A. V. Pavlenko

Microstructure and dielectric and piezoelectric properties of PbFe0.5Nb0.5O3 ceramics modified with Li2CO3 and MnO2

Unmodified lead ferroniobate (PFN) and samples modified with 1 wt % Li2CO3 (PFNL) and 1 wt % MnO2 (PFNM) have been prepared by solid-state reactions followed by sintering by a conventional ceramic processing technique. The modifiers have been shown to change the nature of the recrystallization sintering process, reduce the optimal sintering temperature of the material, increase its average grain size, stabilize its dielectric properties, and improve its piezoelectric performance. The observed effects are interpreted in terms of the crystal-chemical specifics of the modifiers and their location in the structure of the parent compound.

Synthesis, structure, and optical characteristics of barium–strontium niobate thin films

Films of the Ba0.5Sr0.5Nb2O6 (BSN) solid solution on the MgO(001) substrate were fabricated by high-frequency RF sputtering in oxygen. Optical spectra of discharge glow when sputtering the BSN ceramic target and the structure and optical characteristics of BSN/MgO(001) films at room temperature were investigated. It was shown that the BSN films grow from a dispersed phase in the discharge gap, while their growth rate with the used deposition mode at the initial stage is 8–9 nm/min. It was established that the grown films are single-crystal, contain twins, and film surfaces are parallel to the crystallographic planes (001). The angle, at which the reflection intensity is independent of the film thickness, was found in the family of specular reflection curves of H-polarized radiation with wavelengths of 500–800 nm from the films under study at room temperature. The tangent of this angle is equal to the refractive index of the film material, while its presence indicates the identity of optical characteristics of the film material of different thicknesses and low roughness of their surfaces.

Optimizing conditions of fabrication and the properties of BaNb2O6-SrNb2O6 binary ceramics

Conditions for fabricating (Ba0.5Sr0.5)Nb2O6 ceramics are optimized. It is shown that materials synthesized at T = 1250°C and sintered at T = 1375–21400°C exhibit the best ceramic characteristics. The (Ba0.5Sr0.5)Nb2O6 solid solution is found to be a ferroelectric with a diffuse phase transition. The possibility of fabricating Ba0.5Sr0.5Nb2O6 thin films from ceramic targets prepared in the resulting optimum regimes is shown.

Phase diagram of the system of (1–х)BiFeO3–xPbFe0.5Nb0.5O3 solid solutions at room temperature

Experimental samples of solid solutions of the (1–x)BiFeO3–xPbFe0.5Nb0.5O3 (0.00 ≤ x ≤ 1.00, Δx = 0.025–0.05) system have been prepared according to the conventional ceramic technology. Their structural and dielectric characteristics have been studied. A phase diagram of the system at room temperature has been plotted taking into account the crystallochemical specificity, spatial inhomogeneity, and structural imperfection of the samples. This diagram is characterized by the presence of solid substitutional and interstitial solutions; the formation of concentration ranges with a dominant role of BiFeO3 and PbFe0.5Nb0.5O3; the presence of five single-phase regions, two regions of coexistence of phase states, and three morphotropic regions; and the formation of six regions with a constant experimental unit-cell volume. Correlations between the structural characteristics and dielectric properties of the ceramics under study have been established.

Granular structure and dielectric characteristics of the (Ba0.5Sr0.5)Nb2O6 ceramics

The granular structure and the dielectric characteristics of the ceramic (Ba0.5Sr0.5)Nb2O6 solid solution are studied. The ceramic is found to be characterized by a homogeneous, dense, almost pore-free microstructure consisting of crystallites 5–10 µm in size. At room temperature, (Ba0.5Sr0.5)Nb2O6 exhibits elongated hysteresis loops. The ceramic undergoes a diffuse phase transition from a paraelectric state into the state of relaxor ferroelectric in the temperature range T = 340–385 K upon cooling. Scaling is shown to weakly change the ceramic characteristics of the material.

Structure and dielectric characteristics of PbFe0.5Nb0.5O3 single crystals grown under different conditions

The structure and dielectric and magnetic characteristics of plumbum ferroniobate crystals grown from a solution–melt containing potassium fluoride have been investigated. The obtained crystals have a cubic shape, 4-mm edges, and a rhombohedral structure at room temperature. Iron ions in the samples have the valence state of Fe3+. A change in the Mössbauer spectra with a change in temperature has been registered; this is indicative of strong diffusion of the magnetic phase transition in the range from–130 to–230°C, which is enhanced due to incorporation of fluorine atoms into the structure of the basic compound accompanying the synthesis process and clusterization of this structure. The latter phenomena also lead to a decrease in the temperature of transition from the ferro- to paraelectric phase.

Maxwell–Wagner relaxation and magnetodielectric properties of Bi0.5La0.5MnO3 ceramics

The complex permittivity ε = ε′–iε″ of manganite bismuth–lanthanum Bi0.5La0.5MnO3 ceramics has been measured at temperature T = 78 K in the frequency range f = 200–105 Hz and in the magnetic induction range B = 0–5 T. Dielectric relaxation and the pronounced magnetodielectric effect have been detected. The explanation based on the superposition of Maxwell–Wagner relaxation and the magnetoresistance effect has been proposed.

Effect of lithium carbonate on the ferroelectric properties of lead ferroniobate ceramics

We have studied the grain and crystal structures and the dielectric (300–700 K) and piezoelectric characteristics of ceramic samples of unmodified multiferroic lead ferroniobate and materials modified with lithium carbonate above stoichiometry during synthesis. The addition of the modifier has been shown to improve the microstructure of the samples, increase their resistivity, improve their dielectric controllability, and raise their piezoelectric activity. The observed effects have been tentatively attributed to the formation of Li-containing liquid phases during synthesis of the material and to partial Li cation incorporation into the crystal structure of the host compound. The optimal modifier concentration is 1–2 wt %.

Structure and dielectric characteristics of (1 – x)BiFeO3–xPbTiO3 solid solutions

Undoped (1 – x)BiFeO3–xPbTiO3 binary solid solutions (0 ≤ x ≤ 0.50, Δx = 0.1) are obtained via a solid-state reaction combined with sintering in accordance with conventional ceramic technology. Features of their crystal structure formation and dielectric properties are studied in a wide range of temperatures and frequencies.

Dielectric retardation and relaxation in Bi0.5La0.5MnO3 ceramic at 80 K

Low-temperature (80 K) measurements are made of the frequency dependences of the real and imaginary parts of the complex dielectric constant and complex electric modulus of bismuth lanthanum manganite Bi0.5La0.5MnO3 ceramic. The presence of two (low- and high-frequency) regions of dielectric retardation and relaxation is revealed. A considerable difference between the average rates of retardation and relaxation and the Debye value in the high frequency region is revealed and explained.