Oxygen ordering and phase separation inLa2CuO4+δ

Abstract

We present a detailed NMR study of the expected A and anomalous B Cu lines on a single crystal of ${\mathrm{La}}_2$ ${\mathrm{CuO}}_{4+\mathrm{\delta }}$. Our results in conjunction with those of neutron scattering and La NMR lead us to conclude that oxygen ordering occurs on a microscopic scale in this compound. The ordered interstitial oxygen gives rise to a distribution of tilts of the ${\mathrm{CuO}}_6$ octahedra in the B domains. A sawtooth modulation of the octahedral tilt, in which the sign of the tilt changes when the tilt reaches a maximum value, is deduced. In addition we show that macroscopic phase separation is inhibited in the tetragonal phase where the ${\mathrm{CuO}}_6$ octahedra are not tilted.