A Fe/Nb co-doped Sr(Co0.8Fe0.1Nb0.1)O3 − δ perovskite oxide for air separation: Structural, sintering and oxygen permeating properties

The novel Fe/Nb co-doped Sr(Co_0.8Fe_0.1Nb_0.1)O_3 − δ oxide was synthesized by the solid-state reaction method. Structural and sintering properties of the Sr(Co_0.8Fe_0.1Nb_0.1)O_3 − δ oxide/ceramic were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The oxygen permeation flux of the Sr(Co_0.8Fe_0.1Nb_0.1)O_3 − δ membrane was measured to be 1.80 ml min^− 1 cm^− 2 under an air/helium gradient at 950 °C, and the membrane also shows good oxygen permeation stability. The results demonstrate that the structural stability of the Fe/Nb co-doped Sr(Co_0.8Fe_0.1Nb_0.1)O_3 − δ oxide is improved significantly compared to those of the Sr(Co_0.8Fe_0.2)O_3 − δ and (Ba_0.5Sr_0.5)(Co_0.8Fe_0.2)O_3 − δ oxides. The incorporation of the Fe/Nb cations in the SrCoO_3 − δ oxide result in the improved stability of Sr(Co_0.8Fe_0.1Nb_0.1)O_3 − δ.     

X-ray diffraction study of multicomponent oxides in the Zn2 ? x(TiaZrb)1 ? xFe2xO4 system

The multicomponent refractory oxide system Zn_{2 − x} (Ti _a Zr _b )_{1 − x} Fe_2x O₄ (a + b = 1; a: b = 1: 5, 1: 4, 1: 3, 1: 2, 1: 1, 2: 1, 3: 1, 4: 1; x = 0–1.0; Δx = 0.05) has been studied by X-ray diffraction, using samples prepared by melting appropriate metal oxide mixtures in a low-temperature hydrogen-oxygen plasma. Two phases, both with wide homogeneity ranges, have been identified: α-phase, with a cubic inverse spinel structure, and β-phase, with a tetragonal inverse spinel structure. The phase boundaries in the system have been determined. Structural data are presented for about 100 solid solutions.     

Electrical conductivity of LaCoxFe1 ? xO3 ? δ and LaLi0.1CoxFe0.9 ? xO3 ? δ (0 ≤ x ≤ 0.4) oxides

We have studied the effect of Co and Li concentrations on the phase composition and electrical conductivity of LaCo _x Fe_{1 − x} O_{3 − δ} and LaLi_0.1Co _x Fe_{0.9 − x} O_{3 − δ} perovskite-like oxides synthesized in air at 1470 K. Single-phase materials with an orthorhombic crystal structure were obtained in the range 0 ≤ x ≤ 0.3. The composition dependences of conductivity have a minimum at x _c = 0.1 and 0.2, respectively. In the range x > 0.1, the conductivity of LaCo _x Fe_{1 − x} O_{3 − δ} increases with increasing Co concentration for T > 700 K and decreases for T < 600 K. The conductivity of La(Li_0.1Co _x Fe_{0.9 − x} )O_{3 − δ} in the range 0 ≤ x ≤ 0.1 and for x ≥ 0.2 increases with Co concentration throughout the temperature range studied.     

Structural and dielectric properties of Na1?xBaxNb1?x(Sn0.5Ti0.5)xO3 ceramics

Lead-free (1 − x)NaNbO₃/xBa(Ti_0.5Sn_0.5)O₃ (x = 0.1, 0.125, 0.15, 0.175, 0.2, and 0.3) ceramics were elaborated by the conventional ceramic technique. Sintering has been made at 1523 K for 2 h. The crystal structure was investigated by X-ray diffraction with CuKα radiation at room temperature. As a function of composition, these compounds crystallize with tetragonal or cubic symmetry. Dielectric measurements show that the materials have a classical ferroelectric behavior for compositions in the range 0.10 ≤ x ≤ 0.15 and relaxor one for compositions in the range 0.15 < x ≤ 0.30. Temperatures T _C or T _m decrease as x content increases. The ferroelectric behavior has been confirmed by hysteresis characterization. For x = 0.1, a piezoelectric coefficient d ₃₁ of 42.146 pC N⁻¹ was obtained at room temperature. The evolution of the Raman spectra was studied as a function of temperature for x = 0.1.     

Elastic and inelastic properties of (Co0.45Fe0.45Zr0.1) x (Al2O3)1 ? x nanocomposites

The elastic (Young’s modulus) and inelastic (internal friction) properties of amorphous (Co₄₅Fe₄₅Zr₁₀) _x (Al₂O₃)_{100 − x} nanocomposites with various relative contents of the metallic and dielectric phases have been studied. In the region of low temperatures, the composites exhibit a peak of the internal friction (at ∼240 K), the intensity of which increases with the content of the metallic phase. For compositions above the percolation threshold, the temperature dependence of the internal friction exhibits exponential growth above 300°C, which is related to the migration of vacancy-like defects in the amorphous structure of the metallic phase.     

Synthesis and properties of Ca1 ? xTiSi1 ? xFe2xO5 solid solutions

We have studied the CaTiSiO₅-Fe₂TiO₅ system. Ca_{1 − x} TiSi_{1 − x} Fe_2x O₅ solid solutions were prepared by low-temperature plasma synthesis in a hydrogen-oxygen flame. The CaTiSiO₅-Fe₂TiO₅ system contains two phases of variable composition: α (monoclinic structure) and β (orthorhombic structure). We have determined the homogeneity ranges, unit-cell parameters, and electrical parameters of the synthesized solid solutions. The Ca and Si in CaTiSiO₅ can be replaced by Fe³⁺. Fe³⁺ substitution increases the conductivity of the material by up to five orders of magnitude.     

Properties of LixNa1 ? xTa0.1Nb0.9O3 ferroelectric ceramic solid solutions

We have studied the electrical and elastic properties of Li _x Na_{1 − x} Ta_0.1Nb_0.9O₃ (x = 0–0.16) ferroelectric ceramic solid solutions. The results demonstrate that these properties of the Li _x Na_{1 − x} Ta_0.1Nb_0.9O₃ solid solutions are rather sensitive to the lattice distortions resulting from compositional structural phase transitions. The elastic constants determined by acoustic and contact techniques agree well.     

M?ssbauer Spectroscopy Determination of Iron Foreign Phases in?the Superconducting Systems; RAsFeO1?x, RAsFeO1?xFx, and?Sr1?xKxFe2As2

The recently discovered superconducting—spin density wave materials, containing Fe and As, have raised huge interest. However, most materials prepared to date, suffer from a varying degree of content of foreign Fe–As phases, Fe₂As, FeAs₂, and FeAs, which can lead to wrong conclusions concerning the properties of these materials. We show here that M?ssbauer spectroscopy is able to determine quite easily the relative content of the foreign phases. This procedure is demonstrated by a study of seven samples of superconducting or spin density wave materials, prepared in three different laboratories.      

Preparation, characterization and conductivity studies of Li3?2xAl2?xSbx(PO4)3

New NASICON type materials of composition, Li_3−2x Al_2−x Sb _x (PO₄)₃ (x = 0·6 to 1·4), have been prepared and characterized by powder XRD and IR. D.C. conductivities were measured in the temperature range 300–573 K by a two-probe method. Impedance studies were carried out in the frequency region 10²−10⁶ Hz as a function of temperature (300–573 K). An Arrhenius behaviour is observed for all compositions by d.c. conductivity and the Cole-Cole plots obtained from impedance data do not show any spikes on the lower frequency side indicating negligible electrode effects. A maximum conductivity of 4·5 × 10⁻⁶ S cm⁻¹ at 573 K was obtained for x = 0·8 of the Li_3−2x Al_2−x Sb _x (PO₄)₃ system.     

Effects of additional elements (M) on the thermal stability and structure of (Zr52.2Cu39.1Al8.7)100?xMx (M?=?Ag, Be, Gd, x?=?8, 7, 2) amorphous alloys

The effects of Ag (8 at.%), Be (7 at.%), and Gd (2 at.%) addition on structure and thermal stability, as well as bulk glass forming ability, in (Zr_52.2Cu_39.1Al_8.7)_100−x M _x (M = Ag, Be, Gd) alloys are investigated by means of X-ray diffraction and differential scanning calorimetry. The alloy containing Ag and Be have a critical diameter of more than 10 mm, with larger supercooled liquid region and atomic packing efficiency than Zr_52.2Cu_39.1Al_8.7 alloy, while the (Zr_52.2Cu_39.1Al_8.7)₉₈Gd₂ alloy only has a critical diameter of up to 5 mm and shows smaller supercooled liquid region and atomic packing density. CuZr is the main competing crystal phase with amorphous phase in the present Zr-Cu-based alloys. Ag and Be atoms in Zr_52.2Cu_39.1Al_8.7 alloy decrease the long range diffusion of Cu atoms and hinder the crystallization process under rapid solidification conditions. As a result, the glass forming ability of (Zr_52.2Cu_39.1Al_8.7)₉₂Ag₈ and (Zr_52.2Cu_39.1Al_8.7)₉₃Be₇ alloys are effectively enhanced.     

Superconducting Properties of Carbon and Zn Double-doped Mg1?xZnx(B1?xCx)2

A series of polycrystalline samples of Mg_1−x Zn _x (B_1−x C _x )₂ (x=0.00, 0.02, 0.04, 0.06, 0.08, and 0.10) were synthesized by a conventional solid-state reaction method under a background pressure about 10⁻³ Pa. Phase identification, crystal structure and superconducting transition temperature (T _c) were studied by means of X-ray diffraction (XRD) and resistivity measurements. The results indicated that the lattice parameters a and c show no clear trend in their changes with increasing doping level, and it turned out that the dopants had a marked effect on the crystal-lattice parameters and changed the crystal structure of the samples. The T _c for Mg_1−x Zn _x (B_1−x C _x )₂ decreased with C and Zn doping, but the rate of decrease was slower than single C-doped. We propose that the suppression of T _c by doping originates largely from the structural change.     

Cation mobility in Li1 + xTi2 ? xCrx(PO4)3 NASICON-type phosphates

Li_{1 + x} Ti_{2 − x} Cr _x (PO₄)₃ NASICON-type materials have been prepared and characterized by X-ray diffraction, scanning electron microscopy, and impedance spectroscopy. The results demonstrate that Cr³⁺ doping increases the ionic conductivity of LiTi₂(PO₄)₃ within the single-phase region of the doped material, which extends to x = 0.7. From temperature-dependent ionic conductivity data, the activation energy for lithium transport through interstitial sites and the enthalpy of defect formation in LiTi₂(PO₄)₃ are estimated at 30.0 ± 0.5 and 56 ± 1 kJ/mol, respectively.     

Microwave properties of the systems Ba1?xSrx(Zn1/3Ta2/3)0.94T{i}0.06 O3 and Ba(Zn1/3Nb2/3)1?xZrxO3

By means of a solid-phase synthesis two types of microwave dielectric materials are obtained as follows: Ba_1–xSr_x(Zn_1/3Ta_2/3)_0.94Ti_0.06O₃, where x = 0.20, 0.25, 0.30, 0.35 and 0.40 at sintering temperature T_S = 1350, 1400 and 1450 C; Ba(Zn_1/3Nb_2/3)_1–xZr_xO₃, where x = 0.04, 0.06, 0.08 and 0.10 at T_S = 1300, 1350, and 1400 C. The microwave characteristics of the materials are investigated at f = 10 GHz. The composition Ba(Zn_1/3Nb_2/3)_1–xZr_xO₃ demonstrates _r = 38, Q = 6100 and _f = +15 ppm C^–1 and the composition Ba_0.80Sr_0.20- (Zn_1/3Ta_2/3)_0.94Ti_0.06O₃ has _r = 42, Q = 8200 and _f = –13 ppm C^–1. The composition Ba_0.75Sr_0.25(Zn_1/3Ta_2/3)_0.94Ti_0.06O₃ has _r = 40, Q = 6500 and low _f = –13 C^–1 ppm. This composition could be used successfully for realisation of dielectric microwave resonators for the satellite television.     

Dielectric properties and electrical conductivity of LixNa1?xTa0.1Nb0.9O3 ferroelectric solid solutions

We have studied the dielectric properties and electrical conductivity of Li _x Na_{1 − x} Ta_0.1Nb_0.9O₃ (x = 0.03−0.135) ferroelectric solid solutions at temperatures from 290 to 700 K and frequencies from 25 to 10⁶ Hz. The results demonstrate that charge transport in these materials is due to the Li⁺ ion and that their conductivity is dominated by volume ion transport. In the temperature range studied, the Li _x Na_{1 − x} Ta_0.1Nb_0.9O₃ solid solutions undergo a first-order ferroelectric phase transition close to second order. Increasing the lithium content enhances features characteristic of second-order transitions.     

X-ray photoelectron study on Ba0.5Sr0.5CoxFe1?xO3?δ (BSCF: x?=?0.2 and 0.8) ceramics annealed at different temperature and pO2

X-ray diffraction (XRD) and the X-ray photoelectron spectroscopy (XPS) were measured for the sintered BSCF ceramics (Ba_0.5Sr_0.5Co _x Fe_1−x O_3−δ, x = 0.2 and 0.8: BSCF5528 and BSCF5582, respectively), which were annealed at different temperatures (700 and 950 °C) and gases (O₂ and Ar). The unit cell of the annealed BSCF5528 at 950 °C under Ar expanded by 0.8%, while contracting by 0.45% under O₂. The cubic and rhombohedral phases coexist in the BSCF5582 annealed at 700 °C under O₂. The XPS peak areas of lattice oxygen (O²⁻) in O_1s , ~528 eV, and the shoulder peak of Co_2p /Ba_3d in BSCF5582 (~778 eV) increased significantly after being annealed in O₂. The areas of the peaks for BaCO₃ (87.9/90.2 eV) in Ba_4d preferentially were shown to decrease in Ar and increase in O₂.     

Nanocrystalline spinel NixCu0.8?xZn0.2Fe2O4: a novel material for humidity sensing

The humidity sensing property of the ferrite systems Ni _x Cu_0.8−x Zn_0.2Fe₂O₄ with 0.0 ≤ x ≤ 0.8 (x = 0, 0.2, 0.4, 0.6, 0.8) was studied using the standard ceramic technique. The spinel structure of the compounds was confirmed by X-ray diffraction studies, BET study and surface morphology by scanning electron microscopy. The compounds were subjected to dc electrical conductivity studies at room temperature. The resistance measurements as a function of relative humidity (RH) in the range of 5–98% were done and the humidity sensing factors (S _f = R _5%/R _95%) were calculated. The composite NiCuZn-3 (x = 0.4) possessed the highest humidity sensing factor of 3051.9 ± 500, whilst CuZn–1 (x = 0) possessed the lowest humidity sensing factor of 45.3 ± 12. The other compounds possessed lower humidity sensing factors of 116.7 ± 35, 783.4 ± 160 and 416.2 ± 65 for x = 0.2, 0.6 and 0.8, respectively.     

Crystal structure and magnetic properties of high-coercivity Sr1 ? xPrxFe12 ? xZnxO19 solid solutions

Sr_1−x Pr _x Fe_{12 − x} Zn _x O₁₉ ferrites with x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5 have been prepared by solid-state reactions between praseodymium, iron, and zinc oxides and strontium carbonate in air at 1470 K. According to X-ray diffraction results, the samples with x ≤ 0.2 were single-phase and those with 0.3 ≤ x ≤ 0.5 contained, in addition to the magnetoplumbite phase, small amounts of α-Fe₂O₃, ZnFe₂O₄, and PrFeO₃. The mixed-phase samples further fired twice at 1470 K for 4 and 2 h contained no impurity phases at x = 0.3 and contained only α-Fe₂O₃ at x = 0.4 and 0.5. In the composition range 0 ≤ x ≤ 0.3, the a and c cell parameters, unit-cell volume V, and X-ray density ρ_x of the magnetoplumbite phase vary linearly according to the relations a(?) = 5.8869 − 0.0162x, c(?) = 23.027 + 0.449 x, V(?³)= 691.10 + 9.65x, and ρ_x(g/cm³) = 5.102 + 0.230 x. The highest degree of combined heterovalent substitution of Pr³⁺ for Sr²⁺ and Zn²⁺ for Fe³⁺ in the SrFe₁₂O₁₉ ferrite (formation of Sr_1−x Pr _x Fe_{12 − x} Zn _x O₁₉ solid solutions) at 1470 K is x = 0.32−0.36. The saturation magnetization per formula unit (n _s) of the x = 0.1 ferrite exceeds that of SrFe₁₂O₁₉ by 1.7% at 6 K and by 15.2% at 308 K. The 308-K n _s and coercive force (_σ H _c) of the x = 0.2 ferrite exceed those of SrFe₁₂O₁₉ by 7.6 and 8.5%, respectively.     

Structural and electrical studies of nano structured Sn1?x SbxO2 (x?=?0.0, 1, 2.5, 4.5 and 7 at%) prepared by co-precipitation method

SnO₂ semiconducting nanopowders doped with antimony Sn_1−x Sb _x O₂ (x = 0.0, 1, 2.5, 4.5 and 7 at%) was achieved by co-precipitation method. TG/DTA and FT-IR studies revealed the removal of organic residuals in the precursor leading to the formation of oxides during calcinations process. A change in color from white to bluish occurred on calcinations of the powder at 500 °C in air. The distortion ratio, strain and particle size were measured from X-ray diffraction (XRD) spectra and their changes with dopants concentration were determined. Transmission electron microscopy (TEM) images support to conform the particle size. The electrical resistivity and activation energy of the ATO particles decreases as compared with pure SnO₂, due to the incorporation of on Sn⁴⁺ ions by as Sb⁵⁺ ion in the host SnO₂ matrix. Incorporation of Sb⁵⁺ was evidenced through the XPS spectrum.     

Single Crystal Growth and Effect of Doping on Structural, Transport and Magnetic Properties of A1?xKxFe2As2 (A = Ba, Sr)

We demonstrate the preparation of large, free-standing iron pnictide single crystals with a size up to 20×10×1 mm³ using solvents in zirconia crucibles under argon atmosphere. Transport and magnetic properties have been investigated to study the effect of potassium doping on the structural and superconducting property of the compounds. The spin density wave (SDW) anomaly at T _s ∼138 K in BaFe₂As₂ single crystals from self-flux shifts to T _s ∼85 K due to Sn solvent growth. We show evidence for an incorporation of Sn on the Fe site. The electrical resistivity data show a sharp superconducting transition temperature T _c ∼38.5 K for a single crystal of Ba_0.68K_0.32Fe₂As₂. A nearly 100% shielding fraction and the bulk nature of the superconductivity for the single crystal are confirmed by magnetic susceptibility data. A sharp transition T _c ∼25 K occurs for the single crystal of Sr_0.85K_0.15Fe₂As₂. There is direct evidence for a coexistence of the SDW and superconductivity in the low doping regime of Sr_1−x K _x Fe₂As₂ single crystals. Structural implications of the doping effects as well as the coexistence of the two order parameters are discussed.