O. Z. Yanchevskii

Influence of impurities on the properties of rare-earth-doped barium- titanate ceramics

Investigations of impurity centers, electrical resistivity and microstructure of BaTiO3 ceramics doped with rare-earth ions Y, La, Nd, Sm, Dy and Lu at concentrations x = 0.001–0.005 were carried out. Electron paramagnetic resonance, X-ray diffraction and electron microscopy were used for measurements. The most intense EPR lines were shown to belong to paramagnetic complexes Fe3+–VO and Ti3+–Ln3+ (Ln = rare-earth ion, VO = oxygen vacancy). A change in symmetry of the center Fe3+–VO at the transition temperature from the ferroelectric to paraelectric phase has been revealed for the first time. Measurements of the dependence of EPR line intensities and electrical resistivity with rare-earth ion concentrations were performed. The observed correlation in their behaviour showed an essential role of the identified paramagnetic complexes in the appearance of BaTiO3 ceramic semiconducting properties and the positive temperature coefficient of resistance (PTCR) effect. The latter effect was at a maximum for x ≈ xc where xc ≈ 0.002–0.003 is the critical rare-earth ion concentration which determines the excess charge compensation mechanism. Up to xc, the rare earths investigated, (except for the small ion Lu), substitute for barium, and the main compensation mechanism is an electronic mechanism. At high concentrations (x > xc) in the case of large ions (e.g. La), substitution is at barium sites, with the creation of titanium vacancies, whereas intermediate ions (e.g. Y) begin to substitute for titanium. The influence of impurities on the BaTiO3 microstructure, including the grain sizes, is discussed.

Crystallographic, electrical, and magnetic properties of the system La0.7Sr0.3Mn1−xFexO3

On the basis of x-ray structural data and studies of the electrical, magnetic, and magnetoresistive properties and the ferromagnet resonance spectra of ceramic samples of La0.7Sr0.3Mn1−xFexO3 (0⩽x⩽0.10) it is established that a competition between structural changes influencing the ferromagnetism leads to a monotonic weakening of the ferromagnetism (a lowering of TC by around 5K∕%Fe). The increase of the magnetoresistance in the low-temperature region and the large values of the low-field contribution to the magnetoresistance are indicative of an inhomogeneous character of the electrical conductivity and magnetization of the samples at T<TC, which may be due to the coexistence of the ferro- and paramagnetic phases over a wide temperature region.

Oxidation state of copper ions in (La0.7Sr0.3)(Mn1 − xCux)O3 ± δ ceramics and their magnetic properties

Bulk ceramic samples of (La0.7Sr0.3)(Mn1 − xCux)O3 ± δ manganites are prepared by solid-state reactions. The unit-cell parameters and Mn-O bond distances in the manganites are determined using the Rietveld profile analysis method, and their magnetic properties are studied with the use of ferromagnetic resonance measurements. The results attest to the formation of solid solutions. Their lattice parameters follow Vegard’s law. The way in which the saturation magnetization of the manganites varies with composition depends on x. For x ≤ 0.07, the saturation magnetization is a weak function of composition; for x > 0.07, it drops rapidly with increasing x. These results can be understood under the assumption that the only oxidation state of copper in (La0.7Sr0.3)(Mn1 − xCux)O3 ± δ is 2+.

Structural, electrical, and magnetic properties of La0.7Ca0.3 − xNaxMnO3 ± γ solid solutions

AbstractLa0.7Ca0.3 − xNaxMnO3 ± γ (LCNM) solid solutions with x = 0, 0.04, 0.06, 0.08, and 0.10 have been synthesized (rhombohedral structure, sp. gr. R

Structural, electrical, and magnetic properties of La0.7Sr0.3Mn1−y CryO3

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Codoping of scandium-containing zirconia-based solid electrolytes with iron, cerium, and copper oxides

c). Sodium volatility during sintering is shown to lead to the formation of vacancies on the lanthanum and oxygen sites. Ca2+ → Na+ substitution does not increase the fraction of Mn4+ in LCNM, but the increase in the concentration of lanthanum vacancies with increasing sodium content leads to an increase in ferromagnetic ordering temperature TC and magnetoresistance, which depend, in addition, on heat-treatment conditions on account of the sodium volatility.

Preparation and electrical properties of (1 − x)(Ba,Y)TiO3 · xPbTiO3 materials containing low-melting B2O3-PbO-SiO2 glass additions

Rounded nanosize particles of Co3O4 and NiO were prepared by precipitation with ammonium carbonate from cobalt and nickel nitrate solutions. Cobalt and nickel oxides and their precursors were characterized by thermal and X-ray phase analyses, electron microscopy, and IR spectroscopy.

Preparation and electrical properties of Pb(Mg1/3Nb2/3)O3-PbTiO3 solid solutions

Detailed structural data are presented for La0.7Sr0.3Mn1−yCryO3 solid solutions with 0 < y ≤ 0.10. Chromium substitution on the manganese site is shown to reduce the TC of the solid solutions at a rate of 4 K/mol % Cr. The 300-K magnetoresistance of La0.7Sr0.3Mn1−yCryO3 attains 8% in a field of 1.2 MA/m.