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 Fe 3 O 4 /γ-Fe 2 O 3 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 Cu 0.6 Fe 2.4 O 4 was calculated. Mössbauer 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 Fe 2+ , Fe 3+ and Cu 2+ cations in the spinel structures. The magnetic measurements also confirmed that there is no Cu incorporation into the electrospun hematite.