Structural evolution in the X‐ray amorphous precursors to La 2 Sn 2 O 7 and La 2 Ti 2 O 7 is examined using IR and Raman spectroscopy. These precursors are prepared by rapid coprecipitation from mixed aqueous solutions of the corresponding metal chlorides. Rapid coprecipitation from an SnCl 2− 6 and La 3+ ‐containing aqueous solution yields microcrystalline particles of SnO 2 · n H 2 O and La(OH) 3 , which instantaneously interconnect to form an ultimate, complex colloid particle. The Ti(OH) 2+ 2 and La 3+ in the other solution system coprecipitate into a different, complex colloid (an unidentified phase), which is definitely not a mixed dispersion of single‐component colloids. A comparative examination of the vibrational spectra of the coprecipitates heated to various temperatures indicates that the SnO 2 and anatase phases develop in the respective precursors before crystallization of the desired double oxides. Crystallization itself can be attributed to a solid‐state reaction among the various microcrystallites of each single‐metal oxide in a gel particle of the precursor.
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Takahashi et al. (1989) studied this question.
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