D.A. Belov

Ag 1 − x Mg 1 − x R 1 + x (MoO 4 ) 3 Ag + -conducting NASICON-like phases, where R = Al or Sc and 0 ≤ x ≤ 0.5

Ag1 − xMg1 − xR1 + x(MoO4)3 NASICON-like solid solutions, where R = Al or Sc and 0 ≤ x ≤ 0.5, were prepared; their crystal lattice parameters and thermal stabilities were determined. Silver-ion conductivity was measured, and conductivity activation energy values were calculated for various temperature ranges. Above 400°C, Ag1 − xMg1 − xR1 + x(MoO4)3 phases have ionic conductivities comparable to the conductivities of sodium-ion and lithium-ion NASICON-like conductors. The conductivity increases as the tervalent cation radius increases or the amount of mobile silver ions increases.

Nanostructuring phenomena in oxygen-conducting complex oxides of heavy REE

In complex oxides of REE (Ln4M3O12 (Ln = Tm, Lu; M = Zr, Hf), Ln2TiO5 (Ln = Er-Yb)) and Ho2TiO5, the following phase transitions of the order-disorder type are studied for different cooling rates: rhombohedral δ-phase-defective fluorite in Ln4M3O12 (Ln = Tm, Lu; M = Zr, Hf), pyrochlor-like phasedefective fluoride in Ln2TiO5 (Ln = Er-Yb), and hexagonal β-phase-pyrochlor in Ho2TiO5. The presence of nanostructuring phenomena typical of fluorite-like polymorphous modifications of complex oxides in the Ln2O3-MO2 (Ln = Ho-Lu; M = Ti, Zr, Hf) systems is confirmed. The conductivity of polymorphous modifications of Ln4Zr3O12 (Ln = Tm, Lu;) and Ln2TiO5 (Ln = Ho-Yb) with different thermal prehistory is studied. The comparative studies of the oxygen-ionic conductivity of fluorite- and pyrochlor-like Ln2TiO5 (Ln = Ho-Yb), pyrochlor Ho2TiO5, and β-Ho2TiO5 and also of the conductivity of fluorite-like compounds and δ-Ln4Zr3O12 (Ln = Tm, Lu) are carried out. The oxygen-ionic conductivity of complex oxides in the Ln2O3-MO2 (Ln = Er-Lu; M = Ti, Zr, Hf) system is shown to decrease in the following series: defective pyrochlor-defective fluorite-rhombohedral δ-phase ∼ hexagonal β-phase.

New alluaudite-related triple molybdates Na25Cs8R5(MoO4)24 (R = Sc, In): synthesis, crystal structures and properties

New triple molybdates Na25Cs8R5(MoO4)24 (R = Sc, In) were prepared as powders and ceramics by solid state reactions, and their single crystals were also obtained from melts by spontaneous crystallization. The structures were determined by single crystal XRD analysis. The electrical conductivity of ceramics was measured by impedance spectroscopy. The crystal structures were determined in monoclinic sp. gr. P21/c, a = 14.0069(3) A, b = 12.6498(3) A, c = 28.6491(6) A, β = 90.007(1)° (Sc) and a = 14.0062(2) A, b = 12.6032(2) A, c = 28.7138(4) A, β = 90.001(1)° (In). Together with triclinic Na25Cs8Fe5(MoO4)24, the titled compounds form a distinctive family of pseudo-orthorhombic alluaudite-related structures with the parent sp. gr. Pbca. Its structural features are alluaudite-like polyhedral layers composed of pairs of edge-shared (R, Na)O6 and NaO6 octahedra connected by bridging MoO4 tetrahedra. The layers are joined together by means of interlayer MoO4 tetrahedra, thus forming open 3D frameworks with cavities filled with Cs+ and Na+ ions. The manner of stacking layers is somewhat different from the alluaudite type. The compounds undergo phase transitions at 668 (Sc) and 725 (In) K accompanied by an abrupt increase of electrical conductivity presumably Na+-ionic in nature. Above these transitions, the conductivity is as high as 10−3 S cm−1, which makes Na25Cs8R5(MoO4)24 (R = Sc, In) promising solid state electrolytes.

Oxygen Interstitial and Vacancy Conduction in Symmetric Ln 2 ± x Zr 2 ± x O 7 ± x/2 (Ln = Nd, Sm) Solid Solutions

We have compared (Ln2 − xZrx)Zr2O7 + x/2 (Ln = Nd, Sm) pyrochlore-like solid solutions with interstitial oxide ion conduction and Ln2(Zr2 − xLnx)O7 − δ (Ln = Nd, Sm) pyrochlore-like solid solutions with vacancy-mediated oxide ion conduction in the symmetric systems Nd2O3-ZrO2 (NdZrO) and Sm2O3-ZrO2 (SmZrO). We have studied their structure, microstructure, and transport properties and determined the excess oxygen content of the (Sm2 − xZrx)Zr2O7 + x/2 (x = 0.2) material using thermal analysis and mass spectrometry in a reducing atmosphere (H2/Ar-He). The Ln2 ± xZr2 ± xO7 ± x/2 (Ln = Nd, Sm) solid solutions have almost identical maximum oxygen vacancy and interstitial conductivities: (3–4) × 10−3 S/cm at 750°C. The lower oxygen vacancy conductivity of the Ln2(Zr2 − xLnx)O7 − δ (Ln = Nd, Sm; 0 < x ≤ 0.3) solid solutions is due to the sharp decrease in it as a result of defect association processes, whereas the interstitial oxide ion conductivity of the (Ln2 − xZrx)Zr2O7 + x/2 (Ln = Nd, Sm; 0.2 ≤ x < 0.48) pyrochlore-like solid solutions is essentially constant in a broad range of Ln2O3 concentrations.

Synthesis, crystal structure and properties of alluaudite-like triple molybdate Na{sub 25}Cs{sub 8}Fe{sub 5}(MoO{sub 4}){sub 24}

A new triple molybdate Na25Cs8Fe5(MoO4)24 was synthesized using solid state reactions and studied with X-ray powder diffraction, second harmonic generation (SHG) technique, differential scanning calorimetry, Mossbauer and dielectric impedance spectroscopy. Single crystals of Na25Cs8Fe5(MoO4)24 were obtained and its structure was solved (the space group P1¯, a=12.5814(5), b=13.8989(5), c=28.4386(9) A, α=90.108(2), β=90.064(2), γ=90.020(2)°, V=4973.0(3) A3, Z=2, R=0.0440). Characteristic features of the structure are polyhedral layers composed of pairs of edge-shared FeO6 and (Fe, Na)O6 octahedra, which are connected by bridging МоО4 tetrahedra. The layers share common vertices with bridging МоО4 tetrahedra to form an open 3D framework with the cavities occupied by the Cs+ and Na+ cations. The compound undergoes first-order phase transformation at 642 K and above this phase transition, electrical conductivity reaches 10−3–10−2 S cm−1. Thus, Na25Cs8Fe5(MoO4)24 may be considered as a promising compound for developing new materials with high ionic conductivity.

New double molybdate Na{sub 9}Fe(MoO{sub 4}){sub 6}: Synthesis, structure, properties

A new double molybdate Na9Fe(MoO4)6 was synthesized using solid state reactions and studied with X-ray powder diffraction, second harmonic generation (SHG) technique, differential scanning calorimetry, X-ray fluorescence analysis, Mossbauer and dielectric impedance spectroscopy. Single crystals of Na9Fe(MoO4)6 were obtained and its structure was solved (the space group R3, a¼14.8264(2), c ¼19.2402(3) A, V¼3662.79(9) A 3 , Z ¼6, R ¼0.0132). The structure is related to that of sodium ion

Oxygen Ion Conductivity of (Yb 0.9 - x Tb x Ca 0.1 ) 2 Ti 2 O 7 - δ Solid Solutions

We have studied terbium substitution for ytterbium in (Yb0.9 − xTbxCa0.1)2Ti2O7 − δ (x = 0.1, 0.2, 0.3, 0.4) pyrochlore solid solutions synthesized through coprecipitation followed by firing at 1550°C. The results indicate that only a small amount of terbium (less than 10%) can be incorporated into the pyrochlore structure of (Yb0.9Ca0.1)2Ti2O6.9 because of the large difference in ionic radius between the terbium and ytterbium cations: Δr = r(TbCN 83+) − r(YbCN 83+) = 0.055 Å. The oxygen ion conductivity of the (Yb0.9 − xTbxCa0.1)2Ti2O7 − δ solid solutions has been determined by impedance spectroscopy in air in the temperature range 300 to 900°C. At high temperatures (t > 640°C), their bulk conductivity was essentially independent of the Yb/Tb ratio. The observed decrease in density and microstructural changes were insignificant. At relatively low temperatures (t < 640°C), the bulk conductivity decreased slightly, and the decrease depended little on terbium concentration.

Curing of a network polyimide modified with a linear component

The curing and relaxation processes in polymeric composites based on blends of network and linear polyimides applied onto a filler were studied by dielectric spectroscopy. The sensitivity of dielectric spectroscopy to processes occurring in the course of curing was examined.

Dielectric relaxation in a thermosetting polyimide modified with a thermoplastic polyimide

Relaxation processes in glass-fiber-reinforced composites with a polymer matrix based on blends of thermosetting and thermoplastic polyimides are studied via dielectric-relaxation spectroscopy. For all investigated blends, two relaxation processes related to the β relaxation of different fragments of the polymer chain are found. Linear flexiblechain polyimide incorporated into the polymer matrix serves as a plasticizer.

Acceptor doping of Ln{sub 2}Ti{sub 2}O{sub 7} (Ln = Dy, Ho, Yb) pyrochlores with divalent cations (Mg, Ca, Sr, Zn)

New LANTIOX high-temperature conductors with the pyrochlore structure, (Ln1� xAx)2Ti2O7� d (Ln = Dy, Ho, Yb; A = Ca, Mg, Zn; x = 0, 0.01, 0.02, 0.04, 0.07, 0.1), have been prepared at 1400-1600 8C using mechanical activation, co-precipitation and solid-state reactions. Acceptor doping in the lanthanide sublattice of Ln2Ti2O7 (Ln = Dy, Ho, Yb) with Ca 2+ ,M g 2+ and Zn 2+ increases the conductivity of the titanates except in the (Ho1� xCax)2Ti2O7� d system, where the conductivity decreases slightly at low doping levels, x = 0.01-0.02. The highest conductivity in the (Ln1� xAx)2Ti2O7� d (Ln = Dy, Ho, Yb; A = Ca, Mg, Zn) systems is offered by the (Ln0.9A0.1)2Ti2O7� d and attains maximum value for (Yb0.9Ca0.1)2Ti2O6.9 and (Yb0.9Mg0.1)2Ti2O6.9 solid solutions:� 2 � 10 � 2 and 9 � 10 � 3 Sc m � 1 at 750 8C, respectively. Ca and Mg are best dopants for Ln2Ti2O7 (Ln = Dy, Ho, Yb) pyrochlores. Using impedance spectroscopy data, we have determined the activation energies for bulk and grain-boundary conduction in most of the (Ln1� xAx)2Ti2O7� d (Ln = Dy, Ho; A = Ca, Mg, Zn) materials. The values obtained, 0.7-1.05 and 1-1.4 eV, respectively, are typical of oxygen ion conductors. We have also evaluated defect formation energies in the systems studied.