Papers by Keyword: Superconductivity

Abstract: This study investigates the absence of superconductivity in bulk type nickelate and analyzes the structural and transport characteristics of the materials. Infinite layer bulk type Nd_1-xSr_xNiO₂ with Sr doping level x for 0.0, 0.1 and 0.2 are synthesized by conventional solid state synthesis method. The crystallographic structure Nd_1-xSr_xNiO₂ of is found to be stable for different doping levels using X-ray diffraction (XRD) analysis and confirms phase purity. Scanning electron microscopy (SEM) analysis reveals the grain morphology and indicates the absence of notable microstructural features that support superconductivity. The nature of grain size distribution of Nd_1-xSr_xNiO₂, with x = 0.0, 0.1 and 0.2 are analyzed. The transport measurement of prepared bulk type nickelate samples are performed by four probe technique with the help of closed cycle cryogenerator. The electrical transport characteristics based on 3D Variable Range Hopping (VRH) conduction models are examined. This study presents the alternative synthesis techniques to stabilize the superconducting phase and an overall insight into the causes for the failure of superconductivity.

Abstract: The suppression of superconductivity (T_c) in electron-doped superconducting materials Eu_1.81Ce_0.19Cu_1-yZn_yO_4+α-δ (ECCZO) heavily overdoped regimes by nonmagnetic impurity Zn with concentration of y = 0, 0.01, 0.02, and 0.03 has been successfully investigated by using XRD and SQUID measurements. All samples were synthesized using the solid-state reaction method. The crystal structure obtained from XRD measurements has a tetragonal T° structure, which matches the crystal structure of electron-doped superconductors in general. The addition of Zn impurity shows no change in the crystal structure, but there is a decrease in the α-lattice and an increase in the c-lattice, unit cell volume, and Cu-O bond length. This causes the distance between the charge reservoir and the conduction layer to increase and affects the disappearance of T_c. Magnetic susceptibility measurements using SQUID were carried out under FC (Field Cooling) conditions with temperatures between 2 - 30 K with a field of 5 Oe. The sample with y = 0 has diamagnetic properties with a superconductivity value (T_c) of about 11 K. The addition of Zn impurities succeeded in suppressing superconductivity as indicated by the disappearance of T_c, so that the sample is in the ground state. The Curie constant and the effective magnetic moment decrease with increasing Zn concentration. This is probably due to the decrease in Cu²⁺ when the non-magnetic Zn²⁺ atoms were added, therefore the overall value of the µ_eff decreases when Zn²⁺ substitutes some Cu²⁺. This result is different from that described by Abrikosov-Gor’kov theory in the hole-doped high-T_c cuprates.

Abstract: The paper presents the results of a study of morphology, chemical composition, microcrystalline structure and properties of thin tapes of alloy grade 20KH23N18S2, obtained by melt spinning. The influence of process parameters on the properties and microstructure of the tapes is established.

Abstract: Non-doped and strontium-doped lanthanum cuprates (La₂CuO₄ (LCO) and La_1.85Sr_0.15CuO₄ (LSCO15)) in nano-sized particles were synthesized by the chemically dissolved technique employing HNO₃ as the dissolving agent. The structural and magnetic properties were investigated by using an x-ray diffraction (XRD) apparatus and a superconducting quantum interference device (SQUID) magnetometer, respectively. The XRD patterns of LCO and LSCO15 show the formation of the single phase without impurities after the calcinations in air at 1100°C for 15 h and the post-annealing in oxygen at 800 °C for 24 h. The average crystallite sizes of LCO and LSCO15 samples were in a range of around 100 nm confirming nano-sized particles. The LCO and LSCO15 nanoparticles exhibit superconductivity at the superconducting (SC) transition temperature, T_c, of 23 K and 38 K, respectively. The magnetization curve measurements have revealed that both samples show the appearance of ferro- and dia-magnetic behavior at room temperature and the appearance of superconductivity at low temperatures. This result may indicate the coexistence of ferromagnetism and superconductivity below T_c in the nano-sized cuprates.

Abstract: We performed an angle-resolved photoemission spectroscopy (ARPES) study of the Ni-based superconductors SrNi2P2. We observe both electron and hole Fermi surface pockets with different shapes and sizes which leads to very poor nesting conditions. Moreover, we observe a band structure reconstruction below the structural transition temperature (325 K), with bands shifting downwards and one extra hole-like band appearing around Г. These behaviors might be attributed to the length reduction of one third of P-P bonds between the adjacent NiP layers. The low temperature phase in SrNi2P2 can be regarded as a partially collapse phase. Our result may facilitate understanding the collapsed behavior which is important to unveil superconductivity mechanism in iron-based superconductors.

Abstract: Polycrystalline samples with the nominal composition YBa₂Cu₃O_7-δ (Y-123) were prepared using the co-precipitation method. The effect of the calcination process (single and multiple calcinations) on the samples was investigated by using the four-point temperature-resistance measurement, x-ray diffraction (XRD) and field-emission scanning electron microscope (FESEM). This study is divided into two parts. For the first part, the obtained oxalate powder underwent two calcination processes at 900 °C for 12 h and 900 °C for 24 h, respectively. Then, the powders were pressed into pellets and sintered at 920 °C for 15 h with oxygen flow during the entire heat treatment. In the second part, only one calcination process was undertaken at 900 °C for 24 h before the sintering process in oxygen flow at 920 °C for 15 h. From the XRD patterns, all of the peaks were indexed to the Y-123 phase showing that this superconducting phase was already formed after the first calcination. The volume fraction of Y-123 of the samples with single calcination process was higher compared to multiple calcination processes. From the temperature-resistance measurement, all the samples showed metallic behavior in the normal state and a superconducting transition to zero resistance. The superconducting transition temperature, T_c, for the samples prepared in a single calcination process is higher than that of the multiple calcination processes.

Abstract: We investigate electric and magnetic properties of quasi-one-dimensional transition-metal carbides Sc₃TC₄ (T = Co, Ru, and Os), and their mixed crystals Sc₃(Co_1-xRu_x)C₄ and Sc₃(Ru_1-xOs_x)C₄. Sc₃CoC₄ exhibits successive phase transitions of charge-density-wave transition at T_CDW ~ 140 K, Peierls-like structural transition at T_s ~ 70 K, and superconducting transition at T_c ~ 5 K. Sc₃RuC₄ and Sc₃OsC₄ exhibit a phase transition at T^* ~ 220 K and 250 K, respectively, which should occur in the low-dimensional electronic structure. For Sc₃CoC₄, it is revealed by the investigation of the electric and magnetic properties of Sc₃(Co_1-xRu_x)C₄ that the phase transitions at T_CDW, T_s, and T_c exhibit different robustness against Ru doping. For Sc₃RuC₄ and Sc₃OsC₄, it is revealed by the investigation of the electric and magnetic properties of Sc₃(Ru_1-xOs_x)C₄ that an identical kind of phase transition occurs at T^*. Additionally, the present study reveals that the phase transition at T^* in Sc₃RuC₄ and Sc₃OsC₄ is inherently different from the phase transitions at T_CDW, T_s, and T_c in Sc₃CoC₄.

Abstract: In order to study the evolution of local crystal and electronic structure of Sr₂CuO₂F_2+x, the synchrotron radiation x-ray absorption (XAS) and x-ray absorption fine structure (XAFS) techniques were both performed on different amount of Sr₂CuO₂F_2+x materials. The relationship between high T_c superconductivity and valence state of cooper was mainly discussed. And the effect of by-reproduce SrF₂ in non-superconductive Sr₂CuO₂F_2+x on physical property of this material was considered. The experimental results showed that the valence state of Cu and the amount of SrF₂ was mainly related with high T_c superconductivity of Sr₂CuO₂F_2+x material, indicating a good method for improving T_c.

Abstract: Several Bi-O-S compounds with nominal composition of Bi₄O₄S₃, Bi₃O₂S₃, Bi₂OS₂ have successfully been synthesized. The superconducting properties present to be similar with each other for Bi₄O₄S₃ and Bi₂OS₂ compounds, but much better than the Bi₃O₂S₃ compound. The former two possess a zero resistance temperature at 4.1 K, whereas the latter one is 3.7 K. Two diamagnetic transitions have been observed in the M-T curve for all three compounds. The starting nominal composition definitely affects the superconductivity of the final products.

Abstract: The review reports on the results of our research work on nanostructured metal films onto porous silicon. Principal steps of the techniques allowing fabrication of metal films completely inheriting morphological pattern of different types of porous silicon are presented. It is shown, that giving of the nanostructured pattern to metal films by means of porous silicon template opens their new structural, optical, mechanical and electrical properties, which can be successfully applied in nanoelectronics and biomedicine, particularly including devices based on superconductivity effect, SERS analysis with picomolar sensitivity and transdermal drug delivery by electroporation.