The compound can be prepared by burning ionite in air, on which ions of trivalent californium are sorbed, at a temperature of 1400 °C.
It can also be obtained by β-decay of berkelium(III) oxide.
[citation needed] Californium(III) oxide forms a yellow-green solid with a melting point of 1750 °C and exists in three modifications.
[2] The body-centered cubic modification forms a crystal lattice with a = 1083.9 ± 0.4 pm.
The transition temperature between body-centered cubic and monoclinic structures is about 1400 °C.