Bushkova V. Sol-gel synthesis, structure and properties of substituted nickel ferrites.

The complex studies of the influence of the synthesis conditions by the sol-gel autocombustion (SGA)-method with the use of citric acid on the structure, morphology and properties of nickel ferrite nanopowders are carried out in the thesis. The influence of substitution Cr3+, Cd2+, Co2+ ions and annealing temperature on the structure, mechanical properties of NiFe2O4 ferrite as well as the Curie temperature and the parameters of magnetic hysteresis loops of coils with nickel-chromium, nickel-cadmium and nickel-cobalt ferrite cores.It is established that during annealing of synthesized powders of SGA-ferrites using citric acid in the temperature range of 300 – 900 K, the particle size increases by not more than 15% of their initial sizes, and in the temperature range 900 – 1400 K their size increases to 80 nm. For compressed and sintered at  1570 K for 5 hours substituted nickel ferrite nanopowders, a conductivity type is established. The substitution by Cr3+, Cd2+ and Co2+ ions leading to an increase in Hall mobility at room temperature. Two temperature intervals with different activation energies and conduction mechanisms are detected, respectively. It is established that small-grain ferrites synthesized by the SGA-method and annealed at  1570 K have an order of magnitude higher microhardness than their analogues obtained by the ceramic method at the same temperature. It is established, the mechanisms of destruction of annealed ferrites depending on the type of substitution ions. SGA- method allows to obtain coils with ferrite cores, which are magnetized to a state of technical saturation at much lower, in the ceramic way obtained their analogs, fields. The specific saturation magnetization and coercive force depend on the size of the crystallites of the ferrite, in particular from the state of their surface.