A study of positron distribution and annihilation characteristics in YBa2Cu3O7-x

The positron distribution and lifetimes have been computed for the model structures of orthorhombic YBa2Cu3O7, tetragonal YBa2Cu3O6.5 and tetragonal YBa2Cu3O6, which consist of different ordered arrangements of oxygen vacancies. The positron potential was obtained as a sum of the full lattice electrostatic potential and the correlation potential in the local density approximation. The positron wavefunction and the eigenvalue of the lowest-lying itinerant positron state was obtained by solving the Schrodinger equation in the finite-difference scheme. The positron wavefunction displays maxima at the oxygen vacancy positions and it is seen that the positron probes predominantly the oxygen vacancies in the basal plane. By computing the overlap of the positron density with the core and valence electron densities, the positron lifetimes for YBa2Cu3O7, YBa2Cu3O6.5 and YBa2Cu3O6 are estimated to be 190 ps, 222 ps and 234 ps, respectively. Calculation of the positron wavefunction and lifetime has also been carried out for a positron localised at an isolated oxygen vacancy along the chain in orthorhombic YBa2Cu3O7. The calculated values of lifetimes for different arrangements of vacancies have been compared with the experimental values of positron lifetimes in YBa2Cu3O7-x measured after various heat treatments.

[1]  T. S. Radhakrishnan,et al.  Oxygen ordering and superconductivity in YBa2Cu3O7-δ , 1988 .

[2]  A. Sood,et al.  Positron Annihilation Study of Oxygen Vacancies in Y1Ba2Cu3O7-x , 1988 .

[3]  A. Sood,et al.  Positron studies on Y1Ba2Cu3O7−x : Charged oxygen vacancies? , 1988 .

[4]  P. Turchi,et al.  Positron annihilation in perovskite superconductors; Theory and experiment , 1988 .

[5]  Chu,et al.  Evidence for a common high-temperature superconducting effect in La1.85Sr0.15CuO4 and YBa2Cu3O7. , 1988, Physical review letters.

[6]  B. Chakraborty,et al.  Response of positrons to clustering in Al-Zn alloys , 1988 .

[7]  A. Sood,et al.  Positron annihilation measurements across the superconducting transition in Y1Ba2Cu3O7−x , 1988 .

[8]  P. Strobel,et al.  Oxygen vacancy ordering in Ba2YCu3O7−x around x= 0.5 , 1988 .

[9]  R. Cava,et al.  OXYGEN DEFICIENCY IN Ba2YCu3O7–δ: THE NEED FOR A MICROSCOPIC DESCRIPTION , 1987 .

[10]  Lynn,et al.  Temperature dependence of positron-annihilation parameters in YBa2Cu3O7-x above and below the superconducting transition. , 1987, Physical review. B, Condensed matter.

[11]  Wille,et al.  Stability analysis of special-point ordering in the basal plane of YBa2Cu , 1987, Physical review. B, Condensed matter.

[12]  Chen,et al.  Single-phase 60-K bulk superconductor in annealed Ba2YCu , 1987, Physical review. B, Condensed matter.

[13]  L. Ganapathi,et al.  Relation between highTc superconductivity and structure: A study of Ba3+xCu6O14+δ and YBa2Cu3O7−δ systems , 1987 .

[14]  Wang,et al.  Positron annihilation in the high-temperature superconductor YBa2Cu3O6+ delta. , 1987, Physical review. B, Condensed matter.

[15]  H. Zandbergen,et al.  The vacancy order — disorder transition in Ba2YCu3O7−δ observed by means of electron diffraction and electron microscopy , 1987 .

[16]  C. Segre,et al.  Structure of the single‐phase high‐temperature superconductor YBa2Cu3O7−δ , 1987 .

[17]  B. Raveau,et al.  Structure of the 100 K Superconductor Ba2YCu3O7 between (5 ÷ 300) K by Neutron Powder Diffraction , 1987 .

[18]  Roth,et al.  Neutron study of the crystal structure and vacancy distribution in the superconductor Ba2YCu , 1987, Physical review. B, Condensed matter.

[19]  R. Nieminen,et al.  CORRIGENDUM: Defect spectroscopy with positrons: a general calculational method , 1983 .

[20]  E. Pajanne,et al.  Electron liquid in collective description. III. Positron annihilation , 1979 .

[21]  T. Chiba.  Covalency effects on momentum distributions in compounds: Positron annihilation in Fe3O4 , 1976 .

[22]  N. Tsuda,et al.  Anisotropy in the angular correlation curves of NiO , 1974 .