Crystal growth and characterization of a new co-ordination complex—barium tetrakis(maleate) dihydrate

Crystals of barium tetrakis(maleate) dihydrate [Ba₄(C₄H₂O₄)₄]^?2H₂O are grown in gelated hydrosilica matrix. Single crystal X-ray diffraction studies show that the crystal system is monoclinic with space group P2₁/c. The unit cell dimensions are a=9.3721(2)  Å, b=20.5880(7)  Å, c=14.0744(4) Å, α=γ=90°, β=90.289(2)°. Powder XRD studies confirmed the single phase nature of the grown crystals. The FTIR data is in conformity with the XRD results. The TG–DTA curves of the material indicate a three-step thermal decomposition. The response of the dielectric properties in the temperature range 30 °C to 500 °C is correlated with the TG–DTA results.     

Polymorphic phase transition and thermal stability in squaric acid (H2C4O4)

Phase transformations in squaric acid (H₂C₄O₄) have been investigated by thermogravimetry and differential scanning calorimetry with different heating rates β. The mass loss in TG apparently begins at onset temperatures T_di=245±5 °C (β=5 °C min^?1), 262±5 °C (β=10 °C min^?1), and 275±5 °C (β=20 °C min^?1). A polymorphic phase transition was recognized as a weak endothermic peak in DSC around 101 °C (T_c⁺). Further heating with β=10 °C min^?1 in DSC revealed deviation of the baseline around 310 °C (T_i), and a large unusual exothermic peak around 355 °C (T_p), which are interpreted as an onset and a peak temperature of thermal decomposition, respectively. The activation energy of the thermal decomposition was obtained by employing relevant models. Thermal decomposition was recognized as a carbonization process, resulting in amorphous carbon.     

Reanalysis of optical-axis perturbation in nonplanar ring resonators in ray matrix approach with appropriate coordinate systems

Ray matrix approach with appropriate coordinate systems has been proposed in this paper. It is employed to analyze the optical-axis perturbation in nonplanar ring resonators. The sensitivities of optical-axis decentration (SD) and optical-axis tilt (ST) in nonplanar resonators with 90° and 270° image rotation are discussed in detail in the region of 0 < K < 8, where K is the ratio of the total cavity length to the radius of the curvature mirrors. There are both four singular points in the whole region of 0 < K < 8. On the left of the first singularity, it is found that the longer the mirror radius, the less the optical-axis decentration sensitivity. This is opposite the behavior of planar ring resonators, but the behaviors of optical-axis tilt sensitivity in planar and nonplanar ring resonators are similar. It is worth to note that SD and ST in the nonplanar resonator with certain parameters have the similar singularities. The analysis in this paper is important for the cavity design and alignment of nonplanar ring resonators.     

High resolution emission spectroscopy of the E2Π–X2Σ+ transition of SrH and SrD

Emission spectra of SrH and SrD have been studied at high resolution using a Fourier transform spectrometer. The molecules have been produced in a high temperature furnace from the reaction of strontium metal vapor with H₂/D₂ in the presence of a slow flow of Ar gas. The spectra observed in the 18 000–19 500 cm^?1 region consist of the 0–0 and 1–1 bands of the E²Π–X²Σ⁺ transition of the two isotopologues. A rotational analysis of these bands has been obtained by combining the present measurements with previously available pure rotation and vibration–rotation measurements for the ground state, and improved spectroscopic constants have been obtained for the E²Π state. The present analysis provides spectroscopic constants for the E²Π state as ΔG(½) = 1166.1011(15) cm^?1, B_e = 3.805503(32) cm^?1, α_e = 0.098880(47) cm^?1, r_e = 2.1083727(89) Å for SrH, and ΔG(½) = 839.1283(23) cm^?1, B_e = 1.918564(15) cm^?1, α_e = 0.034719(23) cm^?1, r_e = 2.1121943(83) Å for SrD.     

Experimental investigation of flame spreading over pure methane hydrate in a laminar boundary layer

Flame spreading over pure methane hydrate in a laminar boundary layer is investigated experimentally. The free stream velocity (U_∞) was set constant at 0.4 m/s and the surface temperature of the hydrate at the ignition (T_s) was varied between ?10 and ?80 °C. Hydrate particle sizes were smaller than 0.5 mm. Two types of flame spreading were observed; “low speed flame spreading” and “high speed flame spreading”. The low speed flame spreading was observed at low temperature conditions (T_s = ?80 to ?60 °C) and temperatures in which anomalous self-preservation took place (T_s = ?30 to ?10 °C). In this case, the heat transfer from the leading flame edge to the hydrate surface plays a key role for flame spreading. The high speed flame spreading was observed when T_s = ?50 and ?40 °C. At these temperatures, the dissociation of hydrate took place and the methane gas was released from the hydrate to form a thin mixed layer of methane and air with a high concentration gradient over the hydrate. The leading flame edge spread in this premixed gas at a spread speed much higher than laminar burning velocity, mainly due to the effect of burnt gas expansion.     

Electrical conductivity and thermal expansion of the oxy-cuspidine Gd4Al2O9 substituted with Ca and Sr

The series of Gd_4 ? xM_xAl₂O_9 ? x/2 (M = Ca, Sr) with x = 0, 0.01, 0.05, 0.10 and 0.25 was prepared by the citrate complexation method. Both Gd_4 ? xCa_xAl₂O_9 ? x/2 and Gd_4 ? xSr_xAl₂O_9 ? x/2 show the monoclinic cuspidine structure with space group of P2₁/c up to 0.05–0.1 and 0.01–0.05 mol for Ca and Sr, respectively. Beyond the substitution limit of Gd₄Al₂O₉, GdAlO₃ and SrGd₂Al₂O₇ appear as additional phases. The highest electrical conductivity obtained at 900 °C yielded σ = 1.49 × 10^? 4 S/cm for Gd_3.95Ca_0.05Al₂O_8.98. In comparison, the conductivity of pure Gd₄Al₂O₉ was σ = 1.73 × 10^? 5 S/cm. The conductivities determined are in a similar range as those of other cuspidine materials investigated previously. The thermal expansion coefficient of Gd₄Al₂O₉ at 1000 °C was 7.4 × 10^? 6 K^? 1. The phase transition between 1100 and 1200 °C reported earlier changes with increasing substitution of Ca and Sr.     

Sintering kinetics and oxide ion conduction in Sr-doped apatite-type lanthanum silicates,La9Sr1Si6O26.5

These last past years, a major interest has been devoted to decrease the working temperature of solid oxide fuel cells (SOFCs) down to about 700 °C.Apatite materials (La_10 ? xSr_xSi₆O_27?x/2) are attractive candidates for solid electrolytes, with a high ionic conductivity at these intermediate temperatures. An apatite powder (x = 1) with a 0.75 µm mean particle size, produced by solid state reaction, was tape cast to obtain green sheets with a thickness of about 260 µm.On one hand, the densification mechanism of the apatite ceramic during the intermediate solid state sintering has been approached. It appeared from the kinetical tests performed under isothermal conditions between 1250 and 1550 °C, that densification could be controlled by the diffusion at grain boundaries of the rare-earth element, La, with an activation energy of 470 kJ/mol.On the other hand, conductivity measurements were performed on apatite samples sintered at 1400 and 1500 °C. The ionic conductivity was mainly sensitive to the presence of secondary phases at 1400 °C. The ionic conductivity of the apatite sintered at 1500 °C (mean grain size = 3.9 µm) is equal to 1.2 × 10^? 2 S/cm at 700 °C.     

Core hole and surface excitation correction parameter for XPS peak intensities

In XPS analysis, surface excitations and excitations originating from the static core hole created during the photoexcitation process are usually neglected. However, both effects significantly reduce the measured peak intensity. In this paper we have calculated these effects. Instead of considering the two effects separately, we introduce a new parameter, namely the Correction Parameter for XPS (or CP_XPS) defined as the change in probability for emission of a photoelectron caused by the presence of the surface and the core hole in comparison with the situation where the core hole is neglected and the electron travels the same distance in an infinite medium. The CP_XPS calculations are performed within the dielectric response theory by means of the QUEELS-XPS software determining the energy-differential inelastic electron scattering cross-sections for X-ray photoelectron spectroscopy (XPS) including surface and core hole effects. This study has been carried out for electron energies between 300 eV and 3400 eV, for angles to the surface normal between 0° and 60° and for various materials, especially metals, semiconductors and oxides. For geometries and energies normally used in XPS, i.e. for emission angle ≤ 60° and photoelectron energy ≤ 1500 eV, we find that CP_XPS values are significantly larger for oxides, (0.55 ? CP_XPS ? 0.75) than for metals and semiconductors (0.45 ? CP_XPS ? 0.6). We show that this behavior is due to the difference in the wave vector dispersion of the energy loss function. This dispersion has been determined from analysis of REELS and is found to be free electron like (α ? 1) for metals but is substantially smaller (α ≈ 0.02–0.05) for materials with a wide band gap. As a result, the group velocity of the valence electrons is very small for oxides with a large band gap. This leads to a reduction in the screening of the core-hole potential before the photoelectron has left the region of interaction and thereby to an increase in the intrinsic excitations caused by the core hole.     

Ce0.8Sm0.2O1.9 synthesis for solid oxide fuel cell electrolyte by ultrasound assisted co-precipitation method

In this study, the synthesis of Ce_0.8Sm_0.2O_1.9 (SDC) solid electrolyte by the ultrasound assisted co-precipitation method was accomplished to explore the effects of ultrasound power, ultrasound pulse ratio and probe type upon the ionic conductivity of SDC as well as the lattice parameter, the microstructure and the density. Fine powders of uniform crystallite sizes (average 11.70 ± 0.62 nm) were obtained, needing lower sintering temperature. The SDC powders were successfully sintered to a relative density of over 95% at 1200 °C (5 °C min^?1) for 6 h. The micrograph of SDC pellets showed non-agglomerated and well-developed grains with average size of about 200 nm. X-ray diffraction analysis showed that the lattice parameter increased with increasing acoustic intensity and reached a maximum for the 14.94 W cm^?2. Further, a linear relationship was detected between the lattice parameter and the ionic conductivity, inspiring a dopant like effect of US on the electrolyte properties. The highest ionic conductivity as σ_800°C = 3.07 × 10^?2 S cm^?1 with an activation energy E_a = 0.871 kJ mol^?1 was obtained with pulsed ultrasound for an acoustic intensity of 14.94 W cm^?2, using 19 mm probe and 8:2 pulse ratio.     

Birefraction of the LiNbO3 crystal in the infrared band

We proposed a spectrum method to determine birefraction of the sample. When the infrared incident light transmits in the birefraction direction of the cube crystal, because of the birefraction of the sample, the transmit spectrum appears interference fringes. The equation Δn = 1/[D(dυ/dm)] shows the relationship between the birefraction and the wave-number, with the interference-number of crystals in the infrared band at room temperature. Via the infrared transmitting along the x-axis of cube lithium niobate crystal, the interference fringes were found. By the fitted polynomial method, the relationship of the birefraction and the wave-number or wavelength of the lithium niobate crystal be educed, which is, Δn = 0.4149 ? 9.00174 × 10^?5υ + 5.64347 × 10^?9υ²,or n = 0.05366 ? 5.20334 × 10^?5λ + 3.99694 × 10^?8λ².     

Conductivity of SnP2O7 and In-doped SnP2O7 prepared by an aqueous solution method

SnP₂O₇ and In-doped SnP₂O₇ have been prepared by an aqueous solution method using (NH₄)₂HPO₄ as phosphorous source. It was found that the solid solution limit in Sn_1 ? xIn_x(P₂O₇)_1 ? δ was at least x = 0.12. All pyrophosphates in the Sn_1 ? xIn_x(P₂O₇)_1 ? δ (x ≤ 0.12) series exhibit 3 × 3 × 3 superlattice structures. The conductivities of Sn_0.92In_0.08(P₂O₇)_1 ? δ in air are 6.5 × 10^? 6 and 8.0 × 10^? 9 S/cm at 900 and 400 °C, respectively, when prepared by an aqueous solution method and annealed at 1000 °C. The conductivity of undoped SnP₂O₇ is slightly lower. However, it was also found that the low-temperature conductivities of pyrophosphates annealed only at 650 °C are several orders of magnitude higher than those annealed at 1000 °C, which could be related to a trace amount of an amorphous secondary phase. The peak conductivity was in this case observed at around 250 °C, which is the same temperature as previously observed in In-doped SnP₂O₇ although the conductivity is still three orders of magnitude lower in the present study. These differences can be related to large differences in particle size and morphology, and all in all, the conductivities of SnP₂O₇-based materials are very sensitive to the synthetic history.     

Tuneability of Sm(1 − x)CexFeO3 ± λ perovskites: Thermal stability and electrical conductivity

Trimetallic perovskite oxides, Sm_(1 ? x)Ce_xFeO_3 ± λ (x = 0–0.05), were prepared by thermal decomposition of amorphous citrate precursors followed by calcinations. The material properties of the substituted perovskites were characterized by X-ray diffraction (XRD), X-ray florescence spectroscopy (XRF), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The doped materials exhibited a single perovskite phase in air up to 1350 °C and have specific surface areas in the range of 2.696–8.665 m²/g. In reducing atmosphere (5%v/vH₂/N₂), the unsubstituted perovskite (x = 0) decomposed into two phases while the ceria stabilized materials (x = 0.01, x = 0.03, x = 0.05) remained in a single phase as revealed by XRD analysis. Their conductivities were measured by the four point probe method in air and in dilute hydrogen (5%v/vH₂/N₂) separately. The ceria substituted materials show increased stability versus reduction and phase separation for a wide temperature range (up to 1000 °C). Although undoped SmFeO₃ has higher conductivity under oxidizing conditions than ceria doped SmFeO₃ due its p-type nature, the situation is reversed under reducing conditions. The ceria substituted perovskites (Sm_(1 ? x)Ce_xFeO_3 ± λ, x = 0–0.05) showed higher conductivity in reducing than in oxidizing conditions, suggesting that ceria doping at the A-site has changed the SmFeO₃ from p-type to n-type semi-conducting behavior.     

Superconductivity in bulk T′-(La,Sm)2CuO4 prepared via a molten alkaline hydroxide route

We have synthesized La_2?xSm_xCuO₄ (0 ? x ? 2.0) with the Nd₂CuO₄ structure via a molten alkaline hydroxide route at temperatures as low as 400–480 °C. After reduction heat treatment in vacuum at 600–750 °C for removal of excess oxygen atoms at the interstitial apical site, superconductivity with T_c = 20–24 K was observed in the samples with x = 0.05–1.0. The superconducting volume fraction is nearly 100% for x = 0.3–0.7. Our results demonstrate that La_2?xSm_xCuO₄ with no nominal carrier doping is a bulk superconductor.     

Thermoluminescence,infrared reflectivity and electron paramagnetic resonance properties of hemimorphite

Silicate mineral hemimorphite has been investigated concerning its TL, IR and EPR properties. A broad TL peak around 180 °C and a weaker and narrower peak around 360 °C were found in a sample annealed at 600 °C for 1 h and then irradiated. The deconvolution using the CGCD method revealed peaks around 132, 169, 222 and 367 °C. The reflectivity measurements showed several bands in the NIR region due to H₂O, OH and Al–OH complexes. No band was observed in the visible region. The thermal treatments were carried out from ∼110 to 940 °C and dehydration was observed, first causing a diminishing optical absorption in general and the disappearance of water and hydroxyl absorption bands. The EPR spectrum of natural hemimorphite, presented Cu²⁺ signals at g = 2.4 and g = 2.1 plus E₁′ signal superposed to Fe³⁺ signal around g = 2.0.     

Field-assisted sustainable O− ion emission from fluorine-substituted 12CaO·7Al2O3 with improved thermal stability

We examined the electric field-assisted thermionic emission of atomic oxygen radical anion (O^?) in a vacuum from fluorine-substituted derivatives of 12CaO·7Al₂O₃ (C12A7) with a composition of (12 ? x)CaO·7Al₂O₃·xCaF₂ (0 ≤ x ≤ 0.8). Unsubstituted C12A7 easily decomposed into 5CaO?3Al₂O₃ (C5A3) and 3CaO?Al₂O₃ (C3A) above 830 °C during the emission experiment in a vacuum. The decomposition temperature range became narrower as the amount of F^? ion substitution increased, e.g. the sample with x = 0.4 kept a single phase after the emission experiment at 900 °C. The emitted anionic species from the x = 0.4 sample were dominated by O^? ions (～ 92%) together with a small amount of O₂^? ions (～ 4%) and F^? ions (～ 4%). The absence of an O₂ gas supply to the opposite side of the emission surface led to a nearly steady co-emission of O^? ions and electrons with a ratio of < 1/1. The O₂ gas supply markedly enhanced the O^? ion emission, and suppressed the electron emission. A sustainable and high-purity O^? ion emission with a current density of 11 nA cm^? 2 was achieved at 830 °C with the supply of 40 Pa O₂ gas. The similarity in these emission features to the unsubstituted C12A7, together with the improved thermal stability demonstrates that the F^? ion-substituted C12A7 is a promising material for higher intensity O^? ion emission at higher temperatures.     

Effect of Eu dopant concentration in SrCe1 − xEuxO3 − δ on ambipolar conductivity

The europium dopant concentration in strontium cerate was studied to achieve maximum hydrogen permeation. In order to determine high ambipolar conductivity, total conductivity and open circuit potential measurements were performed. Among the three different compositions of Eu-doped SrCe_1 ? xEu_xO_3 ? δ (x = 0.1, 0.15 and 0.2) studied, SrCe_0.9Eu_0.1O_3 ? δ showed highest total conductivity between 600 °C and 900 °C. However, transference number measurements showed increasing electronic conductivity with increasing dopant concentration and a stronger temperature dependence for electronic conduction. Therefore, the highest ambipolar conductivity was obtained over the compositional range from SrCe_0.85Eu_0.15O_3 ? δ to SrCe_0.8Eu_0.2O_3 ? δ depending on temperature. Finally, the hydrogen permeation flux was calculated based on the ambipolar conductivity and compared with experimental results.     

Synthesis of Y-doped BaCeO3 nanopowders by a modified solid-state process and conductivity of dense fine-grained ceramics

Powders of BaY_xCe_1 ? xO_3 ? δ (x = 0, 0.1 and 0.15) with specific surface area of 6–8 m²g^? 1 (BET equivalent particle size of 130–160 nm) were prepared by a modified solid-state route using nanocrystalline BaCO₃ and CeO₂ raw materials. These powders showed excellent densification at relatively low temperatures. Dense (96–97% relative density) ceramics with submicron grain size (0–4–0.6 µm) were obtained after sintering at 1250–1280 °C. Ceramics sintered at 1450 °C revealed only a moderate grain growth (grain size ≤ 2 µm), uniform microstructure and very high density (≥ 98%). The total conductivity of the submicron ceramics at 600 °C was comparable with the reference values reported in the literature, meaning that the high number of grain boundaries was not a limiting factor. On lowering temperature, the contribution of the blocking grain boundaries becomes progressively more important and the conductivity decreases in comparison to coarse-grained ceramics. Microscopic conductivities of grain interior and grain boundary are the same irrespective of grain size meaning that the different macroscopic behaviour is only determined by a geometric factor (a trivial size effect).     

Synthesis and crystallographic studies of garnet-related lithium-ion conductors Li6CaLa2Ta2O12 and Li6BaLa2Ta2O12

High-purity specimens of Li₆CaLa₂Ta₂O₁₂ and Li₆BaLa₂Ta₂O₁₂ have been successfully synthesized by solid-state reactions. The analytical chemical compositions of these samples were in good agreement with the nominal compositions of Li₆CaLa₂Ta₂O₁₂ and Li₆BaLa₂Ta₂O₁₂. The Rietveld refinements verified that these compounds have the garnet-type framework structure with the lattice constants of a = 12.725(2) Å for Li₆CaLa₂Ta₂O₁₂ and a = 13.001(4) Å for Li₆BaLa₂Ta₂O₁₂. All of the diffraction peaks of X-ray powder diffraction patterns were well indexed on the basis of cubic symmetry with space group Ia-3d. To make a search for Li sites, the electron density distributions were precisely examined by using the maximum entropy method. Li⁺ ions occupy partially two types of crystallographic site in these compounds: (i) tetrahedral 24d sites, and (ii) distorted octahedral 96h sites, the latter of which are the vacant sites of the ideal garnet-type structure. The present Li₆CaLa₂Ta₂O₁₂ and Li₆BaLa₂Ta₂O₁₂ samples exhibit the conductivity σ = 2.2 × 10^? 6 S cm^? 1 at 27 °C (E_a = 0.50 eV) and σ = 1.3 × 10^? 5 S cm^? 1 at 25 °C (E_a = 0.44 eV), respectively.     

Structural,vibrational study and superprotonic behavior of a new mixed dipotassium hydrogenselenate dihydrogenphosphate K2(HSeO4)1.5(H2PO4)0.5

Ongoing studies of the KHSeO₄–KH₂PO₄ system aiming at developing novel proton conducting solids resulted in the new compound K₂(HSeO₄)_1.5(H₂PO₄)_0.5 (dipotassium hydrogenselenate dihydrogenphosphate). The crystals were prepared by a slow evaporation of an aqueous solution at room temperature. The structural properties of the crystals were characterized by single-crystal X-ray analysis: K₂(HSeO₄)_1.5(H₂PO₄)_0.5 (denoted KHSeP) crystallizes in the space group P 1¯ with the lattice parameters: a = 7.417(3) Å, b = 7.668(2) Å, c = 7.744(5) Å, α = 71.59(3)°, β = 87.71(4)° and γ = 86.04(6)°. This structure is characterized by HSeO₄⁻ and disordered (H_xSe/P)O₄⁻ tetrahedra connected to dimers via hydrogen bridges. These dimers are linked and stabilized by additional hydrogen bonds (O–H–O) and hydrogen bridges (O–H…O) to build chains of dimers which are parallel to the [0, 1, 0] direction at the position x = 0.5.The differential scanning calorimetry diagram showed two anomalies at 493 and 563 K. These transitions were also characterized by optical birefringence, impedance and modulus spectroscopy techniques. The conductivity relaxation parameters of the proton conductors in this compound were determined in a wide temperature range. The transport properties in this material are assumed to be due to H⁺ protons hopping mechanism.     

Structural and vibrational properties of PVT grown Bi2Te3 microcrystals

High-quality Bi₂Te₃ microcrystals have been grown by physical vapor transport (PVT) method without using a foreign transport agent. The microcrystals grown under optimal temperature gradient are well facetted and they have dimensions up to ～100 μm. The phase composition of grown crystals has been identified by X-ray single crystal structure analysis in space group R3?m, a=4.3896(2) Å, b=30.5019(10) Å, Z=3 (R=0.0271). Raman microspectrometry has been used to describe the vibration parameters of Bi₂Te₃ microcrystals. The FWHM parameters obtained for representative Raman lines at 61 cm^?1 and 101 cm^?1 are as low as 3.5 cm^?1 and 4.5 cm^?1, respectively.