Microstructural and magnetic properties of electrospun hematite/cuprospinel composites

Phase composition, microstructural and magnetic properties of electrospun hematite/cuprospinel composites were investigated. Samples were synthesized starting with 0 to 10 mol% of copper relative to iron. The round shape of reference electrospun fibres was preserved upon their heating up to 600 °C in air, whereas at 700 °C hollow substructure was additionally formed. In these reference samples the presence of hematite phase was detected by XRPD. A small amount (traces) of Fe3O4/γ-Fe2O3 was also found, due to the reduction conditions created during the burning of the polyvinylpyrrolidone matrix. Rietveld analysis of samples containing 10 mol% copper and produced at 500 °C and 700 °C did not show the tendency to form solid solutions between hematite and Cu cations. Electrospun fibres containing 10 mol% copper after heating at 500 °C consisted of magnetite and cubic cuprospinel as the dominant phases and hematite as the associated phase. Upon heating at 700 °C the phase composition showed the presence of hematite as the dominant phase and tetragonal cuprospinel as the associated phase. For this tetragonal cuprospinel the formula Cu0.6Fe2.4O4 was calculated. Mossbauer spectra recorded at 20 °C and at liquid helium temperature also showed the presence of hematite and spinel structures. Measured hyperfine magnetic splitting reflected the distributions of Fe2+, Fe3+ and Cu2+ cations in the spinel structures. The magnetic measurements also confirmed that there is no Cu incorporation into the electrospun hematite.