The influence of combustion synthesis conditions on the α-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> powder preparation

Fuel type and fuel/aluminium nitrate molar ratio proved to be of great importance during the preparation of α-Al₂O₃ powders. A stoichiometric amount of urea (U) enabled the formation of α-Al₂O₃ with a surface area of 24 m²/g directly from the combustion reaction. Monoethanolamine, triethylenetetramine, trishydroxymethylaminomethane, and triethanolamine yield amorphous powders. This behaviour was explained by the reaction mechanism, which requires the simultaneous decomposition of metal nitrate and fuel, as shown by thermal analysis. The use of 50% of the stoichiometric amount of U was unable to trigger a combustion reaction. The resulting powder was amorphous and had a surface area of 424 m²/g. A parabolic correlation between the surface area of combustion-synthesized powder and the U/aluminium nitrate molar ratio was found. Due to U consumption during the hydrolysis side-reaction, 50% of U excess above the stoichiometric ratio is required in order to maximize the exothermic effect of the combustion reaction. The use of U excess higher than 150% of the stoichiometric ratio not only increases the surface area of the powder, but also changes the phase composition: as the U excess increases the proportion of α-Al₂O₃ decreases and the amount of γ-Al₂O₃ increases.     

Effect of the precipitation sequence on phase formation in the ZrO<Subscript>2</Subscript>-CeO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> system

We have studied phase formation processes during heat treatment of precipitates in the ZrO₂-Al₂O₃ and ZrO₂-CeO₂-Al₂O₃ systems. During heat treatment of powders prepared by coprecipitation of precursors to ZrO₂, CeO₂, and Al₂O₃, α-Al₂O₃ is formed at higher temperatures, which is due to the formation and decomposition of T-ZrO₂ and metastable Al₂O₃ phases. The precipitation sequence in the ZrO₂-CeO₂-Al₂O₃ system influences the lattice parameters of the forming T-ZrO₂-based solid solutions because of the different degrees of Ce⁴⁺ and Al³⁺ substitutions for Zr⁴⁺.     

Ionic conductivity in the Lu<Subscript>2</Subscript>O<Subscript>3</Subscript>-TiO<Subscript>2</Subscript> system

Nanocrystalline Lu₂O₃-TiO₂ (33.3–44 mol % Lu₂O₃) materials with a partially disordered pyrochlore structure, prepared via heat treatment in the range 1400–1750°C, are found to possess high oxygen ionic conductivity. Their 740°C conductivity is 10^-3 to 10^-2 S/cm, depending on the heat-treatment temperature and composition, which is comparable to that of the well-known fluorite solid electrolyte ZrO₂-9 mol % Y₂O₃.Translated from Neorganicheskie Materialy, Vol. 41, No. 3, 2005, pp. 324–331.Original Russian Text Copyright © 2005 by Shlyakhtina, Mosunov, Stefanovich, Knotko, Karyagina, Shcherbakova.This revised version was published online in April 2005 with a corrected cover date.This revised version was published online in April 2005 with a corrected cover date.     

Cr<Superscript>3+</Superscript> activated Zn<Subscript>3</Subscript>Al<Subscript>2</Subscript>Ge<Subscript>3</Subscript>O<Subscript>12</Subscript>: a novel near-infrared long persistent phosphor

The near-infrared (NIR) long persistent phosphors have gained considerable attention owing to the potential applications in in vivo imaging. A novel NIR long-persistent phosphors Zn₃Al₂Ge₃O₁₂:Cr³⁺ was successfully synthesized by a high temperature solid-state reaction. The luminescent properties and the afterglow behaviors of the Zn₃Al₂Ge₃O₁₂:Cr³⁺ were investigated in detail. On the basis of thermoluminescence analyses, the mechanism of the persistent afterglow of the phosphors was also discussed briefly. The afterglow duration of this phosphor can last more than 12 h with the 650–750 nm emission range after stoppage of 254 nm ultraviolet light irradiation. Specifically, the persistent luminescence intensity and duration were regulated by changing Cr³⁺ doping concentration. All the results indicate that the Cr³⁺ activated Zn₃Al₂Ge₃O₁₂ has promising potential of practical applications.     

Luminescence Study of LiY<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Eu<Subscript>x</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>2</Subscript>

The luminescence spectra of LiY_{1 − x} Eu_x(MoO₄)₂ (x = 0.0005, 0.001, 0.01, 0.05, 0.1, 0.5, 1) scheelite solid solutions are measured under laser excitation at 337.1 nm. The effect of Eu³⁺ concentration on the luminescence behavior of the solid solutions is examined. The highest integrated emission intensity is offered by LiY_0.5Eu_0.5(MoO₄)₂. Eu³⁺ substitution for Y³⁺ has no effect on the symmetry of the emission centers involved. Eu³⁺ is shown to occupy only one site in the structure of the solid solutions. X-ray diffraction and luminescence data indicate that all of the solid solutions have an undistorted scheelite structure.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 7, 2005, pp. 871–875.Original Russian Text Copyright © 2005 by Zaushitsyn, Mikhailin, Romanenko, Khaikina, Basovich, Morozov, Lazoryak.     

K<Superscript>+</Superscript> ion conducting properties in the R<Subscript>2</Subscript>O<Subscript>3</Subscript>-KNO<Subscript>3</Subscript> (R: Rare earths) solid solution series

A new type of polycrystalline potassium ion conducting solid electrolyte doped with potassium nitrite as the starting material, was developed. Since cubic rare earth oxides hold reasonably enough interstitial space for bulky K⁺ ion migration in the crystal lattice, an extraordinary high K⁺ ion conductivity was successfully achieved by forming a polycrystalline (1 − x)R₂O₃-xKNO₃ solid solution, which was realized by doping KNO₂ as the KNO₃ state into the interstitial site of cubic rare earth oxide crystal lattice. The potassium ion conductivity of the (1 − x)R₂O₃-xKNO₃ (R: rare earths) solid solution linearly increased with expanding the R₂O₃ crystal lattice and the highest K⁺ ion conductivity was obtained for the 0.653Gd₂O₃-0.347KNO₃ solid solution, which is three orders of magnitude higher than that of a well-known polycrystalline K⁺ ion conducting K₂SO₄ solid and the value exceeds that in the ab conducting plane of a K⁺-β ”-Al₂O₃ single crystal.     

EPR and photoluminescence properties of combustion-synthesized ZnAl<Subscript>2</Subscript>O<Subscript>4</Subscript>:Cr<Superscript>3+</Superscript> phosphors

An efficient red emitting ZnAl₂O₄:Cr³⁺ powder phosphor material was prepared at furnace temperatures as low as 500 °C by using the combustion method. The prepared powders were analyzed by X-ray diffraction and scanning electron microscopy techniques. The optical properties were studied using photoluminescence technique. The EPR spectra exhibit an intense resonance signal at g = 3.74 which is attributed to Cr³⁺–Cr³⁺ pairs, and the weak resonance signal of at g = 1.97 is attributed to Cr³⁺ single ion transition. The spin population (N) has been evaluated as a function of temperature. The excitation spectrum exhibits two broad bands in the visible region which are characteristic of Cr³⁺ ions in octahedral symmetry and the emission spectrum exhibits zero-phonon line frequencies along with vibronic frequencies. The crystal field parameter (Dq) and Racah parameters (B and C) have been evaluated and discussed.     

Redox processes in fine-particle TiO<Subscript>2</Subscript>-Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> oxides

We have studied the stability of the Cr⁶⁺ ion in fine-particle TiO₂-Cr₂O₃ oxides during storage after calcination in air. The results indicate that, during storage under normal conditions for 720 days, Cr⁶⁺ is reduced to Cr³⁺. The redox process is due to partial surface hydration of the Cr₂O₃ and TiO₂ crystallites.     

Subsolidus Phase Relations in the System Dy<Subscript>2</Subscript>O<Subscript>3</Subscript>-Rh<Subscript>2</Subscript>O<Subscript>3</Subscript>

The Dy₂O₃-Rh₂O₃ system is studied by thermal analysis, x-ray diffraction, and chemical analysis of annealed and quenched samples. The results are used to construct a schematic subsolidus phase diagram of the system. Only one double oxide, DyRhO₃, is obtained. Some of its physicochemical properties are reported.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 8, 2005, pp. 960–965.Original Russian Text Copyright © 2005 by Skrobot, Ugolkov, Grebenshchikov, Gusarov.     

The influence of activation of Y<Subscript>2</Subscript>O<Subscript>3</Subscript> polycrystalline matrices by Bi<Superscript>3+</Superscript> ions on the luminescence of Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript>

The influence of activation of the Y₂O₃ matrix of the Y₂O₃:Eu³⁺ phosphor by Bi³⁺ ions on the luminescence of Eu³⁺ and Bi³⁺ ions in it and on conditions of the excitation energy transfer to luminescence centers is studied. It is shown that the presence of Bi³⁺ ions leads to the appearance of recombination luminescence with participation of bismuth ions at low concentrations (up to 6–8 at %) of the dominant activator europium and to an increase in the threshold of intrinsic concentration quenching of its luminescence.     

Synthesis and crystal structure of Cu<Subscript>2</Subscript>{(UO<Subscript>2</Subscript>)<Subscript>3</Subscript>[(S,Cr)O<Subscript>4</Subscript>]<Subscript>5</Subscript>}(H<Subscript>2</Subscript>O)<Subscript>17</Subscript>

Cu₂{(UO₂)₃[(S,Cr)O₄]₅}(H₂O)₁₇ crystals were prepared by evaporation of aqueous solutions. The crystal structure was solved by the direct method and refined to R ₁ = 0.064 (wR ₂ = 0.177) for 8120 reflections with ¦F _hkl¦ 4 ¦F _hkl¦. Rhombic system, space group Pbca, a = 18.0586(8), b = 19.9898(9), c = 20.5553(8) Å, V = 7420.2(6) ų. The structure is based on {(UO₂)₃[(S,Cr)O₄]₅}^4– anionic layers, formed by combination of UO₇ pentagonal bipyramids and TO₄ tetrahedra through common vertices. The { (UO₂)₃ [(S,Cr)O₄]₅}^4– layers are parallel to the (010) plane. The Cu²⁺ (H₂O)₆ octahedra and additional water molecules are located in the interplanar space and provide binding of the layers in the structure by hydrogen bonds. Based on the occupancy of tetrahedral positions, more accurate chemical formula of the compound should be written as Cu₂{(UO₂)₃[(S_0.804 Cr_0.196)O₄]₅} (H₂O)₁₇.Translated from Radiokhimiya, Vol. 46, No. 5, 2004, pp. 408–411.Original Russian Text Copyright © 2004 by Krivovichev, Burns.     

Luminescence of europium-doped BaO-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

We have prepared europium-doped BaO-Bi2O₃-B2O₃ glasses and investigated the doping effect on the main physicochemical properties and local structure of the glasses. Using Judd-Ofelt analysis, we calculated intensity parameters (Ω₂, Ω₄, and Ω₆), spontaneous emission probabilities, the radiative lifetime, luminescence branching factors, the quantum yield of luminescence, and the stimulated emission cross sections for ⁵ D ₀ → ⁷ F _J transitions.     

Spectroscopy and Structure of Nd<Superscript>3+</Superscript> Activator Centers in Stabilized Cubic ZrO<Subscript>2</Subscript>

The nonuniformly broadened spectra of Nd³⁺ in ZrO₂-Y₂O₃-Nd₂O₃ crystals are studied using selective excitation, different time delays, and measurements of the excited-state lifetime at 77 K. Three basic types of optical spectra are identified and are assigned to three basic configurations of the nearest neighbor environment of Nd³⁺: sevenfold coordination and eightfold coordination with and without an oxygen vacancy among its second neighbors.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 8, 2005, pp. 955–959.Original Russian Text Copyright © 2005 by Voron’ko, Lomonova, Popov, Sobol’, Ushakov.     

Ionic Conductivity of Ln<Subscript>2 + <Emphasis Type="Italic">x</Emphasis></Subscript>Zr<Subscript>2 − <Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>7 − <Emphasis Type="Italic">x</Emphasis>/2</Subscript> (Ln = Sm-Gd) Solid Solutions

The electrical conductivity of Ln_{2 + x} Zr_{2 − x} O_{7 − x/2} (Ln = Sm-Gd) solid solutions prepared from mechanically activated Ln₂O₃ and ZrO₂ is shown to correlate with their structural properties. In the three systems, the x-T regions are determined in which electrical transport is dominated by oxygen-ion conduction. In the Sm₂O₃-ZrO₂ system, ionic conductivities from 5 × 10⁻⁴ to 6 × 10⁻³ S/cm at 740°C are found in Sm_{2 + x} Zr_{2 − x} O_{7 − x/2} with 26.6, 33.3, 35.5, 37, and 40 mol % Sm₂O₃ prepared at 1450, 1530, and 1600°C. Eu_{2 + x} Zr_{2 − x} O_{7 − x/2} and Gd_{2 + x} Zr_{2 − x} O_{7 − x/2} containing 33.3 to 37 mol % Ln₂O₃ have 740°C ionic conductivities of 10⁻³ to ∼7.5 × 10⁻³ and 10⁻³ to 7 × 10⁻³ S/cm, respectively. The activation energy of conduction in Ln_{2 + x} Zr_{2 − x} O_{7 − x/2} (Ln = Sm-Gd), E _a = 0.84–1.04 eV, increases with the atomic number of Ln and x. The highest ionic conductivity is offered by the stoichiometric Ln₂Zr₂O₇ (Ln = Sm-Gd) pyrochlores prepared at 1600°C, owing to the optimal concentration of Ln_Zr + Zr_Ln antistructure pairs (∼5–22%). The grains in the ceramic samples studied range in size from 0.5 to 2 µm.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 8, 2005, pp. 975–984.Original Russian Text Copyright © 2005 by Shlyakhtina, Kolbanev, Knotko, Boguslavskii, Stefanovich, Karyagina, Shcherbakova.     

Phase Relations and Transport Properties of Alloys in the Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript>-TlGaTe<Subscript>2</Subscript> System

Using physicochemical analysis, the Bi₂Te₃-TlGaTe₂ system is shown to contain Bi₂Te³⁻ and TlGaTe₂-based restricted solid-solution series and a liquid-liquid miscibility gap in the composition range ≃12–30 mol % TlGaTe₂. The power factor α²σ of (Bi₂Te₃)_1−x (TlGaTe₂)_x solid solutions with 0.01 ≤ x ≤ 0.02 is suitable for thermoelectric applications.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 7, 2005, pp. 785–786.Original Russian Text Copyright © 2005 by Abilov, Seidov.     

Effect of secondary heat treatment on the spectroscopic properties of Na<Subscript>2</Subscript>O-Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>-P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

We have studied the optical absorption and luminescence spectra of 45Na₂O · xNb₂O₅ · (55 − x)P₂O₅ glasses containing 5, 10, 20, 25, 30, and 35 mol % Nb₂O₅. The results indicate that the absorption band around 26000 cm⁻¹, responsible for the yellow color of the glasses, is due to the [Nb^(5+)--O⁻] center and disappears upon secondary heat treatment. Heat treatment of europium-doped glasses increases the concentration of Eu³⁺ centers in an asymmetric environment, which is accompanied by an increase in luminescence efficiency. The reason for this is that the Eu³⁺ ions are located outside the niobate subsystem of the glass matrix. The europium in the glasses studied acts as a protector ion.     

Reaction in the Al-ZrO<Subscript>2</Subscript>-C system

The reaction in ball milled Al-ZrO₂-C powders with different ZrO₂/C molar ratios was studied by using DSC, XRD and EPMA. During heating fully milled powders, the Al first reacts with ZrO₂ and carbon simultaneously to form ZrAl₃ and Al₄C₃ phases, which further react with each other at about 896^∘C, causing the formation of Zr₂Al₃C₅. Then at 1140^∘C, Zr₂Al₃C₅ reacts with ZrAl₃, producing ZrC and ZrAlC₂ phases. In the un-fully milled powder, only an exothermic reaction between the three starting phases occurs at a higher temperature of about 956^∘C. Heating Al-ZrO₂-C powders with different ZrO₂/C ratio (r) to 1250∘C produces different phases in the final aluminum matrix: Al-Al₂O₃-Zr₂Al₃C₅-Al₄C₃ (r < 2:5), Al-Al₂O₃-Zr₂Al₃C₅ (r = 2:5), Al-Al₂O₃-Zr₂Al₃C₅-ZrC-ZrAlC₂ (2:5 < r < 3:5), Al-Al₂O₃-ZrC-ZrAlC₂ (3:5 ≤ r ≤ 3:4), Al-ZrAl₃-Al₂O₃-ZrC-ZrAlC₂ (r > 3:4). Zr₂Al₃C₅ presents fine platelet morphology, both ZrAlC₂ and ZrC have polygonal shape, ZrAl₃ exhibits flaky morphology at lower temperature, but blocky form at higher temperatures.     

Luminescent and scintillation characteristics of submicron LuBO<Subscript>3</Subscript>:Ce<Superscript>3+</Superscript> powders and related films

Submicron LuBO₃:Ce³⁺ powders and related composite films have been obtained. The phase and granulometric compositions of powders have been determined. The luminescence spectra of the powder under X-ray excitation have been measured and the dependence of the X-ray luminescence intensity on the content of activator impurity (cerium) is established. Using ⁵⁵Fe and ²⁴¹Am γ radiation sources, the dependence of the scintillation characteristics of LuBO₃:Ce³⁺ films on the γ quantum energy and cerium concentration has been studied. Features of the γ quantum energy transfer in the medium comprising heavy scintillator particles dispersed in a light organic binder are briefly discussed.     

Superionic Conductors in the Bi<Subscript>2</Subscript>WO<Subscript>6</Subscript>-Bi<Subscript>2</Subscript>VO<Subscript>5.5</Subscript> System

Bi₂V_xW_{1 − x} O_{6 − y} ceramics are synthesized, and their structure and electrical properties are studied. The results indicate that the Bi₂WO₆-Bi₂VO_5.5 system contains Bi₂WO₆- and Bi₂VO_5.5-based solid solutions in the ranges 0 < x ≤ 0.2 and 0.75 ≤ x < 1, respectively. Tungsten stabilizes the high-temperature, tetragonal phase γ-Bi₂VO_5.5, which persists down to room temperature at 0.75 ≤ x ≤ 0.84. In the range 350–550°C, the electrical conductivity of the bismuth-vanadate-based solid solutions exceeds that of Bi₂VO_5.5 by about one order of magnitude. The conductivity of the Bi₂WO₆-based solid solutions is also higher than that of the host phase.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 7, 2005, pp. 866–870.Original Russian Text Copyright © 2005 by Voronkova, Yanovskii, Kharitonova, Rudnitskaya.     

Structural,optical and magnetic properties of Cr doped In<Subscript>2</Subscript>O<Subscript>3</Subscript> powders and thin films

The (In_1?xCr_x)₂O₃ powders as well as thin films of x = 0.03, 0.05 and 0.07 were synthesized using a solid state reaction and an electron beam evaporation technique (on glass substrate), respectively. The influence of Cr doping concentration on structural, optical and magnetic properties of the In₂O₃ samples was systematically studied. The X-ray diffraction results confirmed that all the Cr doped In₂O₃ samples exist cubic structure of In₂O₃ without any secondary phases presence. The chemical composition analyses showed that all the Cr doped In₂O₃ compounds were nearly stoichiometric. The X-ray photoelectron spectroscopy analysis of the Cr doped In₂O₃ thin films showed an increase of oxygen vacancies with Cr concentration and the existence of Cr as Cr³⁺ state in the host In₂O₃ lattice. A small blue shift in the optical band gap was observed in the powder compounds, when the dopant concentration increased from x = 0.03 to x = 0.07. In thin films, the band gap found to increase from 3.63 to 3.74 eV, with an increase of Cr concentration. The magnetic measurements show that the undoped In₂O₃ bulk powder sample has the diamagnetic property at room temperature. And a trace of paramagnetism was observed in Cr doped In₂O₃ powders. However (In_1?xCr_x)₂O₃ thin films (x = 0.00, 0.03, 0.05 and 0.07) samples shows soft ferromagnetism. The observed ferromagnetism in thin films are attributed to oxygen vacancies created during film prepared in vacuum conditions. The ferromagnetic exchange interactions are established between metal cations via free electrons trapped in oxygen vacancies (F-centers).