Location of the oxygen dopant in the high temperature superconductor HgBa2CuO4+δ from 199Hg NMR

•Oxygen is the primary dopant that leads to superconductivity in HgBa2CuO4+δ.•A technique for oxygen isotope exchange and annealing to change doping is described.•The concentration of dopant oxygen is determined through nuclear magnetic resonance.•Results imply that dopant oxygen atoms are randomly distributed in this cuprate. In the high temperature cuprate superconductor, HgBa2CuO4+δ, it has been determined that the dopant oxygen, Oδ, resides in the Hg-plane. Here we present a systematic investigation of the 199Hg NMR spectrum as a function of dopant oxygen concentration, δ. At high doping levels we observe four distinct 199Hg resonance peaks which follow a binomial distribution in δ corresponding to zero, one, two, and three nearest neighbor Oδ atoms. Additionally, we have measured a linear dependence of the peak frequencies on doping and suggest that these measurements might be theoretically amenable.