Synthesis of Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>〈B〉 solid precursors and LiNbO<Subscript>3</Subscript>〈B〉 batches and their phase compositions

A process has been developed for preparing boron-doped niobium pentoxides Nb₂O₅〈B〉 to be used as precursors in the sysnthesis of nithium biobate batches LiNbO₃〈B〉 having tailored dopant concentrations. Solutions of various origins were used to isolate Nb₂O₅〈B〉. A method has been advanced to account for boron loss as volatile compounds upon the heat treatment of niobium hydroxide in order to determine the boron amount to be added to niobium hydroxide in the form of H₃BO₃. The boron concentration in LiNbO₃〈B〉 during lithium niobate synthesis is shown to be independent of the origin of the Nb₂O₅〈B〉 precursor with the same as-batch boron concentration. The phase compositions of Nb₂O₅〈B〉 and LiNbO₃〈B〉 have been characterized by X-ray powder diffraction and IR spectroscopy and boron concentrations have been determined for the synthesis of single-phase lithium niobate batches for use in the production of optically uniform single crystals and pore-free piezoelectric ceramics.     

Phase equilibria in the Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>–CdO system and the thermal stability of Cd<Subscript>2</Subscript>Nb<Subscript>2</Subscript>O<Subscript>7</Subscript> and CdNb<Subscript>2</Subscript>O<Subscript>6</Subscript>

Phase equilibria were studied in the Nb₂O₅–CdO system in the Nb₂O₅-rich region including CdNb₂O₆ and Cd₂Nb₂O₇. It was determined that CdNb₂O₆ and Cd₂Nb₂O₇ in air are stable to 1150 and 1120°C, respectively, and that, above these temperatures, there is solid-phase decomposition of niobates with CdO release in the gas phase. Along with the cadmium oxide evaporation, the Cd₂Nb₂O₇ decomposition is accompanied by the formation of cadmium metaniobate CdNb₂O₆ and the CdNb₂O₆ decomposition results in the formation of niobium oxide Nb₂O₅. No thermal events were observed in the differential thermal analysis curve for a 1: 1 CdNb₂O₆–Cd₂Nb₂O₇ mixture heated to 1100°C in air, which suggests that there are neither phase transformations in cadmium niobates, nor a eutectic within this temperature and concentration ranges. A study of the morphology of compacted samples of niobates determined specific conditions for producing dense composite ceramics, a mixture of niobates, that is suitable for using as a dielectric material.     

Thermodynamic Properties and Thermal Expansion of Tm<Subscript>2</Subscript>O<Subscript>3</Subscript> · 2ZrO<Subscript>2</Subscript> Solid Solution

The isobaric heat capacity of Tm₂O₃ · 2ZrO₂ solid solution was measured by adiabatic calorimetry and differential scanning calorimetry (DSC), and smoothed values of the enthalpy changes, entropy, and reduced Gibbs free energy in the temperature range 8–1200 K were calculated. Thermal expansion was studied by X-ray diffraction in the temperature range 298–1173 K.     

Distribution of niobium and lanthanum between two immiscible melts in the system LaPO<Subscript>4</Subscript>–SiO<Subscript>2</Subscript>–NaF–Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>

The system LaPO₄–SiO₂–NaF–Nb₂O₅–Fe₂O₃ is characterized by immiscibility fields in the liquid state region. Addition of iron expands fields of immiscibility of melts and decreases the temperature of their coexistence. A fraction of 87–90% of niobium is extracted into iron silicate melt, and 92–98% of lanthanum is extracted into phosphate salt melt.     

Preliminary results on sol-gel processing of 〈100〉 oriented Pb(Mg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript>-PbTiO<Subscript>3</Subscript> thin films using diol-based solutions

A novel sol-gel method is used here for the synthesis of air-stable and precipitate-free diol-based sols of 0.7Pb(Mg_1/3Nb_2/3)O₃-0.3PbTiO₃ (PMN-PT). Sols containing a 15 mol% lead excess have been used for the preparation of PMN-PT thin films. The films were deposited onto (111)Pt/TiO₂/SiO₂/(100)Si substrates, and crystallised in oxygen by Rapid Thermal Processing (RTP), using different temperatures and soaking times. Single perovskite films are obtained when treated at temperatures between 600 and 700°C for 6 s. Those crystallised at other temperatures contain a secondary pyrochlore phase. This phase also appears in the films treated at 650°C with soaking times longer than 6 s. PMN-PT films with a 〈100〉 preferred orientation were prepared by using a PbTiO₃ seeding layer onto the substrate. These PMN-PT films present relaxor-type electrical properties. Dielectric permittivity, , shows significant dispersion. Its temperature dependence presents a broad maximum at 110–130°C, which position shifts towards higher temperatures with frequency. Ferroelectric hysteresis loops show high values of saturation polarisation but very low remanence. The piezoelectric activity of the films has been tested by the measurement of their local piezoelectric hysteresis loops.     

Structural and Temperature Dependent Electrical Conductivity Properties of Dy<Subscript>2</Subscript>O<Subscript>3</Subscript>–Sm<Subscript>2</Subscript>O<Subscript>3</Subscript> CO-Doped Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>

In the present work, Dy₂O₃ and Sm₂O₃ double-doped Bi₂O₃-based materials are synthesized by exploiting the solid-state synthesis method. The structural and temperature dependent electrical properties of these ternary ceramic samples, which are candidate materials for solid oxide fuel cell (SOFCs) electrolyte, are determined by means of a powder X-ray diffractometer (XRD), the four point-probe method (FPPM), and the thermal-gravimetry/differential thermal analysis (TG/DTA). As a result of the XRD measurements, the fluorite-type fcc δ-phase with a stable structure is obtained for higher values of the dopant oxide material, which are the samples with the maximum content of fixed 20% Dy₂O₃ and 15% and 20% Sm₂O₃. The samples with the stable δ-phase structure have higher conductivities. The highest electrical conductivity is found for the (Bi₂O₃)0.6(Dy₂O₃)_0.2(Sm₂O₃)_0.2 sample, which was 2.5×10^–2 (Ohm cm)^–1 at 750 °C. The activation energies are also calculated from the Arrhenius charts, which were determined from the FPPM measurements. The lowest activation energy is found as 0.85 eV for the sample with the highest electrical conductivity.     

Synthesis and properties of γ-Ga<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> solid solutions

The textural and structural properties of mixed oxides Ga₂O₃–Al₂O₃, obtained via impregnating γ-Al₂O₃ with a solution of Ga(NO₃)₃ and subsequent heat treatment, are studied. According to the results from X-ray powder diffraction, gallium ions are incorporated into the structure of aluminum oxide to form a solid solution of spinel-type γ-Ga₂O₃–Al₂O₃ up to a Ga₂O₃ content of 50 wt % of the total weight of the sample, accompanied by a reduction in the specific surface area, volume, and average pore diameter. It is concluded that when the Ga₂O₃ content exceeds 50 wt %, the β-Ga₂O₃ phase is observed along with γ-Ga₂O₃–Al₂O₃ solid solution. ⁷¹Ga and ²⁷Al NMR spectroscopy shows that gallium replaces aluminum atoms from the tetrahedral position to the octahedral coordination in the structure of γ-Ga₂O₃–Al₂O₃.     

Formation of solid solutions of multiferroics in the Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–Nd<Subscript>2</Subscript>O<Subscript>3</Subscript>–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The sequence of phases appearance during the formation of Bi_1–xNd_xFeO₃ solid solutions in powder oxides mixtures of bismuth, neodymium, and iron has been determined. It has been shown that the closeness of the reaction mixture composition to that of the individual compound (BiFeO₃ or NdFeO₃) is essential for the realization of the series of phase transformations yielding solid solutions of multiferroics Bi_1–xNd_xFeO₃ as the final product, due to the prevalence of various interphase contacts in the starting reaction zone.     

Effects of Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> on the crystallization and structure of CaO–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> glass ceramics

Radiation-induced degradation of the weakly and strongly 4-vinylpyridine basic ion exchange resins by gamma radiolysis was investigated in the presence of air and liquid water. This study is focused on evaluating the radiolytic gases (H₂, CO, CO₂ and CH₄) and liquid products (water-solute TOC and NH₄ ⁺). The weakly basic resin yielded lower amounts of H₂ and CO and higher amounts of CO₂ than those of the strongly basic resin. Moreover, the strong basic resin tended to yield greater amounts of NH₄ ⁺. Resins were characterized by the FTIR spectroscopy technique and the results showed that the resins structures are relatively stable.     

Thermal properties of Ga<Subscript>2</Subscript>O<Subscript>3</Subscript>–PbO–P<Subscript>2</Subscript>O<Subscript>5</Subscript> glass system

Thermal behavior of xGa₂O₃–(50 − x)PbO–50P₂O₅ (x = 0, 10, 20, and 30 mol.% Ga₂O₃) and xGa₂O₃–(70 − x)PbO–30P₂O₅ (x = 0, 10, 20, 30, and 40 mol.% Ga₂O₃) glassy materials were studied by thermo-mechanical analysis (TMA) and differential thermal analysis (DTA). Replacement of PbO for Ga₂O₃ is accompanied by increasing glass-transition temperature (263 ≤ T _g/°C ≤ 535), deformation temperature (363 ≤ T _d/°C ≤ 672), crystallization temperature (396 ≤ T _c/°C ≤ 640) and decreasing of coefficient of thermal expansion (5.1 ≤ CTE/ppm K⁻¹ ≤ 16.7). Values of Hruby parameter were determined (0.1 ≤ K _H ≤ 1.3). The thermal stability of prepared glasses increases with increasing of concentration of Ga₂O₃.     

B<Subscript>2</Subscript>O<Subscript>3</Subscript> additives on sintering and microwave dielectric behaviors of Mg<Subscript>4</Subscript>Nb<Subscript>2</Subscript>O<Subscript>9</Subscript> ceramics synthesized through the aqueous sol–gel Process

The relationships between the sintering temperatures and the microwave dielectric properties of (1−x)Mg₄Nb₂O₉-xB₂O₃ (x = 0.5–10 wt. %) compounds were investigated by the sol–gel method in order to reduce the sintering temperature in this study. A suitable amount of B₂O₃ doping was effective in allowing low sintering temperatures without a little detrimental effect on these dielectric properties of the Mg₄Nb₂O₉ compounds. The variations in the dielectric constant (ε _r ) and the quality factor (Q·f) of the Mg₄Nb₂O₉ compounds depended on the amount of B₂O₃ doping and the sintering temperature. As a result, a ε _r value of ~12.8 and a Q·f value of ~142,570 GHz were obtained when the Mg₄Nb₂O₉ compound with x = 3% was sintered at 1,200 °C for 4 h. The temperature coefficient of resonant frequency (τ _f ) of the 3%-B₂O₃ doping Mg₄Nb₂O₉ compound slightly changed from −33 to −48 ppm/°C with an increased sintering temperature.     

Thermal studies of ZnO–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript>–TeO<Subscript>2</Subscript> glasses

The effect of TeO₂ additions on the thermal behaviour of zinc borophosphate glasses were studied in the compositional series (100 − x)[0.5ZnO–0.1B₂O₃–0.4P₂O₅]–xTeO₂ by differential scanning calorimetry, thermodilatometry and heating microscopy thermal analysis. The addition of TeO₂ to the starting borophosphate glass resulted in a linear increase of glass transition temperature and dilatometric softening temperature, whereas the thermal expansion coefficient decreased. Most of glasses crystallize under heating within the temperature range of 440–640 °C. The crystallization temperature steeply decreases with increasing TeO₂ content. The lowest tendency towards crystallization was observed for the glasses containing 50 and 60 mol% TeO₂. X-ray diffraction analysis showed that major compounds formed by annealing of the glasses were Zn₂P₂O₇, BPO₄ and α-TeO₂. Annealing of the powdered 50ZnO–10B₂O₃–40P₂O₅ glass leads at first to the formation of an unknown crystalline phase, which is gradually transformed to Zn₂P₂O₇ and BPO₄ during subsequent heating.     

Impedance Study of the Conductivity of Solid Oxide Electrolyte Films SrZr<Subscript>0.95</Subscript>Y<Subscript>0.05</Subscript>O<Subscript>3–δ</Subscript> and CaZr<Subscript>0.9</Subscript>Y<Subscript>0.1</Subscript>O<Subscript>3–δ</Subscript>

Information on the across-plane conductivity of films of solid-oxide electrolytes SrZr_0.95Y_0.05O_3–δ and CaZr_0.9Y_0.1O_3–δ deposited on ion-conducting supports is acquired by the impedance method. It is shown that the support/film interface and the intergrain boundaries considerably affect the across-plane charge transfer in the film. The effect of the crystallographic orientation of the YSZ support on the microstructure and conductivity of the CaZr_0.9Y_0.1O_3–δ electrolyte film is demonstrated.     

Reduction of Oxide Mixtures of (Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> + CuO) and (Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> + Co<Subscript>3</Subscript>O<Subscript>4</Subscript>) by Low-Temperature Hydrogen Plasma

The paper presents experimental results pertaining to the reduction of oxide mixtures namely (Fe₂O₃ + CuO) and (Fe₂O₃ + Co₃O₄), by low-temperature hydrogen plasma in a microwave hydrogen plasma set-up, at microwave power 750 W and hydrogen flow rate 2.5 × 10^?6 m³ s^?1. The objective was to examine the effect of addition of CuO or Co₃O₄, on the reduction of Fe₂O₃. In the case of the Fe₂O₃ and CuO mixture, oxides were reduced to form Fe and Cu metals. Enhancement of reduction of iron oxide was marginal. However, in the case of the Fe₂O₃ and Co₃O₄ mixture, FeCo alloy was formed within compositions of Fe₇₀Co₃₀, to Fe₃₀Co₇₀. Since the temperature was below 841 K, no FeO formed during reduction and the sequence of Fe₂O₃ reduction was found to be Fe₂O₃ → Fe₃O₄ → Fe. Reduction of Co₃O₄ preceded that of Fe₂O₃. In the beginning, the reduction of oxides led to the formation of Fe–Co alloy that was rich in Co. Later Fe continued to enter into the alloy phase through diffusion and homogenization. The lattice strain of the alloy as a function of its composition was measured. In the oxide mixture in which excessive amount of Co₃O₄ was present, all the Co formed after reduction could not form the alloy and part of it appeared as FCC Co metal. The crystallite size of the alloy was in the range of 22–30 nm. The crystal size of the Fe–Co alloy reduced with an increase in Co concentration.     

Adsorption of chlorobenzene vapor on V<Subscript>2</Subscript>O<Subscript>5</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst under dynamic conditions

Adsorption dynamics of chlorobenzene vapors on a 5% V₂O₅/Al₂O₃ catalyst has been investigated using the frontal chromatography technique. The uptakes of chlorobenzene have been measured as a function of vapor concentration and adsorption equilibrium has been found to follow formally the Langmuir isotherm. The breakthrough time proved to be a linear function of the column length as expected. Breakthrough profiles have been reported for different experimental conditions and quantitatively fitted by a reduced lumped diffusion model. This model provides an analytical solution that facilitates engineering calculations. Model parameters show complex behavior as functions of stream characteristics and depend on column length. When empirical expressions relating model mass transfer coefficients with influencing variables are found the model demonstrates good accuracy in predicting column performance.     

Sol–Gel Synthesis of Na<Subscript>2</Subscript>O-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-P<Subscript>2</Subscript>O<Subscript>5</Subscript> Glasses and their Characterization by NMR,SNMS, and AFM

Sodium aluminophosphate samples with composition 43.8Na₂O12.5Al₂O₃43.8P₂O₅ were prepared by the sol–gel route using different precursors and working in different pH ranges from pH < 1 up to pH > 10. The structures of the gels and of the corresponding glasses were investigated by solid state NMR and compared to that of a glass with the same composition prepared by a traditional melting process. In addition to bulk materials, thin films were deposited by dip coating on silica glasses. Applying secondary neutral mass spectrometry (SNMS), the expected elements and residual carbon were identified. The surfaces of the coatings and fracture surfaces of bulk material were investigated using atomic force microscopy (AFM). Solid state NMR revealed that samples prepared via a lactate route exhibited local Al and P environments closest to that of the melt-prepared glass, with the highest extent of Al-O-P connectivity.     

Thermoelectric power and electrochemical studies on CdI<Subscript>2</Subscript>–Ag<Subscript>2</Subscript>O–V<Subscript>2</Subscript>O<Subscript>5</Subscript>–B<Subscript>2</Subscript>O<Subscript>3</Subscript> system

A quaternary super-ion-conducting system, 20CdI₂ − 80[xAg₂O − y(0.7V₂O₅ − 0.3B₂O₃)] where 1 ≤ x/y ≤ 3, has been prepared by melt quenching technique. The electrical conductivity measured was the order of 10⁻⁴  S/cm at room temperature. The values of silver-ion transport number obtained by electromotive force technique are nearly unity. The thermoelectric power and electrochemical studies were done on the CdI₂–Ag₂O–V₂O₅–B₂O₃ system. The discharge and polarization characteristics were examined for different cathodes to evaluate the utility of these cells as power sources for low energy applications.     

Effect of MoO<Subscript>3</Subscript> additions on the thermal stability and crystallization kinetics of PbO–Sb<Subscript>2</Subscript>O<Subscript>3</Subscript>–As<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

The present paper reports on the effect of MoO₃ on the glass transition, thermal stability and crystallization kinetics for (40PbO–20Sb₂O₃–40As₂O₃)_100−x –(MoO₃) _x (x = 0, 0.25, 0.5, 0.75 and 1 mol%) glasses. Differential scanning calorimetry (DSC) results under non-isothermal conditions for the studied glasses were reported and discussed. The values of the glass transition temperature (T _g) and the peak temperature of crystallization (T _p) are found to be dependent on heating rate and MoO₃ content. From the compositional dependence and the heating rate dependence of T _g and T _p, the values of the activation energy for glass transition (E _g) and the activation energy for crystallization (E _c) were evaluated and discussed. Thermal stability for (40PbO–20Sb₂O₃–40As₂O₃)_100−x –(MoO₃) _x glasses has been evaluated using various thermal stability criteria such as ΔT, H _r , H _g and S. Moreover, in the present work, the K _r(T) criterion has been considered for the evaluation of glass stability from DSC data. The stability criteria increases with increasing MoO₃ content up to x = 0.5 mol%, and decreases beyond this limit.