[en] We have studied high-pressure (2.3 kbar), high-temperature (575 degree C), oxygen-annealed ceramic La_1.84Sr_0.16CuO_4+δ by high-resolution neutron powder diffraction to determine its low-temperature structural properties in comparison to similarly oxygenated La₂CuO_4+δ. Unlike La₂CuO_4+δ, the Sr-containing superconductor shows no low-temperature phase separation. Further, the interstitial oxygen appears to be located at (1/4,1/4,z) with z=0.163(5) and to have a value of δ consistent with La_1.84Sr_0.16CuO_4.019. Such a site is significantly displaced away from the interstitial location, (1/4,1/4,z), with z=0.25, observed in La₂CuO_4+δ and La₂NiO_4+δ. The environment of such an interstitial site is suggestive of a smaller, neutral oxygen rather than a charged species