Fig. 2. (a) A 2 × 2 × 2 supercell of Na2O (Fm3̄m). (b) Supercell of the β-polymorph (Pmmn) that has undergone a unit cell transformation with new lattice vectors 
, 
and 
. (c) Unit cell of the α-polymorph (Pbca). (d) Partial view of a supercell of the γ-polymorph (Pbca), with 
and cut in half along the [001]-direction to include the eight face-centered cubes of the distorted O2−-sublattice.
