Thermodynamic properties of ternary semiconducting alloys

Using the new information supplied by extended-x-ray-absorption-fine-structure measurements and the results of our structural model, we compute the bond probability of a few ternary semiconducting III–V and II–VI alloys as a function of temperature and composition in the framework of a modified quasi-chemical approximation. We derive the thermodynamic functions of mixing, considering both elastic and chemical contributions to the bond energies. We examine how the deviation from the full randomness affects the ordering of such alloys and we construct the phase diagrams in the region of phase separation. Possible formation of ordered compounds at low temperatures is predicted.     

Mössbauer studies on one-dimensional iron phthalocyanines

Summary Magnetic moments and⁵⁷Fe Mössbauer spectra at room temperature and at liquid nitrogen temperature of polynuclear ligand-bridged iron phthalocyanines, FePcL (L = pyrazine and 4,4-bipyridyl), are reported. The experimental data are in agreement with a pseudo-octahedral environment around the iron(II) cation. Partially oxidized derivatives, FePc(pz)I_0.26 and FePc(bipy)I_1.06 have been synthesized and their⁵⁷Fe Mössbauer spectra and magnetic moments within the same temperature range obtained. Oxidation is shown to be metal centred and the iodine is found to be in I^– form for FePc(pz)_0.26 and as both I^– and I ₃ ^– species for FePc(bipy)I_1.06. While the magnetic moment of FePc(pz) increases upon oxidation, the opposite occurs for FePc(bipy).     

Synthesis of 2-(imidazolylamino)benzothiazoles

Treatment of derivatives of 5-phenylthioureido-3H-imidazole-4-carboxylic acid with bromine afforded 2-(imidazolylamino)benzothiazoles.     

A new phase in the Ag−O−S system

The investigations of reaction between Ag₂SO₄ and Ag₂S in air atmosphere have been carried. Results of DTA and X-ray phase powder diffraction of a reaction mixture have confirmed that in the Ag?O?S system exists a new phase. A formula of the phase is Ag₂SO₂.     

Kinetics of the Formation of Goethite in the Presence of Sulfates and Chlorides of Monovalent Cations

The synthesis of goethite by oxidation of Fe²⁺in presence of metallic iron was undertaken in an aqueous medium containing indifferent salts such as Na₂SO₄, (NH₄)₂SO₄, NaCl, and NH₄Cl. Temperature and bubbling air rate were maintained, respectively, at 70°C and 1 L/min. The influence of anions and cations on the kinetics of each step of the process has been followed distinctly, the iron dissolution rate has been determined by the variation of the medium acidity, and the precipitation of goethite has been determined by gravimetric measurements. With respect to Cl⁻, the SO₄²⁻anion decreases the rate of the two reactions. NH₄⁺acts as an inhibitor when it is present at low concentrations and as an accelerator for higher concentrations; the limit corresponding to the change of NH₄⁺behavior depends on the nature of the counter ion. The reaction product is composed of pure goethite in the presence of sulfate salts, whereas a mixture of goethite and lepidocrocite, respectively, 60–70 and 40–30%, was observed in the presence of chloride salts.     

Tetrastrontium dimanganese copper nonaoxide,Sr4Mn2CuO9

Single crystals of Sr₄Mn_2.09Cu_0.91O₉ have been grown by flux synthesis and the structure, closely related to the hexagonal perovskite 2H, was solved from single‐crystal X‐ray data in space group P321. The structure of Sr₄Mn₂CuO₉ is composed of chains of face‐sharing polyhedra with a sequence of two octahedra and one trigonal prism. The octahedra are filled by Mn atoms and the Cu atoms are randomly distributed at the centres of the square faces of the trigonal prism. A stacking fault is observed within one of the two chains, which can be attributed to a shifting of the chain along the c axis.     

Application of High Pressure-DTA for High Pressure-liquid Phase Epitaxy of Doped Mercury and Thallium HTS Formations

The fabrication method of superconducting thin films of compositions HgBa₂Ca₂Cu₃O_8+δ (Hg-1223) and Tl₂Ba₂CuO_y (2201) on single-crystalline SrTiO₃ and LaAlO₃ substrates is reported. The highest obtained T _c was 134 K and J _c over 10⁶ A cm^–2 at 77 K. High pressure DTA(HP-DTA) was applied to grow mercury- and thallium-based high-temperature superconducting crystals and thin films, to identify melting points of particular phases within these oxide systems and determine suitable processing conditions. The DTA system operates at the: maximum temperature of 1200°C, volume up to 5 cm³, working pressure up to 1.5 GPa and at a working atmosphere — inert gas with up to 25% oxygen. This revised version was published online in August 2006 with corrections to the Cover Date.     

Adsorption of Some Essential Amino Acids on Hydroxyapatite

Samples of synthetic hydroxyapatite, Ca(10)(PO(4))(6)(OH)(2), obtained by wet method and calcined at 1173 K in air were used in an adsorption study of some essential amino acids, mainly histidine, methionine, and tryptophan. Adsorption isotherms were obtained using aqueous solutions of concentration range 2.7x10(-2)-1.3x10(-3) M at 303, 318, and 343 K, under near neutral conditions. The mode of adsorption was studied using IR spectroscopy. The results are discussed in terms of the dependence of the adsorption process both on the functional groups on the hydroxyapatite and on the solution chemistry of the aqueous amino acids solutions. Copyright 2001 Academic Press.     

Thin-Layer Chromatography with an Isolated Support and Forced Flow of the Mobile Phase

JPC – Journal of Planar Chromatography – Modern TLC -     

A facile synthesis of novel triazoloquinoxahnones and triazinoquinoxalinones

A series of 1-aryl-s-triazolo[4,3-a]quinoxalin-4-ones, 3 , were synthesized via the pyrolysis of the corresponding hydrazones, 6 . Thus, the cyclodehydrogenation occurred by refluxing them in an inert solvent (e.g. ethylene glycol) to give the triazoloquinoxalin-4-ones in a satisfactory yield. Using DMSO as a solvent for the above transformation afforded as a minor by-product an S-ylid. In contrast to earlier findings, annelation of a six-membered ring was successful and achieved through the pyrolysis of the pyruvate hydrazones derived of the quinoxalin-4-ones at ?230° to give the as-triazino[4,3-a]quinoxalin-5-ones, 4 . The reaction of 5 with acetylacetone afforded 3-(3′,5′-dimethylpyrazol-1-yl)-2(1H)-quinoxalinone, 10 . The structural assignments for the new compounds were based on their elemental analysis and spectroscopic data as well as an independent synthesis.