Neodymium sesquioxide, Nd₂O₃

Neodymium sesquioxide, or neodymia, Nd₂O₃, may be prepared by igniting the hydroxide, carbonate, nitrate, oxalate, etc. The oxide obtained by igniting the oxalate strongly has a pure sky-blue colour. It dissolves readily in acids.

As regards the existence of higher oxides of neodymium, the evidence is conflicting. Auer von Welsbach, Jones, and R. J. Meyer and Koss deny that a higher oxide may be prepared in the dry way, but Marc maintains that neodymia may be peroxidised in the presence of cerium and praseodymium. Waegner also affirms the existence of a higher oxide, Nd₄O₇, and even describes its reflection spectrum, but Joye and Gamier have shown that this spectrum is due to a hydrated oxide, Nd₂O₃.H₂O. Brauner states (without any details) that the oxides Nd₂O₄ and Nd₂O₅ both exist. By the latter Brauner presumably means a hydrated peroxide, Nd₂O₅.xH₂O or (OH)₂Nd^III.O.OH, corresponding to the known lanthanum and praseodymium peroxides. The same authority also mentions the existence of an acetate of the constitution (CH₃.CO)₂Nd^III.O.O.O.Nd^III(OH)(CO.CH₃) + H₂O, analogous to the praseodymium compound.