High‐Pressure Synthesis and Crystal Structure of Neodymium( III ) Oxide Peroxide, Nd2O2(O2)

The most oxygen‐rich compound so far reported for the system neodymiumoxygen was obtained by high‐pressure synthesis from Nd2O3/KO2 mixtures. Respite the composition NDO2, the X‐ray crystal structure analysis revealed at a neodymium(III) oxide peroxide and not a neodymium(iv) dioxide was present. Nd2O2(O2) is remarkably stable at normal pressure and only undergoes transformation to Nd2O3 at 420°C with loss of oxygen.