Terbium peroxide, Tb₄O₇

Terbium peroxide, Tb₄O₇, is produced by calcining the terbium salts of volatile acids in air. Prepared by the ignition of the oxalate in a muffle furnace, it is a dark brown powder, but when obtained from the sulphate at a white heat it is black. The strongly calcined peroxide is not attacked by cold mineral acids and is only slowly acted upon by hot, dilute acids.

Owing to the ready formation of this peroxide and its intense colouring power, the presence of even traces of terbia in europia, gadolinia, dysprosia, and yttria is easily detected.

Terbium may be estimated quantitatively by igniting the oxalate and weighing the residual peroxide.