V. A. Alyoshin

Soft Mode in Heteroepitaxial (Ba, Sr)TiO3MgO Thin Films

Polarized Raman spectra of tetragonally distorted (Ba 1-x Sr,)TiO 3 /MgO ferroelectric films were obtained in special scattering geometries using a micro-Raman set-up. The underdamped E(TO) soft mode was unambiguously observed in the films with x = 0.30 and 0.45. The low-temperature behaviour of the E(TO) soft mode for x = 0.45 was found substantially different from those observed in pure crystals and bulk solid solutions.

Influence of the growth mechanism and thermoelastic stresses on the lattice dynamics of heteroepitaxial films of barium strontium titanate

Heteroepitaxial thin films of Ba0.7Sr0.3TiO3 (BST-0.3) solid solutions were grown on single-crystal (001) MgO substrates by high-frequency cathode sputtering of a stoichiometric ceramic target. The parameters of the tetragonal unit cell of a film were determined by x-ray diffraction methods, and the temperature dependence of the parameter c was studied depending on the synthesis conditions in the temperature range 293–520 K. An E(TO) soft mode was observed in the Raman spectra, the frequency of which correlates with two-dimensional stresses arising in films. It is shown that the two-dimensional stresses in a film are controlled not only by the film-substrate lattice constant mismatch and the difference of their thermal expansion coefficients but also are significantly dependent on the heteroepitaxial growth mechanism. It is shown that the phase transition to the tetragonal paraelectric phase during film heating occurs irrespective of the growth mechanism.

Heteroepitaxial films of (Ba,Sr)TiO3

Abstract Experimental data about certain peculiarities of ferroelectric phase transition revealed by the temperature dependences of unit cell parameters and domain structure specificity are presented.

Domain structure of heteroepitaxial ferroelectric films

Domain structure of heteroepitaxial films of (Ba, Sr)TiO3 and PbTiO3 was studied. A correlation between etch-pattern contrast and magnitude of microscopic strains has been established.

The transition layer in polycrystalline PZT films

Abstract The transition nonferroelectric layer with pyrochlore-type structure forming at the initial film growth step was found to exist in as-grown polycrystalline PZT thin films.

Phase transition and domain structure of heteroepitaxial PbTiO3/(001) MgO films

Abstract Heteroepitaxial PbTiO3 films were studied by X-ray diffraction and electron microscopy methods. A model allowing to predict the type of domain structure that forms as a result of the film-substrate mechanical interaction and to determine the c − and a-domain concentrations is suggested.

Secondary discontinuous recrystallization as a manifestation of the effect of self-organization in niobate ferroelectric ceramics

The use of a synergetic approach in interpreting the results of experimental investigations of micro-structure of ferroelectric ceramics based on niobates of alkali metals is discussed. The observed effect of a secondary discontinuous recrystallization is considered in terms of self-organization. It was established that by varying technological conditions one could eliminate this phenomenon from the process of recrystallization of the niobate ferroelectric ceramics and, thereby, improve their properties.

Relaxor-Like behaviour of thin ferroelectric films with imperfect crystal structure

Abstract Structural aspects of phase transitions in thin ferroelectric films of (Ba, Sr)TiO3 and PbTiO3 were studied by XRD and Raman spectroscopy, with respect to crystal structure perfection. With decreasing crystal structure perfection, numerically estimated by the microstrain value, films acquired features typical of ferroelectrics-relaxors: instead of abrupt phase transition characteristic of bulk material and films where perfect structure, imperfect films demonstrated smeared transition to a macroscopically cubic phase with some film micro-volumes remained polar far above the transition temperature. It is proposed that relaxor-like features are determined by the relationship between the degree of distortion of the crystal lattice in the polar phase and by the crystal structure imperfection, respectively.

Domain structure of (Ba, Sr)TiO3 heteroepitaxial films

Abstract The dependence of domain structure on film structural perfection was studied. Domain structure rearrangement due to both mechanical stresses and temperature variation was observed.

X-ray amd electrophisical studies of anisotropic PbTiO3-based piezoelectric ceramics

Abstract A study of structural, electrophysical and strength, parameters of anisotropic piezoelectric ceramics PCR-70 was carried out over a wide range of sintering temperatures and polarizing fields. The character of correlation between these parameters was established and described.