Phase Purity Of Samples Research Articles

Fabrication and properties of pure-phase Cu2O co-doped with zinc and indium

Cuprous oxide (Cu2O) thin films co-doped with zinc (Zn) and indium (In) were fabricated with direct current (DC) magnetron sputtering. The sputtering voltage of the Cu target was fixed while that of the alloy target of Zn and In was varied. It is found that when the alloy target voltage is below 310 V, pure-phase Cu2O can be obtained while a further increase in the alloy target voltage will result in the presence of metallic copper. The surface morphologies, the atomic ratios of the Zn and In, and the grain size do not have a linear dependence on the sputtering voltage of the alloy target. Higher concentration doping will decrease the lattice constant of Cu2O. Pure-phase samples doped with Zn and In have relatively higher transmittance and larger optical band gaps. The n-type conduction of Cu2O co-doped with Zn and In is realized when the sputtering voltage of the alloy target is 310 V. Zn and In atoms are found to exist as Zn2+ and In3+ in the films and they are possible donors for the n-type conduction.

Synthesis and Structural Characterization of Ca<sub>14</sub>Nb<i><sub>x</sub></i>In<sub>1<i>-</i></sub><i><sub>x</sub></i>As<sub>11</sub> (<i>x</i> ≈ 0.85)

Single-crystals of the new compound Ca14NbxIn1–xAs11 have been obtained from a solid-state reaction in a sealed Nb ampoule. The initial experiment had been set up with the aim to investigate the effect of electron doping (via In) on the crystal structure and physical properties of Ca14MnAs11. Subsequent single-crystal X-ray diffraction and elemental analysis work suggested that instead of Ca14MnxIn1–xAs11, the major product of the reaction is the phase Ca14NbxIn1–xAs11. This supposition was corroborated when the title compound was synthesized from a reaction of Ca, In and As in a sealed Nb ampoule, proving that, 1) Mn metal is not included in the structure, and 2) that the inadvertent side reaction of As with the walls of the Nb container is the source of the niobium. The overall structure is isotypic with the tetragonal Ca14AlSb11 structure type (space group I41/acd), although some marked differences between the two must be noted. Current ongoing work is focused on the synthesis of phase pure polycrystalline samples and determination of the physical properties of this unusual transition metal Zintl phase.

Energetics of a Uranothorite (Th1–xUxSiO4) Solid Solution

High-temperature oxide melt solution calorimetric measurements were completed to determine the enthalpies of formation of the uranothorite, (USiO4)x–(ThSiO4)1–x, solid solution. Phase-pure samples with x values of 0, 0.11, 0.21, 0.35, 0.71, and 0.84 were prepared, purified, and characterized by powder X-ray diffraction, electron probe microanalysis, thermogravimetric analysis and differential scanning calorimetry coupled with in situ mass spectrometry, and high-temperature oxide melt solution calorimetry. This work confirms the energetic metastability of coffinite, USiO4, and U-rich intermediate silicate phases with respect to a mixture of binary oxides. However, variations in unit cell parameters and negative excess volumes of mixing, coupled with strongly exothermic enthalpies of mixing in the solid solution, suggest short-range cation ordering that can stabilize intermediate compositions, especially near x = 0.5.

Synthesis of Bulk BC8 Silicon Allotrope by Direct Transformation and Reduced-Pressure Chemical Pathways.

Phase-pure samples of a metastable allotrope of silicon, Si-III or BC8, were synthesized by direct elemental transformation at 14 GPa and ∼900 K and also at significantly reduced pressure in the Na-Si system at 9.5 GPa by quenching from high temperatures ∼1000 K. Pure sintered polycrystalline ingots with dimensions ranging from 0.5 to 2 mm can be easily recovered at ambient conditions. The chemical route also allowed us to decrease the synthetic pressures to as low as 7 GPa, while pressures required for direct phase transition in elemental silicon are significantly higher. In situ control of the synthetic protocol, using synchrotron radiation, allowed us to observe the underlying mechanism of chemical interactions and phase transformations in the Na-Si system. Detailed characterization of Si-III using X-ray diffraction, Raman spectroscopy, (29)Si NMR spectroscopy, and transmission electron microscopy are discussed. These large-volume syntheses at significantly reduced pressures extend the range of possible future bulk characterization methods and applications.

Synthesis and characterization of metastable transition metal oxides and oxide nitrides

Abstract New routes to vanadium sesquioxide and tantalum oxide nitride (γ- and δ-phase) are presented. Phase pure V2O3 with bixbyite-type structure, a metastable polymorph, was obtained from vanadium fluoride hydrates at ~750 K. It crystallizes in the cubic crystal system in space group I a 3 ¯ $Ia\bar 3$ with lattice parameter a=939.30(5) pm. The catalytical properties of the corresponding oxide nitride phases and their oxidation and reduction solid-state kinetics were investigated. The preparation of γ-TaON as a phase pure sample can be realized by ammonolysis of X-ray amorphous tantalum oxide precursors at 1073 K. This metastable tantalum oxide nitride crystallizes in the monoclinic VO2(B)-type structure in space group C2/m. The same precursors can be used to synthesize the δ-modification with an anatase-type structure at 1023 K. It crystallizes in the tetragonal crystal system in space group I41/amd. A maximum yield of 82 m % could be obtained. The fundamental band gaps of the synthesized and of other metastable TaON polymorphs were calculated from first principles using the GW method. The present results are compared to experimental data and to previous calculations at hybrid DFT level.

Ultrasound-enhanced milling in the synthesis of phase-pure, highly crystalline ZnAl-layered double hydroxide of low Zn(II) content

Dry milling followed by ultrasonic irradiation in the presence of small amounts of aqueous NaOH, was used to synthesise ZnAl-layered double hydroxide (LDH). The synthetic conditions were optimised and the Zn(OH)2, ZnO, and Al(OH)3 contaminants were removed by rinsing with aqueous NH3 solution from the sample prepared in the optimum conditions. Thus, phase-pure ZnAl-layered double hydroxide was obtained with high crystallinity. All materials produced during the syntheses were characterised by X-ray diffractometry, and a rose-like morphology was observed by scanning electron microscopy in the phase-pure sample. By changing the initial Zn/Al ratio, it was revealed that an LDH with low zinc content was always formed, probably through substitution of some of the Zn2+ ions by Al3+ ions in the gibbsite lattice.

Narrow band UVB emitting phosphor LaPO4:Gd3+ for phototherapy lamp

Gd3+ activated inorganic lanthanum phosphate (LaPO4) has been successfully synthesized using re-crystallization method. The crystal structure and the phase purity of samples were characterized using powder X-ray diffractometer. The surface morphology was studied using Scanning Electronic Microscope (SEM). The photoluminescence spectra was studied at room temperature. The excitation spectra of Gd3+ activated phosphor LaPO4 monitored at 312nm shows strong absorption at 275nm. Phosphor emitted at 312 under the excitation of 275nm due to 6PJ→8S7/2 transition of Gd3+ ions. Optimum concentration of Gd3+ ions in the prepared phosphor was found to be 0.04mol. For this concentration the critical distance R0 was calculated to be 15.37Å. Finally, the Stokes shift for the synthesized phosphor LaPO4: Gd3+ was calculated to be 4312cm−1.

Co and Cu co-doped ZnO epitaxial films—A magnetically soft nano-composite

A series of Co/Cu co-doped ZnO epitaxial films has been grown on sapphire substrates to investigate the possibilities of tailoring the magnetic properties in functional ZnO-Co/Cu nano-composites. The growth was performed using reactive magnetron sputtering varying the oxygen partial pressure to tune the incorporation of the dopants and the resulting valence state. At high oxygen pressures, Co2+ is formed and the resulting magnetic properties are very similar to phase pure paramagnetic Co-doped ZnO samples. However, the formation of a secondary CuO phase reduces the overall structural quality of the layers and virtually no substitutional incorporation of Cu2+ in ZnO could be evidenced. At low oxygen pressures, a significant fraction of metallic Co and Cu forming nanometer-sized superparamagnetic precipitates of a Co/Cu alloy can be evidenced which are embedded in a ZnO host matrix.

On new ternary equiatomic scandium transition metal aluminum compounds ScTAl with T = Cr, Ru, Ag, Re, Pt, and Au

Abstract The new equiatomic scandium transition metal aluminides ScTAl for T = Cr, Ru, Ag, Re, Pt, and Au were obtained by arc-melting of the elements followed by subsequent annealing for crystal growth. The samples were studied by powder and single crystal X-ray diffraction. The structures of three compounds were refined from single crystal X-ray diffractometer data: ScCrAl, MgZn2 type, P63/mmc, a = 525.77(3), c = 858.68(5) pm, R 1 = 0.0188, wR 2 = 0.0485, 204 F 2 values, 13 variables, ScPtAl, TiNiSi type, Pnma, a = 642.83(4), b = 428.96(2), c = 754.54(5) pm, R 1 = 0.0326, wR 2 = 0.0458, 448 F 2 values, 20 variables and ScAuAl, HfRhSn type, P6̅2c, a = 722.88(4), c = 724.15(4) pm, R 1 = 0.0316, wR 2 = 0.0653, 512 F 2 values, 18 variables. Phase pure samples of all compounds were furthermore investigated by magnetic susceptibility measurements, and Pauli-paramagnetism but no superconductivity was observed down to 2.1 K for all of them. The local structural features and disordering phenomena have been characterized by 27Al and 45Sc magic angle spinning (MAS) and static NMR spectroscopic investigations.

Thermal evolution of the spin ordering at the concomitant spin–orbital rearrangement temperature in RVO3 (R=Lu, Yb and Tm)

Synthesis, crystal structure and magnetization measurements of phase pure polycrystalline RVO3 (R=Lu, Yb and Tm) are reported. The compounds were stabilized in the orthorhombic structure by thermal treatment of the respective precursors (RVO4) in a reducing atmosphere. Special pressure treatment was carried out during the synthesis to ensure phase pure samples without secondary phases. Magnetization measurements reveal the presence of two spin ordering temperatures in the samples. Interestingly, at the lower spin ordering temperature, TSO2, the uncompensated excess moment of the antiferromagnetic spin structure has different field dependences above and below TSO2, causing a jump in the thermal evolution of the magnetization that changes sign with increasing field strength. This jump is associated with the reported magnetic and orbital rearrangement in the samples, and the different spin configurations in the C- and G-type antiferromagnetic structures.

Antimony oxofluorides - a synthesis concept that yields phase pure samples and single crystals.

The single crystals of the new isostructural compounds Sb3O4F and Y0.5Sb2.5O4F and the two previously known compounds M-SbOF and α-Sb3O2F5 were successfully grown by a hydrothermal technique at 230 °C. The new compound Sb3O4F crystallizes in the monoclinic space group P21/c; a = 5.6107(5) Å, b = 4.6847(5) Å, c = 20.2256(18) Å, β = 94.145(8)°, z = 4. The replacing part of Sb with Y means a slight increase in the unit cell dimensions. The compounds M-SbOF and α-Sb3O2F5 have not been grown as single crystals before and it can be concluded that hydrothermal synthesis has proved to be a suitable technique for growing single crystals of antimony oxofluorides because of the relatively low solubility of such compounds compared to other antimony oxohalides that most often have been synthesised at high temperatures by solid state reactions or gas-solid reactions.

Intrinsic blue-white luminescence, luminescence color tunability, synthesis, structure, and polymorphism of K3YSi2O7

Two polymorphs of K3YSi2O7, crystallizing in the space groups P63/mmc (1) and P63/mcm (2) can be synthesized by high temperature flux crystal growth. The flux growth conditions can be fine-tuned to yield a phase pure sample of polymorph (2), however, not of polymorph (1), which always co-crystallizes with polymorph (2). Polymorph (2) was found to exhibit intrinsic bluish-white light emission. Further studies determined that doping europium and dysprosium onto the yttrium site of this polymorph could readily tune the luminescence, with the purest white light emission found for the K3YSi2O7: 10% Dy, 0.1% Eu composition (K3Y0.899Dy0.1Eu0.001Si2O7) (2-Dy,Eu).

Magnesium and cadmium containing Heusler phases REPd2Mg, REPd2Cd, REAg2Mg, REAu2Mg and REAu2Cd

Twenty-eight new Heusler phases REPd2Mg, REPd2Cd, REAg2Mg, REAu2Mg and REAu2Cd with different rare earth elements were synthesized from the elements in sealed niobium ampoules in a water-cooled sample chamber of an induction furnace. The samples were characterized by powder X-ray diffraction. The cell volumes show the expected lanthanide contraction. The structures of YPd2Cd, GdPd2Cd, GdAu2Cd, Y1.12Ag2Mg0.88 and GdAg2Mg were refined based on single crystal diffractometer data. The magnetic properties were determined for fifteen phase pure samples. LuAu2Mg is a weak Pauli paramagnet with a susceptibility of 1.0(2) × 10−5 emu mol−1 at room temperature. The remaining samples show stable trivalent rare earth ions and most of them order magnetically at low temperatures. The ferromagnet GdAg2Mg shows the highest ordering temperature of TC = 98.3 K. 113Cd and 89Y MAS NMR spectra of YAu2Cd and YPd2Cd confirm the presence of unique crystallographic sites. The resonances are characterized by large Knight shifts, whose magnitude can be correlated with electronegativity trends.

Blue-Emitting Sr3Si8–xAlxO7+xN8–x:Eu2+ Discovered by a Single-Particle-Diagnosis Approach: Crystal Structure, Luminescence, Scale-Up Synthesis, and Its Abnormal Thermal Quenching Behavior

The single-particle-diagnosis approach allows for the fast discovery of novel luminescent materials using powdered samples. This paper reports a new blue-emitting Sr3Si8–xAlxO7+xN8–x:Eu2+ phosphor for solid state lighting and its scale-up synthesis. The structure-, composition-, and temperature-dependent luminescence were investigated and discussed by means of various analytic techniques including single-crystal XRD diffractometer, single-particle fluorescence spectroscopy, FTIR spectra, decay time, low-temperature luminescence, and computed energy level scheme. Sr3Si8–xAlxO7+xN8–x crystallizes in the monoclinic system (space group C2/c, no. 15) with a = 18.1828 (13) A, b = 4.9721 (4) A, c = 15.9557 (12) A, β = 115.994 (10)ο, and Z = 2. The Sr atoms are coordinated to 8 and 6 O/N atoms and located in the voids along [010] formed by vertex-sharing (Si,Al)-(O,N)4 tetrahedra. Phase-pure powder samples of Sr3Si8–xAlxO7+xN8–x:Eu2+ were synthesized from the chemical composition of the single particle by control...

Effect of Synthetic Levers on Nickel Phosphide Nanoparticle Formation: Ni5P4 and NiP2.

Due to their unique catalytic, electronic, and redox processes, Ni5P4 and NiP2 nanoparticles are of interest for a wide-range of applications from the hydrogen evolution reaction to energy storage (batteries); yet synthetic approaches to these materials are limited. In the present work, a phase-control strategy enabling the arrested-precipitation synthesis of nanoparticles of Ni5P4 and NiP2 as phase-pure samples using different Ni organometallic precursors and trioctylphosphine (TOP) is described. The composition and purity of the product can be tuned by changing key synthetic levers, including the Ni precursor, the oleylamine (OAm) coordinating solvent and TOP concentrations, temperature, time, and the presence or absence of a moderate temperature soak step to facilitate formation of Ni and/or Ni-P amorphous nanoparticle intermediates. Notably, the 230 °C intermediate step favors the ultimate formation of Ni2P and hinders further phosphidation to form Ni5P4 or NiP2 as phase-pure products. In the absence of this step, increasing the P/Ni ratio (13-20), reaction temperature (350-385 °C), and time (10-48 h) favors more P-rich phases, and these parameters can be adjusted to generate either Ni5P4 or NiP2. The phase of the obtained particles can also be tuned between pure Ni2P to Ni5P4 and NiP2 by simply decreasing the OAm/TOP ratio and/or changing the nickel precursor (nickel(II)acetylacetonate, nickel(II)acetate tetrahydrate, or bis(cyclooctadiene)nickel(0)). However, at high concentrations of OAm, the product formed is the same regardless of Ni precursor, suggesting the formation of a uniform Ni intermediate (an Ni-oleylamine complex) under these conditions that is responsible for product distribution. Intriguingly, under the extreme phosphidation conditions required to favor Ni5P4 and NiP2 over Ni2P (large excess of TOP), the 20-30 nm crystallites assemble into supraparticles with diameters of 100-500 nm. These factors are discussed in light of a comprehensive synthetic scheme utilized to control P incorporation in nickel phosphides.

Final-state effect on x-ray photoelectron spectrum of nominallyd1andn-dopedd0transition-metal oxides

We investigate the x-ray photoelectron spectroscopy (XPS) of nominally ${d}^{1}$ and $n$-doped ${d}^{0}$ transition-metal oxides including ${\mathrm{NbO}}_{2},\phantom{\rule{0.16em}{0ex}}{\mathrm{SrVO}}_{3}$, and ${\mathrm{LaTiO}}_{3}$ (nominally ${d}^{1}$), as well as $n$-doped ${\mathrm{SrTiO}}_{3}$ (nominally ${d}^{0}$). In the case of single phase ${d}^{1}$ oxides, we find that the XPS spectra (specifically photoelectrons from Nb $3d$, V $2p$, Ti $2p$ core levels) all display at least two, and sometimes three distinct components, which can be consistently identified as ${d}^{0},\phantom{\rule{0.16em}{0ex}}{d}^{1}$, and ${d}^{2}$ oxidation states (with decreasing order in binding energy). Electron doping increases the ${d}^{2}$ component but decreases the ${d}^{0}$ component, whereas hole doping reverses this trend; a single ${d}^{1}$ peak is never observed, and the ${d}^{0}$ peak is always present even in phase-pure samples. In the case of $n$-doped ${\mathrm{SrTiO}}_{3}$, the ${d}^{1}$ component appears as a weak shoulder with respect to the main ${d}^{0}$ peak. We argue that these multiple peaks should be understood as being due to the final-state effect and are intrinsic to the materials. Their presence does not necessarily imply the existence of spatially localized ions of different oxidation states nor of separate phases. A simple model is provided to illustrate this interpretation, and several experiments are discussed accordingly. The key parameter to determine the relative importance between the initial-state and final-state effects is also pointed out.

Navigating the Waters of Unconventional Crystalline Hydrates.

Elucidating the crystal structures, transformations, and thermodynamics of the two zwitterionic hydrates (Hy2 and HyA) of 3-(4-dibenzo[b,f][1,4]oxepin-11-yl-piperazin-1-yl)-2,2-dimethylpropanoic acid (DB7) rationalizes the complex interplay of temperature, water activity, and pH on the solid form stability and transformation pathways to three neutral anhydrate polymorphs (Forms I, II°, and III). HyA contains 1.29 to 1.95 molecules of water per DB7 zwitterion (DB7z). Removal of the essential water stabilizing HyA causes it to collapse to an amorphous phase, frequently concomitantly nucleating the stable anhydrate Forms I and II°. Hy2 is a stoichiometric dihydrate and the only known precursor to Form III, a high energy disordered anhydrate, with the level of disorder depending on the drying conditions. X-ray crystallography, solid state NMR, and H/D exchange experiments on highly crystalline phase pure samples obtained by exquisite control over crystallization, filtration, and drying conditions, along with computational modeling, provided a molecular level understanding of this system. The slow rates of many transformations and sensitivity of equilibria to exact conditions, arising from its varying static and dynamic disorder and water mobility in different phases, meant that characterizing DB7 hydration in terms of simplified hydrate classifications was inappropriate for developing this pharmaceutical.

Synthesis of Polycrystalline LaYO<sub>3</sub> with Different Sintering Temperature

Synthesis of LaYO3 was carried out via conventional solid state reaction method. The polycrystalline samples were sintered at temperatures in the range of 1300 °C to 1500 °C with each deviation is 50 °C. X-ray diffraction (XRD) analysis indicated that the perovskite ceramic obtained its single phase at 1500 °C with ordered monoclinic perovskite structure. The pure phase sample showed 98.79 % relative density and scanning electron micrographs also proved that the porosity of the sample reduced when sample undergo sintering.

Influence of gradual cobalt substitution on lithium nickel phosphate nano-scale composites for high voltage applications

The carbon-free LiNiPO4 and cobalt doped LiNi1−xCoxPO4/C (x=0.0–1.0) were synthesized and investigated for high voltage applications (>4V) for Li-ion batteries. Nano-scale composites were prepared by handy sol–gel approach using citric acid under slightly reductive gas atmosphere (Ar-H2, 85:15%). Structural and morphological characteristics of the powders were revealed by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM) and inductively coupled plasma (ICP). Except for a small impurity phase (Ni3P), phase pure samples crystallized in the olivine-lattice structure with a linear relationship between lattice parameters (a, b and c) and chemical composition. The FE-SEM images proved that LiNiPO4/C particles (50–80nm) did not agglomerate, and showed that as the cobalt content was higher agglomeration had increased. The electrochemical properties of all electrodes were investigated by galvanostatic charge–discharge measurements. Substitution of Ni2+ by Co2+ caused higher electronic conductivities and showed more effective Li+ ion mobility. When the cobalt content is 100%, the capacity reached to a higher level (146.2mAhg−1) and good capacity retention of 85.1% at the end of the 60cycles was observed. The cycling voltammogram (CV) revealed that LiCoPO4/C electrode improved the electrochemical properties. The Ni3+–Ni2+ redox couple was not observed for carbon free LiNiPO4. Nevertheless, it was observed that carbon coated LiNiPO4 sample exhibits a significant oxidation (5.26V)–reduction (5.08V) peaks. With this study, characteristics of the LiNi1−xCoxPO4/C series were deeply evaluated and discussed.

Enhancement of persistent luminescence of ZnTa2O6:Pr3+ by addition Li+, Na+, K+ and Cs+ ions

Enhancement of the persistent emission was achieved by co-doping ZnTa2O6:Pr3+ with Li+, Na+, K+ or Cs+ ions. Phase pure samples were synthesised and it was confirmed by the X-ray diffraction pattern which matches that of the standard data. Incorporation of the co-dopant ions introduced strain into the phosphor, which increased with an increase in the ionic radius of the co-dopant ion. The scanning electron microscope image shows that the particles were agglomerated, and the surface images obtained using the Time of flight secondary ion mass spectroscopy showed that the dopant and the co-dopant ions in the phosphor were homogeneously distributed. The persistent emission was enhanced by the co-dopant ions as shown by the lifetime values calculated from the phosphorescence decay curves, and the corresponding electron trapping centres were quantified by thermoluminescence reader.