EPR of complex paramagnetic center in YBa2Cu3O7-γ induced and suppressed by mechanical processing

Pseudorotational Averaging of EPR Spectrum of Cu(II)O5Complex in YBa2Cu3O7-δin Low Temperatures

“…Below Tc , the high Tc-superconductor is in the mixed state and the local field takes again the value of the external field. Further temperature decrease is accompanied by a break-up of the twocentered Cu2-Cu1 complex [6]. The condensation of the fifth oxygen at O5 site increases the dynamics of the chain complex Cu1O5 while an increase in superconductivity screens the Cu2O 4 complexes in planes.…”

“…0 6 5 o b s e r v e d b y u s , corresponds strictly to the square coordination CuO4 of D4h symmetry and is related to copper in the chains Cu(1)(O1) 2 (O4)2 or to the paramagnetic defect Cu2(O2)2(O3)2 in the oxygen-copper plane in the structure of Y-123. The paramagnetic complex in Y-123 is formed by breaking up the exchange bonding of the chain copper Cu1 with the plane [6]. The values = 2.218 and g║ = 2.065 observed for Y-123 at room temperature are the result of exchange interaction between two copper atoms Cu2-Cu1 which is responsible for paramagnetic excitation of the Y-123 stucture through violation of charge equilibrium.…”

“…An analogous phenomenon takes place in the structure of YBa2Cu3O7-δ. Mechanically induced copper complexes in YBa2 Cu3 O7-δ have, in high temperatures, a spectrum typical of Cu(II)O4 square coordinated in planes or in chains [6]. Oxygen atoms undergoing fast diffusion among the chains make quick jumps among 05 sites and do not attach to Cul copper making flat Cu1(O4)2(O1)2 complexes in the chains (Fig.…”

Calculations of EPRgfactors for the isolated tetragonal Cu2+(II) centre in mechanically processed YBa2Cu3O7−δsuperconductors

“…Since the discovery of the superconducting properties of the La-Ba-Cu-O system at the temperature T > 30 K [1], there has been extensive research into high T c complex copper oxide superconductors. Among them, the electron paramagnetic resonance (EPR) spectra of YBa 2 Cu 3 O 7−δ were measured [2][3][4][5][6][7]. The research found that for the single-phase monolithic YBa 2 Cu 3 O 7−δ , no paramagnetism and no EPR signal (i.e.…”

“…The research found that for the single-phase monolithic YBa 2 Cu 3 O 7−δ , no paramagnetism and no EPR signal (i.e. EPR silence) were observed [4][5][6][7], which may be due to the possible non-magnetic ground state or excessive line broadening. However, when the material is induced and suppressed by mechanical processing, the EPR signal can be found [7].…”