WDS-EPMA nitrogen profile determination in TiN/Ti diffusion couples using homotypic standard materials

Wavelength-dispersive electron probe microanalysis (WDS-EPMA) of TiN/Ti diffusion couples was carried out in order to determine the nitrogen profiles across the phase bands. Thein situ TiN/Ti diffusion couples were used for phase equilibrium studies. The problem of complete overlap of the Ti _L1 and N _K lines was solved using chemically well-characterized single-phase titanium nitride samples (-Ti(N), -Ti₂N and -TiN_1–X ) as external standards. By using such homotypic standard materials it was possible to eliminate systematic errors introduced by imperfect correction algorithms. The composition of the phases in multiphase TiN/Ti diffusion couples could be determined with an accuracy of better than ±1 at% N.     

Thermal analysis and structural characterization of Bi<Subscript>4</Subscript>V<Subscript>2–x</Subscript>Ba<Subscript>x</Subscript>O<Subscript>11–1.5x</Subscript> (0.02≤<Emphasis Type="Italic">x</Emphasis>≤0.50)

This work reports the study of Bi₄V_2–xBa_xO_11–1.5x (0.02≤x≤0.50) series, which is a potential source of solid electrolytes to apply in oxygen sensors. X-ray powder diffraction was used to point out the formation of major ionic conductive phases and minor ones. The modifications of vanadate substructure were probed, at short range, by Fourier-transform infrared spectroscopy. Differential scanning calorimetry evidenced the formation of tetragonal γ phase, which can be ionic conductive, for x=0.14.     

Existence region, structure, and properties of YBa(Cu1? x Fe x )2O5+δ and (Y1? y Ba y )2 CuFeO5+δ solid solutions

We study the effect of Y³⁺ ↔ Ba²⁺ and Cu²⁺ ↔ Fe³⁺ substitutions on the structure, thermal expansion, electrical conductivity, and thermal e.m.f. of layered ferrocuprate YBaCuFeO_{5 + δ} · YBa(Cu_1−x Fe _x )₂O_{5 + δ} solid solutions with 0.45≤x≤0.55 are formed. The unit cell parameters, thermal expansivity, and oxygen nonstoichiometry index of the YBaCuFeO_{5 +δ} phase (δ) are almost independent of variations in the cationic composition of this phase. The electrical conductivity of layered yttrium barium ferrocuprate increases, whereas the activation energy of conductivity decreases in response to Ba²⁺ → Y³⁺ and Cu²⁺ → Fe³⁺ substitutions (with increasing copper(III) proportion in samples). The thermal e.m.f. of ceramics decreases when composition deviates from the cationic stoichiometry (YBaCuFeO_{5 +δ}). Original Russian Text ? A.I. Klyndyuk, E.A. Chizhova, V.M. Kononovich, 2008, published in Zhurnal Neorganicheskoi Khimii, 2008, Vol. 53, No. 10, pp. 1672–1676.     

Investigations in the ternary system Ti-Mo-N by means of EPMA and XRD

Arc-melted ternary Ti-Mo-N alloys were heat treated at 1423 K in order to evaluate the compositions of the equilibrium phases. The composition of the bcc phase-Ti _x Mo_1–x with respect to Mo and Ti was determined by electron probe microanalysis (EPMA) and lattice parameter measurements (XRD). In order to avoid the effects of plastic deformation caused by powdering the ductile-Ti _x Mo_1–x alloys, the lattice parameter measurements were carried out on small particles of the compact samples using Debye-Scherrer cameras. The EPMA and XRD results agree within the expected range of accuracy. Apparently the solubility of nitrogen in-Ti _x Mo_1–x is low and does not perceptibly affect EPMA and XRD results. The relationship between the lattice parameter and the nitrogen content of-TiN_1–x was applied to determine the composition of-TiN_1–x in equilibrium with-Ti_xMo_1-x No solid solubility of Mo in TiN_1–x could be detected. The tie lines at 1423 K between the two phases were established.     

Crystal structure and physicochemical properties of layered perovskite-like phases LnBaCo<Subscript>2</Subscript>O<Subscript>5 + δ</Subscript>

Complex oxides LnBaCo₂O_{5 + δ} (Ln = Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y) were obtained by solid-state synthesis at 1373 K in air. The crystal structure of layered perovskites LnBaCo₂O_{5 + δ} was studied by X-ray and neutron diffraction analyses. It was shown that cobaltites LnBaCo₂O_{5 + δ} crystallized in tetragonal (space group P4/mmm, 0.6 > δ > 0.45) or orthorhombic (space group Pmmm, 0.6 > δ > 0.45) structures depending on the radius of the lanthanide ion and the oxygen content. The dependences of the unit cell parameters of LnBaCo₂O_{5 + δ} on the radius of the lanthanide ion were obtained. The average thermal expansion coefficients at temperatures from 298 to 1373 K in air were determined. The dependence of the chemical component of thermal expansion on the oxygen content was evaluated for LnBaCo₂O_{5 + δ} (Ln = Nd, Sm, Gd, Y).     

Structural features of the formation of La1?xCaxFeO3?δ (0 ≤x ≤ 0.7) hetero valent solid solutions

A synthesis method with the use of polymer-salt compositions (calcination temperature 800°C) provides the preparation of various solid solutions of a La_1−x Ca _x FeO_3−δ series in the 0≤ x≤ 0.7 range, which belong to the perovskite structure type. A morphotropic phase transition occurs from the orthorhombic perovskite modification (0≤ x ≤ 0.4) to the cubic one (0.5 ≤ x≤ 0.7). A growing number of microdistortions in the perovskite structure and the formation of a microblock structure in the morphotropic phase transition region are observed with increasing degree of calcium substitution for lanthanum. Calcination of solid solutions with x = 0.6 and 0.7 at temperatures above 1000°C in the air or under conditions of reduced oxygen partial pressure (laboratory vacuum of 10⁻³ Torr) results in the formation of a nanostructured state with coherently grown blocks of perovskite and Grenier phase, which is due to irreversible oxygen loss.     

Oxygen nonstoichiometry and the thermodynamic and structural properties of double perovskites PrBaCo2 ? xCuxO5 + δ

The special features of the structure, electrophysical properties, and oxygen nonstoichiometry of new double perovskites PrBaCo_{2 − x} Cu _x O_{5 + δ} were studied. Within the homogeneity region with respect to copper 0 < x ≤ 1, solid solution samples had an orthorhombic structure (space group Pmmm) with the parameters a _p × 2a _p × 2a _p , where a _p ≈ 3.8 ?. The oxygen nonstoichiometry of PrBaCo_{2 − x} Cu _x O_{5 + δ} changes as the copper content increases approximately as δ ≈ 0.85 − x/2. The content of oxygen was measured by coulometric titration over wide temperature and oxygen pressure ranges. The partial thermodynamic functions of labile oxygen were calculated and the limits of the thermodynamic stability of the solid solution were established. Original Russian Text ? A.Yu. Suntsov, I.A. Leonidov, A.A. Markov, M.V. Patrakeev, Ya.N. Blinovskov, V.L. Kozhevnikov, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 5, pp. 954–960.     

Region of homogeneity for Lu2 ? xMnxO3 ± δ solid solution in air

The solubility boundaries for Lu₂O₃ and Mn₃O₄ oxides and LuMn₂O₅ manganate in LuMnO_{3 ± δ} are determined on the basis of an X-ray phase analysis of homogeneous solid solutions and heterogeneous compositions with molecular formula Lu_{2 − x} Mn _x O_{3 ± δ} (0.90 ≤ x ≤ 1.16; Δx = 0.02) obtained by ceramic synthesis in air in a temperature range of 900–1400°C. It is found that the solubility of Lu₂O₃ in LuMnO_{3 ± δ} corresponds to the composition of Lu_1.03Mn_0.97O_{3 ± δ} and remains invariable over the investigated range of temperatures, while the solubility of Mn₃O₄ (which corresponds to the composition of Lu_0.91Mn_1.09O_{3 ± δ}) remains invariable in the temperature range of 995–1400°C. It is shown that lutetium manganate LuMn₂O₅ coexists with lutetium manganate LuMnO_{3 ± δ} at temperatures of less than 995°C in air, and its solubility in LuMnO_{3 ± δ} decreases as the temperature of 995°C (corresponding to the composition Lu_0.91Mn_1.09O_{3 ± δ}) falls to 900°C for Lu_0.97Mn_1.03O_{3 ± δ}.     

Synthesis, characterization, and electrical conductivity of new Aurivillius-type oxide-ion conductor

A new oxide-ion conductor of Aurivillius family with a general formula Bi₂Al _x V_{1 − x} O_{5.5 − x − δ}; 0 ≤ x ≤ 0.20 (BIALVOX) was synthesized by the sol-gel citrate route. Powder X-ray diffraction and simultaneous thermogravimetric and differential thermal analyses confirmed that the calcination of BIALVOX xerogels is fully completed at around 500°C after three hours of thermal treatment. It has been found that the β-orthorhombic phase is stabilized with compositions x ≤ 0.07, whereas the stabilization of the γ′-phase takes place for x ≥ 0.10. AC impedance spectroscopic investigation suggested that the charge accumulation at grain boundaries is thermally activated process. However, the maximum electrical conductivity (7.73 × 10⁻⁵ S cm⁻¹) noticed for BIALVOX.13 at 300°C was attributed to the maximum vacancy concentration in the equatorial planes, responsible for the ion diffusion through the structure. This has been further evidenced by the temperature dependence of dielectric permittivity.     

Hydrolytic precipitation of magnesium polyvanadates in vanadium (IV, V) solutions

The phase and chemical composition of precipitates formed in Mg(VO₃)₂-VOSO4-H₂O system at initial pH from 1 to 7 and temperature from 80 to 90°C was studied. Polyvanadates of variable composition Mg _x V _y ⁴⁺V_12-y ⁵⁺¹O_31–δ · nH₂O (0.7 ≤ x ≤ 1.3, 1.2 ≤ y ≤ 2.4, 0.7 ≤ δ = 1.4) were formed at pH from 1 to 4 and V⁴⁺/V⁵⁺ ratio from 0.43 to 9. Compounds with the general formula Mg _x V _y ⁴⁺V_6-y ⁵⁺O_16-δ · nH₂O (0.7 ≤ x ≤ 0.65, y = 1.0, 0.8 ≤ δ ≤ 0.85) were formed at pH from 6.0 to 7.0 and V⁴⁺/V⁵⁺ ratios from 0.11 to 0.25. The maximum V⁴⁺ concentration (y = 2.4) in the precipitates was achieved at the VV⁴⁺/V⁵⁺ solution ratio of 1.0 and pH = 3. The precipitates in solutions with pH 3 were formed only upon addition of VO²⁺ ions with the maximum rate at a V⁴⁺/V⁵⁺ ratio of 0.33. These processes were limited by second-order reactions on the surface of polyvanadates.     

Formulas and numerical table for the radial part of overlap integrals with the same screening parameters of Slater-type orbitals

 The numerical properties of the radial part of overlap integrals with the same screening parameters in the form of polynomials in p = ξR over Slater-type orbitals have been studied and obtained by using three different methods. For that purpose, the characteristics of auxiliary functions were used first, then Fourier transform convolution theorem, and recurrence relations for the basic coefficients of A ^s _{n l λ, n ′ l ′λ} were used. The calculations of the radial part of overlap integrals with the same screening parameters were made in the range 1 ≤ n ≤ 75, 1 ≤ n′ ≤ 75, and 10⁻⁶ ≤ p. Received: 18 January 2001 / Accepted: 5 April 2001 / Published online: 27 June 2001     

Physicochemical properties of non-stoichiometric oxides

One of the most important challenges with solid oxide fuel cells (SOFC) is to find cathode materials with high enough catalytic activity for the dissociation of the molecular oxygen. Oxide mixed conductors with the perovskite structure (ABO₃) and high Co content in the B site have been extensively studied to be used as cathode in SOFC. This is the second part of a review of high temperature properties of two mixed conductors systems. The first part was focused on the n = 2 Sr₃FeMO_6+δ (M = Fe, Co, Ni) Rudlesdden Popper phases, while in this paper we discuss the thermodynamic and transport properties of the perovskite solid solution Sr_1−x La _x Fe_0.2Co_0.8O_3−δ (0 ≤ x ≤ 0.4) in the temperature range 773 ≤ T ≤ 1173 K. In particular, the interest has been focused on the x = 0 sample, which exhibits large ionic conductivity values (σ_i ~1 S cm⁻¹), but suffers a structural transformation from cubic to orthorhombic symmetry because the ordering of the oxygen vacancies when the oxygen partial pressure decreases. Measurements of the oxygen chemical potential ( m_\textO2 \mu_{{{\text{O}}_{2} }} ) as function of oxygen content and temperature, coupled with high temperature X-ray diffraction data, permitted us to broaden the knowledge of the T–δ–p(O₂) phase diagram for the x = 0 sample. In addition, we have investigated the effects of the La incorporation on the stability range of the cubic phases of the Sr_1−x La _x Fe_0.2Co_0.8O_3−δ solid solution.     

Homogeneity regions of yttrium and ytterbium manganites in air

Homogeneous solid solutions and heterogeneous systems of the general formula R_{2 − x} Mn _x O_{3 ± δ} (0.90 ≤ x ≤] 1.10 for R = Y and 0.88 ≤ x ≤ 1.14 for R = Yb; Δx = 0.02) were produced by ceramic synthesis from oxides in air within the temperature range 900–1400°C. The solubility boundaries of simple oxides R₂O₃ (R = Y, Yb), Mn₃O₄, and binary oxide RMn₂O₅ in yttrium and ytterbium manganites RMnO_{3 ± δ} were determined X-ray powder diffraction of these solutions and systems. The results were presented as fragments of phase diagrams of the systems Y-Mn-O and Yb-Mn-O in air. The solubility of Y₂O₃ and Mn₃O₄ in YMnO_{3 ± δ} was found to increase with increasing temperature, and the solubility of Yb₂O₃ and Mn₃O₄ in YbMnO_{3 ± δ} to be insensitive to varying temperature. It was suggested that the solubility of Y₂O₃ and Mn₃O₄ in YMnO_{3 ± δ} and of Yb₂O₃ and Mn₃O₄ in YbMnO_{3 ± δ} is caused by crystal structure defects of yttrium and ytterbium manganites and their related oxygen nonstoichiometry. In dissolving RMn₂O₅ in RMnO_{3 ± δ} (R = Y, Yb) in air within a narrow (∼20°C) temperature range adjacent to the RMn₂O₅ = RMnO₃ + 1/3Mn₃O₄ + 1/3O₂ equilibrium temperature, the solubility of RMn₂O₅ in RMnO_{3 ± δ} ecreases abruptly until almost zero. Conclusion is made that structural studies are necessary necessary to determine the oxygen nonstoichiometry δ of R_{2 − x} Mn _x O_{3 ± δ} solid solutions as a function of x and synthesis temperature; together with the results of this work, these studies will allow one to construct unique crystal-chemical models of these solid solutions.     

Structural, electrical and reflectance studies of the system ZnMn2-2xNixTixO4

X-ray, electrical conductivity and reflectance studies of the system ZnMn_2-2xNi_xTi_xO₄ have been carried out. The system is tetragonal in the range 0 ≤x ≤ 0.25 and cubic in the range 0.5 ≤x ≤ 1. Electrical resistivity temperature behaviour obeys Wilson’s law for all the compounds and the thermoelectric coefficient values vary between 325 and-290 μV/K. The activation energy and p_RT decrease gradually with increase in concentration of charge carriers atB-site except for ZnNiTiO₄. Reflectance spectral studies indicate the presence of Ni²⁺ at the octahedral site.     

Oxygen non-stoichiometry,high-temperature properties,and phase diagram of CaMnO<Subscript>3–<Emphasis Type="Italic">δ</Emphasis></Subscript>

The oxygen content in CaMnO_3–δ is studied by a coulometric titration technique depending on temperature and oxygen partial pressure variations in the ambient atmosphere. The δ–T phase diagram is derived from the obtained data where single-phase fields are outlined for orthorhombic, tetragonal, and cubic structures. The thermal expansion coefficient considerably larger in the cubic phase than in the tetragonal one is related with formation of large Mn³⁺ cations at depletion of oxygen from the crystalline lattice. Negative thermopower is explained by concomitant reactions of oxygen loss and charge disproportionation, 2Mn^{4 +} = Mn^{3 +} + Mn^{5 +} {\hbox{2M}}{{\hbox{n}}^{{{4 + }}}}{\hbox{ = M}}{{\hbox{n}}^{{{3 + }}}}{\hbox{ + M}}{{\hbox{n}}^{{{5 + }}}}{ } . The forbidden energy gap in CaMnO_3–δ is evaluated to be about 0.5 eV.     

1A1 5T2 Spin transition in the solid phases of FexNi1-x(ATr)3(NO3)2 (ATr = 4- amino- 1,2,4- triazole)

The effect of Fe²⁺ substitution by Ni²⁺ in the complex of iron(II) nitrate with 4- amino- 1,2,4- triazole Fe(ATr)₃(NO₃)₂ on the character of the¹A₁ ⁵T₂ spin transition (ST) is studied by magnetic susceptibility and calorimetry methods. Solid phases of Fe_xNi_{1- x}(ATr)₃(NO₃)₂ (0.1 ≤ x ≤ 0.9) were synthesized. The temperature dependences of the effective magnetic moment were measured in the range of 78– 360 K. Heat capacities were measured in the range of 210– 340 K for 0.1 ≤ x ≤ 0.5 and in the range of 230– 340 K for 0.6 ≤x ≤ 0.9. As x decreases, the transition temperature (T_C), hysteresis (δT_C, and transition enthalpy (δH) decrease and the ST is leveled. The results are compared with the data obtained previously for the solid phases of Fe_xZn_{1- x}(ATr)₃(NO₃)₂ (0.01 ≤ x ≤ 0.8). The dependence Μ_eff(T) is analyzed theoretically in terms of both the domain model and the spin equilibrium model. Translated fromZhumal Strukturnoi Khimii, Vol. 38, No. 4, pp. 696–703, July–August, 1997.     

Regions of stability of variable-composition perovskite phases La1?xSrxMn1?yMyO3 (M = Ti, Ni)

The formation of the orthorhombic solid solution series LaMn_1−y Ti _y O₃ with 0.0 ≤ y ≤ 0.15 and LaMn_1−y Ni _y O₃ with 0.0 ≤ y ≤ 0.4 was observed. The stability boundaries of the La_1−x Sr _x Mn_1−y M _y O₃ (M = Ti, Ni) perovskite phases were determined. Fragments of isobaric-isothermal sections of the phase diagrams of the La₂O₃-SrO-Mn₃O₄-TiO₂ and La₂O₃-SrO-Mn₃O₄-NiO systems in air at 1100°C were suggested. Original Russian Text ? E.A. Filonova, A.N. Demina, A.N. Petrov, 2007, published in Zhurnal Fizicheskoi Khimii, 2007, Vol. 81, No. 10, pp. 1787–1790.     

Sintering, microstructures and dielectric properties of Ba1−xPbx(Ti1−xLix)O3−3xF3x ferroelectric ceramics

Various compositions (1−x)BaTiO₃ + xPbF2 + xLiF were prepared, shaped to pellets then sintered at 900°C for 2 h in gold sealed tubes. The purity and the symmetry of the obtained samples were checked by X-ray diffraction. A new solid solution with Ba_1−x Pb _x (Ti_1−x Li _x ) O_3−3x F_3x formula occurs in the composition range 0 ≤ x ≤ 0.20. SEM observations were performed on polished and fractured ceramics. The complex permittivity was measured as a function of temperature (−120°C ≤ T ≤ 250°C) and frequency (50 Hz ≤ f ≤ 4 × 10⁷ Hz). The dielectric performances are the best for ceramic Ba_0.97Pb_0.03(Ti_0.97Li_0.03)O_2.91F_0.09. The real component ε′, exhibits a maximum of approximately 7500 at the ferroelectric Curie temperature T _C ≈ -18°C, the dielectric losses tan δ value being 0.012. At room temperature, the relaxation frequency f _r is around 40 MHz for this ceramic. This novel ferroelectric oxifluoride is a promising material for applications, in particular in the field of Z5U multilayer capacitors.      

Composition and formation kinetics of strontium polyvanadates in vanadium(IV,V) solutions

The phase and chemical compositions of the precipitates forming in the Sr(VO₃)₂-VOCl₂-H₂O system in the V⁴⁺/V⁵⁺ = 0.11–9 range at 80–90°C are reported. At pH 1–3 and V⁴⁺/V⁵⁺ = 0.25−9, the general formula of the precipitated compounds is Sr _x V _y ⁴⁺ V_12−y ⁵⁺O_31−δ·nH₂)(0.37 ≤ x ≤ 1.0, 1.7 ≤ y ≤ 3.0, 0.95 ≤ δ ≤ 2.1). Polyvanadates containing the largest amount of vanadium(IV) are obtained at an initial V⁴⁺/V⁵⁺ ratio of 9 and pH 1.9. Precipitation from solutions at pH 3 takes place only in the presence of the VO²⁺ ion, and the highest precipitation rate is observed at V⁴⁺/V⁵⁺ = 0.11. The process is controlled by a second-order reaction on the polyvanadate surface. Under hydrothermal conditions at 180°C, Sr_0.25V₂O₅·1.5H₂O nanorods are obtained from solutions with a V⁴⁺/V⁵⁺ molar ratio of 0.1 at pH 3. The nanorods, 30–100 nm in diameter and up to 2–3 μm in length, have a layered structure with an interlayer spacing of 10.53 ± 0.08 ?.     

Digenite Cu2?xS: thermodynamic analysis of sulfur activities

Abstract  

Gibbs energy modeling of the intermediate copper–sulfur phase digenite is performed at a total pressure of 1 bar using experimental sulfur activity data from the literature. A two-sublattice approach used in the framework of the compound energy formalism takes into account structural considerations. A limited set of optimized model quantities is obtained, which allows reproduction of all sulfur activity data available in the literature over a wide homogeneity and temperature range of the phase. Phase equilibria calculations applying the modeled Gibbs energy for digenite give very satisfactory phase relations in accordance with experimental data. A partial phase diagram within the composition range 0.0 ≤ x _S ≤ 0.7 up to elevated temperatures is calculated.