A solution combustion technique for the synthesis of different beta-alumina compositions in the Na2O center dot xAl(2)O(3) system (where x = 5, 6, or 7) is described along with the structural characterization of the materials prepared. The amorphous powder obtained after a combustion reaction between the nitrate salts of the cations and aminoacetic acid was calcined in air at different temperatures in the range from 600 degrees C up to 1300 degrees C. The phases were investigated by powder X-ray diffraction (XRD) and infrared spectroscopic measurements. A metastable mullite-like alumina phase was found to form as an intermediate at a minimum calcination temperature of 750 degrees C and stable up to 1000 degrees C, which transformed completely into beta/beta"-alumina phases beyond a temperature of 1100 degrees C. The crystal structure of the mullite-like alumina phase was deduced by rietveld refinement of slow scan powder XRD data. A better understanding of the crystal structure of the mullite-like alumina was possible using other supplementary experimental evidences.