Improving superconducting properties of YBCO high temperature superconductor by Graphene Oxide doping

Accepted Manuscript Improving superconducting properties of YBCO high temperature superconductor by Graphene Oxide doping S. Dadras, S. Dehghani, M. Davoudiniya, S. Falahati PII:

S0254-0584(17)30195-5

DOI:

10.1016/j.matchemphys.2017.03.003

Reference:

MAC 19549

To appear in:

Materials Chemistry and Physics

Received Date: 3 January 2017 Revised Date:

15 February 2017

Accepted Date: 1 March 2017

Please cite this article as: S. Dadras, S. Dehghani, M. Davoudiniya, S. Falahati, Improving Superconducting Properties of YBCO high temperature superconductor by Graphene Oxide Doping, Materials Chemistry and Physics (2017), doi: 10.1016/j.matchemphys.2017.03.003 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Highlights

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Graphene Oxide doping increased the YBCO critical current density. • Graphene Oxide creates a better connection between the YBCO grains. • The normal resistivity of samples were decreased by GO doping to YBCO compounds. • Graphene Oxide doping has a positive effect on the critical transition temperature.

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Improving superconducting properties of YBCO high temperature superconductor by Graphene Oxide doping

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S. Dadras*, S. Dehghani, M. Davoudiniya, S. Falahati Department of Physics, Alzahra University, Tehran, 1993893973, Iran

*Corresponding author: Tel: +98 21 85692642, Fax: +98-21 88613935 *E-mail address: [email protected]

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Abstract

In this research, we report the synthesis and characterization of YBa2Cu3O7-δ (YBCO) high temperature

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superconductor prepared by sol-gel method and doped with Graphene Oxide (GO) in different weight percentages, 0, 0.1, 0.7 and 1 % wt. The x-ray diffraction (XRD) analysis confirms the formation of orthorhombic phase of superconductivity for all the prepared samples. We found that GO doping reduces the crystalline size of the samples. We evaluated the effects of GO doping on the normal state resistivity (ρ), superconducting transition temperature (Tc) and critical current density (Jc). The results show that the GO doping has a positive effect on these properties. Also, the highest Jc is obtained for the

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0.7 %wt GO doped YBCO compound that its critical current density is about 15 times more than the Jc of pure one in 0.4 T magnetic field. The scanning electron microscope (SEM) analysis shows that there are better connections between the grains of GO doped samples.

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Keywords: High temperature superconductor, Graphene Oxide, YBCO, Critical current density,

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Transition temperature.

1. Introduction

Graphene oxide is known as a satisfactory candidate material for the next generation of electronics [1, 2], optoelectronics [3], energy conversion and storage technologies [4–7]. As the discovery of Graphene (G) [8-10], many efforts have been focused on GO [11, 12]. GO can be visualized as individual sheets of Graphene decorated with oxygen functional groups on both basal planes and edges. The presence of oxygen makes GO capable to do more chemical activities. Nevertheless, it disturbs the extended sp2 network of the Graphene hexagonal lattice.

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The effects of different nanostructures doping in MgB2 were investigated and also it is reported that doping G and GO to MgB2 superconductor creates additional flux pinning energy and thus increases the critical current density [13- 15]. Since the discovery of superconductivity in YBCO at 93 K (Tc) [16], a lot of attempts has been made to enhance its superconducting properties. YBCO high temperature

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superconductor is a kind of ceramic superconductor which is very considerable because of its numerous applications [17-19]. It is a layered cuprate with short coherence length. So, the supercurrent couldn’t pass easily through the grain boundary [20]. It has reported that nanostructure materials and carbon base compounds doping in high temperature superconductor create high Jc at high magnetic fields [21, 22].

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Impurity phases and defects present at grain boundaries can act as a weak-link [23]. Also, nanoparticles as a dopant in high temperature superconductors behave as flux pinning centers. They localize between

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grains and increase the grains boundary connections. Therefore, nanoparticles doping increases the pinning energy Uj and critical current density Jc in compounds [21, 22]. In this paper, we are investigating the influences of GO doping on the properties of YBCO high

2. Materials and methods

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temperature superconductor.

We used sol-gel method to synthesize the YBCO samples. First, 0.5M solutions of Y(NO3)3.6H2O, Ba(NO3)2 and Cu(NO3)2.3H2O were separately prepared and then the solutions were mixed together. A

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light blue solution was obtained and the pH was raised to 7 by addition of Ethylenediamine to the mixture as a complexing agent. By heating the solution at 85 °C, the water removed from the solution and a violet gel was created. Since the firing process occurs in the 520°C, we heated the samples in this

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temperature for 2 hours. In this time, the brown NO2 gasses were released and a black powder was produced. Then the powder was calcined at 900 °C. We added GO with different weight percentages to the YBCO powder and mixed well to prepare samples of 0% wt, 0.1 wt%, 0.7 wt% and 1wt% GO doped YBCO. The powder samples were pressed into circular pellets and sintered at 930°C for 19 h by Oxygen flow, cooled down to 630°C, and kept in this temperature for 2 hours [24].

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3. Results and discussions The YBCO samples were analyzed by XRD pattern to indicate phase match and the data were analyzed by X'Pert High Score software. Fig.1 shows the XRD spectrum of GO powder used in our samples.

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Based on Debby-Scherrer equation, the crystalline size of the GO added in YBCO compounds is about 40nm that is calculated and the main peak at 2θ=12.85°.The XRD patterns of all YBCO samples are shown in Fig. 2. The orthorhombic structure is maintained to have the highest peak at 2θ=38.3° with (103) planes for all the samples. In addition, there are other reflections of orthorhombic phase at (003),

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(112), (104), (113), (200), (220), (123), and (130). The lattice parameters computed by MAUD software are a=3.8364Å, b=3.8873Å, and c=11.6719Å. Furthermore, the peak at 2θ=26.53° can also indicate Reduced Graphene Oxide (RGO). The crystalline size of the samples was calculated by using of Debby-

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Scherrer equation. These values for all the prepared samples are tabulated at Table1. It is clearly observed a decreasing trend in the values of crystalline size with addition of GO in YBCO compound. We cut the samples to rectangular form and attached copper wires on them. We measured the electrical resistivity versus temperature (ρ–T) through four-probe method to find the values of critical temperature (Tc). Fig.3 shows the resistivity versus temperature of the pure and GO doped YBCO samples. It

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demonstrates that all of the samples (above the transition temperature onset (Tcon)) have a linear metallic behavior in the normal state. We found that the samples’ normal resistivity reduces by adding GO to the YBCO compound. Furthermore, it is observed that the transition width ∆T of the doped samples is less than the pure one that indicates positive effect of GO doping in the compounds. Table.1 also shows

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calculated values of critical transition temperatures (Tcon, Tcmid, Tcoff), transition width ∆T and normal resistivity of the pure and doped samples. Also, we found that the values of Tc increases by GO doping. It seems that in the sintering process; the oxygen in the functional groups of GO is removed from it and

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entered in the CuO chains in the YBCO structure, and caused to increase the transition temperature. It is reported that the values of oxygen content would have a severe influence on the superconducting properties such as the critical temperature [25]. The values of the oxygen that is measured by iodometry are shown in the table.1.Iodometry, also known as iodometric titration, is a method of volumetric chemical analysis to find the values of the oxygen in the compound [26]. As it is clear, there is a good agreement between the values of oxygen and the increasing trend of temperature transition in the compounds.

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To measure the current–voltages (I–V) values of the samples, we used a four probe setup in the 0.4T magnetic fields at a temperature of 77 K. By E = V/d and J = I/A equations, we calculated the electrical field versus current density (E–J) curve, where d and A are the length and surface area of the samples. Fig.4 shows the E–J diagram in 0.4T magnetic field for pure and GO doped samples. It is obvious that

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adding GO in the YBCO compound, increases the value of critical current dencity.According to the models of J dependence of the Uj, a logarithmic barrier has been proposed by Zeldov et.al for high temperature superconductors [27,28]. Our data are actually stable with this model for all samples, which

J (T , H , J ) = U (T , H )Ln ( C ) eff j J

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implies a potential logarithmic barrier for the flux pinning as follow:

(1)

Where Uj is the characteristic pinning potential energy in the constant current density [29]. We obtained the relation between E and J as in Eq. (3) by substitution of Ueff from the model in Ref.[27] into Eq.(2)

U J j E = E exp( − Ln ( C )) 0 K BT J

Logarithm of this equation is

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U E = E exp( − eff ) 0 K BT

(3)

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U U j j Ln (E ) = [Ln (E ) − LnJ ] + LnJ 0 K T C K BT B

(2)

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So, by the slope of Ln E versus Ln J curves we can compute the Uj. The inset of Fig. 4 shows the linear behavior of Ln E versus Ln J for all the samples in 0.4T magnetic field. The Jc values increase with addition of GO to the YBCO compounds in a constant magnetic field. The 0.7%wt GO doped sample shows the highest Jc value. We obtained Uj and Jc values, by considering Zeldov model and fitting the curves with Eq. (3). The values of Jc and Uj for all the samples in 0.4T magnetic field are tabulated at table 2. Fig.5 shows the Jc versus the GO doping in 0.4T magnetic field for all the samples at 77K. Since the values of Uj and Jc for all the doped samples are increased with respect to the pure one, we can conclude that GO doping has caused vortices to be pinned and has increased the Jc values.

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Fig.6 shows the SEM images of pure and 0.7%wt GO doped YBCO samples that has the higher Jc value in the prepared samples. It seems that GO doping created more homogeneity and better connection among the superconducting grains, and the porosity between them is reduced. It could be a reason for increasing Jc in the GO doped samples. Also, it is possible that in sintering process in temperatures more

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than 650˚C, the oxygens in the functional groups of GO is removed into RGO [30]. So they are acting as conductors and they can improve the grains boundary connections of YBCO compound and transmit the electrical current easily [31].We can conclude that, GO is changed to RGO which it is a good conductor and it is possible that removed oxygens enter to CuO chains and cause increasing the transition

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temperature [25].

4. Conclusions

Overall, we have investigated the effects of GO doping on the properties of YBCO high temperature superconductor. Through XRD and SEM analysis, we found that the structure of all the samples has the Y-123 orthorhombic phase. The results of ρ(T) measurements show that GO has acted in an effective manner and increased the critical current density. It also showed that the normal resistivity of GO doped

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samples were decreased by doping GO to YBCO compounds. Besides, the GO doped YBCO samples display higher Jc values, compared to the pure sample. So an enhancement can be beneficial in both Tc and Jc of GO doped YBCO compounds for the practical applications of these high temperature

Acknowledgment

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superconducting materials.

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The authors would like to acknowledge the financial support by Alzahra University. References

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Figure 1: XRD pattern of the GO used as a dopant in our research. Figure 2: XRD patterns of pure and GO doped YBCO compounds.

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Figure captions:

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Figure 3: Resistivity vs temperature of the pure and doped YBCO samples.

Figure 4: Electrical field versus current density for pure and GO doped YBCO samples in 0.4T magnetic field. The inset shows the E–J curve in logarithmic scale.

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Figure 5: The critical current density versus GO doping in 0.4T magnetic field for all the samples at 77K.

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Figure 6: SEM images of (a) pure and (b) 0.7wt% GO doped YBCO samples.

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Table1:Values of Crystalline size, transition temperatures, Transition width, normal resistivity and calculated Values of oxygen through iodometryfor pure and GO doped YBCO samples. 0.1%wt

0.7%wt

1%wt

YBCO

GO doped

GO doped

GO doped

crystalline size(nm)

83

62

42

20

Tcon(K)

93

99

101

102

Tcmid(K)

87

94

96

97

∆T(K)

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Tcoff(K)

82

89

92

92

5.5

5

4.5

5

1688

2057

1542

6.60

6.93

6.69

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Normal resistivity ( in 200K)

calculated Values of oxygen

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through idometery

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Pure

sample

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Table 2: Values of Ujand Jc in 0.4T magnetic field for all the samples at 77K. Pure

0.1%wt

0.7%wt

1%wt

YBCO

GO doped

GO doped

GO doped

Uj(mev)

4.96

6.79

9.35

6.31

Jc(A/cm2)

0.44

3.88

6.75

1.86

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sample

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