Phase Purity Of Samples Research Articles

Structure and optical properties of LixAg1–xAlSe2

The complete solid solution LixAg1–xAlSe2 was prepared at 850 °C in the form of phase-pure powder samples as well as single crystals. They adopt noncentrosymmetric crystal structures belonging to the tetragonal CuFeS2-type (space group I4‾2d) for x = 0–0.5 and orthorhombic β-NaFeO2-type (space group Pna21) for x = 0.6–1, both being built up from corner-sharing metal-centred tetrahedra and exhibiting complete disorder of Li and Ag atoms. Solid-state 7Li NMR spectra support the presence of unique Li sites. The substitution of Li for Ag atoms allows control of optical band gaps, which increase linearly from 2.7 eV to 3.6 eV. Second harmonic generation responses were measured to evaluate the potential of these compounds as infrared nonlinear optical materials.

Comprehensive investigation into the influence of oxygen vacancies on the ferroelectric properties of spin coated bismuth ferrite thin films

Bismuth ferrite (BFO) is a prime candidate for room-temperature magnetoelectric coupling and multiferroic applications. The rhombohedral R3c phase of BFO is the source of many properties, but the phase purity and oxygen vacancies are still the biggest obstacles to its real-world application. Considering these facts, the present work investigates the effects of oxygen vacancies on the functional properties through manipulation of drying temperatures of spin-cast films, especially at temperatures around 280 °C, where both the secondary phase and oxygen vacancies are prevalent. One of the biggest sources of oxygen vacancy is bismuth volatilisation, and our work deals with the situation head-on, uncovering the effect of bismuth volatilisation on functional properties. The structural properties were studied using x-ray diffraction (XRD), and deeper insights into the surface topography of the samples were obtained using AFM imaging. The electrical and dielectric characteristics help distinguish and analyse the samples in terms of the presence of resistive switching. PUND studies were performed to determine the ferroelectric properties of the samples. A fifty percent reduction in the oxygen vacancies in the presence of secondary phases was observed when compared with the phase-pure sample, as shown by the XPS analysis. Deeper insights were provided into the valence band spectra by first-principles studies. This work shows that phase purity may not be the singular condition for enhancing functional properties, and fine-tuning the presence of secondary phases and oxygen vacancies may be the way forward. The ferroelectric polarisation in one of the samples exhibits a notably higher value when using chemical solution deposition methods, making it a promising candidate for memory devices.

Thermoelectric and photovoltaic properties of 12-BaBi2S4

In this report, we have investigated the structure and properties of the 12-BaBi2S4. A single crystal X-ray diffraction study shows that the 12-BaBi2S4 crystallizes in the hexagonal crystal system (space group = P63/m) with refined lattice parameters of a = b = 25.2687(10) Å, c = 4.1859(2) Å, and formula unit = Z = 12 at room temperature. The structure contains fifteen crystallographic independent sites, including three Ba, four Bi, and eight types of S atoms. A phase pure polycrystalline sample of 12-BaBi2S4 was synthesized by heating stoichiometric amounts of BaCO3 and Bi2O3 under a CS2 atmosphere. The phase pure sample is found to be a semiconductor with a direct bandgap of 1.3(1) eV. The polycrystalline 12-BaBi2S4 exhibits ultra-low thermal conductivity values, varying from 0.47 Wm−1K−1 at 323 K to 0.43 Wm−1K−1 at 773 K. The sample shows high values of the Seebeck coefficient (S = −300 μV/K to −210 μV/K) in the 323 K–773 K range with poor electrical conductivity values. The negative sign of the S implies that the sample is a n-type semiconductor. DFT studies of the 12-BaBi2S4 also predict semiconducting properties. We have explored the 12-BaBi2S4 sample for photovoltaic (PV) applications by fabricating a liquid junction solar cell, TiO2/CdS/12-BaBi2S4/Sn2−/S2−/MWCNTs@Ni, which delivered an efficiency enhanced by ∼12 % to the control cell based on sole CdS as the photo-sensitizer. Theoretical electronic structure calculations suggest the semiconducting nature of the 12-BaBi2S4 in agreement with the optical absorption and electrical resistivity studies.

An expanded plasma jet assisted technique for very high-rate synthesis of 2D α-MoO3 nanomaterials, with surface oxygen vacancies and robust induced ferromagnetism

This article reports a novel, clean and energy-efficient thermal-plasma assisted synthesis technique, for very high rate production of defective, ferromagnetic, 2D stoichiometric molybdenum-oxide, maximum up to 750 g/h, but without compromising with the sizes of the nanomaterials or their state of aggregation. A collimated, laminar beam of plasma with large cross-section and uniform profile is produced as the jet expands supersonically into a vacuum chamber that engulfs a large molybdenum target plate and heat it up in a controlled manner. The surface of the target is rapidly oxidized into a sublimating vapour, from which nanometric metal-oxides are nucleated through gas phase condensation process. Surface oxygen-defects are introduced into the product, but even without employing an additional step of defect-engineering, which endowed them with robust room-temperature ferromagnetic properties (maximum saturation magnetization = 1.84 emu/g) and easy dispersibility in aqueous solutions. It is further demonstrated that the as-synthesized, phase-pure α-MoO3 sample with hierarchical morphology can adsorb cationic methylene blue (MB) dyes from an aqueous solution at 94.1 % in 30 min, and the corresponding maximum adsorption capacity is 1045.9 mg/g. The ferromagnetic nanoadsorbents may be separated from wastewater with a simple lab scale magnetic field, to reduce secondary pollution and for reuse of the adsorbents.

In-situ synthesis of carbon-coated Mo2C: An exceptionally efficient and robust electrocatalyst for hydrogen evolution reaction (HER)

In the present work, the Mo2C electrocatalyst has been synthesized using waste plastic as carbon source. The use of plastic bottle has been chosen to reduce the cost of electrocatalyst as well to address the environmental issues caused due to these wastes. The pure phase sample was synthesized at 800 °C by carburizing MoO3 in an autoclave. The synthesized sample shows high activity towards HER with a lower Tafel slope of 85.7 mVdec−1. One of the exceptional features of the developed electrocatalyst is the long-term stability up to 7 days as determined by chronopotentiometry results. The improved activity and stability have been attributed to the presence of graphene like structures encapsulating the Mo2C particles. The presence of carbon also shows higher storage ability with an electrochemical double layer capacitance (EDLC, Cdl) of 91.0 μF. The synthesized sample shows an efficient and stable electrocatalyst towards HER.

Investigating the Effect of Co-doping on Structural and Electrical Properties of Li7La3Zr2O12 Solid Electrolyte

Garnet-type Li<sub>7</sub>La<sub>3</sub>Zr<sub>2</sub>O<sub>12</sub> (LLZO) has garnered significant attention for solid-state Li-ion batteries due to its commendable Li-ion conductivity, wide electrochemical window, and exceptional chemical and thermal stability. Nonetheless, challenges related to structural instability and air stability persist, impeding its market expansion. Herein, we explore the effects of co-doping (Ga with Sc/Y/In/Er) on the crystal structure and Li-ion conductivity of LLZO through x-ray diffraction (XRD), scanning electron microscope (SEM), and AC impedance measurements. XRD refinement confirms the formation of pure-phase samples with a cubic crystal structure. SEM analysis reveals a dense microstructure with grain sizes exceeding 200 μm and a relative density approaching∼94%. While Ga/Sc and Ga/Y doped LLZO exhibit relatively lower Li-ion conductivity, Ga/Er and Ga/In doped samples demonstrate high conductivity more than 1 mS/cm at room temperature (25°C). Thus, the judicious selection of dopants emerges as an effective strategy for enhancing conductivity in all-solid-state batteries.

Modifying the valence phase transition in Eu2Al15Pt6 by the solid solutions Eu2Al15(Pt1−x T x )6 (T = Pd, Ir, Au; x = 1/6)

Abstract The solid solutions Eu2Al15(Pt1−x T x )6 with T = Pd, Ir, Au and x = 1/6 were prepared by arc-melting the stoichiometric mixture of the elements, and subsequent annealing. For x = 1/6, all three solid solutions adopt the same structure type as Eu2Al15Pt6 according to powder X-ray diffraction data. Since the platinide Eu2Al15Pt6 exhibits a (3 + 1)D modulated structure (approximant in space group P121/m1), only the averaged hexagonal unit cell (P63/mmc, Sc0.6Fe2Si4.9 type) was refined by the Rietveld method. Scanning electron microscopy in combination with energy-dispersive X-ray spectroscopy (SEM/EDX) showed that the degree of substitution is in line with the weighed amounts. For values of x > 1/6, no phase-pure samples could be obtained. The results of the magnetic susceptibility measurements indicate that the isoelectronic substitution of Pd for Pt lowers the temperature of the first-order valence phase transition from T trans = 45 K in Eu2Al15Pt6 to T trans = 42 K in Eu2Al15(Pt5/6Pd1/6)6. For Eu2Al15(Pt5/6Ir1/6)6 and Eu2Al15(Pt5/6Au1/6)6 a change in the electronic situation occurs since the Ir substituted compound exhibits one electron less compared to the pristine Pt compound, while Eu2Al15(Pt5/6Au1/6)6 has one additional electron. As a consequence, Eu2Al15(Pt5/6Ir1/6)6 shows a higher valence phase transition temperature of T trans = 52 K while for Eu2Al15(Pt5/6Au1/6)6 no such transition is obvious.

Band alignment and interfacial charge transfer in sol-gel derived anatase/rutile heterophase TiO2: explaining the synergistic photocatalytic activity.

In this study, we have synthesized nanostructured titanium dioxide (TiO2) photocatalysts under different configurations, viz., anatase, rutile and anatase/rutile heterophase (Eg = 3.14-2.96 eV) through a sol-gel route. The photocatalytic performance of the heterophase samples was better than that of their phase-pure counterparts. Photocatalytic performance was maximum for sample T12H (50% rutile) with a rate constant, k = (7.38 ± 1.48) × 10-2 min-1. This is ca. 47% greater than that estimated via an extrapolation method using the values for phase pure samples indicating synergistic effects. High-resolution transmission electron microscope (HRTEM) analysis and the phase-dependent broadening of core-level X-ray photoelectron spectroscopy (XPS) analysis indicate the formation of well-defined anatase/rutile interfaces. Interfacial charge transfer is the critical factor for this synergistic effect. To analyze the charge transfer pathways, the possible band alignment scheme was analyzed through the precise determination of band alignments from XPS, employing the Ti 2p3/2 core level as a reference. We found a staggered rutile band alignment with the valence band edge of rutile lying above that of anatase, indicating the transfer of photogenerated free electrons from the conduction band of rutile to that of anatase and hole transfer from the valence band of anatase to rutile. These inferences are validated through Mott-Schottky analysis as well.

Pt5Mn2Si, the first platinum-rich ternary intermetallic of the Rh5Ge3 structure type: Synthesis, crystal and electronic structure, and magnetic properties

New ternary intermetallic Pt5Mn2Si was obtained in the form of single crystals and phase-pure polycrystalline bulk samples. This compound is only the second one found in the Pt–Mn–Si system. Pt5Mn2Si (space group Pbam, a = 5.4355(3) Å, b = 10.5955(7) Å, c = 4.0024(3) Å, Z = 2) is isotypic with the Rh5Ga2As structure, an ordered ternary variation of the Rh5Ge3 structure type. This structure type is fairly rare, and Pt5Mn2Si is only the second ternary intermetallic adopting this structure. Magnetic measurements show that the compound has magnetic transition at ca. 80 K, most likely attributed to ferrimagnetic ordering of manganese spins. DFT calculations predict Pt5Mn2Si to be a metallic conductor. Chemical bonding analysis shows a pattern of localized pairwise-like Pt–Mn and Pt–Si bonds.

Boron Chalcogen Mixture Method-Assisted Alkali Halide Flux Crystal Growth of an Extensive Family of Quaternary Rare Earth Transition-Metal Thiosilicates: Investigation of Their Structures and Magnetic Properties.

A series of transition-metal-containing rare earth thiosilicates, RE3TM0.5SiS7 (RE = Gd-Yb; TM = Fe, Co, Ni), was obtained via flux crystal growth utilizing the boron chalcogen mixture (BCM) method. The series includes the first reported ytterbium-containing thiosilicates crystallizing in this structure type. The thiosilicates crystallize in the hexagonal crystal system in space group P63. The use of the BCM method to synthesize phase-pure samples of the title compounds for magnetic measurements is discussed, highlighting how the approach avoids some of the difficulties that plague typical chalcogenide syntheses. Magnetic measurements demonstrate that some of the compounds order antiferromagnetically and exhibit transition temperatures below 15 K.

Experiment and Theory in Concert To Unravel the Remarkable Electronic Properties of Na-Doped Eu11Zn4Sn2As12: A Layered Zintl Phase.

Low-dimensional materials have unique optical, electronic, mechanical, and chemical properties that make them desirable for a wide range of applications. Nano-scaling materials to confine transport in at least one direction is a common method of designing materials with low-dimensional electronic structures. However, bulk materials give rise to low-dimensional electronic structures when bonding is highly anisotropic. Layered Zintl phases are excellent candidates for investigation due to their directional bonding, structural variety, and tunability. However, the complexity of the structure and composition of many layered Zintl phases poses a challenge for producing phase-pure bulk samples to characterize. Eu11Zn4Sn2As12 is a layered Zintl phase of significant complexity that is of interest for its magnetic, electronic, and thermoelectric properties. To prepare phase-pure Eu11-xNaxZn4Sn2As12, a binary EuAs phase was employed as a precursor, along with NaH. Experimental measurements reveal low thermal conductivity and a high Seebeck coefficient, while theoretical electronic structure calculations reveal a transition from a 3D to 2D electronic structure with increasing carrier concentration. Simulated thermoelectric properties also indicate anisotropic transport, and thermoelectric property measurements confirm the nonparabolicity of the relevant bands near the Fermi energy. Thermoelectric efficiency is known to improve as the dimensionality of the electronic structure is decreased, making this a promising material for further optimization and opening the door to further exploitation of layered Zintl phases with low-dimensional electronic structures for thermoelectric applications.

Cementite-type Y3Ru

Abstract Single crystals of Y3Ru were obtained as a side product during phase analytical studies of yttrium-rich compounds in the system Y–Ru–Zn. The structure of Y3Ru was refined from single-crystal X-ray diffractometer data: Fe3C type, Pnma, a = 732.51(7), b = 925.61(8), c = 633.66(10) pm, wR = 0.0639, 811 F 2 values, 23 variables. The ruthenium atoms have coordination number 9 in form of a strongly distorted tricapped trigonal yttrium prism with Ru–Y distances ranging from 275–391 pm. The second substructure concerns empty Y6 octahedra (d(Y–Y) = 344–396 pm). Electronic structure calculations show a net charge transfer from yttrium to ruthenium and underpin the essentially covalent Y–Ru bonding. A phase-pure sample of Y3Ru was synthesized from the elements by arc-melting. Temperature-dependent magnetic susceptibility studies of this sample reveal Pauli paramagnetism (3.6(1) × 10−5 emu mol−1 at T = 300 K).

Perspective on dielectric properties of calcium copper titanate ceramics

Calcium Copper Titanium Oxide (CCTO) Ceramics of composition CaCu3Ti4O12 has emerged as a lead-free ceramic supercapacitor with a large dielectric constant of 104–105 at room temperature. The CCTO microstructure is electrically heterogeneous composed of semiconducting grains and insulating grain boundaries. The origin of the large dielectric constant has therefore been widely attributed to barrier layer capacitance originated at grain boundaries. Our research is focused on understanding the stability and reproducibility of the measured electrical and dielectric properties when they are used as capacitor dielectrics because of the inconsistent results obtained when tested in ambient conditions. The origin of this inconsistency is investigated through the roles of testing atmosphere, sample thickness and doping with alumina on the stability and reproducibility of dielectric properties of CCTO. The solid state reaction method is used to fabricate phase pure and dense samples. AC impedance spectroscopy is used to study the roles of testing atmospheres, temperatures, microstructures, grain boundaries, sample thickness, alumina doping and frequency on the dielectric properties. It is shown that this approach of characterizing fundamental electrical properties of CCTO can be used to eliminate hysteresis to produce stable and reproducible dielectric properties. These perspectives are presented and discussed.

Study of Zn-Zr dopant induced phase changes in strontium hexaferrite using Rietveld refinement and their physical properties

In this study, we report the impact of high concentration of Zn and Zr dopants on the structural, surface morphological and magnetic characteristics of SrFe12O19(SFO) sample. The SrZn1.5Zr1.5Fe9O19 (SZFO) sample was targeted for preparation by giving calcination treatment at 1200 °C for six hours. The Rietveld analysis revealed that certain diffraction peaks in the SZFO sample could not be explained by a single-phase (using the P63/mmc space group) implying the sample to be phase impure. The multiple phase Rietveld analysis further revealed that a five-phase structural model (comprising SZFO, ZnFe2O4, ZrO2(Monoclinic&tetragonal) and SrZrO3 phases) was needed to account for all the diffraction peaks. The GoF (χ2) value for SZFO samples improved from 8.84 (with single phase model) to 1.17 (with five phase model). The surface morphological and magnetic properties of these samples have been compared against the corresponding properties of phase pure SFO sample.

Molten-chlorides assisted rapid preparation and crystallinity-irrelevant properties of nanostructured LiCoO2 as lithium-ion battery cathodes

In this paper, the 850 °C molten-chlorides (NaCl-KCl, eutectic point ∼657 °C) assisted reaction of Co3O4 (melting point ∼895 °C) with LiOH⋅H2O (melting point ∼462 °C) is adopted for the precursor shape-replicated construction of nanostructured LiCoO2, focusing on the rapid formation mechanism and crystallization-irrelevant properties of phase-pure LiCoO2 for Li-ion battery (LIB) cathodes. Temperature−/time-dependent crystallization shows that, after the heterogeneous nucleation of LiCoO2 at 660 °C, the complete consumption of Co3O4 occurs at 850 °C within 10 min and the building block of each of the finally resulting 850 °C/8-h LiCoO2 microspheres has been endowed with a (003)-manifest crystal plane. By comparison, it is due to the complete consumption of Li-insulating Co3O4, not to the increase of LiCoO2 crystallinity, that explains the high electrochemical properties of these phase-pure samples. Especially, cycling stabilities of the 850 °C/10-min and 850 °C/8-h LiCoO2 are close to each other, but each of them is much better than those of the chlorides-absent counterparts obtained at the node of 850 °C/8-h. These, together with the approximate rate capabilities of these chlorides-present LiCoO2, implies an applicable approach of the molten-salt method to the rapid construction of nanostructured LiCoO2 for high-performance LIB cathodes.

Probing the electrocatalytic activity of hierarchically mesoporous M-Co3O4 (M = Ni, Zn, and Mn) with branched pattern for oxygen evolution reaction

The large-scale production of hydrogen energy from the electrolysis of water requires earth-abundant and highly efficient oxygen evolution electrocatalysts. Cation substitution in spinel cobaltite is an efficient approach to tune electronic structure and improve their electrocatalytic activity towards oxygen evolution reaction (OER). In this article, for the first time, we have prepared hierarchically nanostructured Mn, Ni and Zn doped Co3O4 having a branching pattern via a simple hydrothermal and calcination method, and the same was used as an electrocatalyst for OER. Different methods confirmed the doping of transition metal ions. The result of structural characterization shows the formation of pure phase samples without impurity. The tetrahedral and octahedral functional groups were explained by FTIR spectroscopy, confirming the formation of a spinel structure. Ni-doped Co3O4 showed an excellent OER performance with a current density of 10 mA/cm2 at an overpotential of 380 mV in 1 M KOH and a Tafel slope of 63.19 mV/dec in alkaline media. The detailed study unveiled that the large surface area, hierarchically nanostructured branching pattern with porous structure, presence of a high amount of oxygen vacancy and the synergistic effect of Ni and Co are beneficial for increased OER activity and stability of Ni-Co3O4.

Thermoelectric properties of Ag2Te prepared by one-step hot-pressing method

In this work, a series of Ag2Te samples were successfully prepared by the one-step hot-pressing method (OS-HP). The results showed that the microstructure and thermoelectric properties of the samples were greatly affected by temperature and pressure. X-ray diffraction revealed that pure phase samples of Ag2Te can be obtained by OS-HP with a temperature of 673 K and pressure of 10 ∼ 20 MPa in 2 h. The 673K-20 sample illustrated the largest ZT values owing to the relatively high Seebeck coefficient and low thermal conductivity. Overall, the OS-HP with appropriate temperature and pressure could serve as a route to efficiently prepare Ag2Te thermoelectric materials.

Long-range A-site cation disorder in NaA(MO4)2 (M = Mo, W) double scheelite oxides

Synchrotron X-ray and neutron powder diffraction methods have been used to obtain accurate long-range average structures of some double scheelite compounds of the type NaA(BO4)2 (A ​= ​La, Pr, Nd, Sm, Lu, and Bi; B = Mo, W) at room temperature. Phase pure samples were synthesized using standard solid-state methods. Rietveld refinements using combined synchrotron X-ray diffraction (SXRD) and neutron diffraction (NPD) revealed a random distribution of the Na and A-type cations regardless of the presence of 6s2 lone pairs (such as Bi3+) and the difference in oxidation states and ionic radii between the cations. The NaA(BO4)2 (A ​= ​La, Pr, Nd, Sm, Lu, and Bi) series displayed linear trends in lattice parameters and AO8 polyhedra volume with the ionic radius of the A-type cation for the lanthanoids, but a deviation from the trend was observed for A ​= ​Bi3+. The NaBi(BO4)2 structure has a smaller than expected unit cell volume than based on extrapolation from the corresponding NaLn(BO4)2 series, possibly due to short-range ordering of the 6s2 lone pair electrons.

Structural, magnetic and optical properties of Fe3O4@NaGdF4 core-shell composite

Nanoparticles as contrast agents for in-vitro and in-vivo imaging is the most astounding, non-invasive method developed by researchers in the present scenario. To improve the multifunctionality of bio-imaging field, both Magnetic resonance imaging (MRI) and fluorescence based nanoconstructs are appreciated. In this regard, current research is dedicated to fabricate Fe3O4@NaGdF4 core–shell structure as a multifunctional, efficient probe to be useful for said purpose. Concerned core–shell is constructed in layer-by-layer approach with Fe3O4 and NaGdF4 served as core and shell respectively. Phase purity of sample is investigated through X-ray diffraction (XRD) data, seen to have inverse spinel phased Fe3O4 core and hexagonal NaGdF4. Field emission scanning electron microscopy (FESEM) images clarified the average dimension of isolated core and shell grains to be 59.86 and 62.20 nm respectively. Formation of Core-shell is verified through HRTEM images. Fourier transform infrared (FTIR) spectroscopy data reveals the functional group associated with the corresponding components. Magnetic criteria of sample are studied through room temperature magnetic field dependent magnetization (M−H) data in the range of ± 1.5 Tesla. Non-magnetic shell is seen to be dominate on magnetic core for reducing the magnetic saturation value to 9.104 emu/g from 37.891 emu/g of isolated Fe3O4 sample. Downshifting luminescence is also detected through photoluminescence (PL) study in Ultraviolet (UV) B range (309 nm) due to excitation in UVC region (271 nm) of Gd3+ energy states.

Solvothermal synthesis of nanoscale BaTiO3 in benzyl alcohol-water mixtures and effects of manganese oxide coating to enhance the PTCR effect.

A solvothermal method using various benzyl alcohol/water solvent mixtures has been used to synthesise phase pure nanocrystalline BaTiO3 samples with varying particle sizes in the range of 11-139 nm. The crystallite/particle size of BaTiO3 shows an overall decrease as the benzyl alcohol percentage increases, especially at higher percentages (≥80%) of benzyl alcohol. The decrease in crystallite/particle size can be attributed to the increased viscosity of the solvent mixture when raising the percentage of benzyl alcohol. A manganese oxide coating applied to the BaTiO3 surface had a negligible impact on its microstructure and morphology, but significantly enhanced the observed positive temperature coefficient of resistance. This research has been carried out to allow the development of smaller BaTiO3 particles for use in new battery, capacitor and thermistor technologies, whilst maintaining the PTCR property of the material that is typically observed in larger particle sizes.