Phase equilibria and crystal structures of complex oxides in systems La-M-Fe-O (M = Ca or Sr)

Phase equilibria in systems La-M-Fe-O (M = Ca or Sr) at 1100° in air were studied. The homogeneity ranges and structures of solid solutions La_{1 ? x} M _x FeO_{3 ? δ} (0 ≤ x ≤ 0.3 for M = Ca and 0 ≤ x ≤ 0.8 for M = Sr), Sr_{2 ? y} La _y FeO_{4 ? δ} (0.8 ≤ y ≤ 1.0), and Sr_{3 ? z} La _z Fe₂O_{7 ? δ} (0 ≤ z ≤ 0.2) were determined using X-ray powder diffraction. The structural parameters of complex oxides were refined using the full-profile Rietveld technique. Correlations between the unit cell parameters and the compositions of solid solutions were derived. Isobaric/isothermal phase diagrams were constructed for systems La-M-Fe-O (M = Ca or Sr) at 1100°C in air.     

Hydrothermal synthesis, structure and property of nano-BaTiO3-based dielectric materials

A series of Ba_1-xSr_xTi_1-yZr_yO₃ (0≤x≤0.5, 0≤y≤0.4) and BA_1?xZn_xTi_1?ySn_yO₃ (0≤x≤0.3, 0≤y≤0.3) solid solutions were synthesized by low-temperature/low-pressure hydrothermal method below 170°C, 0.8 MPa. XRD pattern and cell parameters-composition figures of these prepared powders demonstrated that they are completely miscible solid solutions based on BaTiO₃. Furthermore, TEM showed that they have a shape of uniform, substantially spherical particles with an average particle size of 70 nm in diameter. The sintered ceramics of those powders doped by Sr²⁺ and Zr⁴⁺ or Zn²⁺ and Sn⁴⁺ have dielectric constant twelve times higher than and dielectric loss 1/6 those of pure BaTiO₃ phase at room temperature.     

Features of phase formation and state of iron in the quasibinary system FeTe1.65-TiTe1.65

A series of tellurides Fe_xTi_1?x Te_1.65 (x = 0, 0.1, 0.2 …, 1.0) synthesized at 850°C were studied by X-ray phase and X-ray fluorescent analysis and Møssbauer spectroscopy on ⁵⁷Fe. In this series two solid solutions are formed: phases I and II with homogeneity regions within the limits of 0 ≤ x ≤ 0.3 and 0.9 ≤ x ≤ 1.0, respectively. Iron in this series exists in two various states: Fe²⁺ _sym and Fe²⁺ _asym as differentiated from the series of tellurides Fe_xTi_1?x Te_1.45 where three states of iron Fe²⁺ _sym, Fe²⁺ _asym, and Fe⁰ were found. On passing from Fe_xTi_1?x Te_1.45 to Fe_xTi_1?x Te_1.65 the number of formed phases decreases, and phase relations become simpler. The absence of Fe⁰ from phase I of tellurides Fe_xTi_1?x Te_1.65 can point to the fact that TiTe_1.45 and TiTe_1.65 belong to different homogeneity regions.     

Synthesis, structure and dielectric properties of Ba1-xSrxMyTi1-yO3 (M = Zr, Sn)

A series of Ba_1-xSr_xM_yTi_1-yO₃ (M = Zr, Sn, 0?x?0.4, 0?y?0.3) solid solutions were synthesized with the soft chemical method below 100 °C. XRD pattern and cell parameters-composition figures of the prepared powder demonstrate that they are completely miscible solid solutions based on BaTiO₃. Furthermore, TEM shows that they have a shape of uniform, substantially spherical particles with an average particle size of 70 nm in diameter. The sintered ceramics of the powder doped with Sr²+and Zr⁴⁺ or Sn⁴⁺ have dielectric constant eight times higher and dielectric loss thirty per cent lower than those of pure BaTiO₃ phase at room temperature.     

Preparation and properties of La1−xCaxCoO3 (0,2 ≤ x ≤ 0,6)

The preparatory conditions for the oxide compositions La_1?xCa_xCoO_3?δ have been determined along with their crystallographic, thermochemical, and electrical properties. Single phase solid solutions of the perovskite structure form atx < 0.6. It has been established that the compounds obtained in the open air atmosphere are oxygen deficient, the deficit increasing withx and temperature. The specific resistivity atx = 0.2–0.6 is (1–2)·10^?3 ohm·cm; it increases with the concentration of oxygen vacancies. At 0.3 ≤ x ≤ 0.6 thep-type conductivity is metallic in character with low temperature resistivity coefficients of the order (1–5)·10^?4 K^?1 in the interval 20–700°C.     

Defects in doped perovskite-like lanthanum cobaltite crystals La1−x SrxCo1−y MeyO3−δ (Me = Cu and Mn)

The paper presents a thermodynamic analysis of the formation of equilibrium defects in perovskitelike La_1?x Sr_xCo_1?y Me_yO_3?δ oxides, where Me = Cu or Mn, x = 0.0 or 0.3, and y = 0.0, 0.25, or 0.3, at high temperatures (873 K ≤ T ≤ 1373 K) depending on the composition and oxygen pressure (10^?8 atm ≤ $p_{O_2 } $ ≤ 1 atm). The results were used to study the nature of charge transfer. Small-radius polarons were shown to be responsible for the electric properties of the cobaltites under consideration; their concentrations and mobilities were calculated.     

Phase formation of BICUVOX solid solutions

Phase formation of Bi₄(V_{1 ? x} Cu _x )₂O_{11 ? z} solid solutions (BICUVOX) with x = 0.00–0.20 and Δx = 0.02 was studied. The concentration stability ranges were determined for the α, β, and γ polymorphs of BICUVOX solid solutions at room temperature, and their unit cell parameters were revised. The following was found to occur as x rises: the α ai β phase transition temperature between the monoclinic and orthorhombic phases shifts down, the β ai γ phase transition temperature to the high-temperature tetragonal phase shifts down, and the order-disorder phase transition temperature between γ′ ai γ tetragonal phases shifts up.     

Crystal structure and conduction of BICUTIVOX

Existence boundaries, structure, and transport parameters were studied for Bi₄V_{2 ? x} Cu _x/2Ti _x/2O_{11 ? x} solid solutions. Doping levels within x = 0.025–0.15 distort the C2/m crystal lattice (this lattice is characteristic of individual the Bi₄V₂O₁₁ phase) and lowers its symmetry to triclinic. The solid solutions with 0.25 ≤ x ≤ 0.30 crystallize in tetragonal space group I4/mmm. High-temperature X-ray diffraction and dilatometry measurements for Bi₄V_{2 ? x} Cu _x/2Ti _x/2O_{11 ? x} (x ≤ 0.35) solid solutions verified the existence of three structural varieties within 298–1023 K. Electrical conductivity of BICUTIVOX was studied by impedance spectroscopy as a function of temperature, composition, and oxygen partial pressure. Equivalent circuits of cells were analyzed. Features of electrical conductivity versus temperature for the structural varieties are noted. Above 873 K, the solid solutions samples with x = 0.05 have the highest conductivity. At lower temperatures, higher conductivities are in the solid solutions that retain the γ phase in the low-temperature region. The dominant oxygen-ion conduction mechanism was discovered in the solid solutions.     

Hydrothermal synthesis and characterization of (Na,K)Ti2(PO4)3 solid solutions

Na_1?x K_xTi₂(PO₄)₃ (0 ≤ x ≤ 1) solid solutions are synthesized through ion exchange under hydrothermal conditions and a sol-gel process. The unit cell parameters are calculated for (Na,K) titanium phosphates. Cation-exchange reactions in the NaTi₂(PO₄)₃-KTi₂(PO₄)₃-NaCl-KCl-H₂O system are studied at T = 973 K and p = 200 MPa. The solid phase with compositions in the range 0 ≤ x ≤ 0.7 is enriched with sodium; in the range 0.7 ≤ x ≤ 1.0, it is enriched with potassium. The excess functions of mixing for the solid solutions are described in terms of the Margules model. Titanium phosphates Na_1?x K_xTi₂(PO₄)₃ show greater nonideality than zirconium phosphates Na_1?x K_xZr₂(PO₄)₃ and lower thermodynamic stability in decay into pure components at high pressures and temperatures.     

Synthesis,electrical and thermal properties of Bi4V2−xMexO11 (Me=Nb,Zr, Y and Cu with x = 0.0 and 0.06) ceramics

Polycrystalline ceramic samples of Bi₄V_2?xMe_xO₁₁ (Me=Nb, Zr, Y and Cu and x = 0.0 and 0.06) have been synthesized by standard solid state reaction method using high purity oxides. The formation of the compounds have been analysed by X-ray diffraction method. The dielectric constant, dielectric loss and AC conductivity as a function of frequency and temperature have been measured. The dielectric studies indicate that the material is highly lossy, and hence, its AC conductivity increases with the increase of temperature. The DC conductivity of material has been measured as a function of temperature from room temperature to 723 K and its activation energy was calculated using the relation σ = σ ₀exp (?E _a/kT). The modulated differential scanning calorimetry has been used to investigate the effect of substitution on the phase transition (heat capacity and heat flow) of the compounds. The results are discussed in detail.     

Isomorphic substitution of neodymium and gadolinium for calcium in synthetic hydroxovanadate

Isomorphic substitution of neodymium and gadolinium for calcium in synthetic hydroxovanadate Ca_{5 ? x} M _x (VO₄)₃(OH)_{1 ? x} O _x (M = Nd, Gd) is studied in the range 700–1000°C using X-ray powder diffraction, single-crystal X-ray diffraction (Rietveld technique), and IR spectroscopy. Single-phase solid solutions at 800°C are formed with x ≤ 0.35 for M(III) = Nd and x ≤ 0.3 for M(III) = Gd. With high x, the apatite solid solution coexists with Ca₃(VO₄)₂, Nd₂O₃, and X phases. With increasing x in the homogeneous region, the intensity of the bands of stretching vibrations and librations of OH groups decrease. Single-crystal X-ray diffraction shows that neodymium and gadolinium substitute for calcium in solid solutions mostly in Ca(2) positions.     

Evolution structurale de quelques solutions solides oxyfluorées de structure pyrochlore

Pyrochlore solid solutions Cd₂Nb_2−2xM^IV_2xO_7−2xF_2x are studied with M = Ge and Sn; the domain of existence is 0 ? x ? 0.5. We can observe two cubic domains for different values of the position parameter u. With M = Zr we obtain a pyrochlore solid solution varying between 0 ? x ? 0.875. It offers a rhomboedric distortion for 0.25 < x < 0.55 due to an ordered distribution of Nb and Zr in the (111) plans of the cell.     

Synthesis,optical properties,and photocatalytic activity of lanthanide-doped anatase

Quasi-one-dimensional (1D) Ti_{1 ? x} Ln _x O_{2 ? x/2} anatase solid solutions were prepared by heating Ti_{1 ? x} Ln _x (OCH₂CH₂O)_{2 ? x/2} precursors, where Ln = Nd, Eu, Tb, Er (x = 0.025), or Sm (0.005 ≤ x ≤ 0.025), in air. These solid solution were found to have a photocatalytic activity in hydroquinone oxidation in aqueous solution under exposure to UV radiation. UV-Vis absorption spectra were recorded for Ti_{1 ? x} Ln _x O_{2 ? x/2} (Nd, Sm, Eu, Tb, or Er). The electronic structure and optical absorption spectra were calculated for anatase doped with neodymium, samarium, or terbium.     

Lithium-cationic conductivity in the Li4 − 2x Cd x GeO4 system

The lithium-conducting solid electrolytes in the Li_{4 ? 2x} Cd _x GeO₄ (0 ≤ x ≤ 0.6) system are synthesized. Their crystal structure and temperature and concentration dependences of conductivity are studied. The specimens with the highest conductivity have a γ-Li₃PO₄-derivative structure. The solid solutions with x = 0.15–0.25 are stable at the room temperature, whereas the specimens with x ≥ 0.3 decompose yielding Li₂CdGeO₄ below 310 ± 10°C. Li_3.6Cd_0.2GeO₄ solid solution exhibits the highest conductivity (5.25 × 10^?2 S cm^?1 at 300°C). The factors, which affect the conductivity of synthesized solid electrolytes, are considered.     

Preparation,structure, and charge transport characteristics of BIFEVOX ultrafine powders

Existence boundaries, structure, and transport parameters of ultrafine powders were studied in Bi₄V_{2 ? x} Fe _x O_{11 ? x} (BIFEVOX) solid solutions. The details of synthesis of the solid solutions via liquid precursors are analyzed comparatively. In general, BIFEVOX formation via liquid precursors is similar to phase formation in solid-phase synthesis. With low iron levels (x = 0.05–0.1), solid solutions are formed in the monoclinic α phase (space group C2/m) The compositions with x = 0.125 and 0.15 are mixtures of α- and β phases. In the range 0.2 < x < 0.7, the Bi₄V_{2 ? x} Fe _x O_{11 ? x} solid solution has the structure of the γ phase of Bi₄V₂O₁₁ (space group I4/mmm). The β phase in the system in question has a very narrow existence range in the vicinity of x = 0.175. The average particle sizes of the powders prepared by various methods are within 0.5–3 μm. In the powders prepared via liquid precursors, however, the distribution peak shifts toward smaller sizes, to 0.3–1 μm. Mechanical activation conserves the structure of the γ phase of BIFEVOX, and unit cell parameters change only insignificantly; however, the crystal lattice is slightly distorted. The electrical conductivity of BIFEVOX was studied as a function of temperature, preparation technology, and composition using impedance spectroscopy. Equivalent circuits of cells were analyzed. The conductivity of samples prepared by solution technology is always higher than for samples prepared by the solid-phase process. Features of electrical conductivity versus temperature for various phases are noted. All transitions on the conductivity curves match the features of linear thermal expansion curves. Compositions with doping levels x= 0.1–0.3 have the highest total conductivities.     

Systems Li<Subscript>2</Subscript>O(Na<Subscript>2</Subscript>O)-CdO-V<Subscript>2</Subscript>O<Subscript>5</Subscript>: Phase composition and phase diagrams

The subsolidus phase composition of the M₂O-CdO-V₂O₅ systems with M = Li or Na is studied. Double orthovanadates MCdVO₄ and MCd₄(VO₄)₃ form solid solutions of composition Li_{1 ? 2x/3}Cd _x/3CdVO₄ (0 ≤ x ≤ 1, orthorhombic space group Cmcm, modulation at x = 0.6) and Na_{3 ? 2x} Cd_{3 + x} (VO₄)₃ (0 ≤ x ≤ 0.10 and 0.30 ≤ x ≤ 1, orthorhombic space group Cmcm and Pn2₁ a or Pnma, respectively). In the range 0.10 < x < 0.30, the end-members of the solid solutions coexist. Isothermal sections of the systems are mapped.     

Study on the solid solution of YMn1−xFexO3: Structural, magnetic and dielectric properties

The solid solution of YMn_1−xFe_xO₃ (x=0.0, 0.1, 0.2, 0.3, 0.5, 1.0) was synthesized from the citrate precursor route. The hexagonal crystal structure related to YMnO₃ was stable for x?0.3. Rietveld refinement was carried out on the composition for x=0.3 and was refined to a major hexagonal phase (∼97%) with 3% of orthorhombic Y(Fe/Mn)O₃ phase. The a-axis lattice constant increases and the c-axis lattice constant decreases with x for x?0.2. The increase in the c-axis lattice constant at x=0.3 could be due to the doping of significant amount of d⁵ ion (high spin Fe³⁺ ion) in a trigonal bipyramidal crystal field. The detailed structural, magnetic and dielectric properties are discussed.     

Homogeneity ranges for yttrium and holmium manganites Ln2−x Mn x O3±δ (Ln = Y, Ho) in air

The homogeneity ranges with respect to the content of metal components in air were determined for yttrium and holmium manganites, based on X-ray phase analysis data for homogeneous solid solutions and heterogeneous compositions with the general formula Ln_2?x Mn _x O_3±δ (Ln = Y, Ho) prepared by ceramic synthesis procedure in air at 900–1400°C. The results were presented as fragments of the composition-temperature phase diagrams of the Ln-Mn-O (Ln = Y, Ho) systems in air.     

Substitutions of neodymium for strontium in the Sr5(VO4)3OH structure

Neodymium-for-strontium isomorphic substitutions in synthetic hydroxovanadate Sr_{5 ? x} Nd _x (VO₄)₃(OH)_{1 ? x} O _x were studied from 600 to 800°C using powder and single-crystal X-ray diffraction (the Rietveld technique) and IR spectroscopy. Single-phase solid solutions at 800°C are formed in the range up to x = 0.14. At higher x, a Sr₃(VO₄)₂ phase exists along with the apatite solid solution. In the range of 0 < x ≤ 0.14, the intensity of the IR bands due to the stretching and libration vibrations of OH groups decreases with increasing x. Single-crystal X-ray diffraction shows that neodymium mostly substitutes for strontium atoms at the Sr(1) sites in the solid solution with x = 0.14.     

Synthesis, structure and dielectric properties of Ba1-xSrx My Ti1-yO3 (M = Zr, Sn)

A series of Ba1-xSrxMyTi1-yO3 (M = Zr, Sn, 0≤x≤0.4, 0≤y≤0.3) solid solutions were synthesized with the soft chemical method below 100 ℃. XRD pattern and cell parameters-composition figures of the prepared powder demonstrate that they are completely miscible solid solutions based on BaTiO3. Furthermore, TEM shows that they have a shape of uniform, substantially spherical particles with an average particle size of 70 nm in diameter. The sintered ceramics of the powder doped with Sr2 and Zr4 or Sn4 have dielectric constant eight times higher and dielectric loss thirty per cent lower than those of pure BaTiO3 phase at room temperature.