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All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Magnetism in EuAlSi and the Eu 1−𝑥 ⁢Sr 𝑥 ⁢ AlSi solid solution solid solution

The magnetic properties of EuAlSi, a compound comprising a honeycomb lattice of Al/Si atoms and a triangular lattice of Eu atoms, are presented. By means of single-crystal x-ray diffraction, we find that EuAlSi crystallizes in an AlB 2 -type structure with space group 𝑃⁢6/mmm and unit cell parameters 𝑎 = 4.2229⁢ (10) ⁢Å and 𝑐 = 4.5268 ⁢(12)⁢ Å. Our magnetic measurements indicate that EuAlSi is a soft ferromagnetic material with 𝑇 Curie = 25.8 K. The susceptibility follows the Curie-Weiss law at high temperatures, which allowed us to determine the paramagnetic Curie temperature 𝜃 𝑃 = 36.2 ⁢(1) ⁢K and an effective magnetic moment 𝜇 eff = 8.07 ⁢(1)⁢ µ 𝐵 /Eu. This value is in agreement with the theoretical value of 7.9 µ 𝐵 for Eu 2+ free ion. Moreover, we have prepared the Eu 1−𝑥 ⁢Sr 𝑥 ⁢ AlSi solid solution, where the atoms in the triangular lattice were systematically exchanged, in order to study the evolution of the collective quantum properties from the ferromagnetic EuAlSi toward the superconducting SrAlSi. Across the Eu 1−𝑥 ⁢Sr 𝑥 AlSi solid solution, the unit cell parameters change linearly, following Vegard’s law, and making the system reliable for studying composition dependence of the interplay between the crystal structure and physical properties. As the Sr content increases, i.e., 𝑥 increases, we note a consistent reduction of 𝜇 eff and 𝑇 Curie . Long-range magnetic order in Eu 1−𝑥 ⁢Sr 𝑥 ⁢ AlSi persists up to 𝑥 = 0.95, whereas superconductivity is only observed for samples with 𝑥 > 0.97.

Walicka, Dorota I. [University of Geneva (Switzerl↗
DOE OSTI2015

Photocatalytic H{sub 2} production from spinels ZnGa{sub 2−x}Cr{sub x}O{sub 4} (0≤x≤2) solid solutions

Solid solutions of ZnGa{sub 2−x}Cr{sub x}O{sub 4} (0≤x≤2) were successfully prepared by solid state reactions. Introducing Cr into ZnGa{sub 2}O{sub 4} crystal structure significantly improves its light absorption and greatly enhances its photocatalytic activity. An optimized Cr content (x=1.5 for ZnGa{sub 0.5}Cr{sub 1.5}O{sub 4}) was found for the solid solutions with the highest photocatalytic hydrogen production rate (~775 μmol/h). Compositional analysis suggests there is a strong enrichment of Cr at the surface of sample ZnGa{sub 0.5}Cr{sub 1.5}O{sub 4} compared with other samples. Theoretical calculations suggest their electronic structures involve spin-polarized conduction band (CB) and valence band (VB) that are mainly composed of Cr 3d orbitals. The highest photocatalytic activity observed in ZnGa{sub 0.5}Cr{sub 1.5}O{sub 4} is probably due to the higher Cr content at the surface that favors the Cr 3d orbital overlapping. - Graphical abstract: Electronic structure and density of states of ZnGa{sub 2}O{sub 4} after partially substituting Ga with Cr. - Highlights: • Complete solid solution can be formed between ZnGa{sub 2}O{sub 4} and ZnCr{sub 2}O{sub 4}. • Optical properties and catalytic activity are improved by adding Cr into ZnGa{sub 2}O{sub 4}. • An optimized Cr content exists for the highest activity. • Enrichment of Cr in the surface is beneficial for a better performance.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Cluster Variation Method Analysis of Correlations and Entropy in BCC Solid Solutions

Solid solutions occur when multiple chemical species share sites of a common crystal lattice. Although the single site occupation is random, chemical interaction preferences bias the occupation probabilities of neighboring sites, and this bias reduced the entropy of mixing below its ideal value. Sufficiently strong bias leads to symmetry-breaking phase transitions. Here, we apply the cluster variation method to explore solid solutions on body centered cubic lattices in the context of two specific compounds that exhibit opposite ordering trends. Employing density functional theory to model the energetics, we show that CuZn exhibits an order-disorder transition to the CsCl prototype structure, while AlLi instead takes the NaTl prototype structure, and we evaluate their temperature-dependent order parameters, correlations and entropies.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Structural, vibrational and photoluminescence properties of Sr{sub (1-x)}Pb{sub x}MoO{sub 4} solid solution synthesized by solid state reaction

Highlights: • The solid solution Sr{sub (1-x)}Pb{sub (x)}MoO{sub 4} is characterized by X-ray diffraction. • Raman spectroscopy confirm that the solid solution is disordered. • Photoluminescence experiments are carried out under X-ray excitation. • Emission bands can be decomposed into four components between 2.1 and 2.9 eV. • The intensities of emission bands reach a maximum for 0.1 < x < 0.4. - Abstract: In this paper, strontium lead molybdate Sr{sub 1-x}Pb{sub x}MoO{sub 4} polycrystalline samples with 0 ≤ x ≤ 1 were prepared by solid state preparation method at 1000 °C. These materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and micro-Raman spectroscopy. Their photoluminescence responses were analyzed under X-ray excitation. Rietveld refinements indicate that all the materials present a scheelite-type tetragonal structure. Micro-Raman spectra confirmed the formation of the solid solution with a specific effect due to Sr-O-Mo and Pb-O-Mo links in the scheelite structure. SEM images showed modifications in the shapes and grain sizes as x increased. Broad photoluminescent emission bands were observed in the energy range 2.1–2.9 eV. The emission bands were decomposed into four gaussian components. The intensities of all components presented a strong maximum in the composition range 0.1 < x < 0.4.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Lattice Parameter Behavior with Different Nd and O Concentrations in (U 1-y Nd y )O 2±x Solid Solution

The solid solution of (U1-yFPy)O- 2±x , has the same fluorite structure as UO 2±x lambda, and the lattice parameter is affected by dissolved fission product and oxygen concentrations. We investigated the relation between the lattice parameter and the concentrations of neodymium and oxygen in the fluorite structure of (U 1-y Nd y )O 2±x using X-ray diffraction. Moreover, the lattice parameter behavior in the (U 1-y Nd y )O 2±x , solid solution shows a linear change as a function of the oxygen-to-metal ratio and solubility of neodymium. The lattice parameter depends on the radii of ions forming the fluorite structure and also can be expressed by a particular rule (modified Vegard's law). Furthermore, the numerical analyses of the lattice parameters for the stoichiometric and nonstoichionietric solid solutions were conducted, and the lattice parameter model for the (U1-yNdy)O 2±x , solid solution was assessed. There is a very linear relationship between the lattice parameter and the Nd and O concentration for the stoichiometry and nonstoichiometry of the (U 1-y Nd y )O 2±x solid solution was verified.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Nitridation Temperature Effects on Electronic and Chemical Properties of (Ga 1-x Zn x )(N 1-x O x ) Solid Solution Nanocrystals

Solid solution nanocrystals of gallium nitride–zinc oxide have been realized as potential photocatalysts for visible light driven overall water splitting. The band gap of these materials has been found to narrow further into the visible region as a function of increasing zinc oxide concentration, and thus, it is desirable to synthesize zinc oxide-rich gallium nitride–zinc oxide solid solutions. In this paper, we discuss the effects of using nitridation temperature to control zinc oxide content on the electronic and chemical properties of gallium nitride–zinc oxide solid solution nanostructures. The effect of nitridation temperature was studied using X-ray absorption fine structure (XAFS), including both X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS), and X-ray excited optical luminescence (XEOL). It was determined that using nitridation temperature as a method of controlling zinc oxide concentration results in solid solutions with poor crystallinity, phase separation, and mixed surface oxide formation. These findings suggest that many complications arise from using nitridation temperature to control zinc oxide concentration in gallium nitride–zinc oxide solid solutions, and thus, it is possible that the resultant materials would exhibit poor photocatalytic activity.

Ward, Matthew James↗
DOE OSTI2015

Influence of chemical substitution on the photoluminescence of Sr{sub (1−x)}Pb{sub x}WO{sub 4} solid solution

The solid solution Sr{sub 1−x}Pb{sub x}WO{sub 4} based on luminescent tungstates SrWO{sub 4} and PbWO{sub 4} has been synthesized by solid-state reaction for all compositions 0≤x≤1. Using Rietveld method, the structural data of all polycrystalline samples have been refined and crystal cell parameters exhibited a linear behavior as a function of x. All substituted structures are of scheelite type. Scanning electron microscopy showed that a high level of crystallization characterized the samples, with modifications in sizes and shapes depending on composition x. Infrared and Raman spectroscopy have been performed to characterize the evolution of vibrational modes with substitution rate. Finally, a systematic study of luminescence under X-ray excitation has been performed: in the composition range x=0.2 to 0.4, intensities of emission exhibited increased values. The luminescence profiles have been interpreted in terms of four Gaussian components, two of them depending on substitution rate. - Graphical abstract: Photoluminescence under X-ray excitation of Sr{sub 1−x}Pb{sub x}WO{sub 4} solid solution: (left) decomposition of emission large band into four components for composition x=0.3; (right) variation of total emission intensity with composition x. - Highlights: • Structural study of solid solution Sr{sub 1−x}Pb{sub x} WO{sub 4} using Rietveld analyses. • Variation of Debye–Waller factor with composition x, disorder parameter. • Existence of four components of luminescence under X-ray excitation. • Effect of substitution of Sr by Pb on two components, due to Pb–O–W interactions. • Enhancement of luminescence intensity in a specific composition range.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Local structure of Ni 80 X 20 (X: Cr, Mn, Pd) solid-solution alloys and its response to ion irradiation

In this work, the local structure of Ni 80 X 20 (X: Cr, Mn, Pd) solid-solution alloys was investigated with x-ray absorption and total scattering x-ray diffraction methods. Atomic pair distribution function (PDF) analysis indicated that the local lattice distortion is strongly relevant to the atomic size mismatch, and the local lattice distortion in Ni80Pd20 alloy is obviously larger than that in other solid-solution alloys. The bond length of different atomic pairs was derived from the fitting of extended x-ray absorption fine structure spectra. Quantitative analysis of the local bonding environment in Ni 80 Cr 20 during Ni ion irradiation suggested that Cr atoms tend to form clusters in Ni 80 Cr 20 with the increase of ion dose.

36 MATERIALS SCIENCE↗
DOE OSTI2016

The origin of ultrahigh piezoelectricity in relaxor-ferroelectric solid solution crystals

The discovery of ultrahigh piezoelectricity in relaxor-ferroelectric solid solution single crystals is a breakthrough in ferroelectric materials. A key signature of relaxor-ferroelectric solid solutions is the existence of polar nanoregions, a nanoscale inhomogeneity, that coexist with normal ferroelectric domains. Despite two decades of extensive studies, the contribution of polar nanoregions to the underlying piezoelectric properties of relaxor ferroelectrics has yet to be established. Here we quantitatively characterize the contribution of polar nanoregions to the dielectric/piezoelectric responses of relaxor-ferroelectric crystals using a combination of cryogenic experiments and phase-field simulations. The contribution of polar nanoregions to the room-temperature dielectric and piezoelectric properties is in the range of 50–80%. A mesoscale mechanism is proposed to reveal the origin of the high piezoelectricity in relaxor ferroelectrics, where the polar nanoregions aligned in a ferroelectric matrix can facilitate polarization rotation. This mechanism emphasizes the critical role of local structure on the macroscopic properties of ferroelectric materials.

36 MATERIALS SCIENCE↗
DOE OSTI2018

ZnxMn1-xO Solid Solutions in the Rocksalt Structure: Optical, Charge Transport, and Photoelectrochemical Properties

Theoretical predictions of ZnO:MnO solid solutions (abbreviated here as ZMO) with the rocksalt-type structure suggest improved visible light absorption and suitable band edge positions for the overall water splitting reaction, but experimental efforts to produce such phases are limited by the low solubility of Zn within this structure type. Here, we produce solid solutions of ZnxMn1-xO, with x = 0.5 and 0.3 in the metastable rocksalt phase, using high-pressure and high-temperature (HPHT) techniques. X-ray diffraction and electron microscopy methods were employed to determine the crystal structure, chemical composition, and homogeneity on the submicron scale. The solid solutions exhibit increased optical absorbance in the visible spectral range as compared to those of the parent oxides ZnO and MnO. Our theoretical calculations for ZnxMn1-xO with x = 0.5, 0.25 predict band gaps of 2.53 and 2.98 eV, respectively, with an unusually large band gap bowing. Our calculations also show small effective electron mass for these materials indicating their potential for solar energy applications. Initial photoelectrochemical tests reveal that ZMO solid solutions are suitable for water oxidation and warrant further experimental optimization.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Solid-Solution CrCoCuFeNi High-Entropy Alloy Thin Films Synthesized by Sputter Deposition

The concept of high configurationally entropy requires that the high-entropy alloys (HEAs) yield single-phase solid solutions. However, phase separations are quite common in bulk HEAs. A five-element alloy, CrCoCuFeNi, was deposited via radio frequency magnetron sputtering and confirmed to be a single-phase solid solution through the high-energy synchrotron X-ray diffraction, energy-dispersive spectroscopy, wavelength-dispersive spectroscopy, and transmission election microscopy. The formation of the solid-solution phase is presumed to be due to the high cooling rate of the sputter-deposition process.

Microstructure↗
DOE OSTI2015

Exploring hardness enhancement in superhard tungsten tetraboride-based solid solutions using radial X-ray diffraction

In this paper, we explore the hardening mechanisms in WB4-based solid solutions upon addition of Ta, Mn, and Cr using in situ radial X-ray diffraction techniques under nonhydrostatic pressure. By examining the lattice-supported differential strain, we provide insights into the mechanism for hardness increase in binary solid solutions at low dopant concentrations. Speculations on the combined effects of electronic structure and atomic size in ternary WB 4 solid solutions containing Ta with Mn or Cr are also included to understand the extremely high hardness of these materials.

36 MATERIALS SCIENCE↗
DOE OSTI2018

A review of recent research on nonequilibrium solid solution behavior in Li X FePO 4 [A review of nonequilibrium solid solution in Li X FePO 4 ]

Li X FePO 4 (0 < X < 1) is one of the most well-studied cathode battery materials and is notable for its large miscibility gap. Although its phase-separating behaviors under equilibrium conditions have been well documented, recent research has shown that phase separation is suppressed at elevated rates of lithium insertion and removal. Specifically, Li X FePO 4 exhibits a nonequilibrium solid solution behavior at elevated cycling rates. This article reviews recent research on nonequilibrium solid solution in Li X FePO 4 ; these insights have been largely enabled by operando characterization techniques. As a result, such studies have not only unambiguously confirmed the existence of this solid solution, but also show how surface reaction and diffusion kinetics ultimately affect phase separation and other spatially nonuniform lithiation and delithiation behavior.

36 MATERIALS SCIENCE↗