Synthesis of metastable perovskite-type YMnO3 and HoMnO3

Metastable, orthorhombic YMnO3 and HoMnO3 with the perovskite-type structure have been prepared by a solution-based procedure via complexation by citrates. The crystallization process has been investigated to obtain knowledge about what happens and how to control the process. Powder X-ray diffraction, thermoanalytical, and magnetic susceptibility data have been recorded for characterization of the reaction products. The oxygen partial pressure during crystallization seems to be the parameter which largely controls the yield of the metastable modification of YMnO3 and HoMnO3. The inorganic precursor appears to consist of an oxide carbonate just prior to the crystallization, however, with manganese in an average oxidation state higher than 3. The crystallization does not occur during the decomposition stage unless a parallel reduction takes place. Cation-deficient o-Y1-uMn1-vO3 and Ho1-uMn1-vO3 may be formed as intermediates and enhance the amount of the o-modification in an oxidizing atmosphere. (C) 1997 Academic Press.