International Journal of Electrochemical Science 18 (2023) 33–37
Contents lists available atScienceDirect
International Journal of Electrochemical Science
journal homepage:www.editorialmanager.com/ijoes
Enhanced superconducting transition temperature for Cr-substituted Tl
2Ba
2CaCu
2O
8-δSyahrul Humaidi
a, A.N. Jannah
b, Anuar Alias
c, R. Abd-Shukor
c,⁎aPost Graduate Program (Physics) FMIPA, Universitas Sumatera Utara, Jln Bioteknologi no 1, Medan 20155, Indonesia
bFaculty of Applied Sciences, Universiti Teknologi MARA, Cawangan Negeri Sembilan, Kampus Kuala Pilah, 72000, Kuala Pilah, Negeri Sembilan, Malaysia
cDepartment of Applied Physics, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia
A R T I C L E I N F O
Keywords:
X-ray diffraction Electrical resistance Transition temperature
A B S T R A C T
Cr-substituted Tl2Ba2CaCu2O8-δ(Tl-2212) high temperature superconductor forx= 0–0.5 has been prepared using the standard solid-state reaction method. The precursor powders consisting of Ba2CaCu2Odwere sintered at 900 °C for 24 h. The powders were then added with Tl and Cr, ground and pressed into pellets. The pellets were heated at 910 °C in oxygen flow for 4 min followed by furnace cooling. The d.c. electrical resistance (R) versus temperature (T) measurements were carried out using the four-point probe method with silver paste contacts. The transition temperature was determined from the slope of the resistance versus temperature graph.
The superconducting critical region was divided into three: onset transition temperature (Tc-onset), middle transition temperature (Tc-mid) and zero-resistance temperature (Tc-zero). The non-substituted sample showed onset transition temperature,Tc-onsetof 97 K. Thex= 0.2 sample (Tl1.8Cr0.2Ba2CaCu2O8-δ) showed the highest Tc-onset(102 K). Further substitutions of Cr (x≥ 0.3) decreased the transition temperature. All samples except the non-substituted samples showed at least two peaks in the dR/dT curves. This indicated that super- conductivity within grains and intergrain occurred at different temperatures for all Cr-substituted samples. This work showed that Cr (x= 0.2) slightly enhanced the transition temperature of Tl-2212.
1. Introduction
The thallium-based superconductor (TBCCO) has one of the high transition temperatures among the cuprates [1]. (Tl,Pb)Sr2Ca2Cu3O9-δ
(Tl-1223) has a transition temperature, Tc = 115 K [2]. The Tl2Ba2CaCu2O8-δ(Tl-2212) system hasTcof around 96 K[3]. The highest transition temperature is found in the Tl2Ba2Ca2Cu3O10+y (Tl-2223) phase with transition temperature of 128 K [4]. The TlBa2CaCu2O8-δ
samples can be prepared from component oxides by heating the pre- cursor at 900 °C for 24 h followed by adding appropriate amounts of Tl2O3and heating at 900 °C for 4–5 min[5]. Various fabrication tech- niques have been employed to improve the physical properties of the material[6–9]. To increase the transition temperature, most researchers substituted the Tl-2212 phase with various elements[10–13].
Superconducting fluctuations behavior (SFB) can influence the properties of superconducting materials. The creation and destruction of the electron pairs gives rise to superconducting fluctuations. The electron pairs are always present in certain number but closer toTcthis
number fluctuates. At temperatures belowTc, thermal fluctuations be- come almost ineffective. As a result, the superconducting electron pairs persist making the material superconducting and reducing the re- sistivity to zero. The effect of fluctuation is manifested in the behavior of the resistivity versus temperature plot[14]. The resistance curve is linear but as the temperature decreases to just aboveTc, it starts to deviate and bends downwards. This decrease in resistivity is due to superconducting fluctuations.
There have been several reports on excess conductivity of Tl-1223, but not many reports on Tl-2212. Substitution of multivalent ions for Tl in the Tl-based superconductors can give rise to interesting results due to the different ionic radius of the various valence states[11–14]. Thus, in this paper we report on the effects of multivalent Cr-substituted Tl- 2212 superconductor. Cr was chosen because it has the ability to sta- bilize the formation of the Tl-based cuprate[13]. The structure was studied using the X-ray diffraction (XRD) method and Eva software was used to analyze the patterns. The transition temperature was de- termined using the four point probe method.
https://doi.org/10.1016/j.ijoes.2023.01.004
Received 9 November 2022; Accepted 26 December 2022 Available online xxxx
1452-3981/© 2023 The Authors. Published by Elsevier B.V. on behalf of ESG. This is an open access article under the CC BY-NC-ND license (http://creative-
]]
]]]]]]]]
⁎ Corresponding author.
E-mail address:[email protected](R. Abd-Shukor).
2. Experimental details
Samples with nominal composition Tl2-xCrxBa2CaCu2O8-δ
(0 ≤x≤ 0.5) were synthesized by two steps conventional solid-state reaction method[12]. High purity BaO, CaO and CuO powders were mixed completely using an agate mortal to obtain a homogeneous mixture. The starting material was sintered at 900 °C for 24 h before being cooled to room temperature. Appropriate amounts of Tl2O3and Cr2O3were then added to the precursor and completely mixed before being pressed into pellets of 1.3 cm diameter and 0.2 cm thickness. The pellets were heated at 900 °C in flowing oxygen for 4 min, followed by furnace cooling to room temperature. In order to compensate thallium loss during heating, excess of 10% Tl2O3were added[11].
The phase was determined using the X-ray diffraction method by employing a Bruker model D8 Advance diffractometer with CuKα
source. The dc electrical resistance measurements from 30 K to 300 K were carried out using the four-point method with silver paste contact in conjunction with a closed cycle refrigerator from CTI Cryogenic Cycle Refrigerator Model 22. A temperature controller from Lake Shore Temperature Controller Model 340[13]was used to control the tem- perature. A 20 mA constant current was used in all measurements. The data acquisition system was fully computer controlled.
3. Results and discussion
The X-ray diffraction patterns showed that the Tl-2212 is the dominant phase in all samples.Fig. 1shows the patterns forx= 0, 0.1, 0.2 and 0.3. The Tl-2212 phase can also be easily identified by the low angle peak around 2θ∼ 6°. Some impurity peaks were observed in the x= 0 sample but were not found in the Cr-substituted samples. This showed that Cr may have resided at the Tl site in these Tl-2212 samples.
Fig. 2shows the normalized resistanceR(T)/R(297 K) versus tem- perature curves of the sample with x= 0.0–0.5. Tl2Ba2CaCu2O8-δ
(Fig. 2(a)) shows a metal-like characteristic above the transition tem- perature. The same characteristic can also be seen in Tl1.9Cr0.1Ba2CaCu2O8-δ (Fig. 2(b)), Tl1.8Cr0.2Ba2CaCu2O8-δ(Fig. 2(c)) and Tl1.7Cr0.3Ba2CaCu2O8-δ(Fig. 2(d)) samples. Metal-like normal state can be considered as an inherent characteristic of optimally doped cuprates.
Zero-resistance temperature,Tc-zero is the temperature where the resistance drops to zero. The onset transition temperatureTc-onsetis the temperature where the resistance begins to drop to zero.Tc-midis the mid-point between the onset and zero-resistance temperature. The re- sistance of the non-substituted sample (x= 0) began to drop slowly at 124 K and a peak in dR/dT, Tcp curve was observed at 97 K. This Fig. 1. XRD patterns of Tl2-xCrxBa2CaCu2O8-δforx= (a) 0, (b) 0.1, (c) 0.2 and (d) 0.3.
Fig. 2. Resistance and dR/dTversus temperature curves of Tl2-xCrxBa2CaCu2O8-δfor (a)x= 0, (b)x= 0.1, (c)x= 0.2, (d)x= 0.3, (e)x= 0.4 and (f)x= 0.5.
maximum peak coincides with the abrupt drop i.e., the onset transition temperature,Tc-onset= 97 K. The deviation from the linear (metallic) normal state behavior curve nearTc-onsetwas due to superconducting fluctuations.
The derivative of resistance with respect to temperature (dR/dT) curves are plotted and shown inFig. 2. Thex= 0 sample showed one peak in the dR/dTcurve. Thex> 0 samples showed at least two peaks, where the first peak marks superconductivity within grains with the grain boundaries are not yet superconducting. The second peak in- dicates the temperature where supercurrent flows between grains through proximity effects. All Cr-substituted samples showed at least two peaks which indicated the inhomogeneous nature of the grains and grain boundaries in the samples.
An enhancement in Tc-zero was observed in the x= 0.1 and 0.2 samples. Whenx= 0.1,Tc-zeroincreased to 94 K andTc-onsetdecreased to 119 K. It can also be seen that there were two peaks in dR/dTfor x= 0.1. A single peak in dR/dT indicated that the superconducting transition within the grains was equal to the transition temperature between grains [11]. The occurrence of two peaks denotes that this sample was inhomogeneous. A significant transition temperature en- hancement was observed in the x= 0.2 sample which showed the highestTc-onsetat 102 K and zero-resistance temperature,Tc-zeroat 96 K.
Further substitution of Cr lowered not onlyTc-onsetbut alsoTc-zero. The excess conductivity region extended for about 6 K from Tc-zero. The x= 0.2 sample showed the optimal transition temperature among all the samples studied in this work.
The effect of Pb together with Cr on the Tl-1212 has also been re- ported[15]. CdTe added Tl2Ba2CaCu2O8-δsuperconductor showedTc- onsetfrom 104 K to 108 K andTc-zerofrom 93 K to 95 K. Thus, in terms of Tc, Cr and CdTe played a similar role in the Tl-2212[16]. A lower Cr concentration is sufficient to obtain a highTc-onsetmost probably due to the high valency of Cr at the Tl site where optimum carrier con- centration for superconductivity can be obtained. Higher Cr valence means a smaller ionic radius and this is made possible by the Jahn- Teller nature of Cu which allows a high flexibility of the Cu-O apical distance[17].Figs. 2(e) and2(f) show the resistance versus tempera- ture forx= 0.4 and 0.5 samples, respectively. FromFig. 2(e), it can be seen that Tl1.6Cr0.4Ba2CaCu2O8-δsample also shows a metal-like normal state. Thex= 0.5 sample showed a non-metallic behavior from 200 K to 300 K i.e., a non-linear characteristic, akin to a semiconducting be- havior in this temperature range. Excess conductivity region extends to 9 K in thex= 0.4 and 21 K in thex= 0.5 samples. Thex= 0.2 sample showed excess conductivity region which extends over 6 K. This was due to the higher transition temperature and very short coherence length[11,18]. As a comparison with a previous report where BaCO3
was employed as the Ba source[7], the use of BaO in this work resulted in a slightly higher transition temperature.
The transition temperatures and transition width, ∆Tcare presented in Table 1. Tc-zero was between 70 K and 96 K. ∆Tc decreased from x= 0.1 tox= 0.3 and then increased with further substitution of Cr.
The small value of ∆Tcfor x= 0.1, 0.2 and 0.3 could be due to the existence of better percolative path for superconductivity to occur[18].
The widest ∆Tcwas found in thex= 0.5 sample. A wide ∆Tccould be due to the presence of macroscopic inhomogeneity as can be seen from more than two peaks in the dR/dTcurves.
In conclusion, Cr substitution enhanced the transition temperature of the Tl-2212 phase. The x= 0.2 was found to be the optimal Cr concentration for the highest superconducting transition temperature.
It was also observed that the 0 ≤x≤ 0.3 samples showed a relatively narrower superconducting transition width. Substitution of other mul- tivalent ions such as Mo and W at the Tl-site of the Tl-based cuprate can be further investigated to understand the effect of multivalent ions on the properties of this superconductor.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influ- ence the work reported in this paper.
Acknowledgements
SH would like to thank LP-USU, Indonesia for the funding under TALENTA-SCHEME No. 4142/UN5.1. R/PPM/2020. RAS would like to thank the Ministry of Higher Education, Malaysia for the support under grant no. FRGS/1/2020/STG07/UKM/01/1.
References
[1] Z.Z. Sheng, A.M. Hermann, Superconductivity in the rare-earth-free Tl–Ba–Cu–O system above liquid-nitrogen temperature, Nature 332 (1988) 55–58,https://doi.
org/10.1038/332055a0
[2] J.L. Jorda, Th Hopfingerl, M. Couach, P. Pugnat, C. Bertrand, Ph Galezl, Ph Galezl, Formation of thallium-1223 superconductors, J. Supercond. 11 (1998) 87–89, https://doi.org/10.1023/A:1022602517307
[3] A. Sundaresan, H. Asada, A. Crisan, J.C. Nie, H. Kito, A. Iyo, Y. Tanaka, M. Kusunoki, S. Ohshima, Preparation of Tl-2212 and Tl-1223 superconductor thin films and their microwave surface resistance, IEEE Trans. Appl. Supercond..13 (2003) 2913–2916,https://doi.org/10.1109/TASC.2003.812045
[4] A. Maignan, C. Martin, V. Hardy, Ch Simon, M. Hervieu, B. Raveau, A crystal study of the 128 K superconductor Tl2Ba2Ca2Cu3O10−δsynthesis and anisotropic mag- netic properties, Phys. C. 219 (1994) 407–412,https://doi.org/10.1016/0921- 4534(94)90394-8
[5] A. Soeta, T. Suzuki, S. Takeuchi, T. Kamo, K. Usami, S.-P. Matsuda, Relationship between crystal structures and solid solution of Tl-Sr-Ca-Cu-O and Tl-Ba-Ca-Cu-O superconductors, Jpn. J. Appl. Phys. 28 (Part 2, No. 7) (1989) L1186–L1189, https://doi.org/10.1143/JJAP.28.L1186
[6] Y. Jiang, H. Yue, J. Wei, M. Chen, X. Han, Y. Jin, P. Tang, G. Huang, Q. Xie, Effects of post-annealing in different gas atmospheres on the properties of Tl-2212 films fabricated by sol-gel method, IOP Conf. Ser. Earth Environ. Sci. 772 (2021) 012078, ,https://doi.org/10.1088/1755-1315/772/1/012078
[7] S. Humaidi, R. Abd-Shukor, Effect of Cr2O3 on the transition temperature and phase formation of Tl2-xCrxBa2CaCu2O8-δ superconductor, Malays. J. Anal. Sci. 24 (2020) 766–771.
[8] C.J. Dark, S.C. Speller, C.R.M. Grovenor, The development of bi-epitaxial texture and high grain boundaryJcvalues in Tl-2212 films on MgO substrates, Supercond.
Sci. Technol. 19 (2006) 484–492,https://doi.org/10.1088/0953-2048/19/6/013 [9] N.H. Ahmad, N.A. Khan, A.K. Yahya, Superconducting fluctuation behavior and
infrared absorption properties of Tl1−xCuxSr1.6Yb0.4CaCu2O7-δand Tl0.5Pb0.5Sr2−yMgyCa0.8Yb0.2Cu2O7−δceramics, J. Alloy Compd. 492 (2010) 473–481,https://doi.org/10.1016/j.jallcom.2009.11.144
[10] M.A. Subramanian, C.C. Torardi, J. Gopalakrishnan, P.L. Gai, J.C. Calabrese, T.R. Askew, R.B. Flippen, A.W. Sleight, Bulk superconductivity up to 122 K in the Tl-Pb-Sr-Ca-Cu-O system, Science 242 (1988) 249–252,https://doi.org/10.1126/
science.242.4876.249
[11] Z.Z. Sheng, D.X. Gu, Y. Xin, D.O. Pederson, L.W. Finger, C.G. Hadidiacos, R.M. Hazen, A new 1212-type phase: Cr-substituted TlSr2CaCu2O7withTcup to about 110 K, Mod. Phys. Lett. B 5 (1991) 635–642,https://doi.org/10.1142/
S0217984991000770
[12] A.I. Abou Aly, R. Awad, L.H. Ibrahim, W. Abdeen, Excess conductivity analysis for Tl0.8Hg0.2Ba2Ca2Cu3O9−δsubstituted by Sm and Yb, Solid State Comm. 149 (2009) 281–285,https://doi.org/10.1016/j.ssc.2008.12.003
[13] M. Ranjbar, R. Abd-Shukor, Formation of Tl-1223 phase in Cr substituted (Tl1-xCrx) Ba2Ca2Cu3O9-δ (x= 0.3 to 0.9) superconductor, Ceram. Int. 4 (2014) 13869–13872,https://doi.org/10.1016/j.ceramint.2014.05.105
[14] M. Irfan, H. Hassan, N.A. Khan, Fluctuation-induced conductivity of five planar Cu0.5Tl0.5Ba2Ca4−xMgxCu5O14−δ(x = 1, 2) superconductors, Phys. C. 469 (2008) 86–90,https://doi.org/10.1016/j.physc.2008.11.007
Table 1
Transition temperatures of Tl2-xCrxBa2CaCu2O8-δ.
x Tc-onset/K Tc-mid/K Tc-zero/K ∆Tc/K
0.0 97 95 93 4
0.1 101 98 94 7
0.2 102 99 96 6
0.3 95 93 91 4
0.4 93 89 84 9
0.5 91 80 70 21
[15] E. Yusrianto, A.N. Jannah, R. Abd-Shukor, Phase formation and critical temperature of (Tl0.5Pb0.5)Sr2Ca(Cu2-xCrx)O7-δ (x= 0 - 0.100) superconductor, Sains Malays.
50 (2021) 1775–1786,https://doi.org/10.17576/jsm-2021-5006-23
[16] K. Muhammad-Aizat, R. Abd-Shukor, Electrical properties and AC susceptibility of CdTe added Tl2Ba2CaCu2O8-δsuperconductor, Sains Malays. 47 (2018) 1579–1583, https://doi.org/10.17576/jsm-2018-4707-28
[17] R. Abd-Shukor, Nor Azah Nik Jaafar, Formation and superconductivity of Pr and Nd-substituted Tl-1212 phase Tl0.85Cr0.15)Sr2CaCu2O7, J. Mat. Sci.: Mat. Elect. 10 (1999) 677–681,https://doi.org/10.1023/A:1008994704163
[18] A.I. Abou-Aly, R. Awad, M. Kamal, M. Anas, Excess conductivity analysis of (Cu0.5Tl0.5)-1223 substituted by Pr and La, J. Low. Temp. Phys. 163 (2011) 184–202,https://doi.org/10.1007/s10909-010-0339-4
