Phase Purity Of Samples Research Articles

Diffraction study of pressure-amorphized ZrW2O8usingin situand recovered samples

High-energy x-ray diffraction data from a series of amorphous ZrW${}_{2}$O${}_{8}$ samples, recovered from a number of different pressures, have been measured and compared with similar data collected from a sample contained within a diamond anvil cell and measured in situ at high pressure. Samples at lower pressures are a mix of crystalline and amorphous phases, whereas those above 7 GPa (both recovered and in situ) appear to be completely amorphous. Although there are only very small changes in the diffraction data from the pure phase samples recovered from different pressures, larger changes are observed in situ as a function of pressure. However, the same structural model can be used to describe all data, albeit using different densities. This strongly suggests that the amorphous phase is undergoing nonreconstructive compression in this pressure range, without fundamental modification of the underlying topology.

Luminescent properties of UV excitable blue emitting phosphors MSr 4(BO 3) 3:Ce 3+ (M = Li and Na)

A series of Ce 3+ doped novel borate phosphors MSr 4(BO 3) 3 (M = Li or Na) were successfully synthesized by traditional solid-state reaction. The crystal structures and the phase purities of samples were characterized by powder X-ray diffraction. The optimal concentrations of dopant Ce 3+ ions in compound MSr 4(BO 3) 3 (M = Li or Na) were determined through the measurements of photoluminescence spectra of phosphors. Ce 3+ doped phosphors MSr 4(BO 3) 3 (M = Li or Na) show strong broad band absorption in UV spectral region and bright blue emission under the excitation of 345 nm light. In addition, the temperature dependences of emission spectra of M 1+ x Sr 4−2 x Ce x (BO 3) 3 (M = Li or Na) phosphors with optimal composition x = 0.05 for Li and x = 0.09 for Na excited under 355 nm pulse laser were also investigated. The experimental results indicate that the M 1+ x Sr 4−2 x Ce x (BO 3) 3 (M = Li or Na) phosphors are promising blue emitting phosphors pumped by UV light.

Magnetic and dielectric properties study of cobalt ferrite nanoparticles synthesized by co-precipitation method

Abstract:Cobalt ferrite nanoparticles were prepared by co-precipitation method and were heat treated at 100 oC, 200 oC, 400 oC and 600 oC for 2 h to increase the particle size. Phase purity of samples was confirmed by X-ray diffraction. Scherrer formula calculations showed crystallite size varied from 12 to 24 nm when heated from 100 oC to 600 oC. Transmission electron microscopy reveals a uniform and narrow particle size distribution about 12 nm for as-prepared cobalt ferrite particles. Room temperature saturation magnetization was found to vary from 40.8 to 67.0 emu/g as the particle size increased from12 nm to 24 nm. Increase in saturation magnetization with increase in particle size was attributed to the presence of magnetic inert layer on the surface of nanoparticles. Inert layer thickness calculated at 10 K and 300 K was 6 Å and 11 Å respectively. The dielectric properties ε’, tanδ, Z and θ have been studied as a function of frequency and particles size. For the 12 nm grain size, the dielectric constant is one order higher than that of bulk cobalt ferrite. Increase in the grain size showed an increase in the dielectric constant. The increase in the conductivity with grain size is mainly due to the grain size effects. The present study shows that the dielectric properties can be tailor-made to suit the requirement of a particular application by controlling the grain size.

Structural variety in iridate oxides and hydroxides from hydrothermal synthesis

We report the results of an exploratory synthetic study of iridium-containing materials using hydrothermal methods from simple metal salts. Three alkali-earth iridium hydroxides are isolated as phase-pure samples and their structures examined by single-crystal or powder diffraction methods: each contains Ir(IV)-centred octahedra, isolated from each other and sharing bridging hydroxides or fluoride with alkali-earth (Ca, Sr or Ba) centres. One of these hydroxides, Ca2IrF(OH)6.OH, possesses a unique open structure, consisting of a positively-charged framework that has one-dimensional channels in which infinite chains of hydrogen-bonded hydroxide anions are encapsulated. The addition of hydrogen peroxide or sodium peroxide to otherwise identical hydrothermal reactions yields dense oxide materials in which iridium is found in an oxidation state between +4 and +5: the novel oxide Na0.8Sr2.2Ir3O10.1 has a KSbO3-type structure with an iridium oxidation state of +5, while the new pyrochlore (Na0.27Ca0.59)2Ir2O6·0.66H2O contains iridium with an average oxidation state close to +4.5. Our results illustrate the utility for hydrothermal synthesis in the discovery of novel complex structures that may be inaccessible using conventional high-temperature synthesis, with control of the metal oxidation state possible with judicious choice of reagents.

Investigation on the microwave-derived LiFePO 4/C cathode material

A facile preparation of the LiFePO 4/C composite is achieved through the microwave irradiation method in several minutes. Electrochemical measurements were conducted to examine the evolution of the impurity phase during the microwave heating. It is found that a short microwave heating usually leads to the existence of an amorphous, ferric intermediate, while microwave firing longer than 3 min favors the formation of the Li 3Fe 2(PO 4) 3 impurity. A further calcination treatment on the microwave-derived sample has been proved to be an effective way to eliminate the ferric impurity and thus-obtained, phase-pure sample can release a capacity of 160 mAhg − 1 .

Hydrothermal Synthesis of a B-Site Magnetic Ruthenate Pyrochlore

The pyrochlore oxide (CeIV0.67Na0.33)2RuIV2O7 crystallizes directly as a phase-pure sample, without the need for postsynthesis annealing, from aqueous solutions of Ru3+, Ce3+, and sodium hydroxide in the presence of hydrogen peroxide as oxidizing agent at less than 250 °C. The structure has been refined using powder neutron diffraction and is consistent with electron diffraction and EDXA analysis performed using transmission electron microscopy (cubic Fd3m with a = 10.1659(1) A). The pyrochlore phase is metastable and upon heating to ∼400 °C begins to phase separate to ultimately yield a mixture including Na2Ru4O9, RuO2, Ce2O3, and CeO2. Magnetization measurements confirm that the material is a new example of a B-site magnetic pyrochlore, analogous to the known phase Y2Ru2O7, but that show evidence for magnetic frustration at low temperatures. Heat capacity measurements and low-temperature neutron diffraction indicate the possibility of spin-glass-like behavior with no evidence of long-range magnetic ord...

Phase segregation in Na x CoO2 for large Na contents

We have investigated a set of sodium cobaltates (NaxCoO2) samples with various sodium content (0.67 \le x \le 0.75) using Nuclear Quadrupole Resonance (NQR). The four different stable phases and an intermediate one have been recognized. The NQR spectra of 59Co allowed us to clearly differentiate the pure phase samples which could be easily distinguished from multi-phase samples. Moreover, we have found that keeping samples at room temperature in contact with humid air leads to destruction of the phase purity and loss of sodium content. The high sodium content sample evolves progressively into a mixture of the detected stable phases until it reaches the x=2/3 composition which appears to be the most stable phase in this part of phase diagram.

Thermal decomposition route for synthesis of Mn 3O 4 nanoparticles in presence of a novel precursor

The synthesis of manganese oxide (Mn 3O 4) nanoparticles by using thermal decomposition and its physicochemical characterization are being reported in present investigation. As a new precursor, [bis(2-hydroxy-1-naphthaldehydato)manganese(II)] complex was used in the presence of oleylamine (C 18H 37N) as both surfactant and solvent to control the size of resulting nanoparticle. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and Raman spectrum. Synthesized manganese oxide nanoparticles have a tetragonal structure with average size of 9–24 nm. The phase pure samples were characterized by using X-ray photoelectron spectroscopy (XPS) for Mn 2p level. The values of binding energies are consistent with the relative values are reported in the literature. As a comparison between two methods, the novel precursor thermally was treated in solid state reaction in different temperature, 400, 500, and 600 °C and the products were characterized by SEM images. Magnetic property of the as-prepared Mn 3O 4 nanoparticle shows a ferromagnetic behavior with high saturation magnetization and coercivity.

Multi-temperature synchrotron PXRD and physical properties study of half-Heusler TiCoSb

Phase pure samples of the half-Heusler material TiCoSb were synthesised and investigated. Multi-temperature synchrotron powder X-ray diffraction (PXRD) data measured between 90 and 1000 K in atmospheric air confirm the phase purity, but they also reveal a decomposition reaction starting at around 750 K. This affects the high temperature properties since TiCoSb is semiconducting, whereas CoSb is metallic. Between 90 K and 300 K the linear thermal expansion coefficient is estimated to be 10.5 × 10(-6) K(-1), while it is 8.49 10(-6) K(-1) between 550 K and 1000 K. A fit of a Debye model to the Atomic Displacement Parameters obtained from Rietveld refinement of the PXRD data gives a Debye temperature of 395(4) K. The heat capacity was measured between 2 K and 300 K and a Debye temperature of 375(5) K was obtained from modelling of the data. Coming from low temperatures the electrical resistivity shows a metallic to semiconducting transition at 113 K. A relatively high Seebeck coefficient of ∼-250 μV K(-1) was found at 400 K, but the substantial thermal conductivity (∼10 W mK(-1) at 400 K) leads to a moderate thermoelectric figure of merit of 0.025 at 400 K.

Phase-Pure Cu,Zn,Al Hydrotalcite-like Materials as Precursors for Copper rich Cu/ZnO/Al2O3 Catalysts

A series of hydrotalcite-like (htl) compounds of the general composition (Cu,Zn)1−xAlx(OH)2(CO3)x/2·m H2O was prepared with a fixed Cu:Zn ratio of 70:30. Phase pure samples could be obtained for 0.3 ≤ x ≤ 0.4. The htl precursors thermally decompose in multiple steps. After dehydration and dehydroxylation amorphous materials were obtained at 330 °C. Phase segregation during this mild calcination was only observed for samples with a Zn:Al ratio deviating strongly from 1:2. A mechanism for this low-temperature segregation process basing on the preformation of the ZnAl2O4 phase within the amorphous material is proposed. Samples with Zn:Al ratios near 1:2 form an amorphous carbonate-modified mixed oxide “(CuO)x(ZnAl2O4)y” of homogeneous microstructure. Crystallization occurs upon carbonate decomposition at temperatures higher than 500 °C. Despite the small size of the Cu nanoparticles (around 7 nm) formed upon reduction, the accessible Cu surface area is below 5 m2g−1. This can be explained by the unfavorable microstructure of the resulting Cu/ZnAl2O4 catalyst: The Cu particles are to a large extent embedded in a compact oxide matrix. The applicability as Cu/ZnO/Al2O3 catalysts and the role of htl precursor phases in course of industrial catalyst preparation are discussed.

One-pot, glycine-assisted combustion synthesis and characterization of nanoporous LiFePO 4/C composite cathodes for lithium-ion batteries

Nanoporous LiFePO 4/C composite cathodes have been synthesized by a novel one-pot, glycine-assisted combustion (GAC) method in presence of 2 wt.% Super P carbon in both Ar and 90% Ar–10% H 2 atmospheres at 750 °C for a short time of 6 h. While the Ar atmosphere offers phase pure samples, the Ar–H 2 atmosphere leads to the formation of impurity phases as indicated by X-ray diffraction data. The combustion-initiated expulsion of gases aids the formation of a nanoporous LiFePO 4/C composite structure as evident from electron microscopic analysis, which could allow easy penetration of the electrolyte and realization of an electronic–ionic 3D network. The nanoporous LiFePO 4/C sample synthesized in Ar atmosphere exhibits a high discharge capacity of 160 mAh g −1 with 3% capacity fade in 50 cycles and high rate capability. With a short reaction time, the GAC method offers an energy efficient approach to synthesize high performance olivine LiFePO 4/C composite cathodes.

Intrinsic exchange bias inZnxMn3−xO4(x≤1)solid solutions

Bulk specimens of the het\ae{}rolite solid solution ${\text{Zn}}_{x}{\text{Mn}}_{3\ensuremath{-}x}{\text{O}}_{4}$ with $x=0$, 0.25, 0.5, 0.75, and 1 have been prepared as homogeneous, phase-pure polycrystalline samples as ascertained by neutron-diffraction measurements. Samples with $x=0.25$, 0.5, and 0.75 exhibit shifted magnetic hysteresis loops at low temperature, characteristic of exchange bias typically seen in magnetic composites. We propose that the unusual magnetic behavior arises as a result of a nanoscale mixture of ferrimagnetic and antiferromagnetic regions that are distinct but lack long-range order. While some glassy behavior is seen in ac magnetic measurements, its magnitude is not sufficient to account for the observed dramatic exchange bias. Furthermore, isothermal and thermoremanent magnetization measurements distinguish this material from a pure spin glass. The title system offers insights into the alloying of a ferrimagnet ${\text{Mn}}_{3}{\text{O}}_{4}$ with an antiferromagnet ${\text{ZnMn}}_{2}{\text{O}}_{4}$ wherein distinct magnetic clusters grow and percolate to produce a smooth transition between competing orders.

Control of Phase in Phosphide Nanoparticles Produced by Metal Nanoparticle Transformation: Fe2P and FeP

The transformation of Fe nanoparticles by trioctylphosphine (TOP) to phase-pure samples of either Fe(2)P or FeP is reported. Fe nanoparticles were synthesized by the decomposition of Fe(CO)(5) in a mixture of octadecene and oleylamine at 200 degrees C and were subsequently reacted with TOP at temperatures in the region of 350-385 degrees C to yield iron phosphide nanoparticles. Shorter reaction times favored an iron-rich product (Fe(2)P), and longer reaction times favored a phosphorus-rich product (FeP). The reaction temperature was also a crucial factor in determining the phase of the final product, with higher temperatures favoring FeP and lower temperatures Fe(2)P. We also observe the formation of hollow structures in both FeP spherical nanoparticles and Fe(2)P nanorods, which can be attributed to the nanoscale Kirkendall effect. Magnetic measurements conducted on phase-pure samples suggest that approximately 8 x 70 nm Fe(2)P rods are ferromagnetic with a Curie temperature between 215 and 220 K and exhibit a blocking temperature of 179 K, whereas FeP is metamagnetic with a Neel temperature of approximately 120 K. These data agree with the inherent properties of bulk-phase samples and attest to the phase purity that can be achieved by this method.

SYNTHESIS AND CHARACTERIZATION OF AURIVILLIUS-PHASE Bi4Srn-3TinO3n+3 (n = 3 AND 4) NANOFERROELECTRIC CERAMICS

Bi4Ti3O12 (BIT) and Bi4SrTi4O15 (BIST) ceramics with particle sizes of approximately 36 and 27 nm, respectively, have been successfully prepared by a new poly(ethylene glycol methacrylate-co-acrylic acid)-based copolymerization method. XRD, FTIR, and Raman investigations on the BIT and BIST samples revealed that the phase pure nanosized ferroelectric samples were obtained relatively at lower temperatures compared to other techniques. The phase transition temperatures and the peak dielectric constant observed at the Curie temperatures for nano-sized BIT and BIST samples obtained in this work are higher than that of conventional ceramic samples with micrometer grain size.

Investigation of magnetic behaviour of Ni–Fe–O prepared by the solid state method

Polycrystalline Fe doped NiO was prepared by the solid state method with the aim of exploring its suitability as a functional material for spintronics applications. Phase pure samples (up to 2% doping of Fe) as evident from x-ray diffraction were characterized to investigate the magnetic, electric and dielectric properties. Magnetic measurements using the vibrating sample magnetometer clearly reveal ferromagnetic behaviour at room temperature. The activation energies of the doped samples, determined from impedance spectroscopy, were found to be relatively higher than that of undoped NiO. It is also observed that Fe doping has no significant effect on the dielectric properties of the samples. Thermogravimetric analysis, carried out to find the Curie temperature (TC), leads to a remarkable insight into the observed ferromagnetism by identifying the presence of secondary phase NiFe2O4.

SYNTHESIS OF MONODISPERSE Mn3O4 NANOCRYSTALS

Mn3O4 nanocrystals have been prepared using [bis(2-hydroxyacetophenato)manganese(II)] as precursor. Transmission electron microscopy analysis demonstrated nanocrystals Mn3O4 with an average diameter of about 20 nm. The structural study by X-ray diffraction indicates that these nanocrystals have pure tetragonal phase. The phase pure samples were characterized using X-ray Photoelectron Spectroscopy for Mn 2p level. The values of binding energies are consistent with the relative values reported in the literature.

The influence of partial substitution of Ca by Sm on dissipation processes in (Bi6Pb0.4)(Sr1.8Ba0.2)(Ca1-xSmx)2Cu3Oy superconductor

Superconducting polycrystalline samples (Bi6Pb0.4)(Sr1.8Ba0.2)(Ca1_xSmx)2Cu3Oy with 0^le; x ≤ 0.05 were prepared by the conventional solid-state reaction. X-ray diffraction measurements showed the influence of Sm concentration on the phase purity of samples. The influence of partial substitution of Ca by Sm on the normal state properties and the flux dynamics were investigated by electrical resistance versus temperature and systematic a.c. susceptibility measurements function of temperature and Hac field amplitude. The evolution of some parameters sensitive to Sm concentration were evaluated from resistivity data and a.c. susceptibility data. The influence of Sm on the intergranular pining force density was discussed by using Muller critical state model for experimental linear dependence of Tp for maximum of imaginary χ" (T) peak as a function of Hac

Magnetic Ordering in CeZnGe

CeZnGe crystallizes with the hexagonal YPtAs-type structure, space group P63/mmc, a = 430.0(2), c = 1678.8(10) pm. A phase-pure sample was synthesized from the elements in a sealed tantalum crucible in a high-frequency furnace. Magnetic susceptibility measurements have revealed a trivalent cerium with an experimental magnetic moment of 2.67(1) μB/Ce atom. Ferromagnetic ordering sets in at TC = 4.6(2) K.

Synthesis of monodisperse nanocrystals of manganese oxides

The nanocrystals Mn3O4 powder have been prepared using [Bis(salicylidiminato)manganese(II) ] as precursor. Effect of oleylamine and triphenylphosphine on particle morphology has been investigated. Transmission electron microscopy (TEM) analysis demonstrated nanocrystals Mn3O4 with an average diameter of about 20 nm. The structural study by X-ray diffraction (XRD) indicates that these nanocrystals have pure tetragonal phase. The phase pure samples were characterised using X-ray photoelectron spectroscopy (XPS) for both Mn 2p and Mn 3s levels. The values of binding energies are consistent with the relative values reported in the literature.

Polymorphism and variable structural dimensionality in the iron(III) phosphate oxalate system: a new polymorph of 3D [Fe2(HPO4)2(C2O4)(H2O)2]·2H2O and the layered material [Fe2(HPO4)2(C2O4)(H2O)2

Two new iron (III) phosphate oxalates have been isolated under hydrothermal conditions as phase-pure samples and their crystal structures determined from single crystal X-ray diffraction. [Fe(2)(HPO(4))(2)(C(2)O(4))(H(2)O)(2)] x 2 H(2)O, I, is a polymorph of a known phase and differs in the local arrangement of hydrophosphate, oxalate and coordinated water about iron, presenting a mer orientation of three coordinated phosphates, rather than fac as previously seen. The structure of I is three-dimensionally connected with similar network connectivity to the known phase but different overall topology. [Fe(2)(HPO(4))(2)(C(2)O(4))(H(2)O)(2)], II, has a layered structure constructed from octahedral Fe(III) centres coordinated by hydrophosphate, oxalate and water in a fac arrangement. The amount of water used in synthesis is one of the key experimental parameters in stabilising one phase over the other. Thermogravimetric analysis shows that both I and II ultimately collapse into dense tridymite type FePO(4) above 600 degrees C and variable temperature powder XRD shows that this occurs via crystalline intermediate phases. Variable temperature magnetisation measurements show that both materials order antiferromagnetically at low temperatures, with similar Néel temperatures (approximately 29 K) despite their long-range structural differences.