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.     

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.     

Synthesis and structure of alkali metal zirconium vanadate phosphates

Mixed vanadate phosphates in the systems MZr₂(VO₄) _x (PO₄)_{3 ? x} , where M is an alkali metal, were synthesized and studied by X-ray diffraction, electron probe microanalysis, and IR spectroscopy. Substitutional solid solutions with the structure of the mineral kosnarite (NZP) are formed at the compositions 0 ≤ x ≤ 0.2 for M = Li; 0 ≤ x ≤ 0.4 for M = Na; 0 ≤ x ≤ 0.5 for M = K; 0 ≤ x ≤ 0.3 for M = Rb; and 0 ≤ x ≤ 0.2 for M = Cs. Apart from the high-temperature NZP modification, lithium vanadate phosphates LiZr₂(VO₄) _x (PO₄)_{3 ? x} with 0 ≤ x ≤ 0.8 synthesized at temperatures not exceeding 840°C crystallize in the scandium tungstate type structure. The crystal structures of LiZr₂(VO₄)_0.8(PO₄)_2.2 (space group P2₁/n, a = 8.8447(6) Å, b = 8.9876(7) Å, c = 12.3976(7) Å, β = 90.821(4)○, V = 985.4(1) ų, Z = 4) and NaZr₂(VO₄)_0.4(PO₄)_2.6 (space group $R\bar 3c$ = 8.8182(3) Å, c = 22.7814(6) Å, V = 1534.14(1) ų, Z = 6) were refined by the Rietvield method. The framework of the vanadate phosphate structure is composed of tetrahedra (that are statistically occupied by vanadium and phosphorus atoms) and ZrO₆ octahedra. The alkali metal atoms occupy extra-framework sites.     

Conduction mechanisms of antimony selenide

The electrical resistivity, π, and Seebeck coefficient,S, of the system Sb₂Se₃ were measured in the ambient temperature range 323≤T≤573 K. Both parameters were found to be affected considerably by the temperature of annealing,T _a, in the range 493≤T _a≤653 K and by the time of annealing,t _a, for periods extending to 16h. Additionally, both depended strongly on the ambient temperature. The activation energy of ordering of the present system could be calculated by using the effects of isothermal annealing on the considered physical parameters.     

Preparation and Superconductivity of a Series of Bi2CaSr2-XBaxCu2O8+δ

By means of the addition of Ba into the Bi-Ca-Sr-Cu-O 2122 system, a series of Bi₂CaSr_2-xBa_xCu₂O_8+δ (0 ≤ × ≤ 2) quinary metal oxides were prepared by the citrate route and by the conventional powder reaction method. The samples prepared by the former method have better properties than the latter. It was found that 5 was not equal to zero for all of them and that it increased with decreasing Tc. Two phases were indentified in the oxides containing all five metal elements. One is the Bi-Ca-Sr-Cu-O 2122 phase, the other is a new insulating phase which probably contains Bi-Ca-Ba-Cu-O with undetermined stoichiometry. Superconductivity was found in those samples for which × ≤ 1.50 with their Tc onsets between 93–78 K by resistivity measurements. Superconductivity decreased monotonically with increasing x. However, residual resistance was found in those samples for which 1.00 ≤ × ≤ 1.50, The Meissner effect appears in the samples where × ≤ 1.00 with Tc onsets between 88–80 K. For x = 1.75 and 2.00, the samples were semiconductors with resistivities of 6.66 × 10² and 6.96 × 10³ Ω cm at 290 K, and activation energies of 0.109, and 0.298 eV, respectively.     

Dehydration of Magnesium Bromide Hexahydrate Studied by in situ X‐ray Powder Diffraction

Laboratory X‐ray powder diffraction data were used to investigate the dehydration process of magnesium bromide hexahydrate in the temperature range 300 K ≤ T ≤ 420 K. By heating of the as synthesized hexahydrate (MgBr₂ · 6H₂O, observed in the temperature range 300 K ≤ T ≤ 349 K), three lower hydrates can be obtained in overlapped temperature regions: MgBr₂ · 4H₂O (332 K ≤ T ≤ 367 K), MgBr₂ · 2H₂O (361 K ≤ T ≤ 380 K) and MgBr₂ · H₂O (375 K ≤ T ≤ 390 K). Although the crystal structure of the hexahydrate was published almost eighty years ago, there are no data on the structures of the lower hydrates. The crystal structures are reported and are found to be isotypical with the structures of the respective chlorides. The structure of MgBr₂ · 6H₂O is characterized by discrete Mg(H₂O)₆ octahedra and is the only hydrate of this group that contains unbonded Br^– anions. MgBr₂ · 4H₂O is composed of discrete MgBr₂(H₂O)₄ octahedra, and the structure was found to be disordered. The crystal structure of MgBr₂ · 2H₂O is formed by single chains of edge‐sharing MgBr₄(H₂O)₂ octahedra, while in the case of MgBr₂ · H₂O double chains of edge‐shared MgBr₅H₂O are formed. By increasing the temperature, as expected, positive thermal expansion was evidenced. Thermal expansion coefficients, based on the changes of the unit cell parameters, were derived for the following hydrates: MgBr₂ · 6H₂O, MgBr₂ · 4H₂O, and MgBr₂ · 2H₂O.     

Phase composition,formation parameters,and morphology of precipitates in the LiVO<Subscript>4</Subscript>-VOSO<Subscript>4</Subscript>-H<Subscript>2</Subscript>O system

The phase and chemical compositions of the precipitates formed in the LiVO₃-VOSO₄-H₂O system at initial pH within 1 ≤ pH ≤ 4 and 90°C were studied. The following phases were prepared: an α phase Li_1.4(VO)_1.3[H₂V₁₀O₂₈] · nH₂O and a β phase Li_{0.6 ? x} H_{1.4 + x} [V₁₂O_{31 ? y/2}] · nH₂O (0 ≤ x ≤ 0.5, 1.3 ≤ y ≤ 2.0) with a layered structure. Li_0.4V₂O₅ · H₂O nanorods with the interlayer distance 10.30 ± 0.08 Å were synthesized at 180°C in an autoclave. The morphology, IR spectra, and main formation processes for these polyvanadates were studied.     

Spectral characteristics of aqueous dispersions enriched in oxygen

The IR absorption and reflection spectra of aqueous dispersions consisting of (H₂O)_n, O₂(H₂O)_n, and (O₂)₂(H₂O)_n clusters (10 ≤ n ≤ 50) were calculated by the method of molecular dynamics using a flexible model of molecules. The frequency distribution of the power scattered by the cluster systems was obtained in the range 0 ≤ ω ≤ 3000 cm^?1. The capture of one oxygen molecule by the clusters is accompanied by a decrease in the absorption of the low-frequency IR radiation and by a peak of the absorption intensity in the vicinity of ω 2704 cm^?1. This is also accompanied by a decrease in the reflection coefficient throughout the frequency range and a decrease in the emission power at ω < 1030 and ω > 1700 cm^?1. Addition of two oxygen molecules to the clusters decreases the capability of the dispersions for the absorption, reflection, and scattering of IR radiation.     

Laser-Assisted Chemical Vapor Deposition of Boron

Ar⁺ laser-induced chemical vapor deposition (LCVD) of B from gaseous mixtures of BCl₃ and H₂ has been investigated for temperatures between 1000 K and 2250 K and for partial pressure within the ranges 25 mbar ≤ p(BCI₃) ≤ 800 mbar and 10 mbar ≤p(H₂) ≤ 400 mbar. For the lowest temperatures, deposition is controlled by the chemical kinetics which, with p(BCI₃) = p(H₂) = 100 mbar, is characterized by an apparent chemical activation energy of about 26.5 kcal/mol. In this regime, the deposited boron is amorphous. At high temperatures, deposition becomes limited by gas-phase transport and polycrystalline boron with βrhombohedral structure is obtained.     

Medium‐sized phosphorus cluster cations P+2m+1 (6 ≤ m ≤ 32) studied by collision‐induced dissociation mass spectrometry

Medium‐sized phosphorus cluster cations were generated by laser ablation of red phosphorus and investigated by the method of collision‐induced dissociation mass spectrometry. Experimental results show that the primary dissociation channels of phosphorus cluster cations of P ⁺ _2m+1 (6 ≤ m ≤ 11) are all characterized by the loss of P₄ unit. For larger cluster cations, their dissociation pathways were more complex. For those magic cations of P ⁺ _8k+1 observed previously, their dissociation pathways progressively change from the loss of P₄ unit (for k = 3) to the loss of P₈ unit (for k = 4, 5). A new dissociation pathway characterized by the loss of P₁₀ unit was also indentified for larger cations of P ⁺ _8k+1 (6 ≤ k ≤ 8). Theoretical calculation also shows that, for cations of P ⁺ _2m+1 (4 ≤ m ≤ 10), the dissociation channel characterized by the loss of P₄ unit is more energetically favorable than other dissociation channels, which is in good agreement with the experimental results. Copyright © 2015 John Wiley & Sons, Ltd.     

Darstellung,Kristallstrukturen und Eigenschaften der Chrom(II)-phosphat-halogenide Cr2(PO4)Br und Cr2(PO4)I

Synthesis, Crystal Structures, and Properties of the Chromium(II) Phosphate Halides Cr₂(PO₄)Br and Cr₂(PO₄)I The new compounds Cr₂(PO₄)Br and Cr₂(PO₄)I have been obtained by reaction of CrPO₄, Cr and Br₂ or I₂ in evacuated silica tubes at elevated temperatures (Cr₂(PO₄)Br: 900 °C, Cr₂(PO₄)I: 700 °C). Single crystals of deep blue Cr₂(PO₄)Br and turquoise Cr₂(PO₄)I with edge-lengths up to 2 mm and 0.3 mm, respectively, have been grown in experiments involving the gaseous phase. Single crystal data have been used for structure determination and refinement. Though being not isotypic, the two crystal structures are closely related. Two crystallographically independent Cr²⁺, in polyhedra [Cr1O₃X₃] and [Cr2O₅X], form dimers [Cr1₂O₂O_2/2X₄] and [Cr2₂O₈X₂]. Distances are 1.978 Å ≤ d(Cr–O) ≤ 2.096 Å (for the iodide: 1.959 Å ≤ d(Cr–O) ≤ 2.105 Å), 2.587 Å ≤ d(Cr–Br) ≤ 3.158 Å and 2.867 Å ≤ d(Cr–I) ≤ 3.327 Å. The structures of bromide and iodide can be distinguished by the different way of connection of the Cr1 containing dimers. The phosphate group shows slightly distorted tetrahedral geometry with 1.491 Å ≤ d(P–O) ≤ 1.559 Å (1.486 Å ≤ d(P–O) ≤ 1.567 Å) and angles of 106.48° ≤ ∠(O–P–O) ≤ 111.69° (106.57° ≤ ∠(O–P–O) ≤ 111.72°. IR-spectra of Cr₂(PO₄)Br and Cr₂(PO₄)I, the Raman-spectrum of Cr₂(PO₄)Br and electronic spectra of the two compounds in the UV/vis region at low temperature are reported and discussed.     

Cyclooctane Metathesis Catalyzed by Silica‐Supported Tungsten Pentamethyl [(SiO)W(Me)5]: Distribution of Macrocyclic Alkanes

Metathesis of cyclic alkanes catalyzed by the new surface complex [(?SiO)W(Me)₅] affords a wide distribution of cyclic and macrocyclic alkanes. The major products with the formula C_nH_2n are the result of either a ring contraction or ring expansion of cyclooctane leading to lower unsubstituted cyclic alkanes (5≤n≤7) and to an unprecedented distribution of unsubstituted macrocyclic alkanes (12≤n≤40), respectively, identified by GC/MS and by NMR spectroscopies.     

Crystal structure and magnetism of the FexNi8-xSi3 materials, 0 ≤ x ≤ 8

The crystal structure and magnetic properties of the materials Fe_xNi_8-xSi₃ with 0 ≤ x ≤ 8 have been investigated to estimate any possible magnetocaloric effect and compare it to that in known magnetocalorics. Two structural ranges could be identified in this system by X-ray and neutron diffraction. The structure of the samples with 0 ≤ x ≤ 4 is related to the trigonal structure of Ni₃₁Si₁₂. Doubled c lattice parameters compared to the one in Ni₃₁Si₁₂ are observed in the samples with x = 2 and x = 3. The average structure of Fe₂Ni₆Si₃ has been determined by X-ray single-crystal diffraction. The compounds with the compositions 5 ≤ x ≤ 8 crystallize in cubic Fe₃Si-type structure. Magnetic measurements have shown that the compound Fe₃Ni₅Si₃ displays a phase transition close to room temperature. However, its magnetocaloric effect is much smaller than the one in the promising magnetocaloric materials.     

Untersuchungen an einigen Einkristallen des Systems CuxHg1–xCr2Se4

Study of Some Single Crystals of the Cu_xHg_1–xCr₂Se₄ System Single crystals of the Cu_xHg_1–xCr₂Se₄ for 0 ≤ x ≤ 0.077 were prepared by the chemical transport method. The crystals were analyzed and investigated by X-rays. Some electric and magnetic properties of the single crystals were determined and the results obtained are discussed.     

Computer simulation of the adsorption of acetylene by disperse aqueous medium. IR spectra

Adsorption of acetylene molecules by water clusters at T 230 K was studied by the method of molecular dynamics. Addition of already two C₂H₂ molecules to (H₂O) _n clusters (10 ≤ n ≤ 20) makes them thermodynamically unstable. With an increase in the acetylene concentration in the disperse aqueous system, the IR absorption by the cluster system in the frequency range 0 ≤ ω ≤ 1000 cm^?1 increases. Depending on the number of C₂H₂ molecules per water cluster, the IR reflection by cluster systems can either increase or decrease. The power of the thermal radiation emitted by the clusters considerably increases after the adsorption of C₂H₂ molecules and grows with an increase in the acetylene concentration in the disperse aqueous system.     

Preparation and Morphologies of AB6¯ Block‐Graft Copolymers

Microphase‐separated structures of a series of AB₆ block‐graft copolymers were studied by TEM and SAXS. Ten copolymers with the same polystyrene (S) backbone and six polyisoprene (I) grafts on the average but with different graft chain lengths were carefully synthesized by living anionic polymerization, covering the range 0.21 ≤ ?_S ≤ 0.90, where ?_S denotes polystyrene compositions. From TEM observation of the AB₆ block‐graft copolymers, it turns out to be clear that they show four microphase‐separated structures, S‐spheres, S‐cylinders(S‐prisms), alternative lamellae, and I‐cylinders. Among them, for example, the samples with 0.54 ≤ ?_S ≤ 0.58 shows prism structures whose cross sections of the S domains are close to hexagons, not circles, due to packing frustration of grafts. Composition dependence of morphologies of the present AB₆ block‐graft copolymers reveals their phase diagram is extremely asymmetric with respect to ?_S = 0.5. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 952–960     

Computer-assisted structure simulation, synthesis, and phase formation of molybdophosphates A1−x Zr2(PO4 3−x (MoO4)x (A is an alkali metal)

Structure simulation is performed for molybdophates of variable composition A_1?x Zr₂(PO₄)_3?x (MoO₄)_x, where A is Na (0≤x≤0.6), K (0≤x≤0.6), K (0≤x≤0.3), Rb (0≤x≤0.2), or Cs (0≤x≤0.1), using the minimization of the interatomic interaction energy; these molybdophosphates crystallize in the NaZr₂(PO₄)₃ (NZP) structure type. The results of the computer-assisted structure simulation are verified by the synthesis of the molybdophosphates and their characterization by X-ray powder diffraction and IR spectroscopy. The crystallization field of the NZP molybdophosphate shrinks as the alkali cation size increases. The key factors that govern the stability of the NZP structure in alkali zirconium molybdophosphates are determined.     

Synthesis and Structure Analysis of Aurivillius Phases Pb1‐xBi4‐+Ti1‐xMnxO15

Synthesis Pb_1‐xBi_4+xTi_4‐xMn_xO₁₅ compounds (0 ≤ × ≤ 1) were carried out by molten salts method using eutectic mixture of Na₂SO₄/K₂SO₄ salts (1:1 molar ratio) as the flux. The samples were characterized by X‐ray powder diffraction and refined by Le Bail method using Rietica program. The refinement results revealed that the compounds with the composition 0 ≤ x ≤ 0.6 formed Aurivillius phase with the space group A2₁am while the other composition (x ≥ 0.8) showed another phase beside A2₁am. The ratio b/a of the lattices constants for all the samples are larger than 1 indicating the direction of the orthorhombic along the b axis of their cells. The lattice parameters and volume of the unit cells decrease as the Mn content increasing from x = 0 to 0.6, for x ≥ 0.8 a second phase were observed. The morphologies of Pb_1‐xBi_4+xTi_4‐xMn_xO₁₅ samples were observed by SEM and show plate‐like aggregate crystals, typical of layered compounds belonging to the Aurivillius phase.     

The diffusion of oxygen and ion transport in lanthanum cobaltite LaCoO<Subscript>3-δ</Subscript>

The chemical diffusion coefficient of oxygen vacancies and oxygen ion conductivity in lanthanum cobaltite LaCoO₃ were determined by the polarization method as functions of oxygen partial pressure \(p_{O_2 } \) (atm) and temperature T(K) over the ranges ?4 ≤ log \(p_{O_2 } \) ≤ 0 and 1173 K ≤ T ≤ 1323 K. The mobilities (cm²/(V s)) of oxygen vacancies calculated over the temperature range studied satisfy the inequalities 1.8 × 10^?5 ≤ \(v_{v_0 } \) ≤ 3.4 × 10^?5. The transfer numbers of oxygen vacancies were calculated. These numbers change depending on oxygen partial pressure over the range 5 × 10^?7 ≤ t ₀ ≤ 1 × 10^?5. The activation energy of self-diffusion of oxygen vacancies was found to be E _a= 104 ± 10 kJ/mol (1.1 ± 0.1 eV).     

Phase equilibria in the V2O5-NaVO3-Ca(VO3)2-Mn2V2O7 system and interactions of phases with H2SO4 and NaOH solutions

Phase composition of the V₂O₅-NaVO₃-Ca(VO₃)₂-Mn₂V₂O₇ system was studied, and a subsolidus phase diagram constructed. The tetrahedration of the diagram is determined by the fact that the end-member of Ca_1–x Mn _x (VO₃)₂ solid solution is in equilibrium with all compounds of the system (V₂O₅, NaVO₃, Ca(VO₃)₂), vanadium β-bronzes Na _x V₂O₅ (0.22 ≤ x ≤ 0.40) and κ-bronzes (0.25 ≤ x ≤ 0.45, 0 ≤ y ≤ 0.16), Mn₂V₂O₇, and Na₂Mn₃(V₂O₇)₂ and with the end-members of reciprocal solid solutions based on calcium and sodium metavanadates. At 20°C, the degree of vanadium dissolution α for Na₂Ca(VO₃)₄ is 100% for 0.5 ≤ pH ≤ 10; for the other phases of the system, vanadium dissolution ranges from 100 to 10% for pH below 3.5; in the alkaline pH range, ≤ 10%. Sodium for calcium substitution in Ca(VO₃)₂ increases α in aqueous NaOH to 20%. For Na₂Mn₃(V₂O₇)₂, α decreases from 92 to 80% as pH changes from 0.5 to 2.5; at pH above 4, α = 30%.