[𝐶𝑎 24 𝐴𝑙 28 𝑂 64 ] 4+ (4𝑒 -) often written as ( 𝐶12𝐴17: 𝑒 -). This material can be considered a zero-dimensional 0D electride, as the anion electrons are trapped in a cavity in the crystal structure. There are also 1D electrides, where anion electrons are confined in a channel of the structure and 2D electrides, in which anion electrons reside as layers.