Low-temperature synthesis and properties of LaMnO/sub 3+or-d/ and La/sub 0.67/R/sub 0.33/MnO/sub 3+or-d/ (R=Ca, Sr, Ba) from citrate precursors

LaMn/sub 1-y//sup 3+/Mn/sub y//sup 4+/O/sub 3+or-d/ and La/sub 0.67/R/sub 0.33/Mn/sub 1-y//sup 3+/Mn/sub y//sup 4+/O/sub 3+or-d/ (R=Ca, Sr, Ba) phases were synthesized at 350 degrees C by using very reactive, amorphous precursors obtained from the stoichiometric citrate solutions. The chemical process was optimized with respect to the solution concentration, pH, and additives. The precursor reactions were investigated as a function of the cation stoichiometry and the additive by simultaneous thermal and thermogravimetric analysis and X-ray diffraction. The reaction pathway was found to be independent of the cation stoichiometry, but related to the acid or base additive. The annealing temperature was systematically increased in the 350-1200 degrees C interval and the La/sub 0.67/Sr/sub 0.33/MnO/sub 3+or-d/ properties (i.e., crystal sizes, Mn average valence, Curie temperature, magnetization, magnetic susceptibility) were measured and found to vary consistently as a function of it.