J.S. Hawa

Influence of Na, Mg and Yb Substitution for Ca in Bi(Pb)-2223 Superconductor

The effect of Ca substitution by Na, Mg and Yb on the structural and transport properties of Bi1.6Pb0.4Sr2Ca2-xMxCu3Oy (M = Na, Mg and Yb) (x = 0.0 and 0.2) superconducting samples have been investigated. The samples were prepared by the coprecipitation (COP) method. The samples were characterized by x-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), electrical resistivity measurement and critical current density. The critical current density (Jc) and transition temperature (Tc zero) of Na, Mg and Yb substituted with x = 0.2 were found to be lower than the pure sample. Tc zero varies between 100 K and 63 K. Mg concentration was found to give the highest Tc zero of 93 K. Tc zero gradually decreased from Mg, Yb to Na corresponding to a small change in the carrier concentration. Jc decreased with Mg, Yb and Na substitution, and it was measured to be 7.4611 A/cm2, 0.0667 A/cm2, 1.4579 A/cm2 and 1.2479 A/cm2 for pure, Na, Mg and Yb substitution, respectively at 60 K. XRD analysis showed that the decrease of the volume fraction for the 2223 phase and increase of the volume fraction for the 2212 phase with substitution of Na, Mg and Yb. The proportion of Bi-2223/Bi-2212 (%) was estimated from 78.13/21.87 for pure to 51.71/48.29 for Na substitution.

Electrical and Structural Properties of Ca Substitution in High and Low Density Y(Ba1-xCax)2Cu3O7-δ Superconductor

The effect of Ca substitution on the electrical and structural properties in high and low density Y(Ba1-xCax)2Cu3Oδ where x = 0.00, 0.10, 0.20 and 0.30 via solid state reaction method has been investigated. The electrical properties, elemental analysis, and structural identification were measured by the four-point probe technique, energy dispersive x-ray (EDX) and X-ray diffraction (XRD) respectively. The electrical properties such as critical temperature (Tc) and critical current density (Jc) were found to be strongly dependent in both high and low densities Y(Ba1-xCax)2Cu3O7-δ. These parameters were decreased monotonously with the increasing of Ca substitution. An obvious results of the Ca-doped samples can be seen in x = 0.20 where Tc zero of high density sample is 77 K, which is higher than that of the low density sample that occurred at 73 K. Meanwhile, Jc at 60 K for high density is 1.842 A/cm2 compared to 1.410 A/cm2 in low density sample. EDX analysis confirmed the existence of Ca in all doped samples. The crystallographic structure remained orthorhombic and the volume of unit cell increased towards further increased of Ca concentration.

Effect of Heat Treatment on Ca Substitution in a Porous Y(Ba1-xCax)2Cu3O7-δ Superconductor

The effect of heat treatment on the superconducting properties of porous Y(Ba1-xCax)2Cu3Oδ with Ca substitution x = 0.00, 0.10, 0.20, and 0.30 via a solid-state reaction method have been investigated. The superconducting parameters, zero critical temperature, Tc zero and critical current density, Jcwere measured by the standard four point probe method in the temperature range from 20 K to 300 K, while the morphology of the samples was investigated by field emission scanning electron microscopy (FESEM). In addition structural identification was also investigated. All the samples received a heat treatment at 900 °C for 5 hours, and the Jc improved from 1.410 A/cm2 to 7.013 A/cm2 for x = 0.30 at 60 K. The heat treatment process did not change the morphology, while the crystallographic structure remained orthorhombic structure. The lattice parameter cdecreased, and the volume of the unit-cell with increasing Ca substitution.The heat treatment also led to an improvement in oxygen content to nearly 7.

Comparison of K, Ca and Zn Substitution on the Superconducting and Structural Properties of YBa2Cu3-xMXOδ

The comparison substitution with K, Ca and Zn respectively at the Cu site of YBa2Cu3-xMxOδ (x = 0.00 and 0.20) was performed based on superconducting and structural properties. All samples were prepared via a solid state technique. Resistivity and current density measurements (zero magnetic fields) were done using the four probe method and the structural and morphological properties were characterized using X-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM) respectively. The critical current density (Jc) and critical temperature (Tc zero) of the substituted samples were found to be lower than that of the pure sample. Tc zero with K and Zn substitution was 78 K and 21 K respectively. This is due to the change in the hole concentration. Jc measured at 50 K showed values of 3.9790 A/cm2, 4.4483 A/cm2 and 2.9854 A/cm2 for the pure sample, K and Ca substituted samples respectively. The decrease in Jc was due to the hole porosity and grain connection. All samples showed an orthorhombic crystal structure. The morphology of the fracture surface of samples as observed by FESEM displayed a loose structure of grain arrangement for sample Ca and Zn substituted samples.

Effect of Yb Substitution in Bi1.6Pb0.4Sr2Ca2-xYbxCu3Oy Superconductor

This paper reports on the results of Yb substitution for Ca on the superconductivity and structural properties of Bi1.6Pb0.4Sr2Ca2-xYbxCu3Oy superconducting samples with x = 0.000, 0.025, 0.050, 0.100 and 0.200 which prepared by coprecipitation (COP) method. The samples were characterized by X-ray diffraction (XRD), field-emission scanning electron (FESEM), electrical and resistivity measurement by four-probe method. It was found that the substitution of Yb decreased the critical temperature (Tc zero), critical current density (Jc) and volume fraction of Bi-2223 phase. The samples have Tc zero in the range 77 to 100 K. Tc zero gradually decreased with an increase in Yb concentration, corresponding to small change of the carrier concentration. Jc was measured to be 5.7512 A/cm2 for pure sample and decreased to 4.1910 A/cm2 for x = 0.025 at 77 K. The crystallographic structure was found to change slightly from tetragonal to orthorhombic in Yb substituted samples. The lattice parameter c of Yb samples decreased due to the incorporation of Yb3+ (0.858 Å) with smaller ionic size compare to Ca2+ (0.99 Å). From the SEM observation, the grain connectivity became weak with smaller plate-like grain for x > 0.025 Yb concentration resulting in the decreased of Jc.

Superconducting Properties of Bi1.6Pb0.4Sr2Ca2-xDyxCu3Oy Prepared via Co-Precipitation Method

The samples with nominal composition of Bi1.6Pb0.4Sr2Ca 2-xDyx Cu3Oy where x = 0.000, 0.025, 0.050, 0.100 and 0.200 were prepared by the co-precipitation (COP) method. The samples were characterized by x-ray diffraction, electrical resistivity measurement and critical current density. The critical current density (JC) and superconductivity transition temperature (TC) of Dy substituted were found to be lower than the Dy-free sample. The TC values vary between 100 K and 75 K toward Dy concentration due to a small change of carrier concentration. The highest TC in Dy-doped sample was found at 96 K in x = 0.025. The JC decreased towards Dy substitution, and it was measured to be 5751.2 mA/cm2 in Dy-free and 3769.8 mA/cm2 in x = 0.025 at 77 K. XRD analysis showed the substitutions of Dy reduced the volume fraction of the 2223 phase and increased the volume fraction of the 2212 phase. The proportion of Bi-2223/Bi-2212 (%) were estimated from 76.74/23.26 in Dy free to 18.90/81.10 in x = 0.200.

Superconducting Properties of Calcium Substitution in Barium Site of Porous YBa2Cu3O7 Ceramics

The influence of calcium substitution at the barium site of porous Y(Ba1-xCax)2Cu3Oδ (x= 0.00, 0.10, 0.20 and 0.30) samples prepared via solid-state reaction method have been investigated. The structure, morphology, critical temperature and critical current were determined by x-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM) and four-point probe method, respectively. Generally, the curves of normalized resistance for all samples displayed normal metallic behavior above Tc onset. The Tc zero was between 84 K and 71 K with increase in Ca concentration corresponding to a small change of carrier concentration. The critical current density, Jc decreases with increase in Ca concentration. The highest Jc of 2.657 A/cm2 at 50 K was obtained in Ca-free porous YBCO which is higher than that of Ca-free non porous YBCO. Further substitution of Ca at Ba site decreased Jc monotonously. The increase of Ca concentration decreased the volume of unit cell but the crystallographic structure remains in the orthorhombic form where a≠b≠c. The grains are highly compacted and randomly distributed while the grain size decreased as the Ca concentration increased.

Effect of Ca Substitution at Y-Site of YB2C3O7 Superconductor Prepared via Co-Precipitation Method

The effect of Ca substitution in Y1-xCaxBa2Cu3O7 superconductor prepared via co-precipitation method has been investigated. The concentration of Ca substitution was varied from x = 0.05 to x = 0.20. The samples were characterized using X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (SEM), resistivity measurement and current density measurement (without magnetic field). The critical temperature of the samples decreased as the concentration of Ca be increased whereby the highest value of critical temperature (Tc zero) was 83 K at x = 0.05. The crystallographic structure of pure sample was evidenced to be orthorhombic form where a ≠ b ≠ c.. At x = 0.10, the microstructure showed an improvement in grain alignment compared to other Ca concentration. The critical current density (Jc) increased with Ca concentration. The value of Jc for x = 0.05 at 50 K and 60 K was 1.51 A/cm2 and 1.00 A/cm2, respectively.