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Synthesis and Investigation of Effect of Pr Doping on the Compound Y(3-x) Pr x Ba5 Cu8 O(19-δ)-F
, M.Sc. Thesis Sharif University of Technology ; Akhavan, Mohammad (Supervisor)
Abstract
Synthesis and Investigation of Effect of Pr Doping on the Compound Y_(3-x) 〖Pr〗_x 〖Ba〗_5 〖Cu〗_8 O_(19-δ)-FInvestigation of doping of the parent compounds with different elements is important to understand the origin of high-Tc superconductivity. Several research groups have attempted to improve the properties of superconductivity and better understand the superconductivity mechanism of cuprate through doping different elements. In this research, at first, optimization of Y_3 〖Ba〗_5 〖Cu〗_8 O_(19-δ) F_z samples with z=0.2 ,0.4 ,0.6 ,0.8 ,1 ,2 ,3 ,4 have been done. By doping fluorine instead of oxygen, we expected an increase in the transition temperature, based on some the reports. But after...
Comparative Study of Superconductivity in Y112 and Y123
, M.Sc. Thesis Sharif University of Technology ; Akhavan, Mohammad (Supervisor)
Abstract
After the discovery of high temperature superconductivity in (LaM)2CuO4, different type of cuprate superconductors have been synthesized. Among them, YBCO compounds (e.g. YBa2Cu3O7-δ) have drawn more attention by researchers due to some advantages such as easier conditions of synthesis high quality samples in comparison with the other cuprate superconductors. However, superconductivity properties of these compounds are very sensitive to structural imperfections; hence it is important to study the effect of the microstructure on the behavior of the compounds. The compound YBaCu2Ox (Y112) is one of these microstructures that may form in YBa2Cu3O7-δ (Y123) samples. On the...
Flux Pinning Energy in Nd1-x Smx Ba2Cu3 O7-δ
, M.Sc. Thesis Sharif University of Technology ; Akhavan Farshchi, Mohammad (Supervisor)
Abstract
Physical properties of $Re_1 Ba_2 Cu_3 O_{7-\delta} (Re123)$ high-temperature cuprate superconductors attract many of physicists due to their high transition temperature (above Nitrogen boiling point), relatively simple synthesizing and high critical current density. Among this family, Nd123 and Sm123 single-crystal compounds have the highest transition temperature and critical current density in the magnetic fields less than 2 Tesla. In addition, due to the near ionic radius of Nd and Sm elements, it is possible to synthesize $Nd_{1-x} Sm_x Ba_2 Cu_3 O_{7-\delta} (0 \leq x \leq 1)$ compounds with no significant dislocation. In order to investigate the effects of such doping on electrical...
Structural phase of y358 superconductor comparison with Y123
, Article Journal of Superconductivity and Novel Magnetism ; Volume 25, Issue 7 , October , 2012 , Pages 2253-2258 ; 15571939 (ISSN) ; Daadmehr, V ; Rezakhani, A. T ; Khosroabadi, H ; Tehrani, F. S ; Akbarnejad, R. H ; Sharif University of Technology
Springer
2012
Abstract
We analyze an experiment in which two distinct superconducting phases YBa2Cu3O7-δ (Y123) and Y 3Ba5Cu8O18-δ (Y358) coexisted. This experiment enabled us to characterize the recently introduced Y358 phase in contrast to the Y123 phase, thus to resolve some discrepancies reported in associated properties of Y358. Specifically, our experiment indicates the transition temperature Tmid C = 105 K and 94 K for Y358 and Y123, respectively, and that Y358 has five CuO2 planes and three CuO chains, with Pmm2 symmetry and lattice parameter (a, b, c) = (3.845, 3.894, 31.093) Å, in agreement with density functional theory predictions for this specific structure
First-principles study on lattice instabilities and structural phase transitions in Ba doped La2 CuO4
,
Article
Physica C: Superconductivity and its Applications
;
Volume 517
,
October
,
2015
,
Pages 20-25
;
09214534 (ISSN)
; Akhavan, M
; Draxl, C
;
Sharif University of Technology
Elsevier
2015
Abstract
We present linear-response density-functional theory calculations for the high-Tc superconductor La2- x Bax CuO4 to study the doping dependence of phonon dispersion. Using the virtual crystal approximation, the doping range up to x = 0.20 is investigated. We find unstable phonon modes that soften around high-symmetry points of the Brillouin zone. These branches are analyzed as a function of doping and pressure. The structural distortions related to these phonons are in accordance with the observed phase transitions from the high-temperature tetragonal (HTT) phase to the low-temperature orthorhombic (LTO) and the low-temperature tetragonal...
The effect of chemical pressure in rutheno-cuprates
, Article Physica C: Superconductivity and its Applications ; Volume 470, Issue 4 , 2010 , Pages 285-290 ; 09214534 (ISSN) ; Khajehnezhad, A ; Hadipour, H ; Akhavan, M ; Sharif University of Technology
Abstract
We have studied the effect of negative chemical pressure in the RuGd 1.5(Ce 0.5-xPr x)Sr 2Cu 2O 10-δ with Pr content of 0.0 ≤ x ≤ 0.2. This is also investigated using the bond length results obtained from the Rietveld refinement analysis. The c parameter and cell volume increase with x for 0.0 ≤ x ≤ 0.15. The width of the resistivity transition also increases with Pr concentration, indicating higher inhomogeneity and oxygen deficiency. The difference in the ionic valences of Pr 3+,4+ and Ce 4+ causing different hole doping, the difference in the ionic radii, and oxygen stoichiometry affect the superconducting transition. The magnetoresistance shows a cusp around 135 K which lies between the...