Persistent luminescence of Zn<Subscript>2</Subscript>GeO<Subscript>4</Subscript>:Mn<Superscript>2+</Superscript>/Pr<Superscript>3+</Superscript> phosphors

Zn₂GeO₄, Zn₂GeO₄:Mn²⁺, Zn₂GeO₄:Pr³⁺ and Zn₂GeO₄:Mn²⁺/Pr³⁺ phosphors were fabricated by a solid state reaction. The phase and luminescent properties of the fabricated phosphors were investigated. The XRD patterns show that all of the fabricated phosphors have an orthorhombic structure. The fabricated Zn₂GeO₄ shows an emission band in the range of 350–550 nm. The fabricated Zn₂GeO₄:Mn²⁺ and Zn₂GeO₄:Pr³⁺ phosphors show emission bands corresponding to Mn²⁺ and Pr³⁺ ions, respectively. The fabricated Zn₂GeO₄:Mn²⁺/Pr³⁺ phosphor shows the emission band results from Mn²⁺ and the codoped Pr³⁺ enhances the emission intensity of Mn²⁺. Moreover, Zn₂GeO₄:Mn²⁺/Pr³⁺ phosphor exhibits longer decay time than that of Zn₂GeO₄:Mn²⁺. The higher intensity and longer lifetime of Mn²⁺ emission are induced by the energy transfer from Pr³⁺ of various vacancies to Mn²⁺ in Zn₂GeO₄:Mn²⁺/Pr³⁺ phosphors.     

Mechanochemical Synthesis of Crystalline Compounds in the Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–GeO<Subscript>2</Subscript> System

Crystalline mechanochemical synthesis products in the Bi₂O₃–GeO₂ system are studied by x-ray diffraction. The results indicate the formation of sillenite (Bi₁₂GeO₂₀), eulytite (Bi₄Ge₃O₁₂), and Aurivillius (Bi₂GeO₅) phases. The Aurivillius phase is shown to be in mechanochemical equilibrium with the sillenite phase in the 2Bi₂O₃ + GeO₂ system and with the eulytite phase in the Bi₂O 3 + GeO 2 system. The structural parameters of the synthesized metastable solid solutions are determined. The three phases contain high concen-trations of vacancies. In addition, the sillenite and Aurivillius phases are characterized by compositional disordering. Structural and ESR data point to partial reduction of the oxides, which accounts for the formation of the Aurivillius phase. According to x-ray photoelectron spectroscopy results, mechanical activation of bismuth oxide produces reduced binding energy states of Bi and O, which is tentatively attributed to clustering and the formation of complex radicals.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 6, 2005, pp. 711–719.Original Russian Text Copyright © 2005 by Zyryanov, Smirnov, Ivanovskaya.     

Preparation of porous ZrO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> macrobeads from ion-exchange resin templates

In this work, we will report a method to prepare porous ZrO₂ and ZrO₂/Al₂O₃ macrobeads using cation-exchange resins with sulfonate groups as templates. The preparation process involves metal ion-loading, ammonia-precipitation, and calcination at an appropriate temperature. Several characterization methods, such as TGA, XRD, SEM with EDX, TEM and N₂ adsorption and desorption, were used to characterize the ZrO₂ and ZrO₂/Al₂O₃ macrobeads. The results showed that the porous structures of the resin templates were negatively duplicated in the two kinds of macrobeads. We found the following interesting results: (1) The ZrO₂/Al₂O₃ macrobeads are composed of tetragonal zirconia nanocrystals that are more technologically important, while the pure ZrO₂ macrobeads consist of a mixture of tetragonal and monoclinic zirconia. (2) In the ZrO₂/Al₂O₃ macrobeads, the size of ZrO₂ nanocrystals is about 5 nm smaller than that (about 19 nm) found in the pure ZrO₂ macrobeads. (3) The ZrO₂/Al₂O₃ macrobeads have more mesopores and, therefore, have a larger surface area than the pure ZrO₂ macrobeads. These oxide macrobeads will have potential applications in catalysis by taking advantage of their macrobeads shape and pores structure.     

Synthesis and High-Temperature Heat Capacity of Sm<Subscript>2</Subscript>Ge<Subscript>2</Subscript>O<Subscript>7</Subscript> and Eu<Subscript>2</Subscript>Ge<Subscript>2</Subscript>O<Subscript>7</Subscript>

The Sm₂Ge₂O₇ and Eu₂Ge₂O₇ germanates have been prepared by solid-state reactions via multistep firing of stoichiometric mixtures of Sm₂O₃ (Eu₂O₃) and GeO₂ in air at temperatures from 1273 to 1473 K. The molar heat capacity of the samarium and europium germanates has been determined by differential scanning calorimetry in the range 350–1000 K and the C _p (T) data have been used to evaluate their thermodynamic properties.     

Photoluminescence of Si<Subscript>0.9</Subscript>Ge<Subscript>0.1</Subscript>O<Subscript>2</Subscript> and GeO<Subscript>2</Subscript> films irradiated with silicon ions

We have studied the photoluminescence (PL) of GeO₂ and 90 mol % SiO₂-10 mol % GeO₂ films synthesized by method of RF magnetron sputtering and then irradiated with silicon ions and annealed. The PL of silicon-implanted GeO₂ films, related to the presence of Si nanocrystals (nc-Si), was observed for the first time. It is established that the transformation of the defect centers responsible for the PL in the spectral range 350–600 nm, as well as the formation of nc-Si emitting in the region of 700–800 nm, significantly depend on the matrix type. In particular, the PL intensity at 700–800 nm in 90 mol % SiO₂-10 mol % GeO₂ films is weak. The role of the isovalent substitution of Si and Ge atoms in the transformation of defect centers and the formation of nc-Si is discussed.     

Structure of multilayer ZrO<Subscript>2</Subscript>/SrTiO<Subscript>3</Subscript>

Multilayered oxide heteroepitaxial systems, including that of a 1-nm-thick Y₂O₃-stabilised ZrO₂ (YSZ) sandwiched between layers of SrTiO₃ (STO) [1], have been a subject of much interest lately due to their significantly enhanced ionic conductivities as compared to the bulk materials. We aim to provide the foundation for understanding this increase in conductivity by considering the atomic configurations at the interfaces of such systems, specifically a ZrO₂/STO multilayer system. Possible stable lattice structures of pure ZrO₂ in the system are explored using a genetic algorithm in which the interatomic interactions are modelled by simple pair potentials. The energies of several of the more stable of these structures are then evaluated more accurately within density functional theory (DFT). We find that the fluorite ZrO₂ phase is unstable as a coherently strained epitaxial layer in the multilayer system. Instead, anatase-, columbite-, rutile-, and pyrite-like ZrO₂ epitaxies are found to be more stable, with the anatase-like epitaxy being the most stable structure over a wide range of chemical potential of the components. We also find a high energy metastable structure resembling the tetragonal fluorite structure which is predicted by DFT to be stabilised by SrO-terminated STO but not by TiO₂-terminated STO.     

A novel method for producing open-cell Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-ZrO<Subscript>2</Subscript> ceramic foams with controlled cell structure

A novel method was introduced to prepare open-cell Al₂O₃–ZrO₂ ceramic foams with controlled cell structure. This method used epispastic polystyrene (EPS) spheres to array ordered templates and centrifugal slip casting in the interstitial spaces of the EPS template to obtain cell struts with high packing density. Aqueous Al₂O₃–ZrO₂ slurries with up to 50 vol.% solid contents were prepared and centrifuged at acceleration of 2,860g. The effect of the solid contents of slurries on segregation phenomena of different particles and green compact uniformity were investigated. In multiphase system, the settling velocities of Al₂O₃ and ZrO₂ particles were calculated. Theory analysis and calculated results both indicated segregation phenomenon was hindered for slurries with 50 vol.% solid content. The cell struts of sintered products had high green density (61.5%TD), sintered density (99.1%TD) and homogeneous microstructures after sintered at 1,550 °C for 2 h. The cell size and porosity of Al₂O₃–ZrO₂ ceramic foams can be adjusted by changing the size of EPS spheres and the load applied on them during packing, respectively. When the porosity increased from 75.3% to 83.1%, the compressive strength decreases from 3.82 to 2.07 MPa.     

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).     

Effect of Zr Addition on Bi<Subscript>1.8</Subscript>Pb<Subscript>0.4</Subscript>Sr<Subscript>2.0</Subscript>Ca<Subscript>1.1</Subscript>Cu<Subscript>2.1</Subscript>O<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> Superconductor

The polycrystalline Bi_1.8Pb_0.4Sr_2.0Ca_1.1Cu_2.1 M_xO _y , with M = Zr (x = 0.0, 0.02, 0.04), were synthesized by solid-state reaction method and studied by X-ray diffraction analysis (XRD), scanning electron microscopy equipped with energy dispersive of X-ray analysis (SEM/EDX) and resistivity versus temperature measurements. The influence of the Zr addition on the Tc and microstructure properties of the superconducting compounds has been studied. SEM observations show whiskers grains randomly distributed and microstructural change due to the addition of Zr. The ZrO₂ was incorporated into the crystalline structure of BSCCO system in all samples. The crystallographic structure remains in a tetragonal form where a= b≠c. Generally, all samples exhibit semiconductor behaviour above \(T_{\mathrm {c}}^{\text {onset}}\). The onset critical temperature \(T_{\mathrm {c}}^{\text {onset}}\) increases up to 86 with x = 0.02. There is an enhancement in the critical temperature for doped samples as compared with pure Bi_1.8Pb_0.4Sr_2.0Ca_1.1Cu_2.1O _y .Changes in superconducting properties of ZrO₂ nanoparticle added Bi-2212 system were discussed.     

Effect of V<Subscript>2</Subscript>O<Subscript>5</Subscript> content on the optical,structural and electrochromic properties of TiO<Subscript>2</Subscript> and ZrO<Subscript>2</Subscript> thin films

Vanadium oxide (V₂O₅) mixed titanium oxide (TiO₂) and zirconium oxide (ZrO₂) thin films were fabricated on glass substrates (corning 2947) and on indium tin oxide (ITO) coated glass substrates by sol gel spin coating process. Their optical, structural and electrochromic properties were investigated. The results were compared with pure TiO₂ and ZrO₂ thin films. Mixture of V₂O₅ with both types of film reduces the transmittance at the higher wavelengths. The refractive index of the V₂O₅ mixed TiO₂ and ZrO₂ films increases when compared with pure TiO₂ and ZrO₂ films. AFM images demonstrate no significant topographical changes for V₂O₅ mixed TiO₂ whereas for V₂O₅ mixed ZrO₂ films a topographical change is observed. V₂O₅ mixed TiO₂ showed slight increase in their charge capacity.     

Effect of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> on the properties of nanocrystalline ZrO<Subscript>2</Subscript> + 3 mol % Y<Subscript>2</Subscript>O<Subscript>3</Subscript> powder

We have studied the properties of nanocrystalline ZrO₂〈3 mol % Y₂O₃〉 and 90 wt % ZrO₂〈3 mol % Y₂O₃〉-10 wt % Al₂O₃ powders prepared via hydrothermal treatment of coprecipitated hydroxides at 210°C. The results demonstrate that Al₂O₃ doping raises the phase transition temperatures of the metastable low-temperature ZrO₂ polymorphs and that the structural transformations of the ZrO₂ and Al₂O₃ in the doped material inhibit each other.     

Thermodynamic properties of Dy<Subscript>2</Subscript>O<Subscript>3</Subscript> · 2ZrO<Subscript>2</Subscript> and Ho<Subscript>2</Subscript>O<Subscript>3</Subscript> · 2ZrO<Subscript>2</Subscript> in the range 10–340 K

The low-temperature heat capacity of Dy₂O₃ · 2ZrO₂ and Ho₂O₃ · 2ZrO₂ has been determined by adiabatic calorimetry in the temperature range 10–340 K. The results have been used to calculate the entropy, enthalpy increment, and reduced Gibbs energy of the zirconates without taking into account their low-temperature magnetic transformations.     

High-Temperature Heat Capacity and Thermodynamic Properties of HoBiGeO<Subscript>5</Subscript> and ErBiGeO<Subscript>5</Subscript>

Polycrystalline HoBiGeO₅ and ErBiGeO₅ samples have been prepared by solid-state reactions, by firing stoichiometric mixtures of Ho₂O₃ (Er₂O₃), Bi₂O₃, and GeO₂. The effect of temperature on the heat capacity of the synthesized compounds has been investigated by differential scanning calorimetry in the range 350–1000 K. The experimental C_p(T) data have been used to evaluate the thermodynamic functions of bismuth holmium and bismuth erbium germanates: enthalpy increment, entropy change, and reduced Gibbs energy.     

Lithium ion conductivity of LiLaO<Subscript>2</Subscript>-Li<Subscript>2</Subscript>ZrO<Subscript>3</Subscript> solid solutions

The limits of the LiLaO₂-and Li₂ZrO₃-based solid solutions in the LiLaO₂-Li₂ZrO₃ system have been determined: 0–10 mol % Li₂ZrO₃ and 0–5 mol % LiLaO₂, respectively. We have studied the transport properties (electronic conductivity, temperature and composition dependences of conductivity and activation energy) of lithium lanthanate and the solid solutions in the LiLaO₂-Li₂ZrO₃ system. Conduction in LiLaO₂ is likely due to lithium ion transport through a polyhedral network.     

Sorption of U(VI) onto TiO<Subscript>2</Subscript>/ZrO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> Mesoporous Materials from Sulfate Solutions

New nanostructured mesoporous materials of the composition TiO₂/ZrO₂/SiO₂ were prepared by the template sol–gel method using a siloxane–acrylate emulsion as a template. The morphology and structure of these materials and their ability to take up U(VI) were studied. The influence of various factors (ZrO₂ content, pH of solution) on the sorption properties was studied. The suggested materials allow efficient sorption of U(VI) from sulfate solutions with low U(VI) concentrations and can be used in final purification processes.     

Influences of ZrO<Subscript>2</Subscript> nanoparticles on the microstructure and mechanical behavior of Ce-TZP/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocomposites

Influences of ZrO₂ nanoparticles on the mechanical properties and microstructure of hot-pressing Ce-TZP/Al₂O₃ ceramics were investigated. Meanwhile, t-ZrO₂ to m-ZrO₂ transformation toughening mechanism was investigated by X-ray diffractometry (XRD) method, and deflection of samples under applied stress were recorded too. The results show that when the percentage of ZrO₂ was 20%, the mechanical properties and microstructures of materials are optimum. Moreover, TEM observation show dislocation structures formation both in the Al₂O₃ and on the grain boundary. Because the dislocation agglomeration and fixation by ZrO₂ nanoparticles could deflect cracking or stop cracking development, a strengthening and toughening effect could be achieved.     

Phase relations in the aluminothermic reduction of ZrO<Subscript>2</Subscript>

This paper presents thermodynamic evaluation of reactions between ZrO₂ and aluminum, which indicates that the aluminothermic reduction of zirconium oxides at temperatures above 600°C is only possible when Al _x Zr _y intermetallic compounds form in the metallic phase. Thermodynamic analysis results are supported by experimental data, which demonstrate that, at ZrO₂: Al ratios in the range 0.4–1.4, the aluminothermic reduction of ZrO₂ leads predominantly to the formation of the congruently melting compounds Al₂Zr and Al₃Zr. The phase formation in the slag yields various forms of calcium aluminates and calcium zirconates and leads to a gradual reduction in the oxidation state of the zirconium.     

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⁺.     

Synthesis and High-Temperature Heat Capacity of Dy<Subscript>2</Subscript>Ge<Subscript>2</Subscript>O<Subscript>7</Subscript> and Ho<Subscript>2</Subscript>Ge<Subscript>2</Subscript>O<Subscript>7</Subscript>

The Dy₂Ge₂O₇ and Ho₂Ge₂O₇ pyrogermanates have been prepared by solid-state reactions in several sequential firing steps in the temperature range 1237–1473 K using stoichiometric mixtures of Dy₂O₃ (or Ho₂O₃) and GeO₂. The heat capacity of the synthesized germanates has been determined as a function of temperature by differential scanning calorimetry in the range 350–1000 K. The experimentally determined C _p (T) curves of the dysprosium and holmium germanates have no anomalies and are well represented by the Maier–Kelley equation. The experimental C _p (T) data have been used to evaluate the thermodynamic functions of the Dy₂Ge₂O₇ and Ho₂Ge₂O₇ pyrogermanates: enthalpy increment H°(T)–H°(350 K), entropy change S°(T)–S°(350 K), and reduced Gibbs energy Ф°(T).     

High-temperature heat capacity and thermodynamic properties of TbBiGeO<Subscript>5</Subscript> and DyBiGeO<Subscript>5</Subscript>

Polycrystalline TbBiGeO₅ and DyBiGeO₅ samples have been prepared by solid-state reactions, by firing stoichiometric mixtures of Tb₂O₃ (Dy₂O₃), Bi₂O₃, and GeO₂ in air at 1003, 1073, 1123, 1143, 1173, and 1223 K. The molar heat capacity of the bismuth terbium and bismuth dysprosium germanates has been determined by differential scanning calorimetry. The experimental C _p (T) data obtained in the range 350–1000 K have been used to evaluate the thermodynamic functions of the synthesized oxide compounds: enthalpy increment, entropy change, and reduced Gibbs energy.