A study of the thermal analysis of the solid solution (AgxK1−xNO3

The effect of partial replacement of K⁺ by Ag⁺ in the mixed system of KNO₃ and AgNO₃ during a set of DSC heating cycles was studied by means of a modern computerized DSC system. Thermal analysis was performed in the vicinity of the phase transition II I for pure KNO₃. The results revealed a large change in enthalpy and the phase transition temperature close to the morphotropic boundary x=0.5–0.6. At this boundary, the transformation enthalpy reached the maximum value of 101 J g^–1. On the basis of the data obtained from this accurate thermal analysis work, a model is suggested for the energy barrier of rotation of the nitrate ion in the mixed nitrate system.     

Synthesis and characterization of the ZnxCd1−xIn2S4 pseudoternary solid solution

We have synthesized several compounds of the Zn_xCd_1−xIn₂S₄ family by solid phase reactions and chemical transport reactions using iodine. The reaction products have been characterized as to composition, structure, and lattice dynamics. Here we discuss and compare the different results obtained by the two synthesis methods.     

Sodium motion in the Nasicon related Na1+xZr2−xInx(PO4)3 solid solution: An NMR study

Sodium ion motion in Na_1+xZr_2−xIn_x(PO₄)₃ Nasicon-related materials (0 ≤ x ≤ 1.85) has been studied by NMR at two resonance frequencies from 170 to 450 K. At 8 MHz the resonance lines due to M1- and M2-type sites are well resolved. They are split by a strong second-order quadrupolar effect (ν_Q = 1.5 Megacycles (Mc)/sec). For NaZr₂(PO₄)₃ only the M1 site is occupied at RT, while a new site M5 appears at rising temperature (410 K). At 21 Mc/sec the line narrowing observed at increasing temperature illustrates the Na⁺ ion mobility within the skeleton. According to the temperature and the value of the ionic conductivity two diffusion mechanisms seem to occur.     

Crystal structure and properties of the Na1−x Ru2O4 phase

Sodium ruthenium(III,IV) oxide Na_1−x Ru₂O₄ was synthesized by the solid state reaction of Na₂CO₃ and RuO₂ in inert atmosphere and characterized by X-ray powder diffraction, electron diffraction, and high-resolution transmission electron microscopy. The compound crystallizes in the CaFe₂O₄-type structure (space group Pnma, Z = 4, a = 9.2641(7) Å, b = 2.8249(3) Å, c = 11.1496(7) Å). Double rutile-like chains of the RuO₆ octahedra form a three-dimensional framework, whose tunnels contain sodium cations. The structure contains two crystallographically independent sites of ruthenium atoms randomly occupied by the Ru^III and Ru^IV cations. The superstructure with the doubled b parameter found for one of the samples under study using electron diffraction is caused, probably, by ordering of the Ru cations in the rutile-like chains. The Na_{1− x} Ru₂O₄ compound exhibits temperature-independent paramagnetism with χ₀ = 1.9·10⁻⁴ cm³ (mole of Ru⁻¹). Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1655–1660, October, 2006.     

High-pressure Raman study of the β-BaB2O4 crystal and pressure-induced phase transitions

A high-pressure Raman study of β-BaB₂O₄ reveals the occurrence of four pressure-induced phase transitions near 48, 70, 80 and 96 kbar, respectively. Above 96 kbar, β-BaB₂O₄ becomes amorphous and the transition is irreversible. A Raman quartet originating from Davydov splitting and the pressure-scanned Fermi resonance effect is observed.     

A study on the structure and catalytic performance of ZnxCu1−xAl2O4 catalysts synthesized by the solution combustion method for the esterification reaction

A Zn_xCu_1−xAl₂O₄ catalyst was prepared via the microwave-assisted solution combustion method (MSC). This method presents a fast procedure for industrial scale catalyst preparation. The physicochemical properties of the fabricated catalyst were characterized using XRD, FTIR, BET, SEM and TEM analyses. The catalytic performance through the esterification reaction was examined under the following conditions: reaction temperature = 180 °C, catalyst concentration = 3% (w/w), molar ratio of oleic acid to methanol = 9 and reaction time = 6 h. XRD results showed that loading both zinc and copper oxides on alumina at a ratio of amounts that were nearly the same resulted in decreased crystalline size and well-dispersed copper-alumina and zinc-alumina crystals. Moreover, the mean pore diameter of the sample was increased by simultaneous loading of zinc and copper oxides on alumina that enhanced permeation of the reactants within pores and increased the interaction of the reactant with the catalyst active sites. The catalyst showed minimum tendency towards adsorbing moisture from air, which was attributed to it having less atoms on the surface through which binding with H₂O molecules takes place. The highest level of activity in the esterification reaction (96.9%) was obtained at the optimum ratio of the Zn:Cu molar ratio, identified to be 2:3. The sample particles ranged from 10 to 30 nm in size, without agglomeration.     

Normal pressure synthesis of (Tl1−yCy)Ba2Ca3Cu4O12−δ superconductor

Single phase (Tl_1−yC_y)Ba₂Ca₃Cu₄O_12−δ (Tl_1−yC_y-1234) (y = 0, 0.25, 0.5 and 0.75) superconductor samples have been prepared by solid state reaction method. The FTIR absorption measurements have confirmed the substitution of carbon at thallium site in the charge reservoir layer, (Tl_1−yC_y)Ba₂O_4−δ. The electron micrographs of these samples have shown that the carbon substitution has improved the grain morphology of Tl_0.75C_0.25-1234 sample. The y = 0.25 was found to be the optimum carbon concentration to achieve higher superconducting transition temperature T_c[0] and improved grain morphology. The superconducting transition temperature of Tl_0.75C_0.25-1234 sample has been increased to 100 K whereas a decrease in the superconducting transition temperature of Tl_1−yC_y-1234 (y = 0.5 and 0.75) samples was observed. However, the magnitude of diamagnetism has been decreased in all the carbon substituted samples.     

High-pressure synthesis and characterization of the alkaline earth borate β-BaB4O7

The new orthorhombic barium borate β-BaB₄O₇ was synthesized under high-pressure/high-temperature conditions in a Walker-type multianvil apparatus at 7.5 GPa and 1100 °C, starting from stoichiometric mixtures of the binary oxides. β-BaB₄O₇ crystallizes in space group Pmnb with Z = 2 and lattice parameters a = 1099.4(2), b = 901.7(2), c = 430.73(9) pm, R1 = 0.0199, and wR2 = 0.0406 (all data). The network-structure is built up exclusively from BO₄-tetrahedra, linked via common corners. Its structural differences to the ambient-pressure phase α-BaB₄O₇ and structural agreements with the isotypic high-pressure phases β-MB₄O₇ (M = Ca, Hg, Sn) and the ambient-pressure phases MB₄O₇ (M = Sr, Pb, Eu) are discussed. β-BaB₄O₇ and a hypothetical BaB₄O₇ in the β-MB₄O₇ (M = Ca, Hg, Sn) structure were studied as high-pressure phases of α-BaB₄O₇, using density functional calculations. The transition pressure of α-BaB₄O₇ into the structure of β-BaB₄O₇ was calculated to 1.5 GPa; the transition pressure of β-BaB₄O₇ into BaB₄O₇ in the β-MB₄O₇ (M = Ca, Hg, Sn) structure to 7.5 GPa.     

Spark plasma sintering synthesis of Ni1−xZnxFe2O4 ferrites: Mössbauer and catalytic study

Nickel-zinc ferrite nanoparticles, Ni_1−xZn_xFe₂O₄ (x = 0, 0.2, 0.5, 0.8, 1.0) were prepared by combination of chemical precipitation and spark plasma sintering (SPS) techniques and conventional thermal treatment of the obtained precursors. The phase composition and structural properties of the obtained materials were investigated by X-ray diffraction and Mössbauer spectroscopy and their catalytic activity in methanol decomposition was tested. A strong effect of reaction medium leading to the transformation of ferrites to a complex mixture of different iron containing phases was detected. A tendency of formation of Fe-carbide was found for the samples synthesized by SPS, while predominantly iron-nickel alloys ware registered in TS obtained samples. The catalytic activity and selectivity in methanol decomposition to CO and methane depended on the current phase composition of the obtained ferrites, which was formed by the influence of the reaction medium.     

Structural investigation of the Zn1−xCdxSb solid solution by density-functional theory approach

A peculiar behaviour was already reported in literature from experimental investigations in the Zn_1?xCd_xSb solid solution around x = 0.5. This behaviour was assumed to be linked to an ordering in the phase; however this assumption was never confirmed. The aim of this work was to understand this behaviour from a theoretical point of view. DFT calculations were performed to calculate the energy and the lattice parameters for all the possible structures of Zn_1?xCd_xSb with several compositions (x = 0.125, 0.25, 0.375, 0.5, 0.625, 0.75, 0.875, 1.0). The results show that an ordering appears in the most stable structure for x = 0.5. This ordering consists in stacked planes each containing only one chemical species.     

Thermal magnetic investigation of the decomposition of NixMn1−xC2O4·2H2O

The systems Ni_xMn_1?xC₂O₄·2H₂O (x = 0.11, 0.34) are characterized by XRD, SEM, TG/DTA, EGA-MS and magnetic measurements. The last confirmed that the studied samples are real solid solutions. The SEM reveals that the morphology depends on both the excess of C₂O₄^2? and the initial ratio Ni/Mn. The thermal magnetic investigations (in situ) show that: (i) the presence of Ni in Ni_xMn_1?xC₂O₄·2H₂O leads to decreasing in the decomposition temperature in regard to that of the manganese oxalate; (ii) upon increasing the Ni content the temperature of decomposition (in air) is growing up; (iii) the presence of Ni stabilizes the manganese with respect to oxidation, in spite of the occurring process of decomposition.     

An investigation of the polythermal diagram of the H2ONa2HPO4Na2SO4 system

The polythermal diagram of the ternary system H₂ONa₂HPO₄Na₂SO₄ has been established, setting up nine isotherms obtained between 0 and 25°C by conductimetric analysis. The solubility domains of the various solid phases have been determined. One eutectic, three stable and one metastable transitional transformations have been observed. Temperature and composition of the eutectic point have been obtained by thermal analysis at constant flow.     

Defect structures in the brannerite-type vanadates: VIII. Synthesis of the Mg1−yLiyV2−yMoyO6 and Mg1−x−yØxLiyV2−2x−yMo2x+yO6 solid solutions: Effect of strengthening the crystal lattice by substitution of monovalent ion for bivalent ion

It is shown that MgV₂O₆ and LiVMoO₆, both of the brannerite-type structure, exhibit miscibility in the entire composition range resulting in the formation of MgLi = Mg_1−yLi_yV_2−yMo_yO₆ solid solutions. For y > 0.5 significant capacity of the MgLi matrix to the excess Mo⁶⁺ cations compensated by cation vacancies Ø appears and MgLiØ = Mg_1−x−yØ_xLi_yV_2−2x−yMo_2x+yO₆ solutions become stable. Pronounced negative deviations from Vegard's law are simultaneously observed for MgLi solid solutions. An unusual phenomenon is thus observed: monovalent cation (Li⁺) substituted for bivalent cation (Mg²⁺) strengthens the brannerite-type lattice and increases its toleration to cation vacancies. A similar effect has recently been observed for ZnLi and ZnLiØ solid solutions (K. Mocała and J. Ziółkowski, J. Solid State Chem. 71, 426 (1987)); the effect is absent, however, in the case of MnLi and MnLiØ (J. Ziółkowski, K. Krupa, and K. Mocała, J. Solid State Chem. 48, 376 (1983)). Some speculations concerning this effect and some predictions are offered. X-ray data are listed for MgLi solid solutions of various compositions.     

The electrochemical behaviour of polycrystalline silver electrodes in Na2CO3 solution and the effect of ClO− 4 ions

The electrochemical behaviour of polycrystalline silver electrodes in Na₂CO₃ solutions was studied under potentiodynamic and potentiostatic conditions and complemented with X-ray diffraction analysis. Potentiodynamic E/i anodic curves exhibit active passive transition prior to an oxygen evolution reaction. The active region involves a small peak AI followed by a major peak AII before the passive region. Peak AI is assigned to the formation of an Ag₂O layer while peak AII is due to the formation of an Ag₂CO₃ layer. The height of the anodic peaks increases with increasing Na₂CO₃ concentration, scan rate and temperature. The effect of increasing additions of NaClO₄ on the electrochemical behaviour of Ag in Na₂CO₃ solutions was investigated. The perchlorate ions stimulate the active dissolution of Ag, presumably as a result of the formation of soluble AgClO₄ salt. In the passive region, ClO⁻ ₄ ions tend to break down the dual passive film, leading to pitting corrosion at a certain critical pitting potential. The pitting potential decreases with ClO⁻ ₄ concentration. Potentiostatic current/time transients showed that the formation of Ag₂O and Ag₂CO₃ layers involves a nucleation and growth mechanism under diffusion control. However, in the presence of ClO⁻ ₄ ions, the incubation time for pit initiation decreases on increasing the anodic potential step. Received: 3 July 1998 / Accepted: 10 March 1999     

A study of the perturbations between the A1Σ+u and b3Πu states of Na2

The interaction between the A¹Σ⁺_u and b³Π_Ωu states of Na₂ is explored by resonantly exciting A states via A-X transitions and, after an adjustable delay time, photoionizing them. For long delays signals arise only from states with significant fractions of both A and b state character. Thus the regions where the interaction is important stand out clearly in the spectrum. Using this technique we have investigated perturbations of the A v' = 3, 7 and 8 states by the b v' = 10, 13 and 14 states.     

Electrophysical properties of solid solutions of Zn2 − x (Zr a Sn b )1 − x Fe2x O4 compositions

The electrophysical properties of the multicomponent Zn₂ZrO₄ ? Zn₂SnO₄ ? ZnFe₂O₄ system are studied. The electrophysical parameters of solid solutions of Zn_{2 ? x} (Zr _a Sn _b )_{1 ? x} Fe_2x O₄ (x = 0–1.0, Δx = 0.1, a + b = 1) are determined. It is found that the formed solid solutions are semiconductors with electrophysical properties that change in a regular fashion with composition and are distinguished by high values of resistivity (107–1012 Ω cm).