Lattice sum calculations and electric field gradients for orthorhombic and tetragonal phases of YBa2Cu3Ox

Electronic defects in lattices of YBa2Cu3O7 and La2 − xSrxCuO4

“…Effective charges accurately present the valence states of ions at the lattice sites and the significant deviations from their standard valence states (Seregin, Masterov, Nasredinov 1992;Seregin, Marchenko, Seregin et al 1992;. Such calculations for the YBa 2 Cu 3 O 7 and La 2 − x Sr x CuO 4 lattices have been carried out in many works (see, for example, (Adrian 1989;Garcia, Bennemann 1989;Lyubutin et al 1989;Seregin et al 1992;Shimizu 1993)), but their results are in poor agreement with experimental data (Ishida et al 1991;Masterov et al 1995;Ohsugi 1995;Ohsugi et al 1994;Pennington et al 1989;Shore et al 1992;Takigawa et al 1989 This study describes effective charge determination for atoms in the copper metal oxides YBa 2 Cu 3 O 7 and La 2 − x Sr x CuO 4 . The calculated EFG tensor parameters are compared with the experimental NQI tensor parameters measured by NMR/NQR or MS using the lattice probes located at the lattice sites.…”

Studies on the Gamma Radiation Responses of High Tc Superconductors

“…In order to promote these aspects, a methodology developed by Abreu et al (Abreu et al, 2009) was used to consider the structural defects influence in the quadruple splitting observed values; through the calculation of the electric field gradient (EFG) components in this situation by the point charge model (Abreu et al, 2009;Lyubutin et al, 1989). Specifically the point defects are taken in to consideration through different oxygen configurations, like cluster formation around the 57 Fe position and vacancies; and electron trapped in vacancies near this position too, like negative vacancies.…”

“…Parameters reported for the YBCO (Liu et al, 2005;Lyubutin et al, 1989;Santoro, 1991) were used to calculation the EFG values for the ideal tetragonal and orthorhombic structure. These calculations were made following point charge model algorithm; reaching a precision order in the sum of 10 −6 for the atoms located inside a sphere with radius R = 380 Aº.…”

“…Finally, it becomes necessary to obtain the corresponding splitting values due to the hyperfine quadruple interaction of the nuclear sublevels ∆E Q , which are observed in the experiment. This magnitude could be calculated from the following expression (Abreu et al, 2009;Lyubutin et al, 1989) 1 2 2 11 23…”

“…To evaluate ∆E Q the following values of this parameters for the 57 Fe (I = 3/2) were used in all cases, Q = 0.16b and γ ∞ = −9.14 (Abreu et al, 2009;Lyubutin et al, 1989). The calculation results are presented in Fig.…”