γ-alumina $(\gamma -{\mathrm{Al}}_2{\mathrm{O}}_3)$ derived from boehmite has historically been described as having a cubic spinel structure with $\mathrm{Fd}3\mathrm{}¯m$ symmetry, despite reports of tetragonal distortion in the structure. Based on neutron diffraction, transmission electron microscopy, and magic angle spinning NMR data, we propose a tetragonal model for the structure of boehmite-derived $\gamma -{\mathrm{Al}}_2{\mathrm{O}}_3$ with ${I4\mathrm{}}_1/amd$ space group symmetry, a maximal subgroup of $\mathrm{Fd}3\mathrm{}¯m.\mathrm{}$ It is also demonstrated that an accurate average structural model cannot be achieved if the cations are restricted to spinel positions.

• Received 10 March 2003

DOI:https://doi.org/10.1103/PhysRevB.68.144110