Search Results (17)

Neutron powder diffraction experiments were carried out to characterize mechanochemically synthesized (Fe₂O₃)_1−x(Al₂O₃)_x solid solutions with corundum-type structure, focusing on their lattice and magnetic structures with varying temperature and composition. The neutron diffraction experiments for (Fe₂O₃)_0.5(Al₂O₃)_0.5 in the temperature range between 4 K and 300 K reveal that no significant structural phase transition occurred. The behavior of temperature variation of lattice parameters is different from α-Fe₂O₃ and α-Al₂O₃ and reveals the thermal expansion coefficients of α_a = 5.76(2) × 10⁻⁶ K⁻¹ and α_c = 6.19(5) × 10⁻⁶ K⁻¹ between 200 K and 300 K. The room temperature neutron diffraction of (Fe₂O₃)_1−x(Al₂O₃)_x shows a linear decrease in lattice parameters with the aluminum substitution, following Vegard’s law, along with a decrease in the magnetic moment, indicating the dilution effect on spin interactions. With the increase in the aluminum substitution from x = 0 to 0.5, the deduced magnetic moment decreases from 2.224 μ_B to 0.862 μ_B. Full article

We report on the arc melt syntheses of HoB₂ and Nb-substituted HoB₂ polycrystalline ingots and their magnetocaloric and microstructural properties. XRD data and microstructural analysis reveal that a nominal 10% Nb addition during synthesis results in changes to unit cell parameters and grain morphology. Interpretation of the refined cell parameters using Vegard’s law shows that Nb substitutes into HoB₂ with stoichiometry Ho_0.93Nb_0.07B₂. Arc-melted products are polycrystalline bulk samples containing minor phases such as Ho₂O₃, Ho, and HoB₄. Nb substitution results in a smaller grain size (~sub-micron) and a higher Curie temperature, T_C, compared to HoB₂. With a 10 T applied field, the maximum magnetic entropy, ΔS_M, for HoB₂ and for Ho_0.93Nb_0.07B₂, is 46.8 Jkg⁻¹K⁻¹ and 38.2 Jkg⁻¹K⁻¹ at 18 K and 21 K, respectively. Both samples show second-order phase transitions. Despite high totals of minor phases (e.g., ~10 wt.% and ~25 wt.%), the calculated relative cooling powers are greater than 1300 Jkg⁻¹ and 600 Jkg⁻¹ at 10 T and 5 T, respectively. The magnetocaloric properties of both samples are consistent with Holmium boride compounds prepared via alternative methods. Full article

In addressing the global need for sustainable energy conversion, this study presents a breakthrough in thermoelectric materials research by optimizing the Bi₂O₂Se_1–xTe_x system in the Bi₂O₂Se/Bi₂O₂Te pseudobinary series. Leveraging the principles of innovative transport mechanisms and defect engineering, we introduce tellurium (Te) doping into Bi₂O₂Se to enhance its thermoelectric properties synergistically. With the help of various advanced characterization tools such as XRD, SEM, TEM, XPS, FTIR, TGA, LFA, and DSC, combined with relevant resistance and density measurement techniques, we conducted an in-depth exploration of the complex interactions between various factors within thermoelectric materials. We recognize that the balance and synergy of these factors in the thermoelectric conversion process are crucial to achieving efficient energy conversion. Through systematic research, we are committed to revealing the mechanisms of these interactions and providing a solid scientific foundation for the optimal design and performance enhancement of thermoelectric materials. Finally, the advantage coefficient (ZT) of the thermoelectric material has been significantly improved. The crystallographic analysis confirms the formation of a continuous series of mixed crystals with varying Te concentrations, adhering to Vegard’s law and exhibiting significant improvements in electrical and thermal conductivities. The Bi₂O₂Se_1–xTe_x crystals, particularly the Bi₂O₂Se_0.6Te_0.4 composition, demonstrate a peak ZT of 0.86 at 373 K. This achievement aligns with recent advancements in defect-enabled mechanisms and band convergence and sets a new standard for high-performance thermoelectrics. The study’s findings contribute significantly to the ongoing quest for efficient thermal-to-electrical energy conversion, offering a promising avenue for future sustainable energy technologies. Full article

In order to explore the mechanism of the influence of Sn contents on the relevant properties of Cu–Sn alloys, the structure, elasticity, electronic, and thermal properties of Cu–Sn alloys doped with different proportions of Sn (3.125 at%, 6.25 at%, and 9.375 at%) were established using the first-principles calculation based on density functional theory. Firstly, their lattice constants and Sn concentration comply with Vegard’s Law. From the mixing enthalpy, it can be seen that Sn atoms can be firmly dissolved in the Cu matrix, and the structure is most stable when the Sn content is 3.125 at%. In addition, the introduction of mismatch strain characterized their solid solution strengthening effect. The elastic and electronic properties showed that when the Sn content is 6.25 at%, the Cu–Sn alloy has the best plasticity and the highest elastic anisotropy; when the Sn content is 3.125 at%, the Cu–Sn alloy is the most stable and has stronger bulk and shear modulus, which was mainly due to a stronger Cu-Cu covalent bond. Finally, the Debye temperature, thermal conductivity, and melting point were calculated. It is estimated that the thermal conductivity of Cu–Sn alloy is relatively good when the Sn content is low. Full article

In body-centered cubic (BCC) alloys of transition elements, elemental addition or substitution in the vanadium-based alloys can be beneficial for improving the hydrogen storage properties and for reducing the production cost. In this context, the current study focused on the effect of the substitution of Cr by Fe in Ti₁₆V₆₀Cr_24−xFe_x + 4 wt.% Zr alloys where x = 0, 4, 8, 12, 16, 20, 24. The microstructure of each alloy was composed of a matrix having a chemical composition close to the nominal one and a Zr-rich region. From X-ray diffraction patterns, it was found that the matrix has a BCC structure, and the Zr-rich regions present the C14 Laves phase structure. The lattice parameter of BCC phases decreased linearly with x, in accordance with Vegard’s law. The measurement of the first hydrogenation at 298 K under 3 MPa of hydrogen revealed a decrease in the maximum hydrogen capacity: 3.8 wt.% for x = 0, 3.1 wt.% for x = 4 and around 2 wt.% for x = 8 to 24. The XRD patterns after hydrogenation showed a BCT phase for all alloys, with a C14 phase for x = 4, 8, 12 and with C14 and C15 for x = 16, 20 and 24. Full article

Rare-earth-doped mixed crystals have demonstrated tunable optical properties, and it is of great importance to study the structural characteristics of the mixed-crystal hosts. Herein, Lu_xGd_1-xVO₄ (0 ≤ x ≤ 1) solid solution nanocrystals were synthesized by a modified sol–gel method, with a pure crystalline phase and element composition. The X-ray diffraction (XRD) and Rietveld refinement results showed that Lu_xGd_1−xVO₄ nanocrystals are continuous solid solutions with a tetragonal zircon phase (space group I4₁/amd) and the lattice parameters strictly follow Vegard’s law. The detailed local structures were studied by extended X-ray absorption fine structure (EXAFS) spectra, which revealed that the average bond length of Gd-O fluctuates and decreases, while the average bond length of Lu-O gradually decreases with the increase in Lu content. Furthermore, the binding energy differences of core levels indicate that the covalent V-O bond is relatively stable, while the ionicity of the Lu-O bond decreases with the increasing x value, and the ionicity of the Gd-O bond fluctuates with small amplitude. The valence band structures were further confirmed by the first-principles calculations, indicating that the valence band is contributed to by the O 2p nonbonding state, localized Gd 4f and Lu 4f states, and the hybridized states between the bonding O 2p and V 3d. The binding energies of the Lu core and the valence levels tend to decrease gradually with the increase in Lu content. This work provides insight into the structural features of mixed-crystal hosts, which have been developed in recent years to improve laser performance by providing different positions for active ions to obtain inhomogeneous broadening spectra. Full article

In the present work, pure and Cr-doped MoO₃ microrods were successfully prepared through the sol gel auto combustion method. The phase evaluation and microstructural, dielectric, and optical properties of synthesized samples were investigated by using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and an impedance analyzer (1 MHz–3 GHz). All the samples showed hexagonal structure with space group (P63). According to Vegard’s law, lattice parameters increase with the increase in chromium (Cr³⁺) contents. In addition, the Williamson–Hall (W–H) plot was drawn for evaluating the micro-strain (ε_W-H) and crystallite size (D_W-H) parameters. From microstructural analysis it was found that the size of microrods increased along with Cr³⁺ contents. Decreasing band gap energy was observed (from 2.98 to 2.71 eV) with increasing Cr³⁺ contents. The variation of the dielectric constant and tangent loss of MoO₃ microrods with respect to frequency were analyzed. Full article

We synthesized a combinatorial library of Cu_xNi_1−x alloy thin films via co-sputtering from Cu and Ni targets to catalyze graphene chemical vapor deposition. The alloy morphology, composition, and microstructure were characterized via scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS), and X-ray diffraction (XRD), respectively. Subsequently, the Cu_xNi_1−x alloy thin films were used to grow graphene in a CH₄-Ar-H₂ ambient at atmospheric pressure. The underlying rationale is to adjust the Cu_xNi_1−x composition to control the graphene. Energy dispersive x-ray spectroscopy (EDS) analysis revealed that a continuous gradient of Cu_xNi_1−x (25 at. % < x < 83 at.%) was initially achieved across the 100 mm diameter substrate (~0.9%/mm composition gradient). The XRD spectra confirmed a solid solution was realized and the face-centered cubic lattice parameter varied from ~3.52 to 3.58 $\dot{\mathrm{A}}$, consistent with the measured composition gradient, assuming Vegard’s law. Optical microscopy and Raman analysis of the graphene layers suggest single layer growth occurs with x > 69 at.%, bilayer growth dominates from 48 at.% < x < 69 at.%, and multilayer (≥3) growth occurs for x < 48 at.%, where x is the Cu concentration. Finally, a large area of bi-layer graphene was grown via a Cu_xNi_1−x catalyst with optimized catalyst composition and growth temperature. Full article

This paper presents the influence of Mn²⁺ substitution by Ni²⁺ on the structural, morphological and magnetic properties of Mn_1−xNi_xFe₂O₄@SiO₂ (x = 0, 0.25, 0.50, 0.75, 1.00) nanocomposites (NCs) obtained by a modified sol-gel method. The Fourier transform infrared spectra confirm the formation of a SiO₂ matrix and ferrite, while the X-ray diffraction patterns show the presence of poorly crystalline ferrite at low annealing temperatures and highly crystalline mixed cubic spinel ferrite accompanied by secondary phases at high annealing temperatures. The lattice parameters gradually decrease, while the crystallite size, volume, and X-ray density of Mn_1−xNi_xFe₂O₄@SiO₂ NCs increase with increasing Ni content and follow Vegard’s law. The saturation magnetization, remanent magnetization, squareness, magnetic moment per formula unit, and anisotropy constant increase, while the coercivity decreases with increasing Ni content. These parameters are larger for the samples with the same chemical formula, annealed at higher temperatures. The NCs with high Ni content show superparamagnetic-like behavior, while the NCs with high Mn content display paramagnetic behavior. Full article

There has been a considerable amount of interest in the ion-exchange properties of layered zirconium phosphates. Potential applications in the remediation of nuclear waste have renewed interest in these inorganic materials, due to their high stability under the acidic conditions typically found in legacy waste pools. It has been well documented that the substitution of metals with different ionic radii into the frameworks of inorganic materials can alter the chemical properties including ion-exchange selectivity. The work presented here focusses on the synthesis and characterisation of yttrium-doped α-zirconium phosphates which are reported for the first time. Two different synthetic methods were used, reflux and hydrothermal syntheses, and the products were characterised by various methods such as powdered X-ray diffraction, MAS-NMR and scanning electron microscopy. It was found that up to 15% of zirconium could be replaced by yttrium before any noticeable impurity phases could be observed. Rietveld refinement from the doping showed that the products did not obey the Vegard’s law. However, the ion-exchange results clearly showed enhanced capacities and selectivity towards Co²⁺ ions for the substituted materials. Full article

The aim of this study is to synthesize Li_1+xAl_xTi_xSn_2−2x(PO₄) sodium super ion conductor (NASICON) -based ceramic solid electrolyte and to study the effect of dual metal substitution on the electrical and structural properties of the electrolyte. The performance of the electrolyte is analyzed based on the sintering temperature (550 to 950 °C) as well as the composition. The trend of XRD results reveals the presence of impurities in the sample, and from Rietveld Refinement, the purest sample is achieved at a sintering temperature of 950 °C and when x = 0.6. The electrolytes obey Vegard′s Law as the addition of Al³⁺ and Ti⁴⁺ provide linear relation with cell volume, which signifies a random distribution. The different composition has a different optimum sintering temperature at which the highest conductivity is achieved when the sample is sintered at 650 °C and x = 0.4. Field emission scanning electron microscope (FESEM) analysis showed that higher sintering temperature promotes the increment of grain boundaries and size. Based on energy dispersive X-ray spectroscopy (EDX) analysis, x = 0.4 produced the closest atomic percentage ratio to the theoretical value. Electrode polarization is found to be at maximum when x = 0.4, which is determined from dielectric analysis. The electrolytes follow non-Debye behavior as it shows a variety of relaxation times. Full article

Iron-nickel alloy is an example of bimetallic nanostructures magnetic alloy, which receives intensive and significant attention in recent years due to its desirable superior ferromagnetic and mechanical characteristics. In this work, a unique starfish-like shape of an iron-nickel alloy with unique magnetic properties was presented using a simple, effective, high purity, and low-cost chemical reduction. There is no report on the synthesis of such novel shape without complex precursors and/or surfactants that increase production costs and introduce impurities, so far. The synthesis of five magnetic iron-nickel alloys with varying iron to nickel molar ratios (10–50% Fe) was undertaken by simultaneously reducing Fe(II) and Ni(II) solution using hydrazine hydrate as a reducing agent in strong alkaline media for 15 min at 95–98 °C. The effect of reaction volume and total metal concentration on the properties of the synthesized alloys was studied. Alloy morphology, chemical composition, crystal structure, thermal stability, and magnetic properties of synthesized iron-nickel alloys were characterized by means of SEM, TEM, EDX, XRD, DSC and VSM. ImageJ software was used to calculate the size of the synthesized alloys. A deviation from Vegard’s law was recorded for iron molar ration higher than 30%., in which superstructure phase of FeNi₃ was formed and the presence of defects in it, as well as the dimensional effects of nanocrystals. The saturation magnetization (Ms), coercivity (Hc), retentivity (Mr), and squareness are strongly affected by the molar ratio of iron and nickel and reaction volume as well as the total metal concentration. Full article

In this paper, the synthesis and characterization of CuIn_1−xGa_xSe₂ (0 ≤ x ≤ 1) nanocrystals are reported with the influences of x value on the structural, morphological, and optical properties of the nanocrystals. The X-ray diffraction (XRD) results showed that the nanocrystals were of chalcopyrite structure with particle size in the range of 11.5–17.4 nm. Their lattice constants decreased with increasing Ga content. Thus, the x value of the CuIn_1−xGa_xSe₂ nanocrystals was estimated by Vegard’s law. Transmission electron microscopy (TEM) analysis revealed that the average particle size of the nanocrystals agreed with the results of XRD. Well-defined lattice fringes were shown in the TEM images. An analysis of the absorption spectra indicated that the band gap energy of these CuIn_1−xGa_xSe₂ nanocrystals was tuned from 1.11 to 1.72 eV by varying the x value from 0 to 1. The Raman spectra indicated that the A₁ optical vibrational mode of the nanocrystals gradually shifted to higher wavenumber with increasing x value. A simple theoretical equation for the A₁ mode frequency was proposed. The plot of this equation showed the same trend as the experimental data. Full article

Aluminum-doped tin oxide (SnO ${}_2$ :Al) thin films were produced by an ultrasonic spray pyrolysis method. The effect of aluminum doping on structural, optical, and electrical properties of tin oxide thin films synthesized at 420 ${}^{°}$ C was investigated. Al doping induced a change in the morphology of tin oxide films and yielded films with smaller grain size. SnO ${}_2$ thin films undergo a structural reordering and have a texture transition from (301) to (101), and then to (002) preferred cristallographic orientation upon Al doping. The lattice parameters (a and c) decreases with Al doping, following in a first approximation Vegard’s law. The optical transmission does not change in the visible region with an average transmittance value of 72–81%. Conversely, in the near infrared (NIR) region, the plasmon frequency shifts towards the IR region upon increasing Al concentration in the grown films. Nominally undoped SnO ${}_2$ have a conductivity of ∼1120 S/cm, which is at least two orders of magnitude larger than what is reported in literature. This higher conductivity is attributed to the Cl ${}^{-}$ ions in the SnCl ${}_4$ ·5(H ${}_2$ O) precursor, which would act as donor dopants. The introduction of Al into the SnO ${}_2$ lattice showed a decrease of the electrical conductivity of SnO ${}_2$ due to compensating hole generation. These findings will be useful for further studied tackling the tailoring of the properties of highly demanded fluorine doped tin oxide (FTO) films. Full article

We synthesized Pd-Fe series nanoparticles in solid solution using pulsed plasma in liquid with Pd-Fe bulk mixture electrodes. The Pd-Fe atomic percent ratios were 1:3, 1:1, and 3:1, and the particle size was measured to be less than 10 nm by high-resolution transmission electron microscopy (HR-TEM). The nanoparticles showed face-centered cubic structure. The lattice parameter increased with increasing Pd content and followed Vegard’s law, and energy-dispersive X-ray spectra were consistent with the ratios of the starting samples, which showed a solid solution state. The solid solution structure and local structure were confirmed by HR-TEM and X-ray absorption fine structure. Full article