Effect of biphase on dielectric properties of Bi-doped lead strontium titanate thin films

Pb_0.4Sr_0.6TiO₃ (PST) thin films doped with various concentration of Bi were prepared by a sol-gel method. The phase status, surface morphology and dielectric properties of these thin films were measured by X-ray diffraction (XRD), scanning electron microscopy (SEM) and impedance analyzer, respectively. Results showed that the thin films with the maximum dielectric constant and minimum dielectric loss were obtained for x=0.15. For x<0.15, only pure PST perovskite phase were in the thin films. For 0.2<x<0.4, the PST/Bi₂Ti₂O₇ biphase were obtained. The thin films with pure Bi₂Ti₂O₇ pyrochlore phase were obtained for x=0.67. The biphase thin films had high tunability and high figure of merit (FOM). The FOM of PST/Bi₂Ti₂O₇ biphase thin film was about 6 times higher than that thin films formed with pure perovskite phase or pure pyrochlore phase.     

Structural relationships,phase stability and bonding of compounds PdSnn (n=2, 3, 4)

The Sn rich part of the binary system PdSn has been investigated for possible temperature dimorphism. Well-shaped single crystals of PdSn₄, PdSn₃ and PdSn₂ were obtained under self-flux condition where the stannide is in equilibrium with the melt. The melt was subsequently removed by centrifugation at the synthesis temperature. The obtained products were characterised by X-ray diffraction, thermal analysis and ¹¹⁹Sn Mössbauer spectroscopy. The crystal structures of the obtained products corresponded to the already assigned structure types PtSn₄, PdSn₃ and PdSn₂. The structures of PdSn_n (n=2, 3, 4) represent stackings of similar building blocks and are closely related. Structural stability of compounds PdSn_n (n=2, 3, 4) with respect to different stacking possibilities of building blocks was investigated by ab initio calculations in the framework of density functional theory. It was found that differently stacked alternatives to the experimentally determined structure types are very close in energy. Nevertheless, experimentally no indications of polytype formation or even stacking disorder were obtained for PdSn_n (n=2, 3, 4). The peritectic decompositions of PdSn_n were investigated by differential scanning calorimetry. The obtained decomposition temperatures are 330, 370, 617±3 °C for n=4, 3, 2, respectively. The ¹¹⁹Sn Mössbauer isomer shifts of compounds PdSn_n are relatively high (δ≈2.4 mm s⁻¹) and decrease with increasing Pd content. This behaviour coincides with the trend in the number of occupied Sn 5s states as obtained from theoretical calculations.     

Thermodynamic determination of solvation potentials of various metal chlorides by (1,4-dioxane + water) mixtures through EMF measurements

The EMF data of different metal chlorides (2:1 electrolytes) were obtained by using a cell [M_X Hg|MCl₂ (m)|AgCl–Ag] at two temperatures. Stock solutions of metal chlorides (CoCl₂, CuCl₂ and ZnCl₂) were prepared by weight in 1,4-dioxane–aqueous mixtures. There was a significant change in the EMF values with change of metal chloride, its concentration and solvents composition. The standard electrode potential (E°) values of the above cell were calculated from the measured EMF of these mixtures. The standard thermodynamic functions (ΔG°, ΔH° and ΔS°) and respective transfer parameters of MCl₂ from water to 20, 45 and 70% dioxane–water mixtures were also evaluated. Equilibrium dissociation constants (K₁ and K₂) as well as the degrees of dissociation (α₁ and α₂) were obtained by iterative procedures. The data were analyzed in terms of solute–solvent interactions depending on standard and transfer thermodynamic parameters and mean activity coefficients (γ_±) of electrolytes.     

Photocatalytic inhibitory effect of immobilized TiO2 semiconductor on the growth of Escherichia coli studied by acoustic wave impedance analysis

The effect of immobilized TiO₂ photocatalyst on the growth of Escherichia coli was investigated with acoustic wave impedance (AWI) analysis technique for the first time. The motional resistance variation (ΔR₁) curves under different growth conditions were obtained and compared. By fitting ΔR₁ versus time curves toward the impedance response model, three growth kinetic parameters (A, μ_m and λ) for different growth situations were gained. The results showed the lag time (λ) was prolonged, and the maximum specific growth rate (μ_m) and the asymptote (A) were decreased in the presence of UV light and TiO₂ photocatalyst. In addition, the quantificational relationships between the growth parameters and TiO₂ dosage were also investigated, which reflect the inhibitory effect of TiO₂ under a certain light intensity on the growth of E. coli. The three kinetic growth parameters (A, μ_m and λ) obtained from the impedance response model are close to those obtained from the Gompertz popular growth model. These results showed that the AWI analysis technique adapts to study the effect of TiO₂ photocatalyst on the growth of bacteria on the qualitative and quantificational level.     

In situ Mössbauer spectroscopy studies of the electrochemical reaction of lithium with KFeS2

In situ Mössbauer spectroscopy has been used to study the electrochemical reaction of lithium with KFeS₂. Compositions KLi_xFeS₂ with Δx = 0.25 were obtained by coulometric titration for one complete discharge and recharge. Mössbauer spectra were obtained at each composition. Three new iron sites are identified in addition to Fe³⁺ in KFeS₂. A mechanism to account for the electrochemical and Mössbauer data is proposed. The end product KLiFeS₂ has been synthesized and found to be body-centered tetragonal with a = 3.938(2) Å and c = 13.135(5) Å.     

Neutron powder diffraction and first-principles computational studies of CuLixMg2−x (x≅0.08), CuMg2, and Cu2Mg

A small addition of Li changes the orthorhombic structure of CuMg₂ to hexagonal CuLi_xMg_2−x (x=0.08). Determining the Li content of the ternary phase and Li atomic positions was our main objective for this work. For this reason we performed neutron diffraction at several different temperatures below and above room temperature. The results obtained on two neutron powder diffractometers were compared with X-ray diffraction (XRD) data, and with first-principles calculations. The first-principles calculations are in good agreement with Rietveld-refined data from neutron diffraction, but do not show a marked preference for one of several possible Li sites. The pair distribution function (PDF) fitting is consistent with Li substituting only Mg1 (1/2, 0, z). Interstitial spaces in the structure of CuMg₂ and of CuLi_xMg_2−x were also considered, but are unlikely to be occupied by Li. Neutron diffraction data for binary CuMg₂ and Cu₂Mg were also obtained.     

One-pot synthesis of a novel C1-symmetric diphosphine from 1,3-cyclic sulfate. Asymmetric hydroformylation of styrene

Preparation of a novel homochiral diphosphine with C₁-symmetry from the cyclic sulfate of (2R,4R)-2,4-pentanediol is reported. Reaction of a lithium phosphide salt with the cyclic sulfate affords a γ-phospholylsulfate which can be converted to a diphosphine ligand on treatment with a second equivalent of lithium phosphide. Using this ligand in the platinum-catalyzed asymmetric hydroformylation of styrene, outstanding levels of regio- and enantiocontrol were obtained (89/11 iso/n isomeric ratio and 89% e.e.). The results are compared with those obtained with the analogous ligands (bdpp and bdbpp) having C₂-symmetry. The novel unsymmetric ligand possessed the advantageous catalytic features of the C₂-symmetric parent ligands.     

Synthesis and structure determination of the new Sm2Ti2O5S2 compound

Sm₂Ti₂O₅S₂ was obtained in an attempt to prepare an oxysulfide of samarium and titanium in a way similar to the obtention of the quaternary Sm₃NbO₄Se₃ compound. The structure was determined by single-crystal X-ray diffraction. The following crystal data were obtained: M_r = 540.6 g mol⁻¹, tetragonal symmetry with unit cell parameters a = 3.819(1) A, c = 22.964(5) A, space group I4/mmm (139). Refinement for 127 unique reflections with I > 3σ(1), and 11 variables, converged to the reliability factor R = 1.77 %. The structure can be described as a stacking, along the c-direction, of [Sm₂S₂] slabs of a rock-salt type (two-atom-thick-layers) separated by a 2D network of corner-sharing octahedra [= Ti₂O₅] of a ReO₃ structure type.     

Stereoselective adduct formation of α-acylcamphorato-copper(II) chelates with some chiral Lewis bases

The formation constants of the mono-adducts of α-acylcamphorato-copper(II) chelates such as (+)-Cu(facam)₂, (?)-Cu(facam)₂, (+)-Cu(hfbc)₂ and (?)-Cu(hfbc)₂ with some chiral Lewis bases were determined spectrophotometrically in benzene. In order to compare the adduct formation constants obtained with the (+)- and (?)-forms, some pairs of chiral Lewis bases such as 1-amino-2-propanol [(R)(?), (S)(+)], 1-(α-naphthyl)ethylamine [(R)(+), (S)(?)], α-phenyl ethylamine [(R)(+), (S)(?)] and also quinine and quinidine were examined as neutral ligands. Although not very pronounced, the effects of combinations obtained for (+)- or (?)-Cu(II) chelates and (+)- or (?)-ligands indicate that formation constants obtained by the formation of adducts with the ligands having different directions of the optical rotation seems to be superior to those with the same direction.     

Synthesis of pure stereoisomers of benzo[b]thienyl dehydrophenylalanines by Suzuki cross-coupling. Preliminary studies of antimicrobial activity

Several benzo[b]thienyldehydrophenylalanines were synthesized from pure stereoisomers of the methyl ester of N-(tert-butoxycarbonyl)-β-bromodehydrophenylalanine as an extension of our previously reported method for the synthesis of dehydrotryptophan analogues to dehydrophenylalanine derivatives. The latter were obtained in high yields by N-deprotection and bromination of N,N-bis-(tert-butoxycarbonyl)-(Z)-dehydrophenylalanine using TFA and NBS. This was carried out in two steps or in a one pot procedure resulting in different E/Z ratios. These compounds were coupled under Suzuki cross-coupling conditions [Pd(PPh₃)₄, Na₂CO₃, DME/H₂O] with several boronic benzo[b]thienyl acids in good to high yields maintaining the stereochemistry of the starting materials. The best yields were obtained when the boronic acid was in position 7 of the benzo[b]thiophene and with the E isomer of the brominated dehydrophenylalanine. In some cases it was possible to increase the lower yields by changing the Pd source to PdCl₂(PPh₃)₂. A model dipeptide was prepared coupling a benzo[b]thienyldehydrophenylalanine with the methyl ester of alanine. Preliminary antimicrobial studies were performed with both isomers of one of the β, β-diaryldehydroalanines obtained. The results show that the compounds are selective and very active (very low MICs) against Gram positive bacteria (B. cereus and B. subtilis) the Z-isomer being more active. The compounds are also active against Candida albicans presenting similar MICs.     

Imino- and bis-imino-pyridines with N-ter-butyl-N-aminoxyl group: synthesis, oxidation and use as ligand towards M ( Mn, Ni, Zn) and Gd

Imino- and bis-iminopyridine ligands bearing N-ter-butylhydroxy groups were synthesized by the condensation reaction between a N-ter-butylhydroxy substituted aniline and 2-formylpyridine, 2-acetylpyridine and 2,6-bis-acetylpyridine. The N-ter-butylaminoxy radicals obtained after oxidation using PbO₂ or Ag₂O were studied by EPR spectroscopy in solution. Indeed, complete decomposition was observed during isolation of these radical derivatives. The N-ter-butylhydroxy substituted ligands obtained were complexed with Mn²⁺, Ni²⁺, Zn²⁺ and Gd³⁺ salts; the obtained complexes were characterized and oxidized to give the aminoxy analogs, which were studied using IR, UV and EPR spectroscopies.     

Thermal decomposition of lithium-inserted NbO2F

The thermal decomposition of lithium-inserted NbO₂F was studied by differential scanning calorimetry. Samples of Li_xNbO₂F (O ⩽ x ⩽ 1.8) were heated to 800 and 950 K. The thermograms revealed that decomposition started within the temperature range 640–780 K followed by a second step at approximately 900 K. The products were characterized by X-ray powder diffraction and electron diffraction patterns and by high resolution electron microscopy. The following phases were obtained at 800 K: LiF, NbO₂F, the low pressure form of Nb₃O₇F, and lithium-enriched forms of PNb₂O₅, NbO₂ and LiNbO₃. At 950 K, NbO₂F disappeared, and LiNb₃O₈ and the high pressure form of Nb₃O₇F coexisted with the other phases obtained at 800 K. The formation of structures built up of approximately hexagonally close-packed anion arrangements is discussed, as well as the role of lithium as a stabilizing component.     

Synthesis of podands with nido-carboranyl groups as a basis for construction of crown ethers with an incorporated metallacarborane moiety

The reactions of the dioxane derivative of 7,8-dicarba-nido-undecaborate anion (nido-carborane), [10-O(CH₂CH₂)₂O-nido-7,8-C₂B₉H₁₁], with a series of O,O′-dinucleophiles (pyrocatechol, resorcinol, hydroquinone, and ethylene glycol) were studied. The nido-carborane-based podand was obtained, which can be used for assembling of crown ethers with an inserted metallacarborane moiety.     

A study of the mechanochemical synthesis of TlCl nanoparticles by the method of dilution with the final product

The kinetics of the solid-state mechanochemical synthesis of the nanosized product (TlCl) in the reaction 2NaCl + Tl₂SO₄ + zNa₂SO₄ = (z + 1)Na₂SO₄ + 2TlCl was studied experimentlaly. The method used was based on the dilution of the initial mixture of powdered reagents (2NaCl + Tl₂SO₄) with another exchange reaction product (Na₂SO₄) at the optimum theoretically estimated z value, z = z* = 11.25. Several special features of the development of this reaction were established. The parameters of the kinetic curve obtained for the mechanochemical synthesis of the desired product were compared with those of the kinetic curve determined theoretically for the model reaction KBr + TlCl + zKCl = (z + 1)KCl + TlBr with z = z ₁ ^* = 13.5. This allowed us to experimentally estimate the mass transfer coefficient in a mechanochemical reactor by mobile milling bodies. This estimate was obtained for the first time. The dynamics of changes in the size of desired product nanoparticles depending on the time of mechanochemical activation in an AGO-2 ball planetary mill was studied.     

Biohydrogen Production Based on the Evaluation of Kinetic Parameters of a Mixed Microbial Culture Using Glucose and Fruit–Vegetable Waste as Feedstocks

Hydrogen (H₂) production from the organic fraction of solid waste such as fruit and vegetable waste (FVW) is a novel and feasible energy technology. Continuous application of this process would allow for the simultaneous treatment of organic residues and energy production. In this study, batch experiments were conducted using glucose as substrate, and data of H₂ production obtained were successfully adjusted by a logistic model. The kinetic parameters (μ _max?=?0.101 h^?1, K _s?=?2.56 g/L) of an H₂-producing microbial culture determined by the Monod and Haldane–Andrews growth models were used to establish the continuous culture conditions. This strategy led to a productive steady state in continuous culture. Once the steady state was reached in the continuous reactor, a maximum H₂ production of 700 mL was attained. The feasibility of producing H₂ from the FVW obtained from a local market in Mexico City was also evaluated using batch conditions. The effect of the initial FVW concentration on the H₂ production and waste organic material degradation was determined. The highest H₂ production rate (1.7 mmol/day), the highest cumulative H₂ volume (310 mL), and 25 % chemical oxygen demand (COD) removal were obtained with an initial substrate (FVW) concentration of 37 g COD/L. The lowest H₂ production rates were obtained with relatively low initial substrate concentrations of 5 and 11 g COD/L. The H₂ production rates with FVW were also characterized by the logistic model. Similar cumulative H₂ production was obtained when glucose and FVW were used as substrates.     

Dissociative excitation of water by metastable argon

The reaction Ar(²P_2,0) + H₂O → Ar + H + OH(A²Σ⁺)was studied in crossed molecular beams by observing the luminescence from OH(A²Σ⁺). No significant dependence of the spectrum on collision energy was found over the 22–52 meV region. Spectral simulation was used to obtain the OH(A) vibrational distribution and rotational temperature, assuming a Boltzmann rotational distribution. Since predissociation is known to strongly affect the rovibrational distribution, the individual rotational state lifetimes were included in the simulation program and were used to obtain the average vibrational state lifetimes. Excellent agreement with experiment was obtained for vibrational population ratios N₀/N₁/N₂ of 1.00/ 0.40/0.013 and a rotational temperature of 4000 K. Correction for the different average vibrational lifetimes gave formation rate ratios P₀/P₁/P₂ of 1.00/0.49/0.25. The differences between these results and those from flowing afterglow studies on the same system are discussed. Three reaction mechanisms are considered, and the vibrational prior distributions are calculated from a simple density-of-states model. Only fair agreement with experiment is obtained. The best agreement for the mechanisms giving OH(A) in two 2-body dissociation steps is obtained by assuming 1.0 eV of internal energy remains in the second step. The OH(A) vibrational population distribution of the present work is similar to that found in the photolysis of H₂O at 122 nm, where there is 1.10 eV of excess internal energy.     

Growth and characterization of n-WS2 and niobium-doped p-WS2 single crystals

Single crystals of n- and p-WS₂ were obtained by chemical vapor transport using chlorine and bromine as transporting agents. The best niobium-doped WS₂ crystals were obtained when the concentration of the charge (formulated (1 ? x)WS₂ · (x)NbS₂) was ? 37 mg charge/ml of tube, and x = 0.01 to 0.03. A thermodynamic analysis of the crystal growth process is consistent with the observed doping concentration and other properties of the crystals obtained by this process. The crystals grown are characterized by electrical transport and surface photovoltage measured capacitance techniques.     

Solid state NMR spectroscopy of metal carbonyls. The influence of site symmetry on the solid state spectrum of cis-(η5-C5H5)2Fe2(CO)4

Solid state carbon-13 NMR spectra of metal carbonyls are readily obtained using commercial instrumentation. The observed isotropic chemical shifts are in good agreement with solution values. Furthermore there is a one-to-one correspondence between crystallographically unique carbonyls and magnetically distinguishable carbonyls in the absence of accidental degeneracies. For cis-(η⁵-C₅H₅)₂Fe₂(CO)₄ the site symmetry is C₁ while the molecular symmetry is C_2ν. The lower solid state symmetry gives rise to more resonances in the solid spectrum than in solution. Magic angle tuning and chemical shifts were obtained using hexamethylbenzene as a standard.     

Thermal behaviour of Uranium(VI) complexes. Uranyl acetate dihydrate-thiourea system: Synthesis and decomposition

The solid-state syntheses of uranyl acetate adducts with thiourea were attempted directly in a DSC apparatus according to the scheme: UO₂Ac₂·2 H₂O_(s)+n thiourea_(s) → → UO₂Ac₂·thiourea_n(s)+2 H₂O_(v) (n=1–6), and the correspondingδH values were evaluated. At all stoichiometric ratios the same UO₂Ac₂·thÌourea product was obtained, to which a pentagonal bipyramidal structure was attributed. Thermoanalytical (TG and DTG) and infrared spectra measurements were also performed and agree with the DSC results.     

Oxidative C-H/C-H Coupling of Dipyrromethanes with Azines by TiO2-Based Photocatalytic System. Synthesis of New BODIPY Dyes and Their Photophysical and Electrochemical Properties

Oxidative C-H/C-H coupling reactions of dipyrromethanes with azines in the presence of a heterophase oxidative photocatalytic system (O₂/TiO₂/visible light irradiation) were carried out. As a result of cyclization of obtained compounds with boron trifluoride etherate, new hetaryl-containing derivatives of 4,4-difluoro-4-boron-3a,4a-diaza-s-indacene were synthesized. For the obtained compounds, absorption and luminescence spectra, quantum yields of luminescence as well as cyclic volt-amperograms were measured.