Polymorphism of ZrO<Subscript>2</Subscript> nanopowders and mechanochemical synthesis of Zr<Subscript>0.88</Subscript>Sc<Subscript>0.1</Subscript>Ce<Subscript>0.01</Subscript>Y<Subscript>0.01</Subscript>O<Subscript>1.955</Subscript>

The structure of ZrO₂ powders prepared by dehydration of zirconium hydroxide and milling (including techniques with the introduction of grinding additives, such as NaF, CaF₂, diamond, and Cu) was investigated using x-ray powder diffraction and Raman spectroscopy. Samples containing crystallites with the smallest size were synthesized in the presence of copper additives. Ceramic powders of the composition Zr_0.88Sc_0.1Ce_0.01Y_0.01O_1.955 with an improved quality for the use as solid electrolytes in fuel cells were prepared by the mechanochemical synthesis from nanoprecursors and then were characterized. An analysis of the X-ray powder diffraction patterns revealed that the symmetry of the structure of strongly aggregated nanopowders of metastable zirconia increases as a result of twinning, which is favored by a high concentration of vacancies.     

Growth and self-organization of nanostructures on interlayer surfaces of A<Stack><Subscript>2</Subscript><Superscript>V</Superscript></Stack>B<Stack><Subscript>3</Subscript><Superscript>VI</Superscript></Stack> layered crystals

This paper examines the formation of arrays of interlayer nanostructures in layered crystals grown by directional solidification and the Bridgman method. Sb₂Te₃ and Bi₂Te₃ layers are shown to contain steplayered structures with nanostructured islands on them. Atomic force microscope images of interlayer nanostructures in such crystals are analyzed in terms of the physics of fractals and self-organization processes.     

Catalytic effect of Ti<Subscript>5</Subscript>Si<Subscript>3</Subscript> on thermal decomposition of Li<Subscript>3</Subscript>AlH<Subscript>6</Subscript>

Fine Ti₅Si₃ powder has been mechanochemically synthesized from a mixture of elemental Ti and Si powders. When Ti₅Si₃ is added as a catalyst into Li₃AlH₆, it shows a good catalytic ability by reducing the decomposition temperature and improving the decomposition kinetics as well. Although its catalytic effect is not as good as well-known TiCl₃, the use of Ti₅Si₃ has a benefit of releasing more hydrogen than TiCl₃ during dehydrogenation. This can be explained by that Ti₅Si₃, unlike TiCl₃, does not incur any chemical reactions with Li₃AlH₆ and thus remains inert during milling for dispersion.     

Effect of Eu<Subscript>2</Subscript>O<Subscript>3</Subscript> doping on the crystallization behavior of BaO-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

We gave studied the crystallization behavior of 30BaO · 25Bi₂O₃ · 45B₂O₃ glasses doped with Eu₂O₃ to different levels. At a Eu₂O₃ content of 7 mol % or higher, the glasses undergo volume crystallization. The only precipitating phase is a solid solution between europium and bismuth oxides. With increasing europium concentration in the glass, the structure of the crystallites changes from cubic to rhombohedral. We have investigated the morphology, physicochemical properties, and luminescence spectra of the glasses and glass-ceramics.     

Investigation of density of states and electrical properties of Ba<Subscript>0.5</Subscript>Co<Subscript>0.5</Subscript>Bi<Subscript>2</Subscript>Nb<Subscript>2</Subscript>O<Subscript>9</Subscript> nanoceramics prepared by chemical route

Barium-cobalt-bismuth-niobate, Ba_0.5Co_0.5Bi₂Nb₂O₉ (BCoBN) nanocrystalline ferroelectric ceramic was prepared through chemical route. XRD analysis showed single phase layered perovskite structure of BCoBN when calcined at 650 °C, 2 h. The average crystallite size was found to be 18 nm. The microstructure was studied through scanning electron microscopy. The dielectric and ferroelectric properties were investigated in the temperature range 50–500 °C. The dielectric constant and dielectric loss plot with respect to temperature both indicated strong relaxor behavior. Frequency versus complex impedance plot also supported the relaxor properties of the material. The impedance spectroscopy study showed only grain conductivity. Variation of ac conductivity study exhibited Arrhenius type of electrical conductivity where the hopping frequency shifted towards higher frequency region with increasing temperature. The ac conductivity values were used to evaluate the density of state at the Fermi level. The minimum hopping distance was found to be decreased with increasing temperature.     

Tailoring magnetic and dielectric properties of Co<Subscript>0.9</Subscript>Cu<Subscript>0.1</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> with substitution of small fractions of Gd<Superscript>3+</Superscript> ions

This paper describes the structural, magnetic, and dielectric properties of Gd³⁺ substituted cobalt–copper ferrite. The influence of Gd³⁺ substitution on the structural, magnetic and electrical properties of cobalt–copper ferrite was investigated through various characterization techniques. Thermal analysis was carried out on the prepared gel to know the combustion and calcination temperature. The detailed structural analysis suggests that the substitution of a Fe³⁺ ion with a Gd³⁺ ion at B site results in lattice distortion, modification in crystallite size and grain size of the material. X-ray photoelectron spectroscopy confirmed the oxidation states of the elements present. Magnetic measurement performed at 300 and 50 K depicts the decrease in saturation magnetization (Ms) and increase in coercivity (Hc) with Gd³⁺ substitution in the cobalt–copper spinel ferrite. The dielectric measurements acquired over a wide range of frequencies and temperature showed an increase in dielectric constant with increasing Gd³⁺ concentration.     

Synthesis of Sn<Subscript>2</Subscript>P<Subscript>2</Subscript>S<Subscript>6</Subscript>

A process that presents no explosion hazard is proposed for the preparation of tin(II) hexathiohypodiphosphate(IV) in a limited amount of air. The reaction of tin(II) sulfide with a mixture of phosphorus sulfides with the overall composition “P₄S₈” is studied, and the influence of synthesis temperature and duration on the completion of the reaction is analyzed.     

Effect of Oxygen Concentration on Superconducting Properties of Rubidium Tungsten Bronzes Rb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>WO<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>

Superconducting transition temperature (T _c) as a function of oxygen concentration for hexagonal rubidium tungsten bronzes Rb _x WO _y with 2.80 ≤ y ≤ 3.07 and x = 0.19, 0.23, and 0.27 has been systematically investigated. Three regions corresponding to T _c < 2 K (denoted as superconductivity suppressed region), T _c∼ 3 K (superconductivity uniform region) and T _c > 3 K (superconductivity enhanced region) were identified in T _c–y phase diagram for Rb_0.19WO _y and Rb_0.23WO _y . No superconductivity enhanced region was observed for Rb_0.27WO _y . The superconductivity suppressed region shifts toward higher oxygen content as rubidium concentration increases. The local ordering of the intercalated rubidium atoms might be responsible for the intriguing T _c–y phase diagram of Rb _x WO _y .     

Properties of nanocrystalline ZrO<Subscript>2</Subscript>-Y<Subscript>2</Subscript>O<Subscript>3</Subscript>-CeO<Subscript>2</Subscript>-CoO-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> powders

We have studied the properties of nanocrystalline ZrO₂-Y₂O₃-CeO₂-CoO-Al₂O₃ powders prepared via hydrothermal treatment of a mixture of coprecipitated hydroxides at 210°C. A number of general trends are identified in the variation of the properties of the synthesized powders during heat treatment at temperatures from 500 to 1200°C. Our results demonstrate that the addition of 0.3 mol % CoO to nanocrystalline ZrO₂-based powders containing 1 to 5 mol % Al₂O₃ allows one to obtain composites with good sinterability at a reduced temperature (1200°C).     

Conductivity of Sm<Subscript>2</Subscript>TiO<Subscript>5</Subscript> and Sm<Subscript>2</Subscript>Ti<Subscript>2</Subscript>O<Subscript>7</Subscript>

The oxygen-ion conductivity of porous materials, the coarse-grained pyrochlore-like Sm₂Ti₂O₇ and fine-grained Sm₂TiO₅ compounds, produced by mechanical activation of initial oxides is studied at 400–1000 °C. The Sm₂TiO₅ samples contain ～15 wt % of the nanosized pyrochlore-like Sm₂TiO₅ phase in addition to the rhombic phase. As determined by impedance spectroscopy, the ionic conductivities of Sm₂TiO₅ and Sm₂Ti₂O₇ at 1000°C are 1.3 × 10^?3 and 1.8 × 10^?4 S cm^?1, and the activation energies of the bulk and grainboundary conductivities of the materials are 1.04 and 1.24 eV for Sm₂TiO₅ and 1.69 and 1.80 eV for Sm₂Ti₂O₇.     

Ab-initio Calculation of Electronic and Magnetic Properties of Mn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Cr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Te

The electronic and magnetic properties of Mn_1−x Cr _x Te of NiAs-type and zinc-blend type structures are theoretically investigated using the first-principles KKR-CPA method. It is concluded that at low concentration region of Cr, an antiferromagnetic state is the ground-state, while a ferrimagnetic state is more stable at higher concentration region of Cr in the both types of structures. In particular, a new type of half-metallic ferrimagnets is found in zinc-blend type Mn_1−x Cr _x Te. On the other hand, a nearly half-metallic behavior is observed in NiAs-type Mn_1−x Cr _x Te, where the Fermi level locates slightly above the minority spin band gap. The features of the half-metallicity of Mn_1−x Cr _x Te in zinc-blend structure are also seen in the results of the conductivity calculations using the Kubo–Greenwood formula.     

Superconducting Properties of Iodine-Intercalated Bi<Subscript>2</Subscript>Sr<Subscript>2</Subscript>Ca<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>10+<Emphasis Type="Italic">x</Emphasis></Subscript>

The superconducting properties of iodine-intercalated high-temperature superconducting Bi₂Sr₂Ca₂Cu₃O_10+x phase (Bi-2223) were systematically studied. It was found that for samples containing a significant amount of Bi₂Sr₂CaCu₂O_8+x , iodine intercalation results in the dramatic decrease of the inter-granular critical current density, as well as a significant decrease of the critical temperature (T _c), the critical current density in the grains (J _cg), and of the amount of Bi-2223. For samples with a large amount of Bi-2223, T _c changes insignificantly, whereas J _cg can even increase. We argue that the different behavior of the superconducting parameters is the result of various oxygen concentrations, and we explain the effect of iodine intercalation based on the parabolic dependence between T _c and the number of holes per CuO₂ layer. The H(T) curves (determined from the peak position in the loss signal of ac susceptibility) for intercalated samples deviate significantly from the quasi 2D-like behavior, pointing toward an enhancement of the 3D fluctuations of vortices. For the change in the values and dimensionality of the flux pinning in the process of the intercalation, we attempted a qualitative explanation based on the models proposed in literature.     

Dielectric Properties of Na<Subscript>0.7</Subscript>CoO<Subscript>2</Subscript> and of the Superconducting Na<Subscript>0.3</Subscript>CoO<Subscript>2</Subscript>·1.3H<Subscript>2</Subscript>O

We present dielectric properties of ceramic anhydrous Na_0.7CoO₂ and the superconducting Na_0.3CoO₂·1.3H₂O materials. The presence of water which induces superconductivity also may increase the dielectric constant (ε) of the hydrated material. This is consistent with the predicted relationship between the highε and the enhancement ofT _c in highT _c superconductors. The anhydrous sample is porous and the transport is due to some percolation via the pores. The porosity is much higher for the hydrated material and the transport is ionic inside bulk water.     

Evolution of the microstructure and mechanical properties of eutectic Fe<Subscript>30</Subscript>Ni<Subscript>20</Subscript>Mn<Subscript>35</Subscript>Al<Subscript>15</Subscript>

The microstructure of the eutectic alloy Fe₃₀Ni₂₀Mn₃₅Al₁₅ (in at.%) was modified by cooling at different rates from 1623 K, i.e., above the eutectic temperature. The lamellar spacing decreased with increasing cooling rate, and in water-quenched specimens lamellae widths of ~100 nm were obtained. The orientation relationship between the fcc and B2 lamellae was found to be sensitive to the cooling rate. In a drop-cast alloy the Kurdjumov–Sachs orientation relationship dominated, whereas the orientation relationship in an arc-melted alloy with a faster cooling rate was \textfcc( [`1]12 )//\textB2( 0 1 1 );  \textfcc[ 1[`1]1 ]//\textB2 [ 1[`1]1 ]  \textand \textfcc( 0[`1]1 )//\textB2( 00 1 );\text fcc[ 0 1 1 ]//\textB2[ [`1][`1]0 ] {\text{fcc}}\left( {\bar{1}12} \right)//{\text{B2}}\left( {0 1 1} \right);\;{\text{fcc}}\left[ {1\bar{1}1} \right]//{\text{B2 }}\left[ {1\bar{1}1} \right] \,{\text{and}}\,{\text{fcc}}\left( {0\bar{1}1} \right)//{\text{B2}}\left( {00 1} \right);{\text{ fcc}}\left[ {0 1 1} \right]//{\text{B2}}\left[ {\bar{1}\bar{1}0} \right] . The hardness increased with microstructural refinement, obeying a Hall–Petch-type relationship. The strength of the alloy decreased significantly above 600 K due to softening of the B2 phase.     

Effect of Y<Subscript>2</Subscript>O<Subscript>3</Subscript> on the crystallization behavior of SiO<Subscript>2</Subscript>–MgO–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

A series of glass comprising of SiO₂–MgO–B₂O₃–Y₂O₃–Al₂O₃ in different mole ratio has been synthesized. The crystallization kinetics of these glasses was investigated using various characterization techniques such as differential thermal analysis (DTA), thermo gravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Crystallization behavior of these glasses was markedly influenced by the addition of Y₂O₃ instead of Al₂O₃. Addition of Y₂O₃ increases the transition temperature, T _g, crystallization temperature, T _c and stability of the glasses. Also, it suppresses the formation of cordierite phase, which is very prominent and detrimental in MgO-based glasses. The results are discussed on the basis of the structural and chemical role of Y³⁺ and Al³⁺ ions in the present glasses.     

Effect of Nd substitution on structure and magnetic properties of Nd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Dy<Subscript>3−<Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript>5</Subscript>O<Subscript>12</Subscript> garnet powders

The properties of light rare earth Nd substitution for heavy rare earth Dy in Dy₃Fe₅O₁₂ (DyIG) garnet ferrite have been studied. The Nd _x Dy_3–x Fe₅O₁₂ (x = 0, 0.25, 0.5, 0.75 and 1) (Nd:DyIG) garnet powders were prepared by sol–gel autocombustion followed by heat treatment. The structure and the magnetic properties of the annealed powders were measured with X-ray diffraction (XRD), the Fourier Transform Infrared (FT-IR) and the Physical Properties Measurement System (PPMS) techniques. The experimental results indicate that a single Nd:DyIG garnet phase structure can be obtained after the samples annealed above 800 °C. With the Nd substitution content increasing, the average lattice constants of the sample, the a−d super-exchange interaction strengthens and the magnetization of unit cell increase. The maximum saturation magnetization is 13.86 emu/g for x = 1, and coercive force is about 136 Oe, for x = 0.75. The reason of increasing in magnetization with Nd substitution is also discussed.     

Crystal structure of Gd<Subscript>14</Subscript>Cu<Subscript>48</Subscript>Ga<Subscript>3</Subscript> and Tb<Subscript>14</Subscript>Cu<Subscript>48</Subscript>Ga<Subscript>3</Subscript>

The compounds Gd₁₄Cu₄₈Ga₃ and Tb₁₄Cu₄₈Ga₃ have been synthesized, and their structures have been determined by powder x-ray diffraction (Gd₁₄Ag₅₁ type).     

Electrical conductivity of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-Tm<Subscript>2</Subscript>O<Subscript>3</Subscript>-Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> solid solutions

New solid solutions, Bi_2?x?y Tm _x Nb _y O_3+δ, with tetragonal and cubic structures have been synthesized in the Bi₂O₃-Tm₂O₃-Nb₂O₅ system, and their electrical conductivity has been measured at temperatures from 670 to 1020 K. The 1020-K conductivity of the tetragonal solid solution Bi_1.8Tm_0.15Nb_0.05O_3+δ is comparable to that of Bi_1.75Tm_0.25O₃, the best conductor in the Bi₂O₃-Tm₂O₃ system.