Evolution of crystalline aluminates from hybrid gel-derived precursors studied by XRD and multinuclear solid state MAS NMR: III. Lanthanum hexaluminate, LaAl11O18

Abstract A hybrid gel synthesis is described which produces crystalline lanthanum hexaluminate at 1200°C without the intermediate appearance of LaAlO 3 . XRD in conjunction with 27 Al and 139 La MAS NMR indicates that until the exothermic appearance of γ-alumina at about 900°C, the gel remains amorphous and contains Al in three types of site, one of which is characterised by an NMR resonance at 36 ppm. By 1200°C, the La ions have moved into the mirror planes between the γ-alumina blocks and the crystallinity of the LaAl 11 O 18 which forms in an exothermic event at about this temperature continues to improve with further heating to 1350°C.