The effect of Fe2O3 dopants on electrophysical and sorption properties of ZnO

The effect of Fe₂O₃ dopants (0–0.8 mol.%) on ZnO conductivity and its chlorine chemisorption ability has been studied in the temperature range of 20–250 °C. Introduction of dopants increases the activation energy of ZnO conductivity and decreases the conductivity. The effective charge of the chemisorbed chlorine species as well as the strength of their bonding to the surface in samples containing Fe₂O₃ are considerably lower than in initial ZnO, which leads to a decrease of reactivity of the doped catalysts in chlorination.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1196–1199, July, 1993.     

The effect of pressure and temperature of self-diffusion coefficients in several concentrated deuterium oxide diamagnetic electrolyte solutions

The pressure dependences of the self-diffusion coefficients of deuterium oxide in 4.5m solutions of LiCl–D₂O and CsCl–D₂O (also 7m) and 3.06m CaCl₂–D₂O have been measured by the NMR spin-echo method at 30°C, 60°C, and 90°C. Shear viscosities and densities of these solutions have also been determined over the same range of experimental conditions. The experimental data show that the diffusion constantD decreases with the increasing structure-making ability of the electrolyte cation Ca⁺²>Li⁺. In contrast, the diffusion coefficient for D₂O in the 4.5 and 7m CsCl solutions is equal to that for pure D₂O at 30°C but lower at 60°C and 90°C. It has been found that the Stokes-Einstein equation relates well the diffusion coefficients to shear viscosity in these concentrated electrolyte solutions.     

Study of the fluorite–pyrochlore–fluorite phase transitions in Ln<Subscript>2</Subscript>Ti<Subscript>2</Subscript>O<Subscript>7</Subscript> (Ln=Lu,Yb, Tm)

The ordering processes in Ln₂Ti₂O₇ (Ln=Lu, Yb, Tm) are studied by X-ray diffraction, thermal analysis, infrared absorption (IR) spectroscopy, and electrical conductivity measurements. The coprecipitation method followed by freeze-drying was used for Ln₂Ti₂O₇ synthesis. The region of low-temperature fluorite phase existence is 600 °C<T<740 °C. The low-temperature fluorite–pyrochlore phase transition in Ln₂Ti₂O₇ takes place at ~740–800 °C. Ln₂Ti₂O₇ (Ln=Lu, Yb, Tm) have the structure of disordered pyrochlore with antisite Ln–Ti defects at 800 °C<T<1,100 °C.The high-temperature pyrochlore–fluorite transformation takes place in Tm₂Ti₂O₇, Yb₂Ti₂O₇, and Lu₂Ti₂O₇ in air at T>1,600 °C. The conductivity values are 5·10^–3 S/cm for Tm₂Ti₂O₇, 6·10^–3 S/cm for Yb₂Ti₂O₇, and 10^–2 S/cm for Lu₂Ti₂O₇ at 740 °C. This order–disorder transition leads to a 2 orders of magnitude conductivity growth and a 10–30 times permittivity increase in Ln₂Ti₂O₇ samples obtained at 1,700 °C.Presented at the OSSEP Workshop Ionic and Mixed Conductors: Methods and Processes, Aveiro, Portugal, 10–12 April 2003     

Synthesis and Electrical Properties of Lithium Metazirconate

Lithium metazirconate Li₂ZrO₃ with a monoclinic lattice is synthesized; the lattice parameters are: a = 0.5432 nm, b = 0.5427 nm, c = 0.903 nm, = 112.72°, and Z = 4. The conductivity of both the stoichiometric compound and samples rich or deficient in Li₂O near this composition is determined. The conductivity of the synthesized compound reaches 0.029 S cm^–1 at 600°C. The activation energy for the high-temperature segment is 13.8 kJ mol^–1. An abnormal behavior (abrupt jump) of the temperature dependence of the conductivity at 430°C is discovered and attributed to a phase transition. The change in the structure in this temperature domain (400 to 500°C) is corroborated by the high-temperature X-ray analysis.     

Studies on hydrolyzable carbides. XXII: The carbothermal reduction of scandium oxide Sc2O3

The composition of the products of carbothermal reduction of Sc₂O₃ is examined by X-ray diffraction and chemical analysis and by the hydrolysis method. At pressures of 10^–2-1 Pa, the reaction starts in the temperature region of 1 000–1 200°C. The first product is Sc₂OC of NaCl type; at 1 Pa and 1 400–1 500°C this substance is formed quantitatively (according to stoichiometry) within 50–100 h, repeated homogenization, however, is necessary, or else Sc₂OC reacts locally with Sc₂O₃ giving Sc₂O_1+x C_1–x . The lattice parameter of Sc₂OC in the presence of Sc₁₅C₁₉ is 457.6₃pm. At temperatures above 1 500°C, Sc₁₅C₁₉ is incompletely formed by subsequent reaction with carbon. The product melts at cca. 1 800°C; carbon dissolves and the final composition approaches ScC₂. Carbon separates during solidification. The phase fractions in the products are affected by evaporation, the vapour pressures above both Sc₂OC and Sc₁₅C₁₉ being comparable with the pressure requisite for the carboreduction process. The results are discussed with respect to the often ambiguous published data.

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Untersuchung hydrolysierbarer Carbide, XXII. Die karbothermische Reduktion von Scandiumoxid

Zusammenfassung Zur Untersuchung von Produkten der karbothermischen Reduktion von Scandiumoxid wurden sowohl röntgenographische und chemische Analyse als auch die hydrolytische Methode verwendet. Bei 10^–2 bis 1 Pa beginnt die Reaktion im Temperaturintervall von 1 000–1 200°C. Das erste Reaktionsprodukt ist das Scandiumoxidcarbid Sc₂OC von NaCl-Typ, das quantitativ (der Stöchiometrie entsprechend) bei 1 400–1 500°C und 1 Pa in 50–100 Stunden entsteht. Eine wiederholte Homogenisierung ist allerdings notwendig, damit es zu keiner lokalen Reaktion zwischen Sc₂OC und Sc₂O₃ kommt, bei der dann die Phase Sc₂O_1+x C_1–x entsteht. In Gegenwart von Sc₁₅C₁₉ ist der Gitterparameter von Sc₂OCa=457.6₃pm. Über 1 500°C führt eine weitere Reaktion mit Kohlenstoff zu einer nicht ganz vollendeten Bildung von Sc₁₅C₁₉. Bei cca. 1 800°C schmilzt das Reaktionsprodukt bei gleichzeitiger Auflösung von weiterem Kohlenstoff und die Zusammensetzung nähert sich der Formel ScC₂, beim Erstarren fällt der Kohlenstoff wieder aus. Die Verteilung der Phasen im Produkt wird von der Verdampfung beeinflußt, da die Dampfdrucke von Sc₂OC und Sc₁₅C₁₉ mit dem zum Karboreduktionverlauf notwendigen Druck vergleichbar sind. Die erhaltenen Ergebnisse werden in Relation mit den nicht eindeutigen Angaben in der Literatur diskutiert.

     

Properties of a nanocomposite polymer electrolyte from an amorphous comb-branch polymer and nanoparticles

Three fully amorphous comb-branch polymers based on poly(styrene-co-maleic anhydride) as a backbone and poly(ethylene glycol) methyl ether of different molecular weights as side chains were synthesized. SiO₂ nanoparticles of various contents and the salt LiCF₃SO₃ were added to these comb-branch polymers to obtain nanocomposite polymer electrolytes. The thermal and transport properties of the samples have been characterized. The maximum conductivity of 2.8×10^–4 S cm^–1 is obtained at 28 °C. In the system the longer side chain of the comb-branch polymer electrolyte increases in ionic conductivity after the addition of nanoparticles. To account for the role of the ceramic fillers in the nanocomposite polymer electrolyte, a model based on a fully amorphous comb-branch polymer matrix in enhancing transport properties of Li⁺ ions is proposed.     

Electroconductivity,Nature of Conduction,Thermodynamic Stability of the BaPr1 –xYxO3 – αCeramics

The electroconductivity and the nature of conduction of vacuum-dense ceramics BaPr_{1 – x} Y _x O_{3 –} (x= 0.05–0.15) is studied at temperatures of 373 to 985°C, of 2.1 × 10⁴to 10^–11Pa, and of 40 to 2400 Pa. The coefficient of linear thermal expansion is measured. The ceramics have a perovskite structure and are practically p-type semiconductors with a maximum conductivity of 0.26 S cm^–1at x= 0.10 and 800°C, in air. The share of ionic (proton) conductivity of the ceramics does not exceed 0.2–0.4%. The conductivity is weakly dependent on the air humidity. In a hydrogen-containing atmosphere, the ceramics undergoes reduction with destruction. Boundaries of thermodynamic stability of BaPr_0.9Y_0.1O_{3 –} at 500–900°C are determined.     

Ionization constants of aqueous ammonia from 25 to 250°C and to 2000 bar

The ionization constant of ammonia has been determined by conductivity measurements and found to vary from 1.77×10^–5 at 25°C to 1.3×10^–6mol-kg^–1 at 250°C. The pressure effect to 2000 bar has been measured and the ratio K₂₀₀₀/K₁ is 6.8 at 25°C and 11 at 250°C. The standard molar volume change for the ionization at 1 bar, V ₁ ^o , changes from –28.8 at 25°C to –67 cm³-mol^–1 at 250°C.     

Low-temperature dry etching of tungsten,dielectric, and trilevel resist layers on GaAs

Dry etching of common masking materials used in GaAs device technology, was examined down to temperatures of –30°C. The etch rates of SiN_x, SiO₂, and W in SF₆/Ar are reduced below 0°C, but the anisotropy of the etching is improved at low temperature. Microwave enhancement of the SF₆/Ar discharges produces increases in etch rates of several times at 25°C, but much lower increases at –30°C substrate temperature. The underlying GaAs surface shows increased S and F coverage after low-temperature etching, but these species are readily removerd either by anex-situ wet chemical cleaning step or an in-situ H₂ plasma exposure. Photoresist etching is less sensitive to temperature, and anisotropic profiles are produced between –30 and +60°C in pure O₂ discharges.     

Electrical properties of poly(bis(β-phenoxyethoxy)phosphazene) and its complexes

Electrical and dielectrical properties of poly(bis(-phenoxyethoxy)phosphazene) (I) and its complexes with various content ratios of AgSO₃CF₃ to monomeric unit (0.25/1 (II) and 0.5/1 (III) in molar ratio) were investigated.Dc conductivity of respective samples at 18 °C were 6.1×10^–12, 4.4×10^–9, and 7.1×10^–8 S/m.Dc conduction was considered to be due to ion hopping. Charge mobility ranged from 3×10^–12 to 6× 10^–11 m²/Vs depending on the applied field in sample II. In sample I, a tan peak was found which can be ascribed to molecular relaxation of main chains. The peak vanished upon introducing AgSO₃ CF₃. Temperature dependence of total conductivity ( _T ) measured byac method in the temperature range between –150 °C and 50 °C showed several peaks at the temperatures corresponding to the peak temperatures of tan. Total conductivities of respective samples at 100 kHz were 4.9×10^–7 (69 °C), 1.7×10^–4 (45 °C), and 1.5×10^–4(40°C)S/m.     

Water-vapor pressure and thermodynamics of the dehydration of manganese,nickel, cadmium,and lead perchlorate hydrates

The water-vapor pressure has been measured by a static method, the temperature limits for existence have been determined, and the parameters of the equation lgp [Torr]=b —a/T have been calculated for the following crystal hydrates: Mn(ClO₄)₂ · 2H₂O (90–130°C, a=3527.0,b=8.487), Ni(ClO₄)₂ · 4H₂O (60–100°C,a=3606.7,b=9.704), Ni(C1O₄)₂ · 2H₂O (110–160°C,a = 4261.7,b = 10.103), Cd(ClO₄)₂ · 6H₂O (25–58.2°C,a = 3143.7,b = 9.356), Cd(ClO₄)₂ · 2H₂O (90–144.8°C,a=3823.3,b = 9.472), Pb(ClO₄)₂ · 3H₂O (10–47°C,a = 2932.9,b = 9.391 and 47–81.5°C,a = 2448.1,b=7.877), Pb(ClO₄)₂ · H₂O (60–102.4°C,a=3610.2,b = 9.857). A hitherto unknown metastable hydrate Cd(ClO₄)₂ · 4H₂O with a phase transition at 30.9°C (20–30.9°C,a = 3669.5,b = 11.343 and 30.9–63.7°C,a=3058.6,b = 9.339) has been detected.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 466–470, March, 1993.     

Thermal analysis of transition metal and rare earth oxide system-gas interactions by a solid electrolyte-based coulometric technique

The oxidation-reduction behaviour of transition metal and rare earth oxide systems in oxygen potential controlled atmospheres was investigated by means of a solid electrolyte-based coulometric technique (SEC) in carrier gas mode to obtain information concerning the extent of oxygen stoichiometry, thep-T-x diagram of any mixed oxide phase, the kinetics of the oxygen exchange and the phase transitions.The direct coupling of SEC and electrical conductivity measurements provides further information about the relationship between oxygen deficiency and conductivity, especially as concerns the oxygen mobility and the transition from ionic to mixed ionic/electronic conductivity in any system.In the fluorite-type phases PrO_2–x, Ce_0.8Pr_0.2O_y–x and Ce_0.8Sr_0.08Pr_0.12O_y–x, the higher oxidation state of Pr is stabilized and the electrical conductivity increases in this sequence. The perovskite-type phase Sr_1–yCe_yFeO_3–x, shows transitions and a second phase reflected in the temperature-programmed spectrum of this substance. The electrical conductivity of Sr_0.9Ce_0.1FeO_3–x changes fromn-type top-type with increasing oxygen pressure.     

Crystallisation Kinetics of β -Spodumene in Lithium Aluminosilicate Sol–Gel Glasses

-spodumene (LiAlSi₂O₆) is one of the crystalline phase of the lithium aluminosilicate (LAS) glass-ceramics, having a low thermal expansion coefficient. The sol–gel process is an advantageous processing route for LAS materials, compared to melting, as it avoids lithium oxide losses and formation of undesired crystalline phases. It is very important to understand the crystallisation kinetics in order to assess the amount of the different crystalline phases formed for a given thermal cycle. This study reports the application of the non-isothermic method for evaluation of crystallization kinetic parameters, based on differential thermal analysis (DTA) experiments under constant heating rates (10, 12, 15 and 20°C min^–1) up to 1000°C. The Johnson-Mehl-Avrami (JMA) theory, modified with distinct approaches, lead to Avrami coefficients, n, in the range of 2.1–2.4 and apparent activation energies, E_a, of 345–362 kJ mol^–1. A simultaneous tridimensional and bidimensional crystal growth mechanism for a constant number of nuclei is proposed for -spodumene crystallization.     

Microstructure and Conduction of Composites Bi<Subscript>2</Subscript>CuO<Subscript>4</Subscript>-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> Near the Eutectic Melting Point

Microstructure and conduction of ceramic composites Bi₂CuO₄ + xBi₂O₃ (x = 5, 10, 15, 20 wt %) near the eutectic melting point (770°C) are studied. Bismuth oxide, initially randomly distributed over the ceramics bulk, after quenching from temperatures exceeding the eutectic melting point, becomes localized at triple junctions and grain boundaries in Bi₂CuO₄, which is caused by wetting grain boundaries and forming a liquid-channel structure. The jumpwise change in the composites’ conductivity near 730 and 770°C caused by polymorphic transformation of Bi₂O₃ and the eutectic melting with simultaneous formation of a liquid-channel structure. Transport numbers of the oxygen ion are measured at 770°C by coulomb-volumetric method. The conduction by oxygen ions increases in the composites with decreasing average size of Bi₂CuO₄ crystallites.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 596–601.Original Russian Text Copyright © 2005 by Lyskov, Metlin, Belousov, Tret’yakov.     

Zinc(II) oxide solubility and phase behavior in aqueous sodium phosphate solutions at elevated temperatures

A platinum-lined, flowing autoclave facility is used to investigate the solubility/phase behavior of zinc(II) oxide in aqueous sodium phosphate solutions at temperatures between 17 and 287°C. ZnO solubilities are observed to increase continuously with temperature and phosphate concentration. At higher phosphate concentrations, a solid phase transformation to NaZnPO₄ is observed. NaZnPO₄ solubilities are retrograde with temperature. The measured solubility behavior is examined via a Zn(II) ion hydrolysis/complexing model and thermodynamic functions for the hydrolysis/complexing reaction equilibria are obtained from a least-squares analysis of the data. The existence of two new zinc(II) ion complexes, Zn(OH)₂(HPO₄)^2– and Zn(OH)₃(H₂PO₄)^2–, is reported for the first time. A summary of thermochemical properties for species in the systems ZnO–H₂O and ZnO–Na₂O–P₂O₅–H₂O is also provided.     

Effect of gallium oxide dopants on electrophysical and sorption properties of zinc oxide

The effect of gallium oxide dopants (0.1–0.3 at.% Ga) on the electrophysical and sorption properties of ZnO was studied in the temperature range from 19 to 350 °C. The introduction of the dopant increasing the conductivity of ZnO is accompanied by a change in the amounts of SO₂ and Cl₂ sorbed and the reactivity of zinc oxide. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 266–270, February, 1999.     

Conductance of Selected Alkali Metal Salts in Aqueous Binary Mixtures of 2-Methoxyethanol at 25°C

Precise conductance measurements have been performed for lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, sodium perchlorate, and sodium tetraphenylborate in 2-methoxyethanol–water mixtures at four different mole fractions, i.e., 0.056, 0.136, 0.262, and 0.486 of 2-methoxyethanol (69.73 D 26.55) at 25°C in the concentration range 0.0004–0.0642 mol-dm^–3. The limiting molar conductivity °, the association constant K _A, and the association distance R for the solvent mixtures have been evaluated from the conductance concentration data using the 1978 Fuoss conductance equation. The single-ion conductances have been estimated using the reference electrolyte tetrabutylam-monium tetraphynylborate(Bu₄NBPh₄). The analysis of the data indicates that for most salts ion association is appreciable in the solvent mixtures with a mole fraction of the cosolvent of 0.262 or higher. The results have been interpreted in terms of ion-solvent interactions and structural changes in the mixed solvent media.     

Conduction and Ion Transport in LaYO<Subscript>3</Subscript> Doped with CaO

Values of partial conductions (ionic: protonic, oxygen, hole) and their activation energies in LaYO₃ are determined at 700–1050°C, pO₂ ranging from air to 10⁻¹⁵ Pa, and pH₂O = 0.04–13.5 kPa for different versions of doping with calcium (when introduced into the lanthanum or yttrium sublattices, or into both sublattices simultaneously). The conductivity increases in the series La_0.97Ca_0.03YO_{3 − α} < LaY_0.97Ca_0.03O_{3 − α} < La_0.985Y_0.985Ca_0.03O_{3 − α}, which means that the stoichiometric composition with a 1 : 1 ratio between Y and La has the highest conductivity.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 610–615.Original Russian Text Copyright © 2005 by Balakireva, Stroeva, Gorelov.     

Disubstituted Rubidium Orthoperiodate Rb2H3IO6: Crystal and Molecular Structures and Properties

The crystal and molecular structures of acid salt Rb₂H₃IO₆ were determined. The anion part of the structure is united via a hydrogen bonding system to form a layer parallel to the xy plane. The proton conductivity in the temperature range of 40–60°C was found to be 10^–7–5 × 10^–6 Ohm^–1cm^–1, E _a = 2 eV.