V. N. Shut

Water-soluble ferroelectric crystals with inhomogeneous impurity distribution

Stabilization of the unipolar state via the formation of inhomogeneous impurity distribution in crystal bulk is considered. Possible growth of crystals with stable characteristics is demonstrated on triglycine sulfate (TGS) crystals with a regular inhomogeneous impurity distribution. The properties of TGS crystals with an inhomogeneous distribution of chromium ions grown above and below the Curie temperature TC are studied. Inhomogeneous TGS crystals of three types are obtained: type-I crystals with a smooth variation of the concentration gradient along the growth direction, type-II crystals with a periodic layer variation of the impurity concentration, and type-III crystals with a sawtooth-like variation of the impurity concentration along the sample length. The TGS crystals with the regular inhomogeneous impurity distribution in the ferroelectric phase are characterized by higher values of the internal bias field Eb, unipolarity coefficient k, and pyroelectric coefficient γ than the inhomogeneous crystals in the paraelectric phase and the crystals with the statistic impurity distribution grown by the conventional method.

Ferroelectrics with composition gradient: On the nature of hysteresis loop shift

Possible reasons of the difference in polarization characteristics of thin-film and bulk ferroelectrics with a composition gradient have been considered.

Polarization characteristics of graded thick Ba1 − xSrxTiO3 films

The barium strontium titanate ceramics Ba1 − xSrxTiO3 with a spatially variable composition has been prepared according to the thick film technology (tape casting). The strontium content over the film thickness is varied from 0 to 30 mol %. The structure and polarization characteristics of the samples prepared have been investigated. It has been found that the polarization characteristics of multilayer structures are determined by the ratio between the thicknesses of layers with different compositions and by their properties. No shift of the hysteresis loops in the graded thick Ba1 − xSrxTiO3 (x = 0–0.3) films has been revealed. The results obtained have been analyzed in the framework of modern theoretical approaches.

Ferroelectric properties of triglycine sulfate crystals with a nonuniform distribution of chromium impurities

The specific features of the ferroelectric behavior of triglycine sulfate crystals with a nonuniform distribution of chromium impurities are analyzed. It is demonstrated that the dielectric hysteresis loops of the samples exhibit large shifts both along the polarization and electric field directions. The results obtained are well explained within the phenomenological approach with due regard for the gradient term in the expansion of the free energy. It is established that the unipolarity coefficient and the pyroelectric signal of nonuniform crystals remain virtually unchanged in multiple heating-cooling cycles.

Formation of a regular domain structure in TGS–TGS + Cr crystals with a profile impurity distribution

A complex investigation of TGS–TGS + Cr crystals with a profile impurity distribution of chromium ions Cr3+ has been carried out at the macrolevel (measurement of dielectric properties by the method of nematic liquid crystals) and microlevel (domain structure according to atomic force microscopy data). It is established that periodic doped layers are formed only in individual growth pyramids in the regions where the polarization vector has a nonzero component along the normal to the growth faces rather than throughout the entire crystal volume. The domain configuration at the boundary of growth layers with different impurity compositions has been studied by piezoelectric force microscopy. The static unipolarity of layers with and without chromium impurity is approximately identical, whereas the domain-wall density in doped regions is higher than that in undoped ones by a factor of about 7.

Effect of a positive temperature coefficient of resistance in thin films of doped strontium-barium titanate

Thin films of doped semiconducting barium-strontium titanate (Ba,Sr)TiO3 are prepared by pulsed laser ablation. It is shown that the crystal structure, morphology, and electrical properties of (Ba,Sr)TiO3 thin films are determined primarily by the actual ablation conditions. The ablation regimes of deposition permitting preparation of uniform polycrystalline thin films with a composition close to that of the target and with grain sizes larger than 0.1 μm are established. These samples have a positive temperature coefficient of resistance in the phase transition region. The change in the resistivity can be as much as 100%.

Crystal structure and magnetic properties of (Ni1–xZnx)Fe2O4 composition graded ceramic

A homogeneous multilayered graded (Ni1–xZnx)Fe2O4 (x = 0–0.2) ferrite-based ceramic is prepared via thick-film technology using the two-stage sintering mode. The unit cell parameters and main magnetic characteristics, such as the Curie temperature, specific magnetization, and magnetic susceptibility are determined; the magnetic hysteresis loops are studied. The temperature and field dependences of specific magnetization and magnetic susceptibility are analyzed. The increasing zinc content in ceramic is shown to favor a rise in the specific magnetization from 45.30 to 70.95 A m2 kg–1 at room temperature and in the magnetic moment from 2.09 to 3.48 μB near the liquid nitrogen temperature. The augmentation of the unit cell parameter a by ~0.8% causes the attenuation of magnetic interplay between the cations and a decrease in the Curie temperature from 790 to 720 K. The magnetization in multilayered structures is examined under the external magnetic field applied parallel and perpendicular to the layer plain. No magnetic hysteresis loop shift is found in the different geometries of the experiment, and the probable causes of its lack are analyzed in the bulk magnetic composition graded materials.

Crystal structure and magnetic properties of (Ni1–x Zn x )Fe2O4 composition graded ceramic

A homogeneous multilayered graded (Ni1–xZnx)Fe2O4 (x = 0–0.2) ferrite-based ceramic is prepared via thick-film technology using the two-stage sintering mode. The unit cell parameters and main magnetic characteristics, such as the Curie temperature, specific magnetization, and magnetic susceptibility are determined; the magnetic hysteresis loops are studied. The temperature and field dependences of specific magnetization and magnetic susceptibility are analyzed. The increasing zinc content in ceramic is shown to favor a rise in the specific magnetization from 45.30 to 70.95 A m2 kg–1 at room temperature and in the magnetic moment from 2.09 to 3.48 μB near the liquid nitrogen temperature. The augmentation of the unit cell parameter a by ~0.8% causes the attenuation of magnetic interplay between the cations and a decrease in the Curie temperature from 790 to 720 K. The magnetization in multilayered structures is examined under the external magnetic field applied parallel and perpendicular to the layer plain. No magnetic hysteresis loop shift is found in the different geometries of the experiment, and the probable causes of its lack are analyzed in the bulk magnetic composition graded materials.

Crystal structure and magnetic properties of (Ni 1– x Zn x )Fe 2 O 4 composition graded ceramic

A homogeneous multilayered graded (Ni1–xZnx)Fe2O4 (x = 0–0.2) ferrite-based ceramic is prepared via thick-film technology using the two-stage sintering mode. The unit cell parameters and main magnetic characteristics, such as the Curie temperature, specific magnetization, and magnetic susceptibility are determined; the magnetic hysteresis loops are studied. The temperature and field dependences of specific magnetization and magnetic susceptibility are analyzed. The increasing zinc content in ceramic is shown to favor a rise in the specific magnetization from 45.30 to 70.95 A m2 kg–1 at room temperature and in the magnetic moment from 2.09 to 3.48 μB near the liquid nitrogen temperature. The augmentation of the unit cell parameter a by ~0.8% causes the attenuation of magnetic interplay between the cations and a decrease in the Curie temperature from 790 to 720 K. The magnetization in multilayered structures is examined under the external magnetic field applied parallel and perpendicular to the layer plain. No magnetic hysteresis loop shift is found in the different geometries of the experiment, and the probable causes of its lack are analyzed in the bulk magnetic composition graded materials.

Domain structure and properties of triglycine sulfate crystals with profile D,L-α- and L-α-alanine-doped layers

A complex investigation of the domain structure and dielectric properties of triglycine sulfate (TGS) crystals containing profile layers doped with D,L-α-alanine (DLATGS) and L-α-alanine (LATGS) impurities is carried out. The images of the DLATGS and LATGS layers and ferroelectric domains are obtained by piezoelectric force microscopy; the parameters of the domain structure and the degree of unipolarity are determined. It is established that DLATGS layers are multidomain and LATGS stripes are mainly single-domain. The experimental data on the macroscopic dielectric properties of the crystals are compared with the results of a microscopic analysis of the domain structure.