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Highlights: [•] The synthesis method of the metal chromites embedded in silica is original. [•] The redox reaction between PVA and the metal nitrates leads to metal carboxylate precursors inside silica matrix. [•] By a thermal decomposition of these precursors MCr2O4/SiO2 nanocomposites are obtained at 600°C. [•] All chromites have been obtained as nanoparticles homogeneously distributed in the silica matrix. [ABSTRACT FROM AUTHOR]

Nanocomposites of the type 30 % CuFeO/70 % SiO were synthesized using the modified sol-gel method starting from tetraethylorthosilicate, metal nitrates (Fe(NO)·9HO, Cu(NO)·3HO) and the diol: 1,3-propane diol. The obtained hybrid gel, which contains within the pores, the metal nitrates and diol, was thermally treated at 140 °C, when the redox reaction between metal nitrates and 1,3-propane diol takes place forming Cu(II)-Fe(III) carboxylate compounds of malonate type. The thermal decomposition of the carboxylates within the gels pores, at ~300 °C, leads to simple or mixed metal oxides, uniformly distributed within the amorphous silica matrix. The spinel system CuFeO/SiO was obtained starting with 700 °C. The evolution of the spinel phase with the annealing temperature was investigated and resulted that at 1,000 °C, the matrix crystallizes into cristobalite and quartz. The formation of bulk CuFeO, starting from the same type of Cu(II)-Fe(III) carboxylate compounds was also investigated. A comparison between the thermal evolution of bulk CuFeO and CuFeO/SiO starting from Cu(II)-Fe(III) carboxylate compounds was made. The magnetic behavior of the ferrite nanocrystallites depending on the annealing temperature was also investigated. [ABSTRACT FROM AUTHOR]