scholarly journals First-principles study of the pressure and crystal-structure dependences of the superconducting transition temperature in compressed sulfur hydrides

2015 ◽  
Vol 91 (22) ◽  
Author(s):  
Ryosuke Akashi ◽  
Mitsuaki Kawamura ◽  
Shinji Tsuneyuki ◽  
Yusuke Nomura ◽  
Ryotaro Arita
Keyword(s):  
Crystal Structure ◽  
Transition Temperature ◽  
First Principles ◽  
Superconducting Transition Temperature ◽  
Superconducting Transition ◽  
First Principles Study

COMPOSITION DEPENDENCE OF SUPERCONDUCTIVITY AND CRYSTAL STRUCTURE IN La(Ba1−xCax)2Cu3O7−y SYSTEM

1989 ◽  
Vol 03 (04) ◽  
pp. 307-311 ◽  
Author(s):  
N. CAO ◽  
J.Q. ZHENG ◽  
X.Y. SHAO ◽  
X.S. CHEN ◽  
W.Y. GUAN
Keyword(s):  
Crystal Structure ◽  
Transition Temperature ◽  
Superconducting Transition Temperature ◽  
Composition Dependence ◽  
Superconducting Transition ◽  
Orthorhombic Structure ◽  
X Ray Diffraction ◽  
X Ray ◽  
Resistivity Measurements ◽  
Zero Resistance

The composition dependence of superconductivity and crystal structure in La ( Ba 1−x Ca x)2 Cu 3 O 7−y system was determined by the resistivity measurements and X-ray diffraction analysis. The superconducting transition temperature is raised with the increase of Ca content till x=0.6, at which the zero resistance temperature of the sample is 81.5 K. In the meanwhile, the crystal structure of the sample changed from tetragonal (x=0) to orthorhombic structure (x=0.2, 0.4, 0.6). With further increase of Ca content, the superconductivity decrease for the sample of x=0.8 with mixed phases including the orthorhombic oxygen-deficient perovskite-like (ODP) structure and no superconducting transition is found at 4.2 K for the sample of x=1 without the ODP structure. A possible explanation of these experimental results is given.

Melt Spinning and Phase Transformations of V2CrA11-xBx and Ti3Nb6Mo3Si4 Alloys

1983 ◽  
Vol 21 ◽  
Author(s):  
B.S. Smith ◽  
R.A. Smith ◽  
M T. Clapp
Keyword(s):  
Crystal Structure ◽  
Transition Temperature ◽  
Phase Transformations ◽  
Superconducting Transition Temperature ◽  
Melt Spinning ◽  
Vickers Microhardness ◽  
Lattice Parameter ◽  
Rapid Quenching ◽  
Superconducting Transition

ABSTRACTMelt spinning was used to rapidly quench V2CrA11-xBx and Ti3Nb6Mo3Si4 alloys. Melt spinning had very little effect on the crystal structure of the V2CrA11-xBx alloys. However, a new (NbTiMo)3 Si A–15 phase was found by rapid quenching of the Ti3Nb6Mo3Si4 alloys; the lattice parameter was 5.08 Å. Melt spinning increased the Vickers microhardness values of the V2CrA11-xBx alloys from 500 to 750, and of the Ti3Nb6Mo3Si4 alloys from 1000 to as high as 1675. Melt spinning increased the superconducting transition temperature of the Ti3Nb6Mo3Si4 alloys from 1.9 to 3.4K.

Use of rescreened pseudopotentials for the superconductivity of aluminum at finite pressures

1981 ◽  
Vol 59 (3) ◽  
pp. 309-314 ◽  
Author(s):  
M. D. Whitmore
Keyword(s):  
Transition Temperature ◽  
Pressure Dependence ◽  
First Principles ◽  
Superconducting Transition Temperature ◽  
Imaginary Axis ◽  
Superconducting Transition ◽  
Volume Changes ◽  
Source Of Error ◽  
Coulomb Pseudopotential ◽  
Phonon Properties

Use is made of the pseudopotential determined by Dagens, Rasolt, and Taylor to calculate from first principles all the microscopic phonon and electron–phonon properties necessary for the superconducting transition temperature of aluminum, Tc, for zero pressure and for volume changes up to −10%. After fitting the Coulomb pseudopotential parameter μ* at zero pressure, Tc is calculated both by solving the Eliashberg gap equations on the imaginary axis, and by employing the approximate formulae of McMillan and of Leavens. The resulting pressure dependence of Tc is unsatisfactory. One source of error appears to be an insufficient pressure-induced shift of the phonon frequencies, indicating a limitation on the use of these pseudopotentials that is not widely appreciated. However, this is not believed to be the only difficulty and other possibilities are briefly discussed.

Sign in / Sign up

Export Citation Format

Share Document