| 摘要 |
An improved method is proposed for the preparation of a powder of rare earth oxide of which the particles have a predominantly polyhedral configuration with a relatively large particle size to be suitable, for example, as a host of phosphors. The method comprises the steps of (a) precipitating a rare earth ammonium oxalate by the admixture of an aqueous solution of a rare earth salt and ammonium oxalate, (b) separating the precipitates from the aqueous medium, (c) washing the same with deionized water to be freed from electrolytes, (d) dispersing and keeping the precipitates in a hot water bath at 50 DEG C. or higher for at least 15 minutes, (e) collecting the precipitates and (f) calcining the precipitates of the rare earth ammonium oxalate into oxide. It is essential that the steps (a) to (c) are conducted at a temperature of 40 DEG C. or below or, preferably, 30 DEG C. or below. The thus obtained precipitates of rare earth ammonium oxalate has a unique crystallographic structure not reported in any literatures, which, however, is a metastable phase gradually transformed into the known crystallographic structure.
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