Berdan Özkurt

Enhancement in superconducting transition temperature and Jc values in Na-doped Bi2Sr2Ca1Cu2−xNaxOy superconductors

The effects of Na substitution on the properties of Bi2Sr2Ca1Cu2−xNaxOy were investigated. The prepared samples are characterized using X-ray powder diffraction, scanning electron microscope, DC electrical resistivity and magnetic-hysteresis loop measurements. It has been found that with increasing Na doping for Cu, the transition temperature gradually increase while crystal lattice parameters slightly change. Magnetic hysteresis measurements have shown that the hysteresis loops of doped samples are greater than the undoped sample. In addition, significant enhancement has been observed in the Jc values of Na-doped samples, which were calculated from the M–H curves by using Bean’s critical state model.

Structural, superconducting and mechanical properties of molybdenum substituted Bi1.8Sr2Ca1.1Cu2.1Oy

The effect of MoO3 addition on the properties of Bi-2212 superconducting ceramic samples prepared by solid state reaction method has been investigated. Mo content was varied from 0 to 0.25 on a general stoichiometric formula Bi1.8Sr2MoxCa1.1Cu2.1Oy. Electrical resistivity showed that transition temperature width increased directly with the Mo amount. XRD data have shown that MoO3 addition in the Bi1.8Sr2MoxCa1.1Cu2.1Oy precursor reduces the amount of Bi-2212 phase. In addition, Jc values of the samples, calculated from the hysteresis loops using the Bean’s model, decreased with increasing Mo substitution. Vickers microhardness measurements show that samples are very sensitive to Mo content and applied load. In addition, various models like Meyer’s Law and Young’s Modulus equations have been used to better explain the mechanical properties of samples.

Effect of Yb substitution in Bi-2212 ceramics prepared by laser floating zone technique

In the present work, the influence of Yb substitution for Bi on the structural, electrical and magnetic properties of textured Bi-2212 ceramics has been investigated. X-ray diffraction studies indicated that the major peaks correspond to the Bi-2212 phase. The SEM images clearly show that there is an increase in the number of secondary phases with raising Yb content while all samples maintain similar grain morphology. Magnetic analysis of all samples has been done by magnetic hysteresis measurements, indicating that an enhancement in the M-H loops is obtained by a low Yb doping. The critical current density of samples was calculated from the M-H curves by using Bean’s critical state model, indicating that sample with 0.05 Yb substitution possesses the highest Jc values.

Observation of magnetocaloric effect in the LaMn1.9Fe0.1Si2 compound at low fields in the vicinity of phase transition around room temperature

Low field magnetic and magnetocaloric properties of the compound LaMn1.9Fe0.1Si2 have been investigated. Using the M-H data measured at various temperatures, we have derived the magnetic entropy change |ΔS| as a function of temperature and magnetic field, by using the Maxwell relation. The temperature dependence of the Landau coefficient has been derived by fitting the magnetization, using the Landau expansion of magnetic free energy and Arrott plots. The results show that LaMn1.9Fe0.1Si2 is ferromagnetically ordered around room temperature (285 K) and the nature of the phase transition at this temperature is found to be second order.