Nanocomposites and nanomaterials

Crystal structure and morphology of Ni-substituted lithium ferrites
Kaykan L.S.1, Mazurenko J.S.2
1 Vasyl Stefanyk Precarpathian National University, 57 Shevchenko str., 76018 Ivano-Frankivsk, Ukraine, e-mail: larysa.kaykan@gmail.com
2 Ivano-Frankivsk National Medical University, Halytska Str. 2, Ivano-Frankivsk, 76018, Ukraine.

We have modified the lithium iron spinel by replacing Ni with ions. It is shown that such substitution causes the transformation of spatial symmetry from  (ordered state) to  (disordered state). The reason for such a transformation is the interruption of ion interchanges  and  in a ratio of 1:3 in octahedral B-positions of a spinel lattice. 
In the case of replacement, Ni cations are distributed on both sub-lattices in the ratio 4:6 (4 - in tetra-sublattice) for all compositions. With increasing in the concentration of Ni2 + there is a gradual increase between cation distances, and in the B-sublattice the distance increases faster than in A.
An increase in the lattice constant observed with increasing concentrations of the substituent element can be explained as an increase in the size of the ion that replaces iron (Ni ions, which is confirmed by Vegard's rule), as the effect of distortion of the lattice due to the influence of the surface.
Studies of post synthesis annealing at temperatures from 573 K to 1023 K showed that annealing at temperatures below 773 K did not significantly affect the size of the particles. Intensive growth of particles is carried out at temperatures above 800K and the dependence of the size of crystallites on annealing temperature is exponential in nature. An additional phase detected in samples replaced by nickel ions remains in the system at all annealing temperatures.
Ultrasonic treatment does not affect the size of the CSR, but with a treatment duration of more than 2 hours, the agglomeration of particles is partially eliminated.