High Dielectric Permittivity in AFe1/2_{1 / 2}B1/2_{1 / 2}O3_{3} Nonferroelectric Perovskite Ceramics (A - Ba, Sr, Ca; B - Nb, Ta, Sb)

AFe$_{1 / 2}$B$_{1 / 2}$O$_{3}$(A- Ba, Sr, Ca; B-Nb, Ta, Sb) ceramics were synthesized and temperature dependencies of the dielectric permittivity were measured at different frequencies. The experimental data obtained show very high values of the dielectric permittivity in a wide temperature interval that is inherent to so-called high-k materials. The analyses of these data establish a Maxwell-Wagner mechanism as a main source for the phenomenon observed.Comment: 6 pages, 7 figure

New, Lead Free, Perovskites With a Diffuse Phase Transition: NaNbO_{3} ~ Solid Solutions

Some of (1-x)NaNbO_3-(x)ABO_3 perovskite solid solutions exhibit a dramatic diffusion of the dielectric permittivity epsilon' maximum and relaxor-type behavior when the second component concentration exceeds a threshold value x_0. The concentration phase transition to the relaxor-like phase is abrupt (of the first order kind) that is seen from the step in the dependence of the epsilon'(T) maximum temperature, T_m, on x. The precursor of this transition is a giant (up to 100 K) temperature hysteresis of epsilon'(T). Some relaxor-like properties appear even at x < x_0 in the course of cooling while disappear in the course of heating. The experimental data obtained are qualitatively described within a Landau-type phenomenological approach, assuming the relaxor-type behavior to be local stress-induced.Comment: 5 figure

Diffusive phase transitions in ferroelectrics and antiferroelectrics

In this paper, we present a microscopic model for heterogeneous ferroelectric and an order parameter for relaxor phase. We write a Landau theory based on this model and its application to ferroelectric PbFe$_{1/2}$Ta$_{1/2}$O$_3$ (PFT) and antiferroelectric NaNbO$_3$:Gd. We later discuss the coupling between soft mode and domain walls, soft mode and quasi-local vibration and resulting susceptibility function.Comment: 6 pages, Fundamental physics of ferroelectrics 200

Condensation of the atomic relaxation vibrations in lead-magnesium-niobate at T=T∗T=T^*

We present neutron diffraction, dielectric permittivity and photoconductivity measurements, evidencing that lead-magnesium niobate experiences a diffuse phase transformation between the spherical glass and quadrupole glass phases, in the temperature interval between 400 K and 500 K, with the quadrupole phase possessing extremely high magnitudes of dielectric permittivity. Our analysis shows that the integral diffuse scattering intensity may serve as an order parameter for this transformation. Our experimental dielectric permittivity data support this choice. These data are important for the aplications desiring giant dielectric responses, in a wide temperature intervals and not related to electron's excitations.Comment: 6 figure

Nontrivial dependence of dielectric stiffness and SHG on dc bias in relaxors and dipole glasses

Dielectric permittivity and Second Harmonic Generation (SHG) studies in the field-cooled mode show a linear dependence of dielectric stiffness (inverse dielectric permittivity) on dc bias in PMN-PT crystals and SHG intensity in KTaO$_{3}$:Li at small Li concentrations. We explain this unusual result in the framework of a theory of transverse, hydrodynamic-type, instability of local polarization.Comment: 5 figure