87 Search Results

A series of quaternary rare-earth containing thiosilicates with the general formula RE₂EuSi₂S₈ (RE = Ce–Nd, Sm, Gd, Tb) has been synthesized via the flux-assisted boron chalcogen mixture (BCM) crystal growth method. High-quality single crystals were obtained, and their crystal structures were determined by single-crystal X-ray diffraction. The RE₂EuSi₂S₈ series crystallizes in the trigonal system, adopting the space group R-3c. Polycrystalline samples were employed for physical property measurements, including magnetic susceptibility measurements, UV–visible diffuse reflectance, and photoluminescent response. Magnetic data of RE₂EuSi₂S₈ (RE = Ce, Nd, and Gd) were collected over the 2–300 K temperature range. The samples were paramagnetic behaviormore » with negative Weiss constants (θ_W = −11.05, −10.55, and −1.35 K respectively). Their thermal stability was investigated using thermogravimetric analysis (TGA). Optical band gaps, estimated from diffuse reflectance spectra, were determined to be 2.2(1) eV for Ce₂EuSi₂S₈, 1.8(1) eV for Nd₂EuSi₂S₈, and 1.7(1) eV for Gd₂EuSi₂S₈ respectively. Finally, photoluminescence measurements were collected on Ce₂EuSi₂S₈ and Tb₂EuSi₂S₈ single crystals.« less

We report a detailed structural analysis of a series of ten quaternary rare-earth-containing seleno-thiosilicates AkRE₂Si₂Se_xS_8-x and selenosilicates, CaRE₂Si₂Se₈ (Ak = Ca and Sr; RE = La, Ce, Pr, Nd, and Sm). Single crystals were obtained by using the flux-assisted boron chalcogen mixture (BCM) method and single crystal X-ray diffraction was used to determine their structures. All members of the AkRE₂Si₂Se_xS_8-x and CaRE₂Si₂Se₈ series crystallize in the space group R$$\bar{3}$$c (space group number 167) of the trigonal crystal system. The single-crystal X-ray diffraction analysis revealed a strong preference for Se/S atoms to occupy one vs. the other of the two availablemore » sites. Polycrystalline samples were used for magnetic susceptibility and UV–visible diffuse reflectance measurements. Magnetic measurements show that CaCe₂Si₂Se₁.₇₃S₆.₂₇ and CaNd₂Si₂Se₂.₅S₅.₅ are paramagnetic with negative Weiss constants (θ = –60.1 and –26.2). Diffuse reflectance analysis gives optical band gaps of 2.7(1) eV (CaLa₂Si₂Se₂.₃₈S₅.₆₂), 2.2(1) eV (CaCe₂Si₂Se₁.₇₃S₆.₂₇), 2.5(1) eV (CaNd₂Si₂Se₂.₅S₅.₅), and 2.0(1) eV (CaCe₂Si₂Se₈), consistent with density functional theory calculations. By partially or fully replacing S sites with Se it was possible to achieve band gap tuning. Photoluminescence behavior was also investigated for CaCe₂Si₂Se_1.73S_6.27 via irradiation with 375 nm ultraviolet light.« less

For this work, a series of six quinary rare-earth sulfides Ce⁴⁺_1.85Eu²⁺_1.15Na_0.30SiS₇, Ce⁴⁺_1.91Eu²⁺_1.09K_0.18SiS₇, Ce⁴⁺_1.96Eu²⁺_1.04Rb_0.08SiS₇, Ce⁴⁺_1.98Eu²⁺_1.02Cs_0.05SiS₇, Ce⁴⁺_1.97Eu²⁺_1.03Ag_0.06SiS₇, and Ce⁴⁺_1.50Eu²⁺_1.50CuSiS₇ were obtained in an alkali iodide flux using the boron-chalcogen mixture (BCM) method. Single crystal X-ray diffraction was used to determine the structures of the high quality single crystals that were grown; their elemental compositions were confirmed by energy-dispersive spectroscopy (EDS). The compounds crystallize in the hexagonal crystal system in the noncentrosymmetric space group P63. The crystal structure consists of a three-dimensional network composed of mixed cerium and europium bicapped trigonal prisms, isolated SiS4 tetrahedra, and monovalent metals (Na, K, Rb, Cs, Ag,more » and Cu) located in cavities created by linked Ce/EuS₈ polyhedra. The structures are charge-balanced when Ce and Eu are in their +4 and +2 oxidation states, respectively. The effective magnetic moment of Ce_1.50⁴⁺Eu_1.50²⁺CuSiS₇ determined from the temperature dependence of the magnetic susceptibility data is consistent with the presence of Ce⁴⁺ and Eu²⁺. Clear correlations between the alkali ion site occupancy, the ionic radius of the alkali cations, and the average bond length of Ce⁴⁺/Eu²⁺–S, were established. UV–vis diffuse reflectance data were collected for Ce_1.50⁴⁺Eu_1.50²⁺CuSiS₇ and a band gap of 1.9(1) eV was established.« less

Two new layered uranyl phosphate compounds, K(UO₂)PO₄(H₂O)₃ and Na(UO₂)PO₄(H₂O)_1.52, crystallizing in an autunite-type sheet structure, were successfully synthesized as both single-crystals and polycrystalline powders under mild hydrothermal conditions. The compound K(UO₂)PO₄(H₂O)₃ crystallizes in the tetragonal crystal system with the space group P4/ncc, exhibiting lattice parameters of a = b = 6.99320(7) Å and c = 17.8389(3) Å. Similarly, Na(UO₂)PO₄(H₂O)_1.52 also crystallizes in the tetragonal crystal system, however, in the space group P4/nmm and exhibits lattice parameters of a = b = 6.9787 Å and c = 8.6303(17) Å. Both compounds adopt layered structures, a characteristic feature of uranyl phosphates, andmore » exhibit intense green fluorescence typical for uranyl-containing materials. As a result, the infrared spectroscopy, photoluminescence, and scintillation properties of these compounds were investigated.« less

Single crystals and polycrystalline powders of rare earth mixed chalcogenide iodides La₃Si₂Se_1.21S_6.79I, Ce₃Si₂Se_1.39S_6.61I, Pr₃Si₂Se_1.22S_6.78I, and Nd₃Si₂Se_1.18S_6.82I were prepared using the reactive flux-assisted boron–chalcogen mixture (BCM) method at 850 °C. All compounds crystallized in the monoclinic crystal system, space group C2/c (space group number 15). The series adopts the La₃Si₂O₈Cl structure type, containing isolated SiQ₄ tetrahedra connected by REQ₈ (RE = La, Ce, Pr and Nd) polyhedra; this arrangement creates tunnels that are filled by I atoms. The partial substitution of S by Se was carried out to modulate the optical properties. Phase pure samples and uniform solid solutions were obtainedmore » for all compositions as determined using powder X-ray diffraction patterns. Polycrystalline powders were used for physical property measurements, including magnetic susceptibility and UV-Vis diffuse reflectance. The solid-state UV-Vis data for the polycrystalline La₃Si₂Se_1.21S_6.79I, Ce₃Si₂Se_1.39S_6.61I, and Pr₃Si₂Se_1.22S_6.78I samples revealed band gaps of E_g = 2.5(1), 2.2(1), and 2.3(1) eV, typical of semiconductors. Magnetic measurements indicated that Ce₃Si₂Se_1.39S_6.61I and Nd₃Si₂Se_1.18S_6.82I exhibit paramagnetic behavior with slightly negative Weiss constants θ = −25 and −38. The photoluminescence spectrum of Ce₃Si₂Se_1.39S_6.61I exhibits a broad emission band around ∼493 nm.« less

Here, a set of self-consistent Gibbs energy functions has been developed to describe the thermochemical behavior of the major reactive fission product ZrCl₄ with key components in chloride molten salt reactors (MSRs): LiCl–ZrCl₄, NaCl–ZrCl₄, KCl–ZrCl₄, CsCl–ZrCl₄, MgCl₂–ZrCl₄ and UCl₃–ZrCl₄. Low ZrCl₄ concentration phase equilibria most relevant to MSR applications have been confirmed via differential scanning calorimetry for NaCl–ZrCl₄, and X-ray diffraction analysis performed on equilibrated samples of NaCl–ZrCl₄, KCl–ZrCl₄, MgCl₂–ZrCl₄, and UCl₃–ZrCl₄. Within the framework of the modified quasi-chemical model in the quadruplet approximation, extrapolations of pseudo-binary models were generated to represent KCl–MgCl₂–ZrCl₄, KCl–NaCl–ZrCl₄, and MgCl₂–NaCl–ZrCl₄, which show agreement withmore » phase equilibria data where available without the use of ternary interaction parameters. The optimized thermodynamic descriptions for these systems and others are available in the open-source compendium Molten Salt Thermal Properties Database – Thermochemical (MSTDB–TC).« less

A series of rare earth magnesium selenosilicates, RE3Mg_0.5SiSe₇ (RE = Ce, Pr, Nd, Sm, Gd, Tb, Dy) were obtained as single crystal using the flux assisted boron chalcogen mixture (BCM) method. The structures of the crystals were determined by single-crystal X-ray diffraction. The RE3Mg_0.5SiSe₇ series crystallizes in the hexagonal crystal system in the space group P6₃. Polycrystalline powders were synthesized to perform physical property measurements. Magnetic measurements over the 2–300 K temperature range reveal that Ce₃Mg_0.5SiSe₇ and Gd₃Mg_0.5SiSe₇ exhibit paramagnetic behavior with negative Weiss constants (θ_W = −14.50, θ_W = −6.13 K, respectively). The optical properties of RE₃Mg_0.5SiSe₇ (RE =more » Ce, Pr, Nd, Sm, Gd) were measured by ultraviolet–visible (UV–vis) diffuse reflectance. Density functional theory (DFT) electronic structure calculations were performed. Furthermore, a second harmonic generation measurement was performed on a polycrystalline powder of Ce₃Mg_0.5SiSe₇ and was found to be SHG active with an efficiency of 0.11 times the standard potassium dihydrogen phosphate (KDP).« less

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