Synthesis and Formation of T11223 and T1223 High-Tc Superconductors

The preparation methods of Tl2Ba2Ca2Cu30,o (T1l223) and Tlo.5Pbo.5Sr1.6Ca.4Cu30g (TI2223) superconductors using a variety of starting compositions and sintering temperatures are discussed. Single-phased Tl2223 with T, between 106 to 109 K can be prepared using T12Ba2C~Cu3010 and Tl1.6Ba2C~4Cu3010as starting compositions in a non-closed system by heating around 20 min at 910°C in flowing 02' Samples with Tl1223 major phase (- 70%) can be prepared from Tlo.5Pbo.5SrI.6C~.4Cu30gcomposition with the sample wrapped in gold foil and sintered in flowing oxygen at 940°C for 3 hours

Data Acquisition System for Resistance Measurement of High-temperature Superconductors

This paper discusses the design of a data acquisition system based on the 80486 microcomputer serving as a controller connected via a PC-Lab 848B card to digital multimeters and a temperature controller using IEEE 488 standard bus. The system is able to log, store and plot temperature versus resistance readings. Resistance measurement on YBa2Cu3074l) phase is reported and compared with previous results. Measurements on (YO.5 EUO.5)Ba2CuS07.S showed an increase in Tc onset and Tc zero; this was explained in terms of change in the internal pressure in the CuO planes due to partial substitution of larger Eu3+ in place of y3+. This data acquisition system is simple to use and very sensitive in detecting small variations in transition temperatures. The temperature can be measured with a precision of 0.1 K and accuracy of ± I K, which is the limit of the platinum resistor temperature sensor. The absolute-zero offset value is less than 0.1 K

Superconductivity in Layerd Cuprate

A series of layered cuprate (Rut_xNb)Sr2GdCups (Ru1212) for 0 :5 x :5 1 has been synthesized by the solid state reaction method. Powder X-ray diffraction analysis indicates that oxygen flow is important in the formation of the Ru1212 phase and superconductivity in the system. Samples with nominal composition (Rul_ x b)Sr2GdCu20 S can be indexed as a tetragonal structure with space group P4/mmm. The undoped compound exhibits the highest superconducting transition with Tc onsel of 65 K and Tc zero of 55 K. Our results also show that doping with b decreases the normal state conductivity and suppresses superconductivity in the system

The effect of sintering temperature on the formation of (Tl, Cr)-1212 superconducting ceramic from coprecipitated oxalate precursors

TlSr1212 superconductors were synthesized by solid‐state reaction using Tl‐containing precursor powder prepared by coprecipitation of metal acetates with stoichiometric ratio based on Tl0.85Cr0.15Sr2CaCu2O7−δ composition. The samples were sintered at temperatures between 960 and 980°C for duration of 5 minutes. XRD patterns for samples sintered at 960°C showed formation of dominant 1212 phase in addition to minor 1201 phase and SrCO3 impurity. At this sintering temperature, the best superconducting behavior with TC(R=0) of 100 K was observed for the sample sintered at 970°C. SEM investigations on the sample revealed elongated grains which belong to 1212 phase with a slight directional grain alignment. The sample with sintering temperature of 960°C showed better grains connection as compared to the rest of the samples

Effect of graphene addition on the transport critical current density of bulk (Tl0.85Cr0.15) Sr2CaCu2O7-δ superconductor

In this work, the effect of graphene addition on the transport critical current density of (Tl0.85Cr0.15) Sr2CaCu2O7-δ (Tl-1212) superconductor was investigated. Thallium-based high temperature superconductor (HTS) with nominal starting composition (Tl0.85Cr0.15) Sr2CaCu2O7-δ was prepared using high purity oxide powders via solid state reaction method. 0.001 – 0.005 wt.% of graphene were added into Tl-1212 superconductors. The characteristic of the samples were determined by powder X-ray diffraction method, scanning electron microscopy (SEM), energy dispersive X-Ray analysis (EDX), electrical resistance measurements and transport critical current density measurements. The zero-resistance temperature, Tc-zero was found to decrease from 95 K to 84 K with the increase of graphene. The temperature dependence transport critical current density (Jc) of the pure and graphene added bulk samples were investigated. Jc of the non-added bulk sample was 1320 mA/cm2 at 30 K while the Jc of sample with 0.001 wt.% graphene was 3660 mA/cm2 at 30 K. Results showed that the Jc of the Tl-1212 samples decreased with increasing graphene addition. Graphene acted as impurity which is believed to perform the flux pinning effect to Tl-1212. Thus, the Jc of Tl-1212 superconductors was enhanced. The phase formation and morphology of samples Tl-1212 were also discussed in this paper

Electrical, magnetoresistance and magnetotransport properties of Nd1−xSrxMnO3

The effects of Sr substitution on the electrical, magnetoresistance and magnetotransport properties of Nd1−xSrxMnO3 were studied. Nd1−xSrxMnO3 samples were prepared using the solid-state reaction method with x=0.12, 0.152, 0.22, 0.252 and 0.32. All samples showed an orthorhombic structure, and no impurities were detected when the samples were examined using the X-ray diffraction method. The grain size was between 10 μm and 16 μm for all samples. The sample with x=0.32 showed the smallest grain size and the lowest To value, where To reflects the MnOMn bond angle. As the Sr concentration increased, the grains grew into more pentagonal and hexagonal shapes, and the insulator–metal transition temperature, Tim, also increased from 131 K to 180 K. The exceptions were the samples with x=0.152 and 0.252, where charge ordering was found at 120 K. The samples with the most pentagonal and hexagonal shaped grains (x=0.32) had the highest Tim. The magnetoresistance (MR) values were found to increase with increasing magnetic field. The sample with x=0.32 showed the highest MR value (31.5%), the highest Tim, the smallest grain size (∼10 μm) and the least bending of the MnOMn bonding angle

Structure, electrical transport and Magneto-Resistance properties of La5/8Ca3/8MnO3 manganite synthesized with different manganese precursors.

We synthesized the polycrystalline manganite of La5/8Ca3/8MnO3 with three different manganese routes prepared through a solid state reaction method. The effects of the manganese route selection on the structure, electrical transport and magneto-transport properties were examined in this study. The samples were characterized using X-ray diffraction (XRD) and SEM to identify their structure and morphology. XRD analysis confirmed that all samples were in single phase with orthorhombic structure and belonged to the Pnma space group. The average grain sized samples with manganese route of Mn2O3 and MnCO3 had a grain size of 1.2–8.7 μm and 2–7.5 μm, respectively. For the MnO2 route, the sample had a small melt-like shape with higher porosity. The metal–insulator transition temperature, TMI, for LCMO (Mn2O3), LCMO (MnO2) and LCMO (MnCO3) samples were 270 K, 266 K and 258 K, respectively. All the samples showed negative magneto-resistance with significant increase in value near the TMI temperature. The highest CMR (colossal magneto-resistance) ratio was found in LCMO (Mn2O3), -22.06% at 270 K, followed by -16.69% for LCMO (MnO2) at 80 K, and 15.2% for LCMO (MnCO3) at 100 K in a 1 T magnetic field

Transport critical current density of Bi-Sr-Ca-Cu-O/Ag superconductor tapes with addition of Fe3O4 as flux pinning center

This paper reports on the flux pinning capability of micron size Fe3O4 in Bi-Sr-Ca-Cu-O superconductor tapes. Ag sheathed high temperature superconductor tapes with starting compositions (Bi,Pb)2Sr2Ca2Cu3O10 (2223) and(Bi,Pb)2Sr2Ca2Cu3O10-(Fe3O4)0.01 were fabricated using the powder in tube method.The Bi-Sr-Ca-Cu-O powders were prepared by using the co-precipitation technique.The effects of Fe3O4 addition on the microstructure, phase formation, critical temperature and transport critical current density, Jc were studied. The Jc value of the Fe3O4 added tapes is higher (6,090 A/cm2 at 77 K and 24,500 A/cm2 at 30 K, in zero field) than the non-added tapes (3,730 A/cm2 at 77 K and 13,3180 A/cm2 at 30 K, in zero field). A sudden decrease of Jc in low magnetic fields (B < 0.12 T) when applied parallel (B||) and perpendicular (B^) to the tapes surface was observed. The destruction of weak links played an important role in the early Jc suppression. The rate of decrease of Jc was observed to decrease when the magnetic field was increased further. Improvement in the flux pinning was observed in (Bi, Pb)2Sr2Ca2Cu3O10-Fe3O4)0.01 tapes. This study shows that magnetic particles such as Fe3O4 can act as effective pinning centers leading to the enhancement of Jc in the system

Isolation and characterisation of a molybdenum-reducing and Metanil Yellow dye-decolourizing Bacillus sp. strain Neni-10 in soils from West Sumatera, Indonesia

A molybdenum reducing bacterium with the novel ability to decolorise the azo dye Metanil Yellow is reported. Optimal conditions for molybdenum reduction were pH 6.3 and at 34°C. Glucose was the best electron donor. Another requirement includes a narrow phosphate concentration between 2.5 and 7.5 mM. A time profile of Mo-blue production shows a lag period of approximately 12 hours, a maximum amount of Mo-blue produced at a molybdate concentration of 20 mM, and a peak production at 52 h of incubation. The heavy metals mercury, silver, copper and chromium inhibited reduction by 91.9, 82.7, 45.5 and 17.4%, respectively. A complete decolourisation of the dye Metanil Yellow at 100 and 150 mg/L occurred at day three and day six of incubations, respectively. Higher concentrations show partial degradation, with an approximately 20% decolourisation observed at 400 mg/L. The bacterium is partially identified based on biochemical analysis as Bacillus sp. strain Neni-10. The absorption spectrum of the Mo-blue suggested the compound is a reduced phosphomolybdate. The isolation of this bacterium, which shows heavy metal reduction and dye-decolorising ability, is sought after, particularly for bioremediation

Sound velocity in perovskite manganites La0.67Ca0.33MnO3 with different grain sizes

The longitudinal and shear sound velocities in colossal magnetoresistive material La0.67Ca0.33MnO3 sintered at 1100, 1250 and 1350 1C with average grain size 1, 3 and 5 mm, respectively, have been measured from 80 to 300K using the pulse-echo-overlap method.A pronounced increase in the longitudinal sound velocity was observed in all samples around the insulator–metal transition temperature (TIM272 K). XRD patterns showed the orthorhombic structure for all samples. The longitudinal and shear velocities showed the largest hysteresis for the sample with 3 mm grain size. A step-like shear sound velocity anomaly near 120K during cooling or warming was observed to be dependent on the grain size