On the Structure of the Cu B Site in La1.85Sr0.15CuO4

Interpretation of nuclear quadrupole resonance spectra in doped La 2 CuO 4

“…Furthermore, the intensity of the B peak is expected to grow proportional to the doping concentration x, as indeed is observed experimentally [7]. This is in agreement with recent measurements [12], which suggest that Cu B sites are formed by contracted CuO 6 octahedra which have an apical oxygen connected to a Sr atom.…”

“…As the majority of the NQR measurements is done at low temperature, where the crystal structure is orthorhombic, we repeated the calculations for the cluster models with an underlying orthorhombic lattice (a = 5.363 Å, b = 5.409 Å and c = 13.17 Å). If a dopant Sr is added to the orthorhombic cluster A, an increase of 9.1% in EFG at the copper site is obtained and an asymmetry η = 0.01, in agreement with experiment [12], which gives η ≤ 0.02 (by symmetry η = 0 for the tetragonal structure). For the orthorhombic cluster B O the optimized location for the apical oxygen near O(i) was found at x a = −0.452 Å, y a = −0.457 Å and z a = 2.26 Å (note the similarity to the equilibrium location as found for the tetragonal cluster).…”

“…In addition, there are some subtle differences between the NQR spectra of Sr-and O-doped samples, such as the asymmetry of the electric field gradient of the B lines, which are not explained by the above model. Thus the assignments of the secondary lines are still the issue of an ongoing debate [12] and the existence of localized holes is of importance in connection with the observation of charge stripe order in these compounds [13].…”