A. T. Kozakov

Bias Field Effect on Dielectric and Pyroelectric Properties of (1-x)Pb(Fe1/2Nb1/2)O3–xPbTiO3 Ceramics

Dielectric, X-ray, pyroelectric and piezoelectric studies of the (1-x)PbFe1/2Nb1/2O3–(x)PbTiO3 ceramics from the 0 ≤ x ≤ 0.2 range fabricated by solid state synthesis and usual sintering have been carried out. In PbFe1/2Nb1/2O3 and compositions with low Ti content anomalies of dielectric, pyroelectric and piezoelectric parameters, corresponding to the transition between two ferroelectric phases have been observed at 85–90°C. A dramatic effect of bias field on dielectric and pyroelectric responces was revealed.

Valence state of manganese ions in the La1−α BiLaβMnLa1−δ OLa3±γ ceramics

The valence state of the Mn ions in ceramic samples of the La1−α BiLaβMnLa1−δ OLa3±γ composition (LBMO) has been studied using the X-ray photoelectron spectroscopy. The presence of Mn3+ and Mn4+ ions in these compounds has been shown. The relative content Mn3+/Mn4+ has been determined by means of fitting the experimental Mn 2p spectra by the superposition of theoretical spectra of Mn3+ and Mn4+ ions. The elemental composition of the samples has been determined by the X-ray photoelectron spectroscopy and electron probe microanalysis. It has been established that the relative content of Mn4+ ions correlates with parameter δ, which characterizes the deviation of the actual elemental composition of the La1−α BiLaβMnLa1−δ OLa3±γ ceramics from stoichiometry La1 − xBixMnO3.

Temperature dependence of the concentration of surface phases in a BaTiO3 single crystal according to X-ray photoelectron spectroscopy data

The composition of the surface and the chemical bonding are studied by X-ray photoelectron spectroscopy (using an ESCALAB 250 instrument) in a BaTiO3 single crystal within the temperature range of T = 296–573 K. The evolution of the surface Ba-O phase is found to be reversible in this temperature range.

Tribochemical aspects of interactions between high-dispersed serpentine particles and metal friction surface

The paper presents the results of experimental investigations of friction-induced chemical modification of steel in the presence of serpentine additives in the lubricating material. This process is accompanied by substitution of magnesium atoms of the mineral structure by iron atoms from the friction surface. As a result, recombination of the crystalline lattice of the initial mineral and the formation of pseudo-mineral structures similar to the plane SiO compounds occur.

Electronic structure of a PbFe1/2Nb1/2O3 single crystal in the ferroelectric and paraelectric states, according to X-Ray photoelectron spectroscopy data and first principle calculations

Electronic structure of the PbFe1/2Nb1/2O3 single crystal is studied by means of X-ray photoelectron spectroscopy on an ESCALAB 250 system and first principle FEFF9 at temperatures of 296 and 403 K.

Electron-beam-induced polarization of lithium- and manganese-modified lead ferroniobate ceramics and its respective emission phenomena

A polarization state is formed with an electron beam in ceramic samples of pure lead ferroniobate (PFN) and PFN modified to a superstoichiometric composition at the stage of synthesis by adding 1 wt % lithium carbonate (PFNL) and 1 wt % of magnesia (PFNM). It is shown that in the case of PFNL, polarization by an electron beam is more efficient than the conventional method of “hot” polarization. Reasons for the observed effects, including enhanced electron emission from local irradiated areas on the surface of the ceramics, are discussed.

Ferropiezoelectric properties and microstructure of PbFe1/2Nb1/2O3 ceramics

Ceramic samples of lead ferroniobate (PFN) having a rhombohedral symmetry at room temperature are obtained. Their ferroelectric and magnetic properties in the vicinity of the antiferromagnetic and ferroelectric phase transition temperatures are investigated. The electrophysical parameters of the polarized ceramic are presented. By means of electron-probe microanalysis, the number of inclusions of Fe-containing impurity phases (∼0.2 vol %) is revealed to be several times higher than that in grains of the PFN ceramics. It is suggested that the above could be caused by the magnetic properties of PFN at room temperature.

Anomalous electron emission spectra and polarization phenomena in a lead magnesium niobate single crystal

The time dependences of the intensity and the energy positions of fine-structure of the spectra of anomalous electron emission from a polarized lead magnesium niobate (PMN) single crystal irradiated with soft x-rays are investigated experimentally. It is shown that the relaxation time of the electret charge can be determined from the graphs of these dependences, and the depth distribution of the potential in the surface layer of the sample can be determined from the profile of the anomalous electron emission spectrum. Estimates of the fields in the surface layers of a polarized PMN single crystal, obtained from the characteristics of the anomalous electron emission spectra, agree with data obtained by electrophysical research techniques.

Specific features and properties of lead-titanate-based anisotropic ceramics

This work has been devoted to certain microstructure peculiarities of anisotropic materials of the form (Pb,Ca)TiO3 - Σ2i=1 PbB1-αBαO3, where B is W, and B is Mg, Zn or Co, Zn. To decrease contamination of the equipment and surroundings the traditional source of a PbO atmosphere (PbO-contained powder) has not been used when the sintering of the ceramics was carried out. In the ceramics under study, a second phase was detected based on titanium oxide whose content and elemental composition have been estimated. The influence of this phase has been studied on structural and electrophysical parameters of relevant materials as their sintering temperature is changed from 1140°C to 1210°C. The increasing content of the second phase in the ceramics diminishes the susceptibility of the material to domain switching resulting in the worsening of electrophysical parameters.

X-ray photoelectron and mössbauer spectroscopy studies of the valence state of transition metal ions in Co1–xFexCr2O4 (x = 0.1, 0.2, 0.5) ceramics

The valence state of transition metal ions in the Co1–xFexCr2O4 (x = 0.1, 0.2, 0.5) system has been investigated using X-ray photoelectron and Mössbauer spectroscopy. It has been shown that, in this system, there are Fe2+ and Fe3+ ions. The relative Fe3+/Fe2+ contents have been determined by fitting the experimental Fe 2p photoelectron spectra by a superposition of theoretical spectra of the Fe2+ and Fe3+ ions, as well as using Mössbauer spectroscopy.