The Effect of Mechanical Activation on the Synthesis and Properties of Multiferroic Lead Iron Niobate
The present work studies the effect of high-energy mechanical activation using the planetary-centrifugal ball mill AGO-2 and subsequent annealing on the synthesis and magnetic properties of PbFe0.5Nb0.5O3 (PFN). This technique enables one to perform the mechanically activated synthesis of PFN at much shorter time. The results of X-ray phase analysis, electron microscopic studies and transmission Mossbauer 57Fe spectra measurement are presented and discussed. Mossbauer studies show that the temperature of magnetic phase transition in PbFe0.5Nb0.5O3 powders can be changed by mechanical activation and subsequent annealing.
Dielectric and Mossbauer Studies of Perovskite Multiferroics
Mossbauer spectra studies were used to determine the temperatures of magnetic phase transitions in some Fe-containing perovskite multiferroics and their solid solutions. In compositionally disordered materials the temperature TN of antiferromagnetic phase transition depends linearly on Fe3+ content. Partial ordering of Fe3+ and B5+ cations in Pb(Fe1/2B1/2)O3 (B = Nb, Ta) ternary perovskites decreases TN by more than 50 K. At the same time the temperature T m of dielectric permittivity maximum remains unchanged for Pb(Fe1/2Nb1/2)O3 and increases for Pb(Fe1/2Ta1/2)O3. These results are in line with existing theoretical models of B-cation ordering effect on TN and T m values in PbB3+ 1/2B5+ 1/2O3 perovskites.
Modeling of chemical reactors—XXIX mixing-cell model for packed bed reactors. Steady state considerations. Problems of multiplicity
Abstract The axial heat and mass transfer in tubular catalytic reactors may be described by mixing-cell model and diffusion model as well. The diffusion description yields for a strong exothermic reaction and adiabatic conditions three steady state profiles, on the other hand the mixing-cell model gives rise to more than three steady states. A simple numerical and graphical analysis for mixing-cell model is presented.