Composition, Microstructure, and Electrical Properties Control of the Powders Synthesized by Sol-Gel Auto-Combustion Method Using Citric Acid as the Fuel.

Nanocrystalline lithium ferrite Li 0.5 Fe 1.7 Mg 0.8 O 4 powders were synthesized by the sol-gel auto-combustion method from the corresponding metal nitrates using citric acid as fuel.The results from XRD, SEM, and AC electrical conductivity studies are summarized as follows: The results of XRD analysis showed that all the samples were formed in single-phase cubic spinel structure at different annealing temperatures from 300 to 700 °C for 2 h. The lattice parameter was found to decrease on increasing the temperature. The microstructure of lithium ferrite powders was temperature dependent. The particle size was increased with the annealing temperature. AC electrical properties were investigated using the super-linear power law and activation energies were calculated for all compositions. The electron mobility in Li 0.5 Fe 1.7 Mg 0.8 O 4 samples ranged from 0.05 to 0.29 eV, which clearly indicated that the present lithium ferrites have semiconductor-like behavior. The frequency exponent "s" of lithium ferrite lies in the range 0.5 < s < 1, which confirms the electron hopping between Fe 2 + and Fe 3 + ions.

Thermochemically activated carbon as an electrode material for supercapacitors.

The results of electrochemical studies of nanoporous carbon as electrode material for electrochemical capacitors (EC) are presented in this work. Nanoporous carbon material (NCM) was obtained from the raw materials of plant origin by carbonization and subsequent activation in potassium hydroxide. It is established that there is an optimal ratio of 1:1 between content of KOH and carbon material at chemical activation, while the maximum specific capacity of NCM is 180 F/g. An equivalent electrical circuit, which allows modeling of the impedance spectra in the frequency range of 10(-2) to 10(5) Hz, is proposed, and a physical interpretation of each element of the electrical circuit is presented.

SAXS investigation of nanoporous structure of thermal-modified carbon materials.

The article investigates the effect of thermal modification of porous carbon material (PCM), obtained from plant feedstock, on its morphology and fractal structure by small-angle X-ray scattering (SAXS) method. The analysis of the scattering intensity curves serve the basis for calculating the parameters of the PCM porous structure: the Porod constant, the Porod invariant, average pore radius, specific surface area, and mass and surface fractal dimensions. It has been found out that the PCMs obtained have fractal structure, formed from mass and surface fractals, the sizes of which increase at the growth of temperature and modification time. PACS: 81.05.Uw; 61.05.cf; 82.47.Aa.