La_(0.7)Sr_(0.3)Cr_(0.4)Mn_(0.6)O_(3-δ) perovskite nanoparticles have been synthetized using an ethylene glycol modified solgel method and impregnated by Cu_(0.75)Ni_(0.25) nanoparticles. The phase transitions and nucleation kinetics were studied by time resolved x-ray diffraction, Rietveld, Raman spectroscopy and high resolution transmission electron microscopy. Findings have shown that, an atomic disorder dominates from room temperature to 400 °C. Nanoparticles with crystal size < 26 nm start through nuclei formation of La_(0.7)Sr_(0.3)Cr_(0.4)Mn_(0.6)O_(3-δ) and SrCrO_4 solid solutions with Pm3m cubic and P2_1/n monoclinic symmetry respectively in the range of 600–650 °C. Symmetry reduction from the Pm3m→R3c space group had been obtained at a lower temperature(750 °C) than those reported in the literature in oxygen atmosphere and it was confirmed by an octahedral distortion, which takes place in the crystallographic direction[221]/(122). The Johnson-Mehl-Avrami model had described the whole process, where the existence of two phases was shown before it reached its complete D_(3d)~6 point group symmetry. (0.7) Sr_ (0.3) Cr_ (0.4) Mn_ (0.6) O_ (3-δ) perovskite nanoparticles have been synthetized using an ethylene glycol modified solgel method and impregnated with Cu_ (0.75) Ni_ (0.25) nanoparticles. and nucleation kinetics were studied by time resolved x-ray diffraction, Rietveld, Raman spectroscopy and high resolution transmission electron microscopy. Findings have shown that an atomic disorder dominates from room temperature to 400 ° C. Nanoparticles with crystal size <26 nm start through nuclei formation of La 0.7 Sr 0.3 Cr 0.4 Mn 0.6 O 3-δ and SrCrO 4 solid solutions with Pm 3m cubic and P 2_1 / n monoclinic symmetry respectively in the range 600-650 ° C. Symmetry reduction from the Pm3m → R3c space group had been obtained at a lower temperature (750 ° C) than those reported in the literature in oxygen atmosphere and it was confirmed by octahedral distortion, which takes place in the crystallographic direction [221] / ( 122) The Johnson-Mehl-Avrami model had de scribed the whole process, where the existence of two phases was shown before it reached its complete D_ (3d) ~ 6 point group symmetry.