Proton conducting composites of heteropolyacid hydrates dispersed with salt hydrates

Proton conduction in the composites of heteropolyacid hydrates (Phosphotungstic acid : PTA·nH₂O and Phosphomolybdic acid : PMA·nH₂O) with salt hydrates like Aluminium sulphate and Ammonium paratungstate (APT) as dispersoids has been studied and compared with the composites PTA : Al₂O₃ and PMA : Al₂O₃. Thermal analysis, XRD and IR studies on acid and salt hydrates dispersed phase systems reveal the formation of composites. A significant increase in the ionic conductivity has been observed in the composites. It has been found that the conductivity of 0.5PTA + 0.5Al₂(SO₄)₃·16H₂O is 1.1 × 10^–2 S·cm^–1 and that of 0.55PMA + 0.45APT is 1.3 × 10^–3 S·cm^–1 at 65% R.H. The temperature and humidity dependence of bulk electrical conductivity of the composites is also reported.     

Modified mixed oxide perovskites 0.7Sr(Al1/2B1/2) O3·0.3LaAlO3 and 0.7Sr(Al1/2B1/2) O3·0.3NdGaO3 (B=Ta5+ or Nb5+) for high-T c superconductor substrate applications

Single-crystal fibres of modified strontium aluminium tantalum oxide (1-x)Sr(Al_1/2Ta_1/2) O₃·xLaAlO₃(SAT-LA) and (1-x)Sr(Al_1/2Ta_1/2)O₃·xNdGaO₃ (SAT·NG), and modified strontium aluminum niobium oxide (1-x)Sr(Al_1/2Nb_1/2)O₃·xNdGaO₃(SAT·NG) and (1-x)Sr (Al_1/2Nb_1/2)O₃·xLaAlO₃ (SAN·LA) were grown using a laser-heated pedestal growth technique. 0.7SAT·0.3LA grows congruently and retains a twin free simple cubic perovskite structure (as the SAT) when cooled down to room temperature. 0.7SAT·0.3LA crystals have a moderate dielectric constant ( = 21.7) and low dielectric loss (tan = 7.5 × 10^–5) at 10 kHz and 90 K. The reduction problem of Ta⁵⁺ is eliminated (which is common in the case of SAT growth). 0.7SAT·0.3NG and 0.7SAN·0.3NG have lower melting temperatures and crystal growth is easier. NdGaO₃ addition to the SAT and SAN enhances the potential of SAT and SAN as large-area substrates for high-T _c superconductor growth. However, the dielectric constants increased from -12 to -16(0.7SAT·0.3NG) and from 18 to 23 (0.7SAN·0.3NG) as a result of NdGaO₃ incorporation.     

On the nano-size intergrowth of Sr4Fe6O13±δ and (Sr1?xLax)FeO3?δ phases in the mixed conductor Sr3.6La0.4Fe6Oz

The microstructures of mixed-conducting Sr₄Fe₆O_13±, and Sr_3.6La_0.4Fe₆O _z (nominal composition) have been studied by electron microscopy. The lanthanum free material shows a microstructure containing mainly Sr₄Fe₆O_13±, with some 5 vol% Sr_1–y La _y Fe₁₂O₁₉embedded as micron-size inclusions. The lanthanum-containing material revealed a significantly different microstructure consisting of 20 vol% micron-size Sr_1–y La _y Fe₁₂O₁₉embedded in 40 vol% (Sr_0.85La_0.15)FeO_3–tetragonal perovskite, and 40 vol% of plate-shaped nano-scale intergrowths between (Sr_1–x La _x )FeO_3–and Sr₄Fe₆O_13±phases. Domains with dimensions of 20–50 nm are observed in the tetragonal perovskite when viewed along its fourfold axis. From compositional analysis it is concluded that there is little or no solubility of La in the Sr₄Fe₆O_13±phase. The observed microstructure is important input in explaining the significant effect of La addition on the transport properties of Sr₄Fe₆O_13±materials.     

Pseudo-binary system Bi2O3-TeO2 in air

The phase equilibria in the pseudo-binary system Bi₂O₃-TeO₂ at 600° 950° C in air were examined by solid-state reaction techniques and X-ray powder diffraction method. Four pseudo-binary compounds appeared, i.e., -Bi₂O₃ type solid solution having a compositional range of (1-x)Bi₂O₃·xTeO₂ wherex=0 0.4 a new compound Bi₆Te₂O₁₅ which has an orthorhombic cell of a=2.27(4) nm, b=1.06(1) nm and c = 0.539(8) nm, 2Bi₂O₃ · 3TeO₂, and an unidentified phase Bi₂O₃·2TeO₂. The formation of the phase Bi₆Te₂O₁₅, in which all the Te ions are hexavalent, was confirmed by the thermogravimetry and by the Mössbauer spectra. The liquidus curves for whole system were determined by DTA method.     

Microstructure and topological analysis of Co : Al2O3 nanocermets in new FCC and BCC metastable Co-structures

Co : Al₂O₃nanocermets are synthesized by co-reducing Co²⁺-cations dispersed in a mesoporous AlO(OH) · H₂O matrix (amorphous) in a pure H₂atmosphere at 850–1150 K. The dispersed Co²⁺-cations in pores co-reduce to separated Co-particles of controlled size, as small as 50 nm, encapsulated in thin Al₂O₃films, which are formed in-situ by molecular decomposition of the matrix, 2AlO(OH) · H₂O Al₂O₃+ (2 + 1)H₂O. The Al₂O₃film which coats Co-particles has an amorphous structure. This is possible only if it is extremely thin limited to a thickness of t< 2r _c, with r _c 1.9 nm the critical size of its nucleation and growth into a stable crystallite. The thin Al₂O₃surface film supports the formation and existence of Co-particles in a modified FCC or BCC crystal structure. As a result, unusually, large crystallites of an average 100 nm diameter could be observed. Normally, such large particles of pure Co-metal exist in an HCP structure which undergoes a reversible martensitic transformation to FCC structure at 695 K. The results are analyzed and discussed in terms of microstructure, x-ray diffraction and XPS studies of nanocermets prepared under selected conditions.     

Stability of Si3N4-Al2O3-ZrO2 composites in oxygen environments

Oxidation of dense Si₃N₄-Al₂O₃-ZrO₂ and Si₃N₄-Al₂O₃ compacts, at 873–1773 K and 98 KPa air atmosphere, results in two different parabolic oxidation regimes. Oxygen diffusion is likely to be the governing step at low temperature (T<1623 K (H= 100kJ mol^–1)), whereas at T> 1623 K (H = 800kJ mol^–1) metal cation diffusion through the grain boundary phase appears limiting. The excellent stability in oxygen environments of the Si₃N₄-Al₂O₃-ZrO₂ composites compared to other ZrO₂-Si₃N₄ materials derives from (i) absence of easy-to-oxidize Zr-O-N phases; (ii) reduced amount of grain boundary phase, and possibly (iii) decreased solubilization rate of the nitride phases in the high viscous oxide film.     

High resolution TEM study of ceramic BaO·Pr2O3·4TiO2

Ceramic specimens of BaO·Pr₂O₃·4TiO₂ (Ba_4.5Pr₉Ti₁₈O₅₄) were prepared by the mixed oxide-route. The single phase products were examined by High Resolution Transmission Electron Microscopy (HRTEM). Orthorhombic symmetry, with cell parameters a22.2 Å, b12.2 Å and c7.6 Å, was confirmed. On the basis of space group pnam (No. 62) and the crystal structural data of Rawn et al., good agreement was obtained between the experimental HRTEM images and images simulated by the multislice method.     

Thermal properties and radiation damage in NaNH4XO4·2H2O single crystals (XO4=SO4,SeO4)

Differential thermal analysis (DTA) studies of NaNH₄SO₄·2H₂O, NaND₄SO₄·2H₂O, and NaNH₄SeO₄·2H₂O single crystals were performed in the temperature range of the ferroelectric-paraelectric phase transition and of the dehydration process. The first-order phase transition at the Curie point was confirmed for NaNH₄SO₄·2H₂O, whereas the transition in the isomorphous NaNH₄SeO₄·2H₂O at the Curie temperature was found to be similar to a contineous (second order) with considerable higher transition enthalpy. Dehydration process of the crystals studied was found to proceed in two stages, with maximum dehydration rates at 355 and 400K. A linear decrease in thermal energy related to the long-range ordering in NaNH₄SO₄·2H₂O crystals was observed with the dose of -cobalt-60 irradiation and discussed with respect to the radiation induced decrease in spontaneous polarization.     

Preparation of barium hexaferrite by a hydrothermal method: structure and magnetic properties

Barium hexaferrite, BaFe¹²O₁₉, was obtained in hydrothermal conditions from a water suspension of -FeOOH and Ba(OH)₂ · 8H₂O at a temperature about 315° C. X-ray and Mössbauer spectroscopy as well as electron microscopy investigations demonstrated the appearance of -Fe₂O₃ as an intermediate phase in the hydrothermal process. The magnetic characteristics of the obtained isotropic magnets are the following: coercive fieldH _c 159 kA m^–1, residual inductionB _r 0.26 T, maximum energy product (BH) _max12 kJ m^–3. The hydrothermal procedure for the preparation of barium hexaferrite in comparison with the conventional one is discussed.     

Chemical and structural properties of the system Fe2O3-Cr2O3

Chemical and structural properties of the mixed metal oxides (1–x)Fe₂O₃+xCr₂O₃ were studied by different techniques. X-ray powder diffraction showed the existence of solid solutions, (Fe_1–x Cr _x )₂O₃, over the whole concentration region, 0x1. The gradual replacement of Fe³⁺ with Cr³⁺ ions in samples prepared at 900°C caused changes in unit-cell parameters; most of these changes took place in the region fromx0.3–0.9. The samples having the fraction of Cr₂O₃ in the region from 0.7–0.8, contained two closely related phases, with slightly different compositions. After an additional heat treatment at 1100°C, these samples contained only one phase.⁵⁷Fe Mössbauer spectroscopy showed a gradual decrease of hyperfine magnetic field with increasing Cr₂O₃ content. The sample having the fraction of Cr₂O₃ of 0.7, and prepared at 900°C, exhibited two separated sextets at room temperature, in comparison with other compositions showing one sextet. It was shown that Fourier transform infrared (FT-IR) spectroscopy is a powerful method for the investigation of structural changes in these solid solutions. The increase in the Cr₂O₃ content resulted in shifts of the corresponding infrared bands. In addition, a gradual transition of the spectrum typical for -Fe₂O₃ to the spectrum typical for Cr₂O₃ was shown. The transition effects observed in the FT-IR spectra were correlated with the X-ray powder diffraction and⁵⁷Fe Mössbauer spectroscopic results.     

Susceptibility and X-Ray Absorption Measurements on Superconducting (Hg,Mo)Sr2CuO4+δ System

In continuation of our recent work [1] on superconducting 1201-type (Hg,M)Sr₂CuO₄₊, M = Cr system, the samples of (Hg_1–x Mx)Sr₂CuO₄₊, M = Mo (x = 0.15, 0.25, and 0.30), were synthesised in partial vacuum. The x = 0.15 composition shows a maximum T _c ^onset of 66 K, while x = 0.25 exhibits T _c ^onset of 50 K. For x = 0.30 sample, the observed T _c ^onset of 36 K is discretely different from the reported values of 20 and 58 K. X-ray absorption measurements on (Hg,Mo)-1201 samples show Hg in divalent state and Cu predominantly in Cu²⁺ state. A weak but distinct Cu¹⁺ signature is also observed in the SC (Hg,Mo)-1201 samples, which is absent in the impurity SrCuO₂ and Sr₂CuO₃ phases. On the basis of available reports, it is viewed that Cu¹⁺ can arise because of a small fraction of Cu occupying the Hg site in (Hg,Mo)-1201 system.     

The synthesis and thermal behaviour of zinc diphosphates

Zinc diphosphates (Zn₂P₂O₇ · 5H₂O, Zn₂P₂O₇ · 3H₂O, 5K_1.4Zn_1.3P₂O₇ · 16H₂O, and 5K_0.8Zn_1.6P₂O₇ · 9H₂O) were made by the wet process. The composition of the products was dependent on the conditions (concentration, pH, and dropping rate of the solution) of the process. When the products were heated, decomposition of the diphosphates to orthophosphate took place below about 150 ·C. Polymerization of the phosphates to phosphates with longer chains was observed in the temperature range 150 to 400 ° C. The amorphous phosphates thermally produced by heating diphosphates other than 5K_1.4Zn_1.3P₂O₇ · 16H₂O, showed reorganization to diphosphate above 400 ° C according to the reaction M₂O₃PO[P(O₂M)O] _n PO₃M₂ +nM₃PO₄(n + 1)M₄P₂O₇ where M represents K and/or 1/2Zn.     

Electrical Conductivity of H2V12 – y W y O31 + δ · nH2O and H x V x W1 – x O3 · nH2O

The electrical conductivity of H₂V_{12 – y} W _y O_{31 +} · nH₂O (0 y 3) and H _x V _x W_{1 – x} O₃ · nH₂O (x = 0, 0.08, 0.17, 0.25, 0.33) prepared by the sol–gel method was measured between 293 and 473 K at a relative humidity of 12%. Partial substitution of tungsten for vanadium or V⁵⁺ and H⁺ for tungsten was found to reduce the conductivity of the phases studied. The only exception is the x = 0.33 phase. Below 373 K, the activation energy of conduction is 0.22–0.29 eV in the amorphous phases (0 y 3; x= 0.25, 0.33) and 0.06–0.11 eV in the crystalline phases (x = 0, 0.08, 0.17). The possible mechanisms of electrical transport are discussed.     

Proton Conductivity in H2 – x (NH4) x V9Mo3O32.5 – δ · nH2O Xerogel Films

The electrical conductivity of _{2 – x} (NH₄) _x V₉Mo₃O_{32.5 –} · nH₂O xerogel films containing different amounts of ammonium ions and water was measured as a function of temperature. The results demonstrate that, in a wide temperature range, the proton conductivity of the films reaches a maximum atx= 1.5. The activation energy of conductivity in the films, equal to 0.1–0.2 eV at low temperatures, rises upon partial dehydration above 100°C. The possible mechanisms of proton formation and transport are discussed.     

X-ray Photoelectron Spectroscopic Study of Hot Particles Formed by Emission from Fuel-Containing Masses Incorporating Ruthenium

X-ray photoelectron spectroscopy was applied to the study of the quantitative elemental and ionic compositions of samples of fuel-containing masses (FCMs) generated under laboratory conditions and incorporating Ru, before and after their heating in air at 1500°C for 2 min, and also of hot particles released in the process and kept in air at 700 and 900°C for 13 s. FCM samples heated under argon at 1900°C for 2 min were studied for comparison. The spectra revealed formation on the FCM sample surface of complex oxides UO_x with x varying in the range 2 >x 3. Ruthenium was detected in at least two oxidation states: Ru(IV) and Ru(VI). The relative concentrations of U and Ru in FCM (89 at. % U and 11 at. % Ru) change, respectively, to 99 and 1 at. % after heating in air and to 80 at. % U and 20 at. % Ru after heating under argon. After treatment of the sample surface with Ar⁺ ions, the carbonate groups disappeared, and the concentrations of the U(IV) and U(VI), as well as of Ru(IV) and Ru(VI) ions, changed. The condensed phase of hot particles consists mainly of ruthenium ions (80 at. %), with a lower content of uranium (20 at. %). Uranyl compounds of the type RuUO₂O₃ are probably formed on the surface of hot particles.     

Aluminium-27 solid state NMR spectroscopic studies of chloride binding in Portland cement and blends

Alumina-rich pozzolanic and latent hydraulic binders such as pulverised fuel ash, metakaolin, and ground granulated blast furnace slag, together with silica fume, are frequently added to Portland cement concrete to improve performance and to retard chloride ingress and thereby inhibit chloride-induced corrosion of the carbon steel reinforcement. ²⁷Al{¹H} MAS and CP/MAS NMR spectroscopies have been used to follow both the hydration processes of the cement blends and the interactions of chloride ion with the hydrated aluminium species. The spectra of the hydrated aluminate phases were interpretable on the basis that the AFt (Aluminate Ferrite tri-) phase ettringite, C ₆ A H ₃₂(3CaO·Al₂O₃·3CaSO₄·32H₂O, or C ₃ A·3CaSO₄·32H₂O), and the AFm (Aluminate Ferrite mono-) phases calcium mono-sulphoaluminate, C ₄ A H ₁₂ (3CaO·Al₂O₃·CaSO₄·12H₂O, or C ₃ A·CaSO₄·12H₂O), and the lamellar tetracalcium aluminate hydrate, C ₄ AH ₁₃ (3CaO·Al₂O₃·Ca(OH)₂·12H₂O, or C ₃ A·Ca(OH)₂·xH₂O) were present as the only hydrated species containing octahedrally-coordinated aluminium. In all cases, only the AFm phase Friedel's salt (3CaO·Al₂O₃·CaCl₂·10H₂O, or C ₃ A·CaCl₂·10H₂O) could be identified as the major chloroaluminate phase produced by the interactions of the cement pastes with chloride ion.     

Transport anomalies in the Zn-substituted La2−x Sr x Cu1−y Zn y O4 with x ∼ 0.115; Possibility of the Pinning of CDW and SDW by Zn

Anomalies in the thermoelectric power and the Hall coefficient, which are analogous to those observed in La _2–x Ba _x CuO ₄ with x 1/8, have been observed in the Zn-substituted La _2–x Sr _x Cu _1–y Zn _y O ₄ with x = 0.115 and y = 0 – 0.025 and with x = 0.15 and y 0.02. Based on the so-called stripe model, these are explained as being due to the formation of the static order of the stripe-patterned CDW and SDW on account of the pinning by Zn. Accordingly, the long-standing problem on the conspicuous suppression of superconductivity in the Zn-substituted La _2–x Sr _x Cu _1–y Zn _y O ₄ with x 0.115 is likely to be attributed to this static order.     

Transport property and battery discharge characteristic studies on 1−x(0.75Agl∶0.25AgCl)∶ xAl2O3 composite electrolyte system

Various experimental studies on a new fast Ag⁺ ion-conducting composite electrolyte system: (1–x) (0.75Agl0.25AgCl)xAl₂O₃ are reported. Undried Al₂O₃ particles of size <10 m were used. The conventional matrix material Agl has been replaced by a new mixed 0.75Agl0.25AgCl quenched and/or annealed host compound. Conductivity enhancements 10 from the annealed host and 3 times from the quenched host obtained for the composition 0.7(0.75Agl0.25AgCl)0.3Al₂O₃, can be explained on the basis of the space charge interface mechanism. Direct measurements of ionic mobility as function of temperature together with the conductivity were carried out for the best composition. Subsequently, the mobile ion concentration n values were calculated from and a data. The value of heat of ion transport q* obtained from the plot of thermoelectric power versus 1/T supports Rice and Roth's free ion theory for superionic conductors. Using the best composition as an electrolyte various solid state batteries were fabricated and studied at room temperature with different cathode preparations and load conditions.     

Solubility Limit and Anisotropy Analysis of Mg Doping in Melt Textured YBa2(Cu1−x Mg x )3O7−δ

Strong signatures of Mg substitution in Yba ₂ (Cu _1–x Mg _x ) ₃ O _7– have been obtained from single domain samples prepared by top seeding using YBa ₂ Cu ₃ O _7– + 30%wt Y ₂ BaCuO ₅ +X%wt MgO mixtures. A drastic decrease of the superconducting transition temperature with increasing X has been obtained reaching values of T _c 40 K for X=16.7. The T _c (x) dependence and thermogravimetric results suggest that Mg atoms substitute Cu(2) sites and that a solubility limit exists. Angular dependent magne-toresistance measurements have been used to determine the anisotropy of YBa ₂ (Cu _1–x Mg _x ) ₃ O _7– samples. These results are discussed on the basis of the recent controversy results reported for Zn-doped samples.     

Effects of Substituting Ni and Zn for Cu in the Electron Doped Sr0.9La0.1CuO2 Superconductor

We used X-ray diffraction, energy dispersive spectroscopy and low field magnetization to characterize Sr_0.9La_0.1Cu_1–x R _x O₂ samples for R=Zn and Ni. We found that both Ni and Zn are substituted at the Cu-site. The value of T _c was almost independent of composition until x0.03 for R=Zn while it was reduced to 30 K at x0.02 for R=Ni. This trend of T _c reduction is very similar to the pair breaking-effect in conventional superconductors and electron-doped (Nd, Ce)₂CuO_4– but the rate of reduction of T _c for R=Ni is larger in Sr_0.9La_0.1CuO₂ than in (Nd, Ce)₂CuO_4–. These results are discussed along with the recent experimental observation of gap symmetry in electron-doped superconductors.