Tetravalent ions substitution in Cu-ferrite; structure formation and electrical properties

The structure and formation of the two systems of mixed ferrites Cu1+xGexFe2-2xO4 and Cu1+xTixFe2-2xO4 (where x = 0.0, 0.2, 0.3 and 0.4) were studied using X-ray diffraction (XRD) and IR absorption analysis. The X-ray analysis indicates that the samples of x = 0 (CuFe2O4) and x = 0.1 of Cu-Ti system were formed in tetragonal structure with lattice parameters a = 0.830 nm and c = 0.854 nm, respectively. All other samples of the two systems were formed in cubic symmetry with constant lattice parameter. For Cu-Ge ferrite the lattice parameter (a) equals 0.837 nm while if equals 0.840 nm for the system of Cu-Ti ferrite. The IR spectra were recorded in the range from 200 up to 1000 cm(-1). The spectra show two main absorption bands nu(1)* and nu(2)*. The band nu(1)* has a constant value 570 cm(-1) for the two systems. The position of nu(2)* is around 400 cm(-1) and slightly increasing with the increase of Ge or Ti content. It was found that the threshold energy corresponding to the threshold frequency for the Cu-Ge ferrite is about 0.103 eV, but for the Cu-Ti ferrite is bit lower, about 0.098 eV. The thermoelectrical power shows that CuFe2O4 and Cu1.1Ge0.1Fe1.8O4 behaves as an n-type semiconductor, but the other composition of the two systems of both ferrites behave as p-type semiconductor at around room temperature. Moreover, the conductivity depends on the concentration of both Ge4+ and Ti4+ ions and on their distribution among the sublattice. (C) 2000 Elsevier Science S.A. All rights reserved.