Phase Purity Of Samples Research Articles

Novel P-T Phase Diagram of the Multiorbital Mott Insulator Sr2VO4.

The electrical and optical properties of the Mott insulator Sr2VO4 are investigated under high pressure on a phase pure polycrystalline sample. The system undergoes a pressure-driven insulator to metal transition (IMT) with a crossover between 20 and 24 GPa. The effect of pressure on the thermally driven electronic changes resulting from spin-orbital ordering transitions is studied. A multiorbital analysis of the low frequency optical conductivity spectra suggests a bandwidth-controlled and orbital selective nature of the Mott IMT transition. Dramatic enhancement of the low energy spectral weight in the high pressure correlated metallic phase is explained in terms of the formation of a quasiparticle peak in the spectral function of the narrow and degenerate d(yz,zx) orbitals. Our results overall establish a novel electronic phase diagram of tetragonal Sr2VO4.

Rare-earth free p-type filled skutterudites: Mechanisms for low thermal conductivity and effects of Fe/Co ratio on the band structure and charge transport

A key driver of cost for a thermoelectric generator is the thermoelectric materials themselves, and the heavy reliance on rare earth (RE) elements as fillers, particularly for p-type formulations, represents a strategic risk. In the present study, we have investigated fully filled p-type skutterudites with nominal compositions CaFexCo4−xSb12 (2⩽x⩽3.5) using both experimental and theoretical methods. High purity samples were successfully synthesized using a combined melt-spinning (MS) and spark plasma sintering (SPS) technique. Structural analysis confirmed phase-pure samples with high filling fraction (>90%), homogeneous filler and transition metal distribution, and exceptionally low levels of oxygen contamination. Electrical and thermal transport property measurements revealed large power factors and unexpectedly low thermal conductivities. Electronic band structure calculations found a rapid increase in the density of states at the Fermi level with increasing Fe content. The large power factors observed in this system are attributable to this effect. Maximum zT of 0.9 was achieved in CaFe3CoSb12 at 773K. To understand the low lattice thermal conductivity in these compounds, lattice dynamics calculations were performed. The small size of Ca atoms and their concomitantly weak interactions with the surrounding Sb atoms result in a small force constant between fillers and the host, giving rise to a heretofore unreported low frequency optical phonon mode. This low frequency mode at 7meV is in addition to the previously described mode at 17meV identified by modeling the Ca as a simple harmonic oscillator. The lower energy phonon mode imparted by Ca filling results in a comparable lattice thermal conductivity reduction to early lanthanide species such as La.

Synthesis and Characterization of Bismuth Nickel Tantalate Pyrochlore

Bi3Ni2Ta3O14 pyrochlores and related materials were prepared by solid state reaction at sintering temperatures ranging from 900°C to 1150°C. The BNT cubic pyrochlores could be represented by a general formula Bi3Ni2-xTa3O14-x and phase pure sample was obtained at temperature 1050°C with x = 0.6. This was confirmed by X-ray diffraction analysis and detailed lattice refinement. The single phase material crystallized in a cubic system, space group Fd3m with a = b = c = 10.5134 Å, α = β = γ = 90o, respectively. The sample was further characterized using a combination of techniques including Fourier-Transform infrared spectroscopy (FT-IR), differential thermal analysis (DTA), thermogravimetric analysis (TGA) and inductively coupled plasma – atomic emission spectrometry (ICP-AES). The material was thermally stable without any thermal events being observed. Electrical properties of the single phase material were studied by ac impedance spectroscopy starting from room temperature to 800 oC over a frequency range of 5 Hz to 13 MHz. The phase formation and solid solutions of cubic pyrochlores in the Bi2O3-NiO-Ta2O5 (BNT) ternary system were studied thoroughly via combination of characterization techniques.

Synthesis and high (pressure, temperature) stability of ZnTiO3 polymorphs studied by Raman spectroscopy

The phase-purity of ilmenite-type ZnTiO3 prepared by the ceramic method was investigated in dependence of the conditions during ball milling. The previously proposed addition of 2 ml ethanol to the starting materials led to a significant contamination of the product phase after a subsequent sintering process at 1073 K. However, by omitting ethanol this synthesis route led to a phase-pure sample of ZnTiO3 as confirmed by X-ray powder diffraction and Raman spectroscopy. High-temperature high-pressure experiments gave an ilmenite-type to perovskite-type phase boundary with a slope of dT/dP∼−135 K GPa−1 crossing ambient temperature conditions at ∼ 24 GPa in good agreement with previous calculations. Room-temperature high-pressure Raman spectroscopy experiments have shown the stability of the ilmenite-type phase up to a pressure of at least 38.5 GPa, the highest pressure applied in this study, indicating the presence of a kinetic barrier in this phase transition. The synthesis of ferroelectric LiNbO3-type ZnTiO3 was confirmed by second harmonic generation.

Doping Qualifications of LiFe1−xMgxPO4-C Nano-scale Composite Cathode Materials

ABSTRACT Pure LiFePO 4 and the nano-sized LiFe 1− x Mg x PO 4 -C ( x = 0.00, 0.02, 0.04, 0.06 and 0.08) cathode materials have been prepared and investigated for Li-ion batteries. Samples were synthesized by handy and cheap sol–gel-assisted carbothermal reduction method. X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM) and inductively coupled plasma (ICP) have been used to study the crystal structure, morphology and chemical composition of all produced materials. XRD findings reveal the slight decrease in crystal lattice of LiFePO 4 after Mg 2+ doping. Phase pure samples crystallize in the olivine-type structure with a linear relationship between lattice parameters ( a , b and c ) and chemical composition. The FE-SEM images have proved that Mg-doped particles are not agglomerated and the particle sizes (40–60 nm) are able to compete with the literature. The synthesized small particles of the sol–gel-assisted carbothermal reduction process lead to a superior capacity in comparison to a common solid-state synthesis. For a Mg content of 0.04% the capacity is reached to a higher level (167 mA h g −1 ) and good capacity retention of 97.0% over 300 cycles is observed. Although doping with Mg has a remarkable effect on improving its electronic or ionic mobility, but serious electrochemical degradation will occur when its doping density is beyond 0.04 mol. The cycling voltammogram (CV) shows that Mg-doped LiFe 0.96 Mg 0.04 PO 4 -C electrode has improved electrical conductivity and diffusion coefficient of Li + ions, in which Mg 2+ is related to effectively act as a pillar in crystal lattice structure to prevent the collapse during lithium intercalation process.

Effects of aluminum substitution on the crystal structure and magnetic properties in Zn2Y-type hexaferrites

Crystal structure and magnetic properties of multiferroic Y-type hexaferrites Ba0.5Sr1.5Zn2(Fe1−xAlx)12O22 (x = 0, 0.04, 0.08, and 0.12) were investigated. The Z- and M-type impurity phases decrease with increasing Al content, and the pure phase samples can be obtained by modulating Al-doping. Lattice distortion exists in Al-doped samples due to the different radius of Al ion (0.535 Å) and Fe ion (0.645 Å). The microstructural morphologies show that the hexagonal shape grains can be observed in all the samples, and grain size decreases with increasing Al content. As for magnetic properties of Ba0.5Sr1.5Zn2(Fe1−xAlx)12O22, there exist rich thermal- and field-driven magnetic phase transitions. Temperature dependence of zero-field cooling magnetization curves from 5 K to 800 K exhibit three magnetic phase transitions involving conical spin phase, proper-screw spin phase, ferromagnetic phase, and paramagnetic phase, which can be found in all the samples. Furthermore, the phase-transition temperatures can be modulated by varying Al content. In addition, four kinds of typical hysteresis loops are observed in pure phase sample at different temperatures, which reveal different magnetization processes of above-motioned magnetic spin structures. Typically, triple hysteresis loops in low magnetic field range from 0 to 0.5 T can be observed at 5 K, which suggests low-field driven magnetic phase transitions from conical spin order to proper-screw spin order and further to ferrimagnetic spin order occur. Furthermore, the coercive field (HC) and the saturation magnetization (MS) enhance with increasing Al content from x = 0 to 0.08, and drop rapidly at x = 0.12, which could be attribute to that in initial Al-doped process the pitch of spin helix increases and therefore magnetization enhances, but conical spin phase eventually collapses in higher-concentration Al-doping.

Luminescence of the self-activated vanadate phosphors Na2LnMg2V3O12 (Ln=Y, Gd)

The self-activated yellow–green emitting garnet vanadate phosphors Na2LnMg2V3O12 (Ln=Y, Gd) were synthesized by a modified sol–gel method. The structure and phase purity of samples were verified through X-ray diffraction (XRD). The photoluminescence excitation (PLE) and emission (PL) spectra, luminescence lifetime, and temperature-dependent photoluminescence were also investigated. Due to its broadband excitation and emission spectra from charge transfer in the VO4 tetrahedron, as well as good thermal stability, Na2LnMg2V3O12 (Ln=Y, Gd) could be a potential yellow-emitting phosphor for the near-UV excited WLEDs or sunlight spectral modification phosphors for solar cells.

Investigation of the NaNixMn1-xO2 (0 ≤ x ≤ 1) System for Na-Ion Battery Cathode Materials

Layered NaNixMn1-xO2 (0 ≤ x ≤ 1) oxides were prepared via solid state reactions. Different reaction conditions were required to obtain phase pure samples, depending on the value of x. The 0 ≤ x ≤ 0.1 compositions were prepared in an inert argon atmosphere at 700°C and had a monoclinically distorted O′3 type structure. The 0.25 ≤ x ≤ 0.33 compositions were prepared in air at 850°C and had a P2-type structure. Compositions in the range of 0.5 ≤ x ≤ 0.66 were synthesized in air at 850°C and had an O3-type structure. Lastly, compositions with 0.9 ≤ x ≤ 1 were prepared in an oxygen atmosphere at 700°C and had a monoclinically distorted O′3 type structure. Electrochemical experiments were performed on pure phase samples. All showed reversibility of sodium ions and high capacities. The highest reversible capacity was achieved for x = 0.66, with a capacity of ∼190 mAh/g and an average discharge voltage of 3.07 V, corresponding to a high energy density of 2705 Wh/L. This is among the highest reported volumetric energy densities for Na-ion battery electrodes.

Magnetic Phase Transition in Nickel Oxide

The researchers worldwide are in a continuous quest to exploit nano-particles for human benefits. Nickel oxide is rated among a class of nano-materials whose structural and magnetic properties are of great interest at reduced size-scale. The present study focuses on the synthesis of phase pure nickel oxide nano-crystallites by a novel auto-ignition route to investigate its magnetic characteristics at nano-scale. The significance of fuel agent in phase stabilization has been revealed. X-ray diffraction confirmed the preparation of phase-pure samples of nickel oxide. Scherrer's relation was utilized to evaluate the crystallite size of the prepared samples. Ferromagnetic nature of the prepared nickel oxide nanocrystallites was determined by using a vibrating sample magnetometer, in contrary to the anti-ferromagnetic nature of the material in bulk form, attributed to the size effect.

Enhanced power factor of higher manganese silicide via melt spin synthesis method

We report on the thermoelectric properties of the higher manganese silicide MnSi1.75 synthesized by means of a one-step non-equilibrium method. The ultrahigh cooling rate generated from the melt-spin technique is found to be effective in reducing second phases, which are inevitable during the traditional solid state diffusion processes. Aside from being detrimental to thermoelectric properties, second phases skew the revealing of the intrinsic properties of this class of materials, for example, the optimal level of carrier concentration. With this melt-spin sample, we are able to formulate a simple model based on a single parabolic band that can well describe the carrier concentration dependence of the Seebeck coefficient and power factor of the data reported in the literature. An optimal carrier concentration around 5 × 1020 cm−3 at 300 K is predicted according to this model. The phase-pure melt-spin sample shows the largest power factor at high temperature, resulting in the highest zT value among the three samples in this paper.

Synthesis and study of the structural properties of pure PbTiO3 ferroelectric ceramics

Lead titanate with perovskite structure (PbTio3) is a Single-phase polycrystalline sample. It has been synthesized using solid-state reaction technique and prepares phase pure, dense, crack-free, and homogeneous samples. Using X-ray diffraction patterns we investigate the sintering behavior of PT -powders. The X-ray powder diffraction data have been analyzed to confirm the phase formation and phase purity, to obtain unit cell parameters and unit cell volume. The porosity of the samples has been obtained through X-ray density and bulk density.

P2-Type Na2/3Fe1/3Mn1/3Co1/3O2 As a New Positive Electrode for Na-Ion Batteries

Introduction A number of P2-type layered cathode materials have been synthesized as possible candidates for Na-ion battery application. These include Na2/3CoO2 [1], Na2/3Fe1/2Mn1/2O2 [2], Na2/3Co2/3Mn1/3O2 [3] among others. Each of these systems each have a unique set of promising characteristics. We have found another promising candidate for a practical Na-ion cathode material. Na2/3Mn1/3Fe1/3Co1/3O2was synthesized and was found to have high energy density, good cycling stability and low polarization. Experimental Phase pure samples were prepared by conventional solid state reaction at 950 °C in O2 from stoichiometric amounts of Na2O2, MnO2, Fe3O4 and Co3O4. X-ray diffraction (XRD) patterns were measured under Ar gas in a gas-tight sample holder. Electrodes were prepared from a slurry with 80% by weight active material, 12% Super-P carbon black and 8% PVDF binder dissolved in NMP. The slurry was then coated on Al foil using a coating bar with a 0.006" gap and dried in air for several hours at 120 °C. 2325 coin-type cells were constructed using 1M NaClO4(98% purity) dissolved in PC electrolyte with 2% by volume FEC. Two Celgard 3501 separators, one blown microfiber separator (3M Company) and a sodium foil counter electrode (Aldrich) were used. Cells were cycled with constant 10 mA/g current in indicated voltage ranges. Results and Discussion Figure 1 shows an XRD pattern of Na2/3Mn1/3Co1/3Fe1/3O2. The pattern shows no noticeable impurities. The pattern was fit using a Rietveld refinement with the P63/mmc space group. Lattice parameters of a = 2.89 Å and c = 11.1 Å were obtained, corresponding to a bulk density of 4.30 g/mL at 2/3 sodiation.Figure 2 shows the first cycle voltage profile for Na2/3Mn1/3Co1/3Fe1/3O2 when charged to different voltages. It was found that substitution of Co into NaxFe1/2Mn1/2O2causes an increase in average voltage [2, 4]. Upon sodiation from 4.5 V, an average voltage of 3.00 V is achieved with 173 Ah/kg / 745 Ah/L of reversible capacity, yielding an estimated energy density of ~ 520 Wh/kg / 2240 Wh/L. When cycled to 4.0 V, average voltage is 2.77 V but the energy density is reduced to ~ 350 Wh/kg (1510 Wh/L), resulting from less access of the high voltage plateau.Figure 2 also shows some of the consequences of accessing voltages above 4.1V using the current electrolyte formulation. Increasing use of the plateau increases voltage hysteresis and reduces reversibility, as evidenced by the decreasing negative capacity of the subsequent sodiation half-cycle. Ex-situ Mössbauer studies and the electrochemical performance of P2-type Na2/3Fe1/3Mn1/3Co1/3O2will be presented. Figure captions Figure 1 Rietveld refinement of the P2-Na2/3Fe1/3Mn1/3Co1/3O2XRD pattern. Figure 2 First cycle voltage profile of P2-Na2/3Fe1/3Mn1/3Co1/3O2at different cutoff voltages.

3D printed high-throughput hydrothermal reactionware for discovery, optimization, and scale-up.

3D printing techniques allow the laboratory-scale design and production of reactionware tailored to specific experimental requirements. To increase the range and versatility of reactionware devices, sealed, monolithic reactors suitable for use in hydrothermal synthesis have been digitally designed and realized. The fabrication process allows the introduction of reaction mixtures directly into the reactors during the production, and also enables the manufacture of devices of varying scales and geometries unavailable in traditional equipment. The utility of these devices is shown by the use of 3D printed, high-throughput array reactors to discover two new coordination polymers, optimize the synthesis of one of these, and scale-up its synthesis using larger reactors produced on the same 3D printer. Reactors were also used to produce phase-pure samples of coordination polymers MIL-96 and HKUST-1, in yields comparable to synthesis in traditional apparatus.

Characterization of the carbon-coated LiNi1−y Co y PO4 solid solution synthesized by a non-aqueous sol-gel route

Nanosize carbon-coated samples of the solid solution LiNi1−y Co y PO4 were prepared and investigated with respect to high-voltage cathode materials (4–5 V) for Li-ion batteries. For the syntheses, a modified non-aqueous sol-gel approach under argon atmosphere was applied. Crystal structure and morphology of the products were analyzed by X-ray powder diffraction, scanning electron microscopy, and Raman spectroscopy. Phase pure samples crystallize in the olivine-type structure with a linear relation between lattice parameters and chemical composition. The mean crystal size of the particles is smaller than 300 nm with increasing agglomeration towards samples with higher nickel content. Effects of the Ni/Co ratio on P-O and M-O bonds were explored by FTIR and UV/VIS measurements, too. Substitution of Ni by Co causes larger cell volumes, longer atomic distances, and weaker P-O and M-O bonds. Additional studies focus on the mechanism of formation of LiNiPO4 and the conditions for the formation of the phosphide by-products Ni3P and Ni12P5 by carbothermal reduction. The electrochemical properties of all compounds were investigated by galvanostatic charge/discharge measurements and differential capacity analysis. The small particles of the sol-gel process lead to a superior capacity in comparison to a common solid-state synthesis. Cyclability of the whole solid-solution is evaluated for the first time. For a Ni content of 33 %, the voltage is shifted to a higher level and a positive effect on capacity retention is observed.

Investigations on Bi25FeO40 powders synthesized by hydrothermal and combustion-like processes

The syntheses of phase-pure and stoichiometric iron sillenite (Bi25FeO40) powders by a hydrothermal (at ambient pressure) and a combustion-like process are described. Phase-pure samples were obtained in the hydrothermal reaction at 100°C (1), whereas the combustion-like process leads to pure Bi25FeO40 after calcination at 750°C for 2h (2a). The activation energy of the crystallite growth process of hydrothermally synthesized Bi25FeO40 was calculated as 48(9)kJmol−1. The peritectic point was determined as 797(1)°C. The optical band gaps of the samples are between 2.70(7)eV and 2.81(6)eV. Temperature and field-depending magnetization measurements (5−300K) show a paramagnetic behaviour with a Curie constant of 55.66×10−6m3Kmol−1 for sample 1 and C=57.82×10−6m3Kmol−1 for sample 2a resulting in magnetic moments of µmag=5.95(8)µBmol−1 and µmag=6.07(4)µBmol−1. The influence of amorphous iron-oxide as a result of non-stoichiometric Bi/Fe ratios in hydrothermal syntheses on the magnetic behaviour was additionally investigated.

Influence of the synthesis parameters onto nucleation and crystallization of five new tin-sulfur containing compounds.

The distinct control of the synthesis parameters achieved crystallization of five new inorganic-organic hybrid tin sulfides with 1,10-phenanthroline (phen) as the organic component: {[Mn(phen)2]2(μ2-Sn2S6)} (1, 3), {[Mn(phen)2]2(μ2-Sn2S6)}·phen (2), {[Mn(phen)2]2(μ2-Sn2S6)}·phen·H2O (4), and {[Mn(phen)2]2[μ-η(2)-η(2)-SnS4]2[Mn(phen)]2}·H2O (5). Compounds 1, 3, and 4 occur successively under static conditions by increasing the reaction time up to 8 weeks. Stirring the reaction mixtures and keeping the educt ratio constant allow preparation of distinct phase pure samples within very short reaction times. At higher autogenous pressure, crystallization and conversion of several compounds are suppressed, and only 1 crystallized. Compound 2 could only be obtained in glass tubes at low pH value of the reaction mixture or at low amine concentration. Adjusting the pH value of the solution, the concentration, and the volume of the solvent, compounds 1-4 crystallize sequentially and were successively converted into each other. Results of thermal stability experiments and solubility studies suggest that compounds 1 and 3 are polymorphs following the density rule. Compounds 2 and 4 may be viewed as pseudopolymorphs of 1 and 3.

Comparative study of physico-chemical properties of laboratory and industrially prepared layered double hydroxides and their behavior in aldol condensation of furfural and acetone

In this article, properties of laboratory and industrially prepared Mg–Al layered double hydroxides (LDH) with Mg:Al molar ratios varied in the range from 2 to 4 were compared. Physico-chemical properties of the studied materials were investigated with XRD, SEM, N2 physisorption, TGA and CO2-TPD methods. Catalytic behavior of the LDH samples was examined in the liquid phase aldol condensation of furfural and acetone at 20 and 60°C. It was found that LDH from the small-scale preparation have different physico-chemical characteristics than the LDH materials originating from the large-scale (industrial) preparation which is also reflected in their catalytic behavior. As-synthesized laboratory LDH catalysts are phase-pure crystalline samples with hydrotalcite structure while the industrial materials also possess MgO as admixture. The laboratory samples possess larger BET surface area and mesopore volume in comparison with the industrially prepared ones. Despite the similarity in basic properties of the studied materials, the samples with molar ratio Mg:Al=3 in both groups of LDH using different method of preparation possess the best activity in aldol condensation. Generally, the calcined laboratory samples are more active than the industrial materials in the reaction. This is explained by the better textural properties of the former ones and their susceptibility to in-situ reconstruction in the presence of water formed during the reaction.

Phase relations and chemical vapor transport of hexagonal indium tungsten bronze InxWO3

Phase pure powder samples of hexagonal indium tungsten bronze InxWO3 (x=0.25–0.35) were synthesized by solid state reaction at 1173K. The phase relations of InxWO3 with neighboring binary and ternary phases were determined in the phase diagram In–W–O. Systematic chemical vapor transport experiments were carried out on source materials with compositions corresponding to miscellaneous two-phase and three-phase regions using NH4X (X=Cl, Br, I) as transport agent. Crystals of hexagonal indium tungsten bronze were deposited beside In2W3O12 with composition corresponding to the indium poor phase boundary and dimensions up to a few mm in a temperature gradient 1173K→1073K starting from ternary mixtures InxWO3/In2W3O12/In0.02WO3. Sole deposition of InxWO3 single crystals with composition x≈0.33 was observed from ternary mixtures InxWO3/W18O49/WO2 with a migration rate of about 0.5mg/h (transport agent NH4Cl).

A molecular picture of the problems in ensuring structural purity of tazofelone

Almost twenty years after the crystal polymorphism of tazofelone was first studied at Lilly, the compound was revisited by calculating the crystal energy landscape and complementing the calculations with experimental work for calibration purposes. The crystal structure prediction study confirmed the stability of racemic form II (RCII) and showed that the racemic compound had greater potential for polymorphism than the single enantiomer. The seeding experiment that has previously been shown to produce a racemic solid solution (SS) correlates with the isostructurality between some low energy racemic structures and the enantiopure form. Other low energy structures have the same layer structure as both racemic polymorphs and the newly-discovered, but closely related, polymorph RCIII, which accounts for the difficulty in obtaining phase pure samples of the metastable RCI and RCIII and the problems of structural purity evidenced by streaked diffraction spots for RCI–III in the single crystal diffraction. This molecular picture of the problems in ensuring structural purity in the layer structure polymorphs of tazofelone not only explains the crystal dependent thermochemistry measurements of tazofelone, but also shows the value of combining a range of experimental and computational techniques to investigate the organic solid state.

Sol-Gel Synthesis and Conductivity Properties of Sodium Ion Solid State Electrolytes Na3Zr2Si2PO12

NASICON-structured Na3Zr2Si2PO12 was synthesized by a Sol-Gel approach. Phase-pure samples were successfully sintered at 1050 degrees C when adding 10% excessive Na and P in the precursors, while a small amount of ZrO2 impurity was detected without adding excessive phosphorus. Electrochemical impedance spectrum tests indicate that the ionic conductivity of the former is as high as 5.4x10(-4) S/cm at room temperature, which is higher than that of samples prepared from the precursors without adding excessive phosphorus (3.7x10(-4) S/cm). Further analysis reveals that the evaporation of phosphorus at high temperature would cause the formation of ZrO2 impurity in the samples, leading to a lower ionic conductivity. Compared with solid state reaction approach, samples with enhanced ionic conductivity can be obtained at a rather lower temperature by Sol-Gel synthesis.