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Ultrafine La0.7Sr0.3MnO3 powders were prepared via homogenization in chelate solutions, followed by the calcination of solid precursors at 700°C in air or oxygen, and their phase composition and average par- ficle size were determined. The solid precursors were obtained from a solution of polynuclear La, Sr, and Mn chelates (diethylenetriaminepentaacetates) by three procedures: (1) gelation of the solution, followed by air drying of the resultant gel; (2) gelation followed by microwave dehydration; and (3) microwave dehydration of the solution. The results demonstrate that the way in which the chelate solution is converted into solid foams has little effect on the phase composition and particle size of the powders. At the same time, the phase composition and particle size of the reaction products depend on the calcination atmosphere (air or oxygen). Calcination in oxygen (700°C, 10 h) ensures the preparation of phase-pure La0.7Sr0.3MnO3 powders, with an average particle size of ... 30 nm, from the three precursors. [ABSTRACT FROM AUTHOR]