SYNTHESIS AND CHARACTERIZATION OF SOL-GEL DERIVED LANTHANUM HEXALUMINATE POWDERS AND FILMS

Powders and thin films of high-yield lanthanum hexaluminate (LaAl11O18 ) were prepared by a sol-gel route and compared with yields obtained b y conventional hot-pressing of oxide powders. X-ray diffraction and tr ansmission electron microscopy (TEM) were used to characterize powders and thin films deposited on TEM grids. While the solid-state kinetics of formation of LaAl11O18 are known to be extremely sluggish, the yie ld of LaAl11O18 formed by the sol-gel route was much higher than that obtained by processing under similar conditions by solid-state reactio n of elemental oxides. The development of a very fine grained microstr ucture at 1200-degrees-C and a coarser, much more mature microstructur e at 1450-degrees-C, with strong texturing of the magnetoplumbite phas e, was observed by TEM. Isolated grains of LaAlO3 were present in all powders and films. Trace impurities, introduced most likely as impurit ies in the initital alumina sol, appear to have segregated to both the grain boundaries and to the external surfaces of grains in as-prepare d films.