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Investigation of the structural features of high-temperature superconducting crystals by the method of channelization and resonant nuclear reactions

“…At small angles of ion beam incidence relative to the <001> direction, the flux density distribution of the Comparing the angular dependence of the yield of close interaction process on the oxygen atoms calculated for different amplitudes of thermal and/or static displacements in directions perpendicular to the reference direction with the available experimental results, the displacement magnitudes can be determined. As demonstrated in [15], agreement between the calculated and experimentally measured minimum yield [3,12] can be obtained if we suggest that a certain fraction (no more than 20%) of the oxygen atoms occupies chaotic positions in the plane perpendicular to the <001> direction. The width of the calculated angular dependence and the position and angular width of the jog observed at angles of ≈0.4° correspond to their experimental values under assumption of displacement of the oxygen atoms in the direction perpendicular to the <001> axis.…”

“…The calculated angular distribution narrower in comparison with the experimental one indicates the absence of large displacements (thermal and/or static) of the oxygen atoms under conditions of the experiment [13]. A larger displacement of the oxygen atoms in [3,12] was apparently due to the fact that first, the thick YBa 2 Cu 3 O 7-x crystal and much greater depths of ion penetration into the crystal were used in experiments [13], and thin crystal films were used in experiments [3,12]. Second, measurements in [3,12], in contrast with [13], were carried out at room temperature.…”

“…The angular dependence of the yield of elastic 16 O(α,α) 16 O resonant scattering of the helium ions on the oxygen atoms relative to the <001> axis measured in [3,12] has a characteristic jog at angles of entry into the crystal of ≈0.4°. An analogous angular dependence of the nuclear reaction yield of protons scattered on the oxygen atoms in the La 2 CuO 4 crystal was discussed in [6][7][8].…”

“…Thus, investigations of the YBa 2 Cu 3 O 7-x crystals by the channelization method have revealed the anomalous stepwise changes in magnitudes of static and/or dynamic displacements of atoms from sites of the crystal lattice at temperatures close to the temperature of phase transition into the superconducting state [2]. The use of the so-called "parapet" regions of angular dependences makes it possible to construct a 3D model of the YBa 2 Cu 3 O 7-x crystal structure with static displacements of the oxygen atoms [3].…”

“…This allows detailed information on the structural features of the crystal lattice and position of the Li admixture atoms in the subsurface region (to depths of 1000 A ) of high-temperature superconducting crystals, including La 2 CuO 4 and Nd 2 CuO 4 , to be obtained by a comparison of the calculated and experimental results for various crystallographic directions [5][6][7][8]. In the present work, the structural features of the YBa 2 Cu 3 O 7-x oxygen sublattice are discussed based on an analysis of the experimental data [3,[12][13][14] on the orientational dependence of the yield of the resonant nuclear reaction 16 O(α, α) 16 O for different energies of the helium ions.…”