Effect of Electric Field on Dielectric Properties of SnO2 Sb2O3 and their Mixed Thin Films

Thin films of various thicknesses in the MIM structure have been prepared from the the powders of SnO₂, Sb₂O₃ and (SnO₂ + Sb₂O₃) of high purity by the thermal evaporation technique in a vacuum of 10⁻⁵ Torr. Dielectric properties of SnO₂, Sb₂O₃, and their mixed thin films have been studied with ac and dc electric fields and frequency. Capacitance and loss tangent are almost independent on dc voltage upto 1.0 V for SnO₂, 10.0 V for Sb₂O₃ and 2.5 V for mixed films. These capacitors become unstable at 1.0 V for SnO₂ films and 2.5 V for mixed films. For higher film thicknesses the decay in these films starts at higher voltages. Capacitance and loss tangent increases with applied ac voltage in SnO₂, Sb₂O₃, and their mixed films. A comparison of the capacitance values of SnO₂, Sb₂O₃, and their mixed films showed that the capacitance values are less in Sb₂O₃ as compared to SnO₂ films. In mixed films the capacitance is greater than the constituent films. These studies have shown that Sb₂O₃ films are found to be more stable compared to SnO₂ and their mixed films for ac and dc voltages. The results thus obtained on SnO₂, Sb₂O₃, and their films are presented and discussed.     

Microhardness and fracture toughness of Y<Subscript>2</Subscript>O<Subscript>3</Subscript>-and Y<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript>-based nanocrystalline laser ceramics

The microhardness and fracture toughness of laser nanocrystalline ceramics based on the cubic oxides Y₂O₃ and Y₃Al₅O₁₂ are determined experimentally. It is shown by comparative measurements that the fracture toughness and microhardness of Y₂O₃ ceramics exceed the corresponding parameters of Y₂O₃ single crystals by factors of 2.5 and 1.3, respectively. The fine morphology of grains and grain boundaries in fractures is investigated. It is ascertained that changes in the mechanical properties of the nanocrystalline ceramics under study are related to both the sizes and structure of grains and the structure of grain boundaries. It is suggested that twinning processes determine the mechanisms of formation of nanocrystalline ceramics.     

Intercalation of O2 and its Effect on the Properties of C60 and C70 Solids

Abstract

The intercalation of O₂ in C₆₀ and C₇₀ solids have been studied. In both gas effusion spectra of C₆₀ and C₇₀ powder exposed to O₂ at room temperature, two evolution peaks of O₂ are found near 80 and 150°C. In both C₆₀ and C₇₀ powder, the peak near 80°C does not depend on a heating ratio and the peak near 150°C shifts to higher temperature with the heating ratio. The activation energy on diffusion of O₂ in C₆₀ and C₇₀ solids are ～0.27eV and ～0.46eV, respectively. The number of O₂ intercalated in C₇₀ powder is larger than that in C₆₀ powder. Electron spin density of 02-intercalated C₆₀ film is larger than that of C₇₀ film. The effect on the properties of C₆₀ and C₇₀ solids by the intercalation of O₂ are discussed.     

Growth of crystals of ferroelectrics Ln2Ti2O7 (LnLa?Nd) with layer-type structure

Single crystals of rare-earth (La-Nd, Sm, Gd) and Y dititanates have been grown either by the method of direct high frequency heating in cold container or/and floating zone optical technique. The crystals Ce₂Ti₂O₇ and Pr₂Ti₂O₇ belong to the structural type of Ca₂Nb₂O₇ and possess dielectric and optic characteristics which are very similar to that of known ferroelectrics La₂Ti₂O₇ and Nd₂Ti₂O₇.     

The influence of Fe2O3 and B2O3 additions on the thermal properties,crystallization kinetics and durability of a sodium aluminum phosphate glass

A sodium aluminum phosphate glass, identified as a potential encapsulating phase for radioactive wastes, has been noted to be thermally unstable, crystallizing upon heat treatment to yield a variety of phases which may be detrimental to the longer term properties of the final wasteform. In an attempt to improve the thermal stability and overall resistance of this glass to crystallization, the influence of various oxide additions including Fe₂O₃ and B₂O₃ has been investigated. It has been shown that quite small additions of B₂O₃ are extremely effective in improving the stability, with ⩾2 mol% B₂O₃ almost completely suppressing crystallization whilst only marginally affecting the excellent chemical durability of the ternary glass, at least at the lower B₂O₃ concentrations. In contrast, addition of Fe₂O₃ or B₂O₃/Fe₂O₃ mixtures does not lead to significant improvements in the thermal stability, although durability relative to that of the ternary composition is improved significantly with increasing Fe₂O₃ content.     

Diffusion and reactions of interstitial oxygen species in amorphous SiO2: A review

This article briefly summarizes the diffusion and reactions of interstitial oxygen species in amorphous SiO₂ (a-SiO₂). The most common form of interstitial oxygen species is oxygen molecule (O₂), which is sensitively detectable via its characteristic infrared photoluminescence (PL) at 1272 nm. The PL observation of interstitial O₂ provides key data to verify various processes related to interstitial oxygen species: the dominant role of interstitial O₂ in long-range oxygen transport in a-SiO₂; formation of the Frenkel defect pair (Si–Si bond and interstitial oxygen atom, O⁰) by dense electronic excitation; efficient photolysis of interstitial O₂ into O⁰ with F₂ laser light (λ = 157 nm, hν = 7.9 eV); and creation of interstitial ozone molecule via reaction of interstitial O₂ with photogenerated O⁰. The efficient formation of interstitial O⁰ by F₂ laser photolysis makes it possible to investigate the mobility, optical absorption, and chemical reactions of interstitial O⁰. The observed properties of O⁰ are consistent with the model that O⁰ takes the configuration of Si–O–O–Si bond. Interstitial O₂ and O⁰ react with dangling bonds, oxygen vacancies, and chloride groups in a-SiO₂. Reactions of interstitial O₂ and O⁰ with mobile interstitial hydrogen species produce interstitial water molecules and hydroperoxy radicals. Interstitial hydroxyl radicals are formed by F₂ laser photolysis of interstitial water molecules.     

Structure of V2O5–P2O5 glasses by X-ray and neutron diffraction

The atomic structures of two V₂O₅–P₂O₅ glasses and vitreous (v-) V₂O₅ were investigated by X-ray and neutron diffraction. The V=O double bond is a common characteristic of the VO_n units that constitute the structures of the glasses. VO₅ square pyramids with elongated bonds of ~ 0.190 nm to the pyramidal base are found for the 50V₂O₅–50P₂O₅ glass. These weaker V–O bonds are balanced in V–O–P bridges by overbonded P–O bonds. The V^(IV) sites, which account for 19.7% and 35.2% of the total V sites in the 73V₂O₅–27P₂O₅ and 50V₂O₅–50P₂O₅ glasses, respectively, form similar pyramids in agreement with the structure of crystalline (VO)₂P₂O₇. The short-range structure of v-V₂O₅ and the 73V₂O₅-27P₂O₅ glass is formed of mixtures of VO₅ and VO₄ pyramids. A significant amount of V···O distances > 0.22 nm found for all glasses belong either to linkages V=O···V or to three-coordinated O sites.     

Growth of oxide fibers by the internal crystallization method

A new approach is developed for growing relatively inexpensive single-crystal and eutectic oxide fibers suitable for the fabrication of high-temperature composite materials. Sapphire (Al₂O₃), YAG (Y₃Al₅O₁₂), mullite (3Al₂O₃ · 2SiO₂), YAP (YAlO₃), and eutectic (Al₂O₃-Y₃Al₅O₁₂, Al₂O₃-ZrO₂ (Y₂O₃), and Al₂O₃-Gd₂O₃) fibers are produced by the internal crystallization method, and their mechanical strength and micro-structures are studied.     

Electrical properties of Al2O3 film deposited at low temperatures

Amorphous Al₂O₃ films were deposited on p-Si by rf magnetron sputtering to investigate their potential as a gate dielectric in organic thin film transistors (OTFTs). The deposition was performed at room temperature, 200 and 300 °C using Al₂O₃ and Al targets. Achieved Al₂O₃ films have higher capacitance values than thermally grown SiO₂ as characterized by capacitance-voltage measurements. It is also found from current-voltage and roughness measurements that the leakage current and the surface roughness can be least when the films are deposited at room temperature. The capacitance of the film obtained from the Al₂O₃ target appears higher than that of the Al₂O₃ film from the Al target while the results of electrical breakdown are opposite. These room temperature processes are promising for applications to the gate dielectrics of organic TFTs.     

Temperature-concentration fields of the crystallization of YbAl<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript> from high-temperature melt solutions based on potassium trimolybdate

The phase relationships in the YbAl₃(BO₃)₄-K₂Mo₃O₁₀-B₂O₃-Yb₂O₃ multicomponent system are investigated in the temperature range 1150–1000°C within the stability region of the YbAl₃(BO₃)₄ compound. The region of single-phase crystallization of the YbAl₃(BO₃)₄ borate is revealed in the section corresponding to the composition containing 15 wt % YbAl₃(BO₃)₄. For the same composition, it is demonstrated that there exists a correlation between the temperatures of saturation of melt solutions with the YbAl₃(BO₃)₄ borate and the composition of the solvent, namely, the contents of B₂O₃, K₂Mo₃O₁₀, and Yb₂O₃ in the solvent. The temperature dependences of the solubility of the YbAl₃(BO₃)₄ compound at different contents are determined for melts of two compositions: melt I containing 55 mol % K₂Mo₃O₁₀ and 45 mol % B₂O₃ and melt II containing 55 mol % K₂Mo₃O₁₀, 40 mol % B₂O₃, and 5 mol % Yb₂O₃. The specific features of the crystallization of the YbAl₃(BO₃)₄ compound are analyzed and compared with those of the yttrium, neodymium, gadolinium, and erbium aluminum borates studied previously.     

Standard stereographic projections of hematite and related corundum-type sesquioxides

Stereographic (0001), (211 0) and (101 0) projections of α-Fe₂O₃ are presented in the form of both figures and tables. These can also be used for α-Al₂O₃, Cr₂O₃, Ti₂O₃ and V₂O₃, for which cases the maximum occurring deviations are indicated.     

Crack resistance and atomic structure of Li2B4O7 single crystals

The nature of destruction of single crystals of lithium tetraborate Li₂B₄O₇ under the action of a concentrated load is investigated. It is established that planes of easy crack propagation in Li₂B₄O₇ single crystals are the (100), (010), (001), and {111} planes. It is found that crack propagation occurs in each case along the atomic layers that are linked by bridge oxygen atoms between main structural units (B₄O₉) and, therefore, are most weakly bound.     

Cryoscopic Investigation of Lead Oxide Mixtures with Garnet Forming Oxides,Garnets, and Related Oxide Compounds

The freezing point depression of PbO as solvent caused by the trivalent oxides and oxide compounds Fe₂O₃, Ga₂O₃, Al₂O₃, Bi₂O₃, Y₂O₃, Gd₂O₃, La₂O₃, YFeO₃, Fe₃O₄, Y₃Fe₅O₁₂, Gd₃Ga₅O₁₂, and PbFe₁₂O₁₉ allows to determine the number of particles which are formed from these compounds in the diluted solutions. — We have measured the liquidus temperatures of binary mixtures with the help of a DTA-equipment. In this way the cryoscopic constant K̄_c = 121 ± 16 K · kg · mole⁻¹ of PbO was determined by addition of ZnO, Cu₂O, PbSO₄, and PbF₂, respectively. The experimental results show that the oxides and oxide compounds dissociate in particles which contain only one cation of the solved compound.     

Raman scattering study of crystalline and melting states of BaO·2B2O3

Melting and crystallization scenarios of barium tetraborate BaB₄O₇ (BaO·2B₂O₃) are studied in situ by Raman spectroscopy. It is shown that the scenario depends on the temperature–time history of melt. Crystallization conditions of the beta modification of barium tetraborate (β-BaB₄O₇) from a stoichiometric glass structure BaO·2B₂O₃ were investigated.     

Growth and scintillation properties of the Na2W2O7 crystal

The growth and scintillation properties of the Na₂W₂O₇ crystal are reported. The solid reaction between Na₂CO₃ and WO₃ is used to synthesise the Na₂W₂O₇ material. The Na₂W₂O₇ single crystal has been grown by the Bridgman method. And the Na₂W₂O₇ single crystal with sizes 14×7×6 mm³ has been achieved. The transmission spectra, the Ultraviolet fluorescence spectra and the X-ray excited luminescence spectra of the Na₂W₂O₇ crystal are measured. The measurement results show that the Na₂W₂O₇ crystal is a promising intrinsic scintillator.     

Cd2Ge2O6 nanowires grown by a simple hydrothermal route

Cd₂Ge₂O₆ nanowires have been synthesized by a simple hydrothermal route in the absence of any surfactants. The diameter and length of the Cd₂Ge₂O₆ nanowires with flat tips are 30‐300 nm and several dozens of micrometers, respectivley. X‐ray diffraction and high‐resolution transmission electron microscopy results show that the nanowires are composed of monoclinic Cd₂Ge₂O₆ phase. The growth condition dependence results show that the formation of the Cd₂Ge₂O₆ nanowires undergoes three morphological changes from spherical particles to nanorods, and finally to nanowires. The photoluminescence spectrum of the Cd₂Ge₂O₆ nanowires exhibits three fluorescence emission peaks centered at 422 nm, 490 nm and 528 nm showing the potential application for optical devices. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

On the Solubility of Garnets in PbO/B2O3 High Temperature Solvents

The paper is concerned with solubility models for Y₃Fe₅O₁₂ (YIG) and Gd₃Ga₅O₁₂ (GGG) solved in PbO/B₂O₃ high temperature solutions containing Fe₂O₃ or Ga₂O₃ in excess. It is shown that a new extended eight-particle model Interprets well the literature data of the solubility of YIG as well as the DTA data of the solubility of GGG. Comparisons of solution enthalpies determined in terms of the single-molecule, eight-particle, and extended eight-particle model are carried out in dependence on the excess concentration of species containing iron or gallium, respectively.     

Hydrothermal crystallization of Na2Ti6O13, Na2Ti3O7, and Na16Ti10O28 in the NaOH-TiO2-H2O system at a temperature of 500°C and a pressure of 0.1 GPa: The structural mechanism of self-assembly of titanates from suprapolyhedral clusters

An increase in the NaOH concentration in the NaOH-TiO₂ (rutile)-H₂O system at a temperature of 500°C and a pressure of 0.1 GPa leads to the crystallization R-TiO₂ + Na₂Ti₆O₁₃ → Na₂Ti₃O₇ → Na₁₆Ti₁₀O₂₈. Crystals of the Na₂Ti₆O₁₃ titanate (space group C2/m) have the three-dimensional framework structure Ti₆O₁₃. The structure of the Na₂Ti₃O₇ titanate (space group P2 ₁/m) contains the two-dimensional layers Ti₃O₇. The structure of the Na₁₆Ti₁₀O₂₈ titanate (space group P-1) is composed of the isolated ten-polyhedron cluster precursors Ti₁₀O₂₈. In all the structures, the titanium atoms have an octahedral coordination (MTiO₆). The matrix self-assembly of the Na₂Ti₆O₁₃ and Na₂Ti₃O₇ (Na₄Ti₆O₁₄) crystal structures from Na₄ M ₁₂ invariant precursors is modeled. These precursors are clusters consisting of twelve M polyhedra linked through the edges. It is demonstrated that the structurally rigid precursors Na₄ M ₁₂ control all processes of the subsequent evolution of the crystal-forming titanate clusters. The specific features of the self-assembly of the Na₂Ti₃O₇ structure that result from the additional incorporation of twice the number of sodium atoms into the composition of the high-level clusters are considered.     

Single-crystal structure of vanadium-doped La2Mo2O9

A high-precision X-ray diffraction study of single crystals of two compositions—La₂Mo_1.78V_0.22O_8.89 and La₂Mo_1.64V_0.36O_8.82—was performed. In the vanadium-doped compounds, as in the structure of the metastable β_ms phase of pure La₂Mo₂O₉, the La and Mo atoms and one of the three oxygen atoms are displaced from the threefold axis, on which they are located in the high-temperature β phase. The structure contains two partially occupied oxygen sites. It was shown that molybdenum atoms are partially replaced by vanadium atoms, which are not involved in the disordering, are located on the threefold axis, and are shifted toward one of the oxygen atoms. This is consistent with the temperature-induced changes in the structure of La₂Mo₂O₉ and the changes in the properties of these crystals caused by the introduction of vanadium atoms into the structure.     

Calculation of thermodynamic parameters of melts from experimentally determined liquidus‐curves

Thermodynamic parameters of melts (ΔH_S, A₀, A₁) in the system Anorthite‐Diopside and Bi₂O₃‐Bi₄B₂O₉ have been calculated by a rigorous application of solution thermodynamics. The data are internally consistent and yield values of ΔH_S for Anorthite = 133 kJ/mole, Diopside = 81 kJ/mole, Bi₂O₃ = 19 kJ/mole and Bi₄B₂O₉ = 39 kJ/mole. The activity of Anorthite and Diopside in an anorhtitic melt deviates negative from ideality, whereas a diopsidic melt behaves almost ideal. In a “Bi₂O₃” melt the activity of the Bi₂O₃ component is strongly positive, that of Bi₄B₂O₉ is strongly negative. The opposite is observed for the “Bi₄B₂O₉” melt. All calculated liquidi except the Bi₄B₂O₉ liquidus closely match the experimental ones. In contrast to the experimental liquidus the calculated Bi₄B₂O₉ liquidus has an inflection point. The crest of the metastable spinode (solvus) for a “Bi₂O₃” melt is close to the liquidus indicating melt separation at undercooling. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)