N. U. Venskovskii

Synthesis and Properties of La2(Mo1 – xMx )2O9 (M = Nb, Ta) Ionic Conductors

La2(Mo1 – xMx )2O9 (M = Nb, Ta; 0 < x ≤ 0.2) solid solutions were prepared, and their physicochemical and electrical properties were studied. Second harmonic generation measurements indicate that the solid solutions have a noncentrosymmetric structure and undergo a structural phase transition accompanied by a sharp increase in ionic conductivity, similar to that of La2Mo2O9 . The transition temperature is found to decrease with increasing Nb or Ta content. The introduction of 5 wt % Nb increases the 800°C conductivity of the material.

Ferroelectric Phase Transitions and Electroconducting Properties of Ceramic BIMEVOX Solid Solutions (Me = La, Zr)

Ceramic solid solutions Bi 4 (V 1−x Zr x ) 2 O 11−z (I), (Bi 1−y La y ) 4 V 2 O 11−z (II) and (Bi 1−y La y ) 4 (V 0.96 Zr 0.05 ) 2 O 11−z (III) with x < 0.30, y < 0.20, were prepared by the solid state reaction method and were investigated by means of various experimental techniques. The low temperature ferroelectric α-phase exists in the solid solutions with x, y ≤ 0.05. The phase transition to paraelectric β-phase was revealed in these compositions by the dielectric spectroscopy, SHG and DTA/DSC methods. Dielectric permittivity measurements confirmed an effect of the domain walls “pinning” due to the presence of oxygen vacancies inherent to the bismuth vanadate based structures. Switching of ferroelectric domains by an external electric field was observed in Piezoresponse Force Microscopy experiments.

Preparation and Properties of Oxygen-Selective LaGaO3-Based Ceramics with Mixed Ionic–Electronic Conduction

A continuous series of (La0.9Sr0.1)[(Ga1 – xFex)0.8Mg0.2]O3 – δ perovskite solid solutions (x = 0–1) were prepared by ceramic processing techniques. X-ray diffraction, dilatometry, thermogravimetry, and dielectric spectroscopy data indicate that increasing the Fe content of the solid solutions leads to a change from oxygen ionic to ionic–electronic conduction.

Synthesis, Structure, Microstructure, and Electrical Conductivity of (La,Sr)(Ga,Mg)O3 – δOxide-Ion-Conducting Ceramics

Oxide-ion-conducting perovskite ceramics (La1 – ySry)(Ga1 – xMgx )O3 – δwere prepared using hydrated Mg and La salts as starting reagents. X-ray diffraction and IR spectroscopy data demonstrate that the symmetry of the solid solutions changes in the sequence orthorhombic–rhombohedral–cubic with increasing Sr + Mg content.

Phase Composition, Microstructure, and Thermal Expansion of B2O3-Modified LaGaO3-Based Ceramics

Data are presented on the phase relations in the La2O3–SrO–Ga2O3system and the effect of B2O3additions on the structure and morphology of (La,Sr)(Ga,Mg)O3 – δceramics. The formation of the perovskite phase (La,Sr)GaO3is shown to proceed through La4SrO7and La2SrO4 + δ . The unit-cell of (La,Sr)(Ga,Mg)O3 – δis found to vary linearly with Sr + Mg content. The introduction of boron-containing additions reduces the sintering temperature of the ceramics by up to ≃200°C.

Phase Transitions in the BIMEVOX Solid Solutions with Me = Ga, Zr

The polymorph phase stability ranges have been studied for the Bi4V2-xMexO11-y solid solutions with Me = Ga and Zr at room temperature. The formation of orthorhombic α- (x = 0.0 and 0.05) and β-phases (x = 0.1, 0.15) and tetragonal phase (0.2 ≤ x ≤ 0.3) has been revealed in BIGAVOX solid solutions. In BIZRVOX solid solutions, α-phase exists at x ≤ 0.05, while β-phase exists at 0.1 ≤ x ≤ 0.3. The second order phase transitions at ~ 308°C (BIGAVOX) and ~ 270°C (BIZRVOX) have been revealed for solid solutions with x = 0.05 using the SHG and DSC methods. In both systems, the β↔γ-phase transition temperatures have been found to decrease with increasing x.

Study of ferroelectric phase transitions in solid solutions based on bismuth vanadate

The structural, thermal, nonlinear optical, and conducting properties of Bi4(V1 − xMex)2O11 − y solid solutions (Me = Zr, Ga, Fe) have been investigated. The effect of domain wall pinning, accompanying the α ↔ β ferroelectric phase transition, is revealed. It is found that the conductivity in all studied series of solid solutions increases with an increase in x.

Ferroelectric Phase Transitions in Ionic Conducting BICUVOX Ceramics

Ceramic solid solutions Bi4(V1 − x Cu x )2O11 − y with x = 0 ÷ 0.2, Δx = 0.02, have been prepared by the solid state reactions. The samples were studied by the DTA/DSC, X-ray diffraction and dielectric spectroscopy methods. Concentration and temperature stabilization regions of the polymorphous α, β and γ ′ modifications have been defined. Decreasing of the ferroelectric α-β phase transition temperature, enlargement of the temperature interval of thermal hysteresis while increasing in temperature of the transition between tetragonal γ′ - γ phases have been revealed. Dielectric measurements gave an indication on the effect of the domain walls “pinning” by oxygen vacancies inherent to the bismuth vanadate based compositions.

Ferroelectric Phase Transitions in the BIMEVOX Solid Solutions

Ceramic solid solutions Bi 4 (V 1 − x Me x ) 2 O 11 − y with x = 0 ÷ 0.3, Me = Zr, Ga, Fe were prepared by the solid state reactions and were studied by the DTA/DSC, X-ray diffraction, dielectric spectroscopy and the second harmonic generation (SGH) method. The temperature dependences of the SHG signal confirmed the noncentosymmetric structure of the samples with x ≤ 0.05 at room temperature. Similar features were observed in the SHG and dielectric property measurements, which give an indication of the strong domain walls “pinning” by oxygen vacancies inherent to the Bi 4 (V 1 − x Me x ) 2 O 11 − y structures.

The Ion Conducting Properties of Perovskite-Type Solid Solutions (La0.5Li0.5) [Ti1-x(M0.5Nb0.5)x]O3 (M = Al, Ga)

The influence of B-site substitution on electroconducting properties of perovskite-type solid solutions (La0.5Li0.5)[Ti1-x(M0.5Nb0.5)x]O3 with M = Al, Ga, have been studied. A decrease in the conductivity due to the unit cell contraction with increasing x in case of M = Al has been revealed. In case of Ga and Nb substitutions for Ti the unit cell volume has been found to increase with increasing x while the conductivity decreases due to the impurity phases presence. The high and low temperature anomalies on the temperature dependences of dielectric characteristic related to both the relaxation effect and phase transitions have been revealed.