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 ferroelectric and magnetic phase transitions in a-site and b-site substituted multiferroic PbFe0.5Nb0.5O3
In the present study, we diluted either A- or B- sublattice of perovskite multiferroic PbFe0.5Nb0.5O3 (PFN) and studied the changes of the magnetic and ferroelectric phase transition temperatures and dielectric properties caused by such dilution. Dielectric studies of PFN single crystals show that, in contrast to the commonly adopted view, the ferroelectric phase transition in PFN is non-diffused and the relaxor-like behavior usually observed in ceramic samples has an extrinsic nature. A-site substitutions (Ba, Ca) lead to the smearing of the permittivity-temperature maximum, lowering its maximum temperature, Tm and inducing relaxor behavior. B-site diluting of PFN by Ti increases Tm and only slightly affects the permittivity maximum diffuseness. Both A-site and B-site substitutions in PFN lead to lowering of its Neel temperature, TN. However, above a certain compositional threshold, fast lowering of TN stops and a new magnetic state with comparatively high (~50K) transition temperature becomes stable in a rather wide compositional range.
Tuning the multiferroic properties of Pb(Fe1/2Nb1/2)O3 by cationic substitution
Abstract A series of substituted lead iron niobate compounds with the general formula Pb 2+ (1− x ) A Z x (Fe {(1−(2− Z ) x )/2} Nb {(1+(2− Z ) x )/2} )O 3 (0 x 3+ , K + or Sr 2+ ) were prepared by a modified solid-state synthesis. The relative concentrations of Fe 3+ and Nb 5+ were adjusted to compensate the charge imbalance due to the aliovalent substitution. The dielectric constant and magnetic susceptibilities were studied as a function of temperature. The temperature of the dielectric maximum, T M , of the substituted compounds decreased linearly with increasing concentration of the substituent ions. The magnetic measurements showed an antiferromagnetic transition at temperatures T N1 due to the superexchange interactions mediated by Fe–O–Fe and an additional antiferromagnetic-type transition at T N2 . T N1 linearly increased with the increasing concentration of Fe 3+ ion at the B-site of ABO 3 -type substituted compounds. T M is shown to be directly dependent on the concentration of the ferroactive Nb 5+ ions at the B-site and Pb 2+ ions at the A-site.