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Low-temperature chemical synthesis of lanthanum monoaluminate

1997-01-01
Taspinar, E
Tas, AC
One of the promising candidates for ferroelectric substrate materials, lanthanum monoaluminate (LaAlO3), was successfully synthesized by two separate chemical powder preparation techniques: (i) homogeneous precipitation from aqueous solutions containing urea (CH4N2O) in the presence of nitrate salts, and (ii) self-propagating combustion synthesis from aqueous solutions containing CH4N2O and the respective nitrate salts of lanthanum and aluminum. The submicrometer, spherical-like particles of the precursors were completely converted to pure LaAlO3 at 850 degrees C in the homogeneous precipitation route, and the same conversion temperature was observed to be 750 degrees C, which becomes the lowest temperature ever reported for the powder synthesis of a pure LaAlO3 phase. The materials were characterized by powder X-ray diffractometry, simultaneous thermogravimetric/differential thermal analysis, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. Structural refinements by Rietveld analysis showed that LaAlO3 was isostructural with BaTbO3 and had the space group R-3c, in contrast to the previously assumed space group of R-3m for this phase. The atomic positions in the structure of LaAlO3 were refined and presented for the first time, with respect to the present space group.