[en] A series of single phase W-type Sr_3-xCe_xFe₁₆O₂₇ (x=0, 0.02, 0.04, 0.06, 0.08, 0.10) hexagonal ferrites prepared by the Sol-Gel method was sintered at 1050 °C for 5 h. The X-ray diffraction analysis reveals that all the samples belong to the family of W-type hexagonal ferrites. The c/a ratio falls in the range of W-type hexagonal ferrites. The grain size was measured by SEM varies from 0.7684 to 0.4366 μm which shows that the Ce³⁺ substituted samples have smaller grain size than pure ferrite Sr₃Fe₁₆O₂₇ which results from the difference in ionic radii of Ce³⁺ (1.034 Å) and Sr²⁺ (1.12 Å). The room temperature resistivity of the present samples varies from 6.5×10⁸ to 272×10⁸ Ω-cm. The coercivity increases from 1370 to 1993 Oe which is consistent with the decrease in grain size. The coercivity values indicate that the present samples fall in the range of hard ferrites. The large value of H_c may be due to domain wall pinning at the grain boundaries.

[en] In this paper, the charge conduction mechanism at high temperature in Al-Gd_2O_3 (MIM) structure has been investigated by performing temperature-dependent current-voltage measurements in the temperature range 280-390 K. MIM structure is realized by electron beam evaporation system where thin films of Gd_2O_3 (40, 60 and 80 nm) and Al metal on both sides of dielectric film were deposited on glass substrate. The possibility of different transport mechanisms has been testified by plotting various graphs. The nonlinear behavior of LnV versus LnI and V"1"/"2 versus LnV/I graphs ruled out the possibility of space-charge-limited conduction (SCLC) and Poole-Frenkel mechanism in Al-Gd_2O_3-Al MIM structure. The straight lines LnI-V"1"/"2 graphs at various temperatures confirmed that Schottky emission is the dominant transport mechanism in Al-Gd_2O_3-Al structure. The calculated values of field barrier lowering coefficient at different measurement temperatures were in good agreement with the theoretical prediction confirming conduction is via Schottky emission. The field-dependent Ln(I/T"2) versus 1000/T plots were obeyed a linear relationship according to Schottky emission theory. Furthermore, the dielectric thickness dependence room-temperature current-voltage characteristics of Al-Gd_2O_3-Al MIM structure were showed strong dependence of current on dielectric film thickness according to Schottky emission theory of conduction current. (orig.)

[en] CoZn ferrite-SiO₂ composites having general formula (1 - x)Co_0.5Zn_0.5Fe₂O₄ + xSiO₂ with x = 0.0-0.8 were prepared by co-precipitation technique. The X-ray diffraction analysis of the composites reveals that they are bi-phase. Room temperature resistivity increases from 10⁵ to 10⁹ (Ω cm) from x = 0.0-0.8. This drastic increase in resistivity may be attributed to the presence of pores and the segregation of Si at grain boundaries. The Arrhenius plots of these samples show that resistivity decreases as the temperature increases indicating their semi conducting behavior. Arrhenius plots show a change of slope at particular temperature (except for x = 0.8) that may be attributed to their Curie temperature. It is observed that the activation energies are small in Para-region as compared to Ferri-region and is an indication of the hopping conduction mechanism. The variation of thermopower with temperature reveals that these samples are degenerate type semiconductors. The values of activation energies calculated from log μ_d vs. 1000/T are slightly lower than the values of activation energies obtained from Arrhenius plots. This suggests that the conduction phenomenon is due to polaron hopping