L. L. Kovalenko

Effect of Isovalent Ba-Site Substitutions on the Properties of (Ba1 – x – yMyYx)TiO3(M = Ca, Sr, Pb) PTCR Ceramics

An approach is proposed for fabricating fine-grained, low-resistivity BaTiO3-based PTCR ceramics via partial isovalent substitutions on the Ba site. The grain size of the ceramics thus prepared is shown to decrease as the ratio of ionic radii r(Ba2+)/r(M2+) (M = Ca, Sr, Pb) increases. Isovalent substitutions on the Ba site narrow down the range of donor dopant (yttrium) concentrations in which PTCR materials can be prepared. The experimental results agree well with thermodynamic calculations under the assumption that the materials contain the Y3+Ti3+O3 phase, as suggested by ESR data, which point to the presence of Y3+–Ti3+ associates. Partial calcium, strontium, and lead substitutions on the Ba site reduce the average grain size of PTCR ceramics, which is probably due to the lattice strain arising from the isovalent substitution. Partial replacement of Ba2+ with mixtures of different isovalent elements (e.g., Sr2+ and Pb2+) offers the possibility of obtaining fine-grained, low-resistivity PTCR ceramics, without changing the phase transition temperature.

Intercalation processes influence the structure and electrophysical properties of lithium-conducting compounds having defect perovskite structure

The structural features and electrophysical properties of lithium-conducting compounds having defect perovskite structure based on Li0.5La0.5Nb2O6 and Li0.5La0.5TiO3 were studied using X-ray diffraction and synchrotron analyses, potentiometry, and complex impedance spectroscopy. Intercalated lithium was found to differently influence ion conductance in titanium- and niobium-containing materials. This difference was found to arise from the structural features of the materials. The systems studied have high chemical diffusion coefficients of lithium (DLi+ = 1 × 10−6 cm2/s for Li0.5La0.5Nb2O6 and DLi+ = 3.3 × 10−7 cm2/s for Li0.5La0.5TiO3).

Electrical properties of BaTi1−x M x O3 (M = Nb, Ta, Mo, W) ceramics

The electrical properties of BaTi1−xMxO3 (M = Nb, Ta, Mo, W) ceramics (partial substitution of Group V (Nb, Ta) or VI (Mo, W) metals on the titanium site) have been studied by impedance spectroscopy. The results indicate that the Group VI metals (Mo and W) are less effective as donor dopants of barium titanate than are Nb and Ta because most of the Mo and W ions reside in the outer layer of the grains, raising its resistance.

Effect of the Distribution of Manganese Ions on the Properties of Mn-Doped (Ba,Y)TiO3 PTCR Ceramics

The electrical properties and microstructure of (Ba,Y)TiO3 PTCR ceramics were studied. The results indicate that the Mn ions increase the intergranular barrier height and produce a high-resistance layer on the grain surface. The temperature-dependent resistances of the grain bulk, surface layer, and grain boundaries, the temperature coefficient of resistance, and the magnitude of the varistor effect were assessed as a function of Mn content.

BaTi1−xSnxO3 Solid Solutions: Solid-Phase and Sol-Gel Syntheses and Characterization

Ba(Ti1−xSnx)O3 solid solutions were synthesized by the sol-gel process and solid-phase reactions, and their electrophysical properties studied. SnCl4 · 5H2O, TiCl4, and BaCO3 were precursors in the sol-gel process. IR spectroscopy, X-ray powder diffraction, and differential thermal analysis were used to study the formation conditions for BaTiO3, BaSnO3, and BaTi0.85Sn0.15O3.

Effect of impurities on the electrical properties of the defect perovskite Li0.33La0.57TiO3

A perovskite phase with the composition Li0.33La0.57TiO3 modified with up to 7 wt % Bi2O3, SiO2, Li3PO4, or Li3BO3 has been prepared by solid-state reactions. The samples in the LLTO–Li3PO4, LLTO–Bi2O3, and LLTO–SiO2 systems were single-phase over the entire composition range studied. In the LLTO–Li3BO3 system, increasing the lithium borate concentration causes a transition from a defect perovskite structure to the layered perovskite-related structure of Li2La2Ti3O10. The addition of Bi2O3 and Li3PO4 has been shown to increase the total conductivity of the ceramics by almost one order of magnitude. Li3BO3, Li3PO4, Bi2O3, and SiO2 additives improve the sintering behavior of the Li0.33La0.57TiO3 ceramics.

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

Codoping with iron, cerium, and copper oxides has been proposed as a means of improving the performance of scandium-containing zirconia-based solid electrolytes. We have examined three procedures for the synthesis of the (ZrO2)0.825(CeO2)0.07(Sc2O3)0.07(Fe2O3)0.035 solid solution through precipitation from solution. It has been shown that the highest oxygen ion conductivity is ensured by the synthesis procedure that includes the mechanochemical activation of presynthesized scandium ferrate (Sc1.33Fe0.67O3) with cerium and zirconium hydroxides and a solution containing 0.5 mol % Cu.

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

Ceramic samples of lead magnesium niobate (PMN) and (1 − x)Pb(Mg1/3Nb2/3)O3−xPbTiO3 (PMN-PT) solid solutions with x = 0, 0.05, 0.10, and 0.30 have been prepared by solid-state reactions, and their structural, electrical, and piezoelectric properties have been studied using x-ray diffraction, Rietveld profile analysis, impedance spectroscopy, and the resonance/antiresonance method. The results indicate that the use of nonstoichiometric columbite niobates enables the synthesis of phase-pure PMN and PMN-PT.

Effect of Fluorine Doping on the Microstructure and Electrical Properties of Barium-Titanate-Based Ceramics

The effect of partial fluorine substitution for oxygen on the properties of BaTiO3 has been studied using thermogravimetry, x-ray diffraction, electron microscopy, complex impedance measurements, and diffuse reflectance spectroscopy. The results indicate that partial fluorine substitution for oxygen influences the composition range of positive temperature coefficient of resistance behavior in ceramics with heterovalent substitution of lanthanum on the barium site.

Substrate effect on the properties of La0.775Sr0.225MnO3 films

La0.775Sr0.225MnO3 films have been produced by screen printing on various substrates (Al2O3, BaTi0.85Zr0.11Sn0.04O3, Ba0.996Y0.004TiO3, Ba0.996Y0.004TiO3 + 0.04%Mn, and Ba0.996Y0.004Ti0.65Sn0.35O3), and their electrical properties have been studied in comparison with those of bulk materials. The structural properties of the substrates are shown to influence the electrical properties of the films.