S. I. Shevtsova

Dielectric and Mossbauer Studies of Pb(Fe1/2Ta1/2)O3 Multiferroic Ceramics Sintered from Mechanoactivated Powders

The effect of high-energy mechanical activation on dielectric and magnetic properties of PbFe1/2Ta1/2O3 (PFT) multiferroic was studied. Mössbauer studies have shown that the Neel temperature TN of the antiferromagnetic phase transition in PFT powders can be changed substantially by mechanical activation and subsequent annealing. The increase of TN by more than 70 K, as compared to PFT single crystal, was achieved in the mechanically activated PFT powder annealed at 700°C. Dielectric studies have shown that in contrast to ceramics obtained by usual sintering, PFT ceramics fabricated by sintering of the mechanoactivated powder does not show the relaxor-like behavior.

Electron microscopy, X-Ray diffraction and Mossbauer studies of PbFe0.5Nb0.5O3, PbFe0.5Ta0.5O3 and BaFe0.5Nb0.5O3 ceramics sintered from mechanoactivated nanopowders

ABSTRACT The effect of high-energy mechanical activation on magnetic phase transition temperature TM of PbFe0.5Nb0.5O3, PbFe0.5Ta0.5O3, and BaFe0.5Nb0.5O3 perovskites has been studied. Mossbauer studies have shown that TM values in all the perovskites studied can be changed substantially by mechanical activation and subsequent annealing. The increase of TM by 40-50 K, as compared to corresponding single crystals and ceramics sintered from the non-activated powders, was achieved in the mechanoactivated powders of both lead-containing and lead-free perovskites studied.

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.

Electron microscopy, XRD, Mossbauer and dielectric studies of Pb(Fe0.5Nb0.5)1-xSnxO3 multiferroic ceramics

ABSTRACT Multiferroic Pb(Fe0.5Nb0.5)1-xSnxO3 (x = 0.025, 0.05, 0.075, 0.10) ceramic compositions were prepared by solid state synthesis and usual sintering. XRD studies have shown a formation of the perovskite structure in all the compositions studied. However, a small amount of pyrochlore phase was detected in Sn-doped compositions with x ≥ 0.05. Scanning electron microscopy studies have shown that at the boundaries of the large grains there exist a lot of small submicron grains enriched by Sn. Concentration dependencies of the unit-cell parameter and ferroelectric phase transition temperatures also imply that solubility of Sn in PFN is limited to ≈ 5 at.%.

Magnetoelectricity in the PbFe1/2Nb1/2O3 Ceramics

The magnetodielectric effect (the influence of a magnetic field H on the dielectric constant ɛ) and the magnetoelectric effect (the influence of an electric field E on the magnetoelectric constant α) of the PbFe1/2Nb1/2O3 ceramics have been investigated at temperatures T in the range from 50 to 200°C, including the Curie point TC ≊ 98°C. It has been demonstrated that there is a correlation of these effects with the shift of the ferroelectric-paraelectric phase transition temperature in a magnetic field.

Structure clusterization preceding concentration phase transitions

The formation and development of bulk crystallochemical defects—mesoscopic clusters representing the nuclei of new phases—was studied in systems exhibiting concentration phase transitions. When a solid solution approaches a morphotropic region, the clusters exhibit a stepwise evolution involving several stages manifested by corresponding changes in macroscopic properties. The role of clusters in the development of the extreme electrophysical properties of the objects studied is discussed.

Studies of Domain and Twin Patterns in NaNbO3-Gd1/3NbO3 Solid Solution Crystals

Studies of (1-x)NaNbO3-xGd1/3NbO3 crystals in polarized light revealed the independence of the temperature of rotational phase transition into the cubic phase on x. This correlates with the similarity of Na+ and Gd3+ ionic radii. Increase of Gd content leads to the diffusion of permittivity maxima and a dramatic decrease of a mean size of twins (domains). This makes both crystallooptic studies and rotating polarizer method ineffective. Multifractal analysis of false-colour image patterns obtained by rotating polarizer method, using the Metripol microscope system enables to detect the changes in domain (twin) pattern in the temperature range of diffuse phase transition.

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.

Preparation, structure, and dielectric characteristics of 0.95 PFN -0.05 BFO single crystals

The structure, Mössbauer effect, and dielectric characteristics of 0.95PFN-0.05BFO crystals prepared via mass crystallization are studied. It is shown that temperatures approaching those of the antiferromagnet → paramagnet and ferroelectric → paraelectric transitions are reached inside these crystals, in contrast to PFN.

Effects of doping of lead titanate with alkaline-earth elements

Solid solutions of the (