Amount Of Impurity Phase Research Articles

Method to Determine the Distribution of Substituted or Intercalated Ions in Transition-Metal Dichalcogenides: FexVSe2 and Fe1–xVxSe2

Multiple techniques are combined to determine the amount of intercalation and/or substitution in transition-metal dichalcogenides. Kiessig fringes in the X-ray reflectivity pattern are used to calculate thickness. Laue oscillations in the specular diffraction pattern of the crystallographically aligned samples determine the number of unit cells in the coherently diffracting domains. The amount of impurity phase(s) is estimated by the difference between the thickness of the films and the size of the domains. If the difference is small relative to the total film thickness, the composition of the crystalline phase can be determined from X-ray fluorescence measurements. The number of unit cells possible can be calculated from the amount of each element determined by X-ray fluorescence measurements using in-plane lattice parameters, and the amount of the anion should agree with the number of unit cells determined from the Laue oscillations. The total amount of the metal relative to that required for the number of unit cells from the Laue oscillations provides a direct determination of the relative amount of intercalation and/or substitution in the crystalline dichalcogenide. The utility of this approach is illustrated in FexV1–ySe2 samples. The relative amount of intercalation versus substitution was determined independently using electron microscopy and Rietveld refinement of diffraction patterns and is consistent with this new approach.

Effects of the substitution of Cu for Sn on structural, magnetic and magnetocaloric properties of half-Heusler CoMnSn alloy

The structure, magnetic transition and magnetocaloric properties of half-Heusler CoMnSn1-xCux alloy have been investigated. X-ray diffraction reveals that a main phase of hexagonal structure was obtained in alloys, and there is no obvious secondary phase observed in the less doped samples. The impurity phases appear only when the Cu doping level is high, and the amount of impurity phases is less than 0.7 mol.% in the sample x = 0.10. The substitution of Cu for Sn is found to decrease in c/a lattice parameter and cell volume. ZFC and FC measurements show that a magnetic transition from ferromagnetic to paramagnetic phase occurs around 150 K in CoMnSn1-xCux alloy, and the magnetization and Curie temperature of samples can be tuned by the Cu content, in which the magnetization of alloys decreases with the increasing Cu content, while Curie temperature increases by 13 K. The maximum of magnetic entropy change (ΔSM) in a magnetic field change of 5 T is found to be 17.4(2) J/(kg·K) with a large refrigerating capacity of 230.3(8) J/kg for x = 0.02, revealing that CoMnSn1-xCux alloy with the second-order magnetic transition can provide a considerable magnetocaloric effect at a low cost, which suggests a promising candidate for magnetic refrigeration materials.

Effect of Carbonate Precipitant on the Microstructure and Electrochemical Properties of LiNi0.5Mn1.5O4 Cathodes

Spinel LiNi0.5Mn1.5O4 cathode materials with Fd3m space group were prepared using the co-precipitation method via adjusting the amount of Na2CO3 precipitant. X-ray diffraction and Rietveld refinement revealed that the impurity phase was effectively inhibited after the addition of more amount of Na2CO3. All samples, including the pristine LiNi0.5Mn1.5O4 sample and that prepared with different extra amounts of Na2CO3, exhibited uniform polyhedron morphology and their average grain sizes increased with the amount of Na2CO3. After adding 5% more Na2CO3, the average grain size of the sample was larger than 500 nm. When compared to other samples, the amount of impurity phase was minimum in the sample prepared with 5% more Na2CO3. Due to the impurity suppression, the LiNi0.5Mn1.5O4 sample prepared with 5% more Na2CO3 exhibited superior electrochemical performance for Li-ion batteries, showing initial discharge capacities of 125.4 mA h g−1 and 126.1 mA h g−1, and high capacity retentions of 90.7% and 87.6% after 200 cycles at 0.1 C and 0.5 C, respectively. It also exhibited the lowest intrinsic resistance and best Li+ diffusion kinetics among all the samples deduced from electrochemical impedance spectroscopy.

High-Temperature Formation Phases and Crystal Structure of Hot-Pressed Thermoelectric CuGaTe2 with Chalcopyrite-Type Structure

Polycrystalline CuGaTe2 with a chalcopyrite-type structure consolidated by hot-pressing is a potential candidate as a medium-temperature thermoelectric (TE) material. However, its high-temperature formation phases have rarely been reported to date. Here, we investigated the temperature-dependent formation phases and crystal structure at 300–800 K of hot-pressed CuGaTe2. From synchrotron x-ray diffraction data and crystal structure analysis of the heating and cooling processes, it was clarified that a certain amount of impurity phases, such as Te and CuTe, precipitated from the CuGaTe2 matrix when the temperature was increased (to 500–650 K). This is the temperature range where CuGaTe2 has been reported to show high TE performance. After CuGaTe2 was heated to 800 K, such impurity phases remained, even when cooled to room temperature. They also affected the tetragonal distortion and the x-coordinate of Te in the CuGaTe2 matrix, probably due to deficiencies of Cu and Te in the matrix. Our results reveal detailed information on the formation phases of CuGaTe2 at high temperature and thus provide insight for evaluation of its high-temperature stability and transport properties.

Thermoelectric Properties of Sb-Doped Mg2Si Prepared Using Different Silicon Sources

Magnesium silicide (Mg2Si) compounds doped with 8000 ppm Sb were prepared using different Si sources via liquid–solid reaction synthesis and hot pressing. The Si sources were solar-grade Si, metal-grade Si, and sludge Si. The Si sludge generated during the cutting of Si wafers was recycled as a Si source. The x-ray diffraction (XRD) patterns of the Si sludge corresponded to Si, silicon dioxide (SiO2), and C, whereas the solar-grade Si and metal-grade Si were indexed as a single Si phase. For the sintered compact samples, the Mg2Si phase was predominant in all the samples. However, small amounts of impurity phases, MgO and SiC, were identified in the sintered Mg2Si that used sludge Si. The thermoelectric properties of the Mg2Si produced using solar-grade Si or metal-grade Si were almost the same at the measured temperature. The efficacy of the low-purity metal-grade Si was demonstrated. However, the power factor and thermal conductivity of the Mg2Si produced using sludge Si were smaller than those of the other samples over the entire measured temperature range. However, the maximum value of ZT was almost the same.

Synthesis of multiferroics BiFe0.5B0.5O3

It is shown that the solid solutions BiFe0.5B0.5O3 (B = Cr, Mn, Sc, Y, [Ni0.5Ti0.5], [Mg0.5Ti0.5], [Ni0.75W0.25], [Mg0.75W0.25], [Mg0.67Nb0.33], [Ni0.67Nb0.33]) with a perovskite structure by the method of solid-state synthesis at atmospheric pressure and with the application of moderate pressures (20 MPa) can hardly be obtained in a pure form (without foreign phases) because of the destabilization of their structures either in terms of the parameters of the strength or the directionality of chemical bonds in them. The use of the method of solid-state synthesis at atmospheric pressure has permitted obtaining only BiFe0.5Mn0.5O3 with a relatively small content of foreign phases, which is explained by the identity of the ionic radii of Fe3+ and Mn3+ and also by the proximity of the parameters of the strength and directionality of the bonds in BiFeO3 and BiMnO3. The application of many-hour isothermal holdings, the synthesis of BiFe0.5Mn0.5O3 by the sol-gel method or in the presence of a small excess of Bi2O3 (5 wt %) have not led to a noticeable decrease in the amount of impurity phases.

Normal and Superconducting Properties of the Noncentrosymmetric Mo3Al2C

We have investigated the noncentrosymmetric superconductor Mo3Al2C prepared by spark plasma sintering, in which the amount of impurity phase was considerably reduced. Another phase transition in the normal state was clearly observed in the spark plasma sintered sample as an abrupt change in the 27Al nuclear magnetic resonance (NMR) spectra and an anomaly in the electrical resistivity. In the transition, a partial gap opening on the Fermi surface is inferred from the decrease in the nuclear spin–lattice relaxation rate \(1/T_{1}\) and the magnetic susceptibility χ below 200 K. The simultaneous presence of two components in the NMR spectra and thermal hysteresis in χ at \({\sim}200\) K indicates the first-order character of the transition. These results imply the formation of the charge-density wave state in Mo3Al2C. In the superconducting state, \(1/T_{1}\) shows a peak just below \(T_{\text{c}}\) and decreases exponentially with temperature, in good agreement with that is expected for the \(s\)-wave super...

Phase relation of LaFe 11·6 Si 1·4 compounds annealed at different high-temperature and the magnetic property of LaFe 11·6– x Co x Si 1·4 compounds

LaFe 11·6 Si 1·4 compounds are annealed at different high temperatures from 1323 to 1623 K. The powder X-ray diffraction patterns show that large amount of NaZn13-type phase begins to be observed in LaFe 11·6 Si 1·4 compound after being annealed at 1423 K for 5 h. In the temperature range from 1423 to 1523 K, the $\boldsymbol{\alpha} $ -Fe and LaFeSi phases rapidly decrease to form 1:13 phase. LaFeSi phase is rarely observed in the XRD pattern in the LaFe 11·6 Si 1·4 compound annealed at 1523 K (5 h). With annealing temperature increasing to 1573 K and 1673 K, La 5 Si 3 phase is detected, and there is a certain amount of LaFeSi phase when the annealing temperature is 1673 K. The amount of impurity phases in the LaFe 11·6 Si 1·4 compound annealed by the two-stage annealing consisting of high temperature ( $\boldsymbol{>}$ 1523 K) and 1523 K is larger than that of the single stage annealing at 1523 K under the same time. According to the results of different high-temperature annealing, LaFe $_{{\bf 11{\cdot}6}-\boldsymbol{x}}$ Co $_{\boldsymbol{x}}$ Si 1·4 ( $\boldsymbol{0{\cdot}1} \boldsymbol{\le} \boldsymbol{x} \boldsymbol{\le} \boldsymbol{0{\cdot}8}$ ) compounds are annealed at 1523 K (5 h). The main phase is NaZn13-type phase, and the impurity phase is a small amount of $\boldsymbol{\alpha} $ -Fe in LaFe $_{{\bf 11{\cdot}6}-\boldsymbol{x}}$ Co $_{\boldsymbol{x}}$ Si 1·4 compounds. With increase in Co content from $\boldsymbol{x} \boldsymbol{=} \boldsymbol{0{\cdot}1}$ to $\boldsymbol{0{\cdot}8}$ , the Curie temperature $\boldsymbol{T}_{\!\boldsymbol{\rm C}}$ , goes up from 207 to 285 K. The introduction of Co element weakens the itinerant electron metamagnetic transition, and also results in the change of magnetic transition type from first to second order at about $\boldsymbol{x = 0{\cdot}5}$ . The magnetic entropy change decreases from 19·94 to 4·57 J /kg K with increasing Co concentration at a low magnetic field of 0–2 T. But the magnetic hysteresis loss around $\boldsymbol{T}_{\!\boldsymbol{\rm C}}$ reduces remarkably from 26·2 J /kg for $\boldsymbol{x = 0{\cdot}1}$ to 0 J /kg for $\boldsymbol{x} \boldsymbol{=} \bf 0{\cdot}8$ .

Fabrication of LiNi0.5Mn1.5O4 thin film cathode by PVP sol–gel process and its application of all-solid-state lithium ion batteries using Li1 + xAlxTi2 − x(PO4)3 solid electrolyte

LiNi0.5Mn1.5O4 thin film on Au and LATP substrates was fabricated by the PVP sol–gel method. The LiNi0.5Mn1.5O4 thin film prepared on Au showed intrinsic electrochemical redox reaction at 4.7V vs. Li/Li+. The thin film exhibited an excellent electrochemical performance. The discharge capacity at a rate of 1C was 145mAhg−1, which was 98% of theoretical capacity (148mAhg−1). The thin film kept high capacity 125mAhg−1, even at 10C. In order to construct all-solid-state battery, LiNi0.5Mn1.5O4 thin film electrodes were prepared on LATP electrolytes at 600, 700, and 800°C. The thin film prepared on LATP showed a reversible current response, indicating that the thin film on LATP worked as the cathode. However, the observed current response was quite small due to impurities originated from the reaction between the thin film and LATP during heat treatment. The amount of impurity phase was increased with increasing heat treatment temperature. In order to improve the electrochemical properties of the interface between LiNi0.5Mn1.5O4 and LATP electrolytes, the optimization of preparation process such as fabrication of a buffer layer, which has non-reactive nature with both LiNi0.5Mn1.5O4 and LATP, is required.

Influence of Citric Acid and Calcination Temperature on Microstructure of the Nano Precursors of La-Mg Hydrogen Storage Alloy

The nano precursors of La-Mg hydrogen storage alloy have been prepared using citric acid, lanthanum nitrate and magnesium nitrate by so-gel technology. The effect of citric acid and calcination temperature on microstructure of the nano precursors of La-Mg hydrogen storage alloy have been studied by Infrared Radiation (IR), thermogravimetric and differential thermal analysis (TG/DTA), X-ray diffraction analyzer (XRD) and Transmission electron microscopy (TEM). IR results indicate the molar ratio of citric acid to metal cations increases from 1 to 1.3, the amount of citrate increases correspondingly, when the molar ration increases to 1.6, the amount of citrate goes up to maximum. The most appropriate amount of citric acid is 1.6 times that of the metal cations. In addition, the amount of citric acid have little influence on size of grains. XRD and TG/DTA results show that with increase of calcination temperature the amount of impurity phase, La(OH)3, decreases markedly. Formation of La2O3and MgO two-phase mixture occurred at 950°C. TEM results reveal that the morphology of the particles is almost flake with the size of ~50nm at 950°C and La, Mg, O three elements are observed in each flake.

Preparation of Lithium Orthosilicate Ceramic Pebbles by Molten Spray Method Process

Lithium orthosilicate (Li4SiO4) ceramic pebbles was prepared by molten spray process, using lithium carbonate (Li2CO3) and silica (SiO2) as raw material. The XRD experimental investigation results showed that the main crystal phase of the ceramic pebbles is Li4SiO4with small amount of impurity phase, Li2SiO3, and some unreacted SiO2. The average pebbles size is 0.22mm. The sphericity of the pebble is 99%.

Low-Loss Microwave Ceramics Based on Non-Stoichiometric Perovskites Ba(Co1/3Nb2/3)O3 and Ba(Zn1/3Nb2/3)O3

The effect of both A-site and B-site non-stoichiometry on the microstructure and microwave dielectric properties of the perovskite niobates Ba(A 2 + 1/3 Nb 2/3 )O 3 (A 2 + = Co, Zn) has been examined. Both the chemical composition of the ceramics and their sintering regimes have been shown to significantly influence the type and the amount of impurity phases which consecutively demonstrate a prevailing effect on the microwave dielectric loss. The highest magnitudes of the Qxf product have been obtained in the Co-deficient BCN (Qxf = 100 000 GHz) and Ba-deficient BZN (Qxf = 90 000 GHz) which both demonstrate noticeable amount of secondary Ba-rich phases.

Giant magnetoresistance in semiconducting DyNiBi

The semiconducting half-Heulser compound DyNiBi shows a negative giant magnetoresistance (GMR) below 200 K. Except for a weak deviation, this magnetoresistance scales roughly with the square of the magnetization in the paramagnetic state, and is related to the metal–insulator transition. At low temperature, a positive magnetoresistance is found, which can be suppressed by high fields. The magnitude of the positive magnetoresistance changes slightly with the amount of impurity phase.

Effect of temperature and soaking time on the synthesis of Mo(Al,Si) 2

Mo(Al,Si) 2 has been prepared by hot pressing elemental powders of Mo, Al and Si, at 1200–1700°C and 22 MPa. Mo 5Si 3 or Mo 5Si 3C have been observed as minor phases in all the samples with 1300°C being the best processing temperature for synthesizing Mo(AlSi) 2: with minimum amount of impurities. As the soaking time increases, the amount of impurity phases also increases.

Magnetic studies on Mn-substituted YBaCuO

Magnetic d.c. and a.c. susceptibility and lattice constant measurements were performed in the normal state of YBa 2Cu 3− x Mn x O 7−δ with Mn concentrations x = 0.075, 0.15, 0.2, 0.25 and 0.3. The orthorhombic structure is preserved throughout the substitution range and some amount of impurity phases were evidenced in the samples with x > 0.2. The inter- and intragrain properties from a.c. susceptibility measurements show different behaviour above and below the x = 0.2 Mn in the YBCO. The measurements of the d.c. susceptibility were analysed using a Curie-Weiss law with a temperature-independent background. The effective magnetic moment obtained per Mn atom, p Mn = 3.29 μ B, suggests the presence of a 4+ oxidation state. The variation of the Curie paramagnetic temperature θ for different x is associated with an antiferromagnetic exchange interaction between the Mn ions. A regular trend of p eff.tot 2 and T c as a function of x suggest that below x = 0.2 Mn ions are substituted in the Cu(1) positions.

Hole Concentration and Tc in the TI2-x-zBa2+xCa2+xCu3O10-y System

ABSTRACTSingle phase Tl-2223 samples were prepared in the TI2-x-zBa2Ca2+xCu3O10-y (z represent Tl vacancies in the range 0.22 – 0.27 and y represent oxygen vacancies in the range 0.17 – 0.33) system with x between 0 and 0.4. A small impurity phase was found at x = 0.6. All samples were found to be tetragonal. The Tc varied between 112 and 118 K for the “as-synthesized” samples. After post-annealing in a sealed quartz tube under vacuum at 750*deg;C for 10 days, the Tc increased from 116 to 122 K for x = 0.3 and from 118 to 120 K for x = 0,4 samples. Although x = 0.3 sample had small impurity phases after post-annealing, a large amount of impurity phases were found for x = 0.4 sample after post-annealing. Wet chemical analysis showed that all samples were both Tl and oxygen deficient. The Tc was found to increase with increasing hole concentration. The origin of the holes for all these samples is due to Ca2+ substitution on the TI3+ sites and overlap of Tl-6s band with the conduction band of the CuO2 sheets.

On the preparation of Y1Ba2Cu4O8

It was demonstrated that superconducting 124 material can be successfully prepared by using oxide-nitrate- mixtures or nitrate-mixtures with short reaction times at normal oxygen pressure conditions. Small quantities of CuO, BaCuO 2 and Y 2BaCuO 5 could be detected as phase impurities by X-ray diffraction. The best quality samples were prepared using freeze-dryed nitrate solution with Na 2CO 3 as an accelerator. The amount of impurity phases in these samples was near the detection limit of X-ray diffractometry.

Magnetic Properties of YBa2(Cu1−xNix)3O7−δ

The influence of Ni substituted for Cu in YBa2Cu3O7−δ on the intra- and intergrain properties is studied. All intragrain critical parameters are gradually degraded with increasing concentration x of nickel. On the contrary, the intergrain critical current at H = 0 A/m is the same for all x in the concentration regime 0 ≦ x ≦ 0.09. It is, therefore, concluded that the amount of impurity phases or defects incorporating nickel increases with x and locates mainly inside grains, deteriorating the intragrain critical parameters. [Russian Text Ignored].

Flux Pinning and Weak Link Structure in Ca2Cu1O3 Doped LnBa2Cu3O7-y (Ln=La and Y)

AbstractFlux pinning and weak link structure were studied on the effect of Ca doping in LnBa2Cu3O7-y system (Ln=La and Y). The magnitude and the magnetic field dependence of the critical current density were improved by Ca doping. A small amount of impurity phase of such as Ca2Cu1O3 may work as a desirable flux pinning center. Moreover, it was found that the current-temperature characteristics for Ca-doped samples showed the evidence of two kinds of superconducting phases which have different transition temperature Tc and Tc'. The experimental result agrees well with the Ambegaokar-Baratoff theory for asymmetric Josephson junctions (S-I-S') in the temperature range of T < Tc' and with the proximity junction theory (S-N-S) in the range of Tc'<T<Tc.

Superconductivity and magnetism of GdMo 6Se 8

The upper critical field and magnetization of the Chevrel phase GdMo 6Se 8 have been determined from a detailed analysis of measurements on a series of samples which include various amounts of impurity phases. The samples were prepared by sintering mixtures of Mo, Se and an excess of Gd. The electrical resistivity and magnetization of these samples were measured in magnetic fields of up to 70 kOe and at temperatures down to 0.5K. From the magnetization it was determined for GdMo 6Se 8 that the Néel temperature T N = 0.95 K and the Curie-Weiss temperature θ = − 0.8 K. A kink in the temperature dependence of the upper critical field was observed at 0.85 K, and the superconducting transition temperature T s was found to be 5.4 ± 0.2 K.