20. [6] T. Egi, J.G. Wen, K. Kuroda, H. Unoki, N. Koshizuka, Appl. Phys. Lett. 67 (1995) 2404. [7] J.S. Schilling, J. Phys. Chem. Solids 59 (1998) 553 – 568. [8] T.K. Jaya Arun, N. Victor Jaya, Published in the Second International Conference on High Pressure Science and Technology Conducted at National Physical Laboratory, New Delhi During Nov. 28–30, 2001. [9] S. Desgreniers, K. Lagarec, J. Appl. Crystallogr. 27 (1994) 432 – 440.