Yurchenko L. Investigation of defect structure of ferroelectric materials with perovskite structure by electron paramagnetic resonance method

Electron paramagnetic resonance (EPR) of Mn2+ ions has been used as a probe of local static and dynamic lattice distortions in the relaxor ferroelectric PbMg1/3Nb2/3O3 (PMN) and solid solutions PMN-PbTiO3 at temperatures from 290 to 800 K. We reveal the regions with reorientable polar nanoregions responsible for the dielectric relaxation in PMN. We have determined parameters of the Vogel-Fulcher law and fraction of polar nanoregions in PMN. An addition of PbTiO3 to PMN decreases total volume of the polar nanoregions and suppresses their reorientational dynamics. Ferromagnetic spin-wave resonance has been observed in BiFeO3 nanoparticles with a sizes 110 nm and 30 nm. It is shown that size effect allows for ferromagnetism. The theoretical modeling of the magnetoelectric (ME) effect in nanograined ceramics of multiferroic-perovskites is carried out. We consider ferromagnetic ferroelectrics Pb(FeМ2)x(ZrTi)1-хO3 (М = Ta, Nb). It is shown that the coefficient of ME effect can increase by 1-3 orders due to size effects in nanoceramics. Room temperature measurements of EPR spectra were performed on BaTiO3 ferroelectrics doped either by Ce or by Nb and Sr with Mn as a probe. The mutual influence of Ce, Mn, Sr and Nb impurities, their charges and position in the lattice on the PTCR effect is discussed. EPR spectra were studied in SrTiO3:Cr crystalline nanopowders, obtained by different methods. It was found that paramagnetic ions are present inside and on the surface of powders, and there is a correlation between O-, O2- spectra and synthesis conditions and particles size. The nature of intrinsic and impurity point defects in lead zirconate titanate (PZT) ceramics has been explored. It was shown that Fe, Pb and Ti concentrations influence on electrophysical parameters of the piezoceramics due to the change of polar distortion. Using EPR several impurity sites have been identified in the materials. It was shown that ion doping by Fe3+ and Ni3+ influence on the formation of an additional phases of magnetoplumbite in PZT