Phase Equilibria in Systems Involving the Rare Earth Oxides. Part III. The Eu2O3?In2O3 System

The equilibrium phase diagram was determined for the Eu₂O₃−In₂O₃ system. An induction furnace, having an iridium crucible as the heating element (susceptor), was used to establish the solidus and liquidus curves. The 1:1 composition melts congruently at 1745 ± 10 °C. Melting point relations suggest that the 1:1 composition is a compound with solid solution extending both to 31 mole percent In₂O₃ and 71 mole percent In₂O₃. The compound is pseudohexagonal with a_H = 3.69 A and c_H = 12.38 A. Isostructural phases also occur in the 1:1 mixtures of both Gd₂O₃ and Dy₂O₃ with In₂O₃. The melting points of Eu₂O₃ and In₂O₃ were determined to be 2,240 ± 10 °C and 1910 ± 10 °C respectively. A eutectic occurs in the Eu₂O₃−In₂O₃ system at 1,730 °C and about 73 mole percent In₂O₃. The indicated uncertainties in the melting points are conservative estimates of the overall inaccuracies of temperature measurement.     

Studies of Beryllium Chromite and Other Beryllia Compounds With R2O3 Oxides

Reactions between BeO and R₂O₃ oxides at high temperatures were studied. Compound formation was observed between BeO and the following oxides: B₂O₃, Al₂O₃, Ga₂O₃, Y₂O₃, La₂O₃, and Cr₂O₃. No reaction was observed with Sc₂O₃, ln₂O₃, and Fe₂O₃. Detailed studies were made of BeO·Cr₂O₃ which is isostructural with BeO·Al₂O₃. BeO·Cr₂O₃ is a semiconductor. Optical and X-ray data are given for all reaction products.     

Polymorphism of Bismuth Sesquioxide. I. Pure Bi2O3

Stability relationships of the four polymorphs of bismuth oxide have been determined by means of DTA and high-temperature x-ray studies. The stable low-temperature monoclinic form transforms to the stable cubic form at 730 ±5 °C, which then melts at 825 ± 5 °C. By controlled cooling, the metastable tetragonal phase and/or the metastable body-centered cubic (b.c.c.) phase appear at about 645 °C. Whereas b.c.c. can be preserved to room temperature, tetragonal will transform to monoclinic between 550 and 500 °C. Tetragonal Bi₂O₃, however, is easily prepared by decomposing bismutite (Bi₂O₃·CO₂) at 400 °C for several hours. The greatest transition expansion occurs at the monoclinic to cubic inversion, and cubic Bi₂O₃ shows the greatest coefficient of volume expansion. With exposure to air, Bi₂O₃ carbonates and partially transforms to bismutite and an unknown phase.     

Phase structure evolution and thermal expansion variation of Sc2O3 doped Nd2Zr2O7 ceramics

(Nd_1−xSc_x)₂Zr₂O₇ (x = 0, 0.1, 0.3, 0.5, 0.7) compounds were synthesized by solid state reaction at 1700 °C for 10 h, and characterized by XRD, Raman spectroscopy, SEM and high-temperature dilatometer. Nd₂Zr₂O₇ exhibited pyrochlore phase, and its lattice parameter increased after Sc₂O₃ doping, which could be attributed to the presence of Sc³⁺ interstitial ions in pyrochlore lattice. Fluorite phase formed in the doped Nd₂Zr₂O₇, and (Nd_0.3Sc_0.7)₂Zr₂O₇ exhibited pure fluorite phase. The thermal expansion coefficient (TEC) of Nd₂Zr₂O₇ was significantly enhanced by 10 mol% Sc₂O₃ doping, but higher Sc₂O₃ doping decreased the TEC. The reduced crystal energy due to the presence of Sc³⁺ interstitial ions could cause the initial increase in the TEC, and the formation of fluorite phase might contribute to the reduced TEC. Considering the alleviation of the thermal expansion mismatch stress for the high-temperature applications of Nd₂Zr₂O₇, Sc₂O₃ was an excellent dopant and there existed an optimal Sc₂O₃ content for the optimization design of compound compositions.     

Phase Composition, Electrical Conductivity, and Stability of ZrO2–Sc2O3–Cr2O3 Solid Electrolytes

The phase composition, electrical conductivity, and structural and electrical stability of ZrO₂–Sc₂O₃–Cr₂O₃ solid electrolytes prepared by solid-state reactions involving three-step firing at 1350, 1850 (vacuum), and 1300°C were studied for compositions along two lines: x(0.91ZrO₂ + 0.09Sc₂O₃)–yCr₂O₃ (I) andx(0.89ZrO₂ + 0.11Sc₂O₃)–yCr₂O₃ (II), x + y = 1, y = 0–0.04. The results indicate that the ternary solid solutions withy= 0.01–0.02 retain a cubic structure in a broad temperature range, down to room temperature. This increases the low-temperature (<600°C) conductivity of the solid electrolytes, especially in system II. In both systems, Cr₂O₃ solubility is about 3 mol %. Stability tests at 900°C for 200 h reduce the conductivity of the solid electrolytes, particularly at the lower Sc₂O₃ content and in the presence of Cr₂O₃. The reduction in conductivity is due to the decomposition of the high-temperature tetragonal phase and the formation of a tetragonal phase with a low stabilizer content.     

Antifungal and antiovarian cancer properties of α Fe2 O3 and α Fe2 O3 /ZnO nanostructures synthesised by Spirulina platensis

Candida albicans (C. albicans) infection shows a growing burden on human health, and it has become challenging to search for treatment. Therefore, this work focused on the antifungal activity, and cytotoxic effect of biosynthesised nanostructures on human ovarian tetracarcinoma cells PA1 and their corresponding mechanism of cell death. Herein, the authors fabricated advanced biosynthesis of uncoated α‐Fe₂ O₃ and coated α‐Fe₂ O₃ nanostructures by using the carbohydrate of Spirulina platensis. The physicochemical features of nanostructures were characterised by UV–visible, high resolution transmission electron microscopy, Fourier transform infrared spectroscopy, and X‐ray diffraction. The antifungal activity of these nanostructures against C. albicans was studied by the broth dilution method, and examined by 2′, 7′‐dichlorofluorescein diacetate staining. However, their cytotoxic effects against PA1 cell lines were evaluated by MTT and comet assays. Results indicated characteristic rod‐shaped nanostructures, and increasing the average size of α‐Fe₂ O₃ @ZnO nanocomposite (105.2 nm × 29.1 nm) to five times as compared to α‐Fe₂ O₃ nanoparticles (20.73nm × 5.25 nm). The surface coating of α‐Fe₂ O₃ by ZnO has increased its antifungal efficiency against C. albicans. Moreover, the MTT results revealed that α‐Fe₂ O₃ @ZnO nanocomposite reduces PA1 cell proliferation due to DNA fragmentation (IC₅₀ 18.5 μg/ml). Continual advances of green nanotechnology and promising findings of this study are in favour of using the construction of rod‐shaped nanostructures for therapeutic applications.Inspec keywords: nanocomposites, toxicology, nanofabrication, cellular biophysics, X‐ray diffraction, iron compounds, biochemistry, cancer, antibacterial activity, transmission electron microscopy, biomedical materials, wide band gap semiconductors, DNA, II‐VI semiconductors, visible spectra, molecular biophysics, ultraviolet spectra, nanomedicine, zinc compounds, nanoparticles, microorganisms, Fourier transform infrared spectraOther keywords: Spirulina platensis, antifungal activity, α‐Fe₂ O₃ nanoparticles, antiovarian cancer properties, Candida albicans infection, cytotoxic effect, biosynthesised nanostructures, human ovarian tetracarcinoma cell PA1, cell death, uncoated α‐Fe₂ O₃ , coated α‐Fe₂ O₃ nanostructures, α‐Fe₂ O₃ ‐ZnO nanocomposite, carbohydrate, physicochemical features, UV‐visible spectroscopy, high resolution transmission electron microscopy, Fourier transform infrared spectroscopy, X‐ray diffraction, broth dilution method, 2′, 7′‐dichlorofluorescein diacetate staining, PA1 cell lines, comet assays, MTT assays, rod‐shaped nanostructures, surface coating, PA1 cell proliferation, DNA fragmentation, green nanotechnology, Fe₂ O₃ ‐ZnO, Fe₂ O₃      

Effect of a Nonequilibrium State on Phase Relations in the System TiO2–Sc2O3 (40–50 mol % Sc2O3)

The phase transitions in TiO₂–Sc₂O₃ (40–50 mol % Sc₂O₃) samples prepared from coprecipitated and mechanically activated oxide mixtures are studied. It is shown that heat treatment below 1000°C leads to the formation of nonstoichiometric, metastable cubic phases with a distorted fluorite structure. With increasing temperature, this structure transforms into a stable fluorite-like structure through (low-symmetry) orthorhombic and hexagonal phases, which is associated with the incorporation of OH groups. Characteristically, the phases studied contain nanoscale regions differing in the degree of ordering, which result from internal stress. The internal stress in mechanically activated phases is shown to be fully relieved by about 1300°C.     

Preparation and characterization of bulk ZnGa2O4

High-quality bulk ZnGa₂O₄ has been synthesized from equimolar mixtures of ZnO and Ga₂O₃ by the conventional solid-state method. For the first time, the sample has been characterized in detail to confirm the formation of pure single phase of spinel ZnGa₂O₄. The formation of ZnGa₂O₄ has been confirmed by sintering the mixtures of ZnO and Ga₂O₃ at different temperatures, ranging from 900–1200 °C. It is observed that the single phase of ZnGa₂O₄ has been formed at and above 1000 °C sintering temperature for 24 h. The crystallinity and phase formation of this single phase has been confirmed by X-ray diffraction. X-ray photoelectron spectroscopic studies have been carried out for bulk ZnGa₂O₄ sintered at 1000 °C for 24 h which showed 14% Zn, 28% Ga and 58% O, indicating stoichiometric ZnGa₂O₄. A new parameter, the energetic separation between the Zn 2p_3/2 and Ga 2p_3/2 peaks, has been used as a sensitive tool to distinguish between a complete formation of ZnGa₂O₄ compound and a mixture of ZnO and Ga₂O₃ powders. Surface morphology studies by scanning electron microscopy reveal that the formation of ZnGa₂O₄ takes place in mosaic rod-like structure. The purity of the compound has also been checked by the energy dispersive X-ray method, indicating the absence of foreign ions and the ratio of zinc to gallium has been calculated and found to be 1 : 2, indicating stoichiometric ZnGa₂O₄.     

Polymorphism of Bismuth Sesquioxide. II. Effect of Oxide Additions on the Polymorphism of Bi2O3

The effect of small oxide additions on the polymorphism of Bi₂O₃ was studied by means of high-temperature x-ray diffractometry. Solidus and occasional liquidus temperatures were approximated, so that tentative partial phase diagrams for 33 oxide additions were constructed. Only the monoclinic and the cubic forms of Bi₂O3 were found to be stable. Other phases, frequently reported by previous investigators, such as tetragonal and body-centered cubic (b.c.c.), were shown to form metastably from cooled liquid or cubic. An impure b.c.c. phase of distinct but variable composition appeared in systems of ZnO, PbO, B₂O₃, Al₂O₃, Ga₂O₃, Fe₂O₃, SiO₂, GeO₂, TiO₂, and P₂O₅. The impure b.c.c. phase in the systems with SiO₂, GeO₂, and TiO₂ melted congruently about 100 °C above the m.p. of Bi₂O₃. The impure b.c.c. phase was formed metastably in systems with Rb₂O, NiO, MnO, CdO, V₂O₅, and Nb₂O₅; the conditions of formation were dependent on composition, preparation, and heating schedules. The impure b.c.c. phases, both stable and metastable, had smaller unit cell dimensions than that of pure Bi₂O₃.     

High-temperature resistivity and thermoelectric properties of coupled substituted Ca3Co2O6

Polycrystalline samples of Ca_3−xNa_xCo_2−xMn_xO₆ (x=0.0–0.5) have been prepared by the sol-gel cum combustion method using sucrose in order to investigate the effects of the coupled substitution of Na and Mn on Ca and Co sites on the transport properties of Ca₃Co₂O₆(Co326). The products were characterized by Fourier transform infrared spectroscopy, powder x-ray diffraction (XRD), thermogravimetry (TGA), differential thermal analysis and scanning electron microscopy. XRD patterns reveal the formation of single-phase products up to x=0.5. Coupled substitution increases the solubility of both Na and Mn on Ca and Co sites, respectively, in contrast to the limited solubility of Na and Mn (x=0.2) when separately substituted. TGA confirms the formation of the Ca₃Co₂O₆ phase at temperatures ∼720 °C. The grain size of the parent and substituted products is in the range 150–250 nm. Electrical resistivity and Seebeck coefficient were measured in the temperature range 300–800 K. Resistivity shows semiconducting behavior for all the compositions, particularly in the low-temperature regime. The Seebeck coefficient increases with temperature throughout the measured temperature range for all compositions. The maximum Seebeck coefficient (200 μV K⁻¹) is observed for x=0.5 at 825 K, and this composition may be optimal for high-temperature thermoelectric applications.     

Phase Equilibria and Crystal Chemistry in Portions of the System SrO-CaO-Bi2O3-CuO,Part IV— The System CaO-Bi2O3-CuO

New data are presented on the phase equilibria and crystal chemistry of the binary systems CaO-Bi₂O₃ and CaO-CuO and the ternary CaO-Bi₂O₃-CuO. Symmetry data and unit cell dimensions based on single crystal and powder x-ray diffraction measurements are reported for several of the binary CaO-Bi₂O₃ phases, including corrected compositions for Ca₄Bi₆O₁₃ and Ca₂Bi₂O₅. The ternary system contains no new ternary phases which can be formed in air at ~700–900 °C.     

Effect of dopant concentration on electrical conductivity in the Sc2O3-ZrO2 system

Electrical conductivity measurements have been made as a function of dopant concentration (4 to 8 mol% Sc₂O₃) in the scandia-zirconia system, All the compositions studied had a tetragonal structure. The hombohedral phase was present only in samples prepared from mechanical mixtures of Sc₂O₃ and ZrO₂. In specimens prepared by coprecipitation, no phase lines were observed and the monoclinic zirconia (m-ZrO₂) phase was present for only Sc₂O₃ contents 5 mol %. The conductivity of Sc₂O₃-ZrO₂ decreased continuously with time up to 300 h anneal time between 700 and 1000° C. X-ray diffraction of coprecipated specimens of 7.8 mol % Sc₂O₃-ZrO₂ composition annealed at 1000° C (28 days), 750° C (42 days) or 460° C (189 days) did not reveal any changes to account for this. However, transmission electron microscopy showed that changes associated with the formation of very fine precipitates had occurred. The activation energy for conduction in the low-temperature region decreased monotonically with decrease in the scandia content. Jumps in the conductivity curves and hysterisis effects were observed in specimens containing m-ZrO₂.     

Compounds in the system BaOSc2O3

The occurrence of compounds in the system BaO-Sc₂O₃ has been investigated. Apart from the already known compounds Ba₃Sc₄O₉ and BaSc₂O₄, tetragonal Ba₂Sc₂O₅ has been found. This phase is the only compound formed at low temperature (1000°C). At higher temperatures Ba₂Sc₂O₅ is transformed into the other stable compounds, whereas remaining Ba₂Sc₂O₅ may dissolve excess BaO, changing the unit cell constants. A tetragonal compound Ba₆Sc₆O₁₅, was also observed.     

Systems Silver Iodide-Sodium Iodide and Silver Iodide-Potassium Iodide

The phase relations for the systems AgI-NaI and AgI-KI have been determined for the temperature range from room temperature to 685° C, using differential thermal analysis techniques. The AgI-NaI system has a eutectic at 50 mole percent NaI and 384° C. The AgI-KI system has eutectics at 20.8 and 28.5 mole percent KI and 254° C and 244° C, respectively. A compound of formula KAg₃I₄ is formed with a congruent melting point of 268° C.     

Phosphinoborine Compounds: Mass Spectra and Pyrolysis

The mass spectra of tetramethylphosphinoborine trimer, [P(CH₃)₂B(CH₃)₂]₃ (I) and a a compound, P₅(CH₃)₉B₅H₉, (II) prepared from dimethylphosphinoborine were observed, and the compounds were pyrolyzed at 300 to 500° C. Most peaks in the spectrum of (I) came from the P—B, B—C, and P—C cleavages. The mass spectrum of (II) was much more complicated with evidence for methyl group redistribution.The pyrolysis of both compounds indicates a very complicated mechanism with many unidentifiable compounds. Trends in the formation of volatile products indicate that both compounds are completely decomposed in 4 hr at 450° C. Compound (I) produces trimethylboron, which disappears rapidly above 400° C. Neither (I) nor (II) formed ethane or elemental phosphorus.     

Secondary electron emission and glow discharge properties of 12CaO·7Al2O3 electride for fluorescent lamp applications

12CaO·7Al₂O₃ electride, a sub-nanoporous compound having a work function of 2.4 eV, was examined as a candidate cathode material in fluorescent lamps. The electron emission yield was higher and the discharge voltage was lower for 12CaO·7Al₂O₃ than for existing cathode materials such as Ni, Mo or W; therefore, the energy consumption of the fluorescent lamps can be improved using 12CaO·7Al₂O₃ cathodes. Prototype glow-discharge lamps using 12CaO·7Al₂O₃ were constructed and exhibited reasonable durability.     

Induced changes in the refractive index of LiNbO3 crystals through Sc2O3 doping

The dependence of the ordinary (n_o) and extraordinary (n_e) refractive indices in congruent Sc₂O₃-doped LiNbO₃ crystals are reported. The Sc³⁺ ion concentrations in the crystals were varied from 0% to 7%. It has been found that n_o shows a clear singularity for a Sc³⁺ ion concentration of 3%. The experimental data of n_o and n_e are described by a generalised Sellmeier equation, which takes into account different Sc³⁺ ions sites location in the host matrix. Additionally, the role of the Sc₂O₃ content in the intrinsic defect distribution in LiNbO₃ crystals has been studied by using Cr³⁺ ions as an EPR probe.     

High temperature creep in a 2-3-4 garnet: Ca3Ga2Ge3O12

High temperature plastic deformation in a single crystal of a 2-3-4 garnet, Ca₃Ga₂Ge₃O₁₂, was investigated. A Czochralski-grown single crystal of Ca₃Ga₂Ge₃O₁₂ was deformed in compression in air along 100 or 110 at temperatures of 1472 to 1573 K (T/T_m = 0.90–0.96). The samples show higher resistance to creep than other 3-3 garnets, namely the flow stress at the strain-rate of 4 × 10^{– 6} s^{– 1} is 200–400 MPa in this temperature range. The TEM observations of dislocation microstructures show little evidence of climb and plastic deformation in this garnet appears to occur exclusively by dislocation glide, using mostly the 1/2111{110} slip systems. Dislocations with b = 100 are frequently observed but they are interpreted as products of dislocation reactions among 1/2111. The single crystal used contained a number of precipitates that grew during annealing and also during deformation. These precipitates act as sources for dislocations but no evidence for their significant effects on creep strength is observed. The normalized flow law of Ca₃Ga₂Ge₃O₁₂ is similar to other 3-3 oxide garnets (e.g., YAG, GGG), but in contrast to 3-3 garnets, the more stable and hence less mobile dislocations have a large edge component.     

Potential use of only Yb2O3 in producing dense Si3N4 ceramics with high thermal conductivity by gas pressure sintering

Yb₂O₃ is an efficient sintering additive for enhancing not only thermal conductivity but also the high-temperature mechanical properties of Si₃N₄ ceramics. Here we report the fabrication of dense Si₃N₄ ceramics with high thermal conductivity by the gas pressure sintering of α-Si₃N₄ powder compacts, using only Yb₂O₃ as an additive, at 1900 °C under a nitrogen pressure of 1 MPa. The effects of Yb₂O₃ content, sample packing condition and sintering time on the densification, microstructure and thermal conductivity were investigated. Curves of the density plotted against the Yb₂O₃ content exhibited a characteristic ‘N’ shape with a local minimum at 3 mol% Yb₂O₃ and nearly complete densification below and above this concentration. The effects of the sample packing condition on the densification, microstructure and thermal conductivity strongly depended on the Yb₂O₃ content. The embedded condition led to more complete densification but also to a decrease in thermal conductivity from 119 to 94 W m^-1 K⁻¹ upon 1 mol% Yb₂O₃ addition. The sample packing condition had little effect on the density and thermal conductivity (102–106 W m⁻¹ K⁻¹) at 7 mol% Yb₂O₃. The thermal conductivity value was strongly related to the microstructure.     

Optical Properties of Ca3Ga2Ge4O14 Crystals

The optical absorption, induced-absorption, luminescence, and excitation spectra and temperature-dependent luminescence intensity of thermochemically colored Ca₃Ga₂Ge₄O₁₄ crystals were measured. The results indicate that the induced-absorption bands at 34000–28000 and 28000–20000 cm^–1 and the emission band at 14800 cm^–1 are related to F-centers.