Eutectic Flux Research Articles

Alkali rare earth double phosphates: Promising new high temperature scintillators

Alkali rare earth double phosphates were investigated for their X-ray induced scintillation. Double phosphates with stoichiometry A3Ln(PO4)2 (A = K or Rb, Ln = Eu or Tb) were synthesized via a eutectic molten salt flux yielding high quality single crystals. The systematic variation of the alkali and rare earth elements in the structure allowed for insights into the effects of the chemical composition on the scintillation output. The radioluminescence of these compositions under X-ray excitation is reported with a discussion of the variance of their luminosity as a function of both the constituent alkali and lanthanide elements. The relative luminosity of Rb3Tb(PO4)2 surpasses BGO by 30 %. The dependance of the scintillation on temperature is also investigated, including an unusual peak intensity increase for higher temperatures that can reach 1.4x of its value at room temperature for Rb3Tb(PO4)2 at 255 °C, and 2.1x for K3Tb(PO4)2 at 495 °C.

Phase Discovery and Selected Synthesis of Subvalent Niobium Tellurides Using a Polytelluride Flux Strategy.

Transition metal subchalcogenides involve electron-rich metals and can facilitate an in-depth understanding of the relationships among quantum properties such as superconductivity, charge density wave, and topological band structures. However, effective experimental routes toward synthesizing transition metal subchalcogenides are still lacking, hindering the development of new quantum materials. Herein, we propose a eutectic polytelluride flux strategy as an excellent solution to address phase discovery and crystal growth in transition metal subtelluride systems. We report new phases easily and selectively synthesized using a eutectic "K3Te4" polytelluride flux upon adjusting the ratio of Nb metal to flux in the starting materials (K/Nb/Te = 3:x:4). Using a high Nb content in the solvent (x = 2 and 1), crystals of KNb3Te3O0.38 and K0.9Nb3Te4 are obtained. Both subtellurides exhibit diverse Nb clusters, including face-sharing and edge-sharing Nb6 octahedral columns and zig-zag Nb chains. Reducing the Nb content to x = 0.33 leads to the formation of a layered compound, K1.06NbTe2. This compound comprises a NbTe6 trigonal prism with K intercalated between the layers. Single crystals of known binary Nb tellurides can also be grown using another eutectic flux "KTe3.2", and the obtained NbTe2 exhibits a new polymorphism with extra trimerization along the b-axis in the Nb-Nb bonded double zig-zag cluster. Precise control over the structural dimensionality and oxidation state, combined with the facile crystal growth process, makes our synthetic strategy an efficient route to explore quantum materials in transition metal subchalcogenides.

Flux Growth of an Intermetallic with Interstitial Fluorides via Decomposition of a Fluorocarbon.

La15(FeC6)4F2 was grown as large crystals by reacting iron in a La/Ni eutectic flux in the presence of decafluorobiphenyl (C12F10) which acts as both a carbon and fluoride source. This mild fluorinating technique enables the isolation of an intermetallic product containing fluoride interstitials, as opposed to forming ionic metal fluorides. The compound adopts a structure in the hexagonal crystal system with space group P6̅ which features FeC6 units composed of a central iron atom coordinated by three ethylenide units in a trigonal planar configuration. The structure is related to the previously reported La15(FeC6)4H, but with fluoride fully occupying the interstitial hydride positions, which induces partial occupancies and site splitting disorder in the adjacent layers of lanthanide ions. No supercell formation is observed.

Flux syntheses and single-crystal structures of CsNa10 M 4(AsO4)9 (M = Zr, Hf).

The isostructural compounds caesium deca-sodium tetra-zirconium nona-arsenate, CsNa10Zr4(AsO4)9, and caesium deca-sodium tetra-hafnium nona-arsenate, CsNa10Hf4(AsO4)9, arose as unexpected single-crystal products from the reactions of Na2CO3, MO2 (M = Zr, Hf) and As2O5 in a eutectic flux of NaCl and CsCl. They consist of MO6 octa-hedra and AsO4 tetra-hedra sharing vertices to generate three-dimensional polyhedral networks encapsulating the caesium and sodium ions. The MO6 groups share all their vertices with adjacent As atoms but the As atoms have one or two 'terminal' O atoms not bonded to Zr or Hf. The Cs+ ion adopts a squashed octa-hedral geometry and the coordination polyhedra of the partially occupied sodium ions are variously trigonal bipyramidal, tetra-hedral, square pyramidal and trigonal pyramidal. Site symmetries: Cs ; M 3; As 1 and 2; O 1; Na 1, 2 and 3. The M = Zr crystal was refined as an obverse/reverse rhombohedral twin.

Metal Flux Growth of Praseodymium Iron Carbides Featuring FeC3 Units

Reactions of iron and carbon in a Pr/Ni eutectic flux have yielded three new Pr/Fe/C carbometalate compounds. Pr14Fe6C13 forms in tetragonal space group P42/mnm; Pr26Fe19C29 forms in orthorhombic s...

Rb2Co1.85Ge1.15O6: The First Quaternary, Noncentrosymmetric Rubidium Cobalt Germanate

Deep blue, prism-shaped, X-ray diffraction quality single crystals of a new quaternary rubidium cobalt germanate, exact composition Rb2Co1.85Ge1.15O6, were grown by soaking a pre-reacted polycrystalline powder in a molten RbCl/RbF eutectic flux (melting point = 546 °C) at 700 °C in a silver reaction vessel. The complex was characterized by single crystal X-ray diffraction and its elemental composition was semi-quantitatively confirmed by energy dispersive spectroscopy (EDS). Rb2Co1.85Ge1.15O6 crystallizes in the noncentrosymmetric orthorhombic space group C2221 with lattice parameters a = 6.5971(2) A, b = 9.8791(3) A and c = 10.8819(3) A in the K2ZnSi2O6 structure type. The crystal structure consists of a three-dimensional network, composed of Co and mixed Co/Ge tetrahedra, and features cavities occupied by Rb cations. X-ray diffraction quality single crystals of a novel rubidium cobalt germanate, Rb2Co1.85Ge1.15O6, were grown by soaking a pre-reacted powder, targeted for preparing Rb4.51Co2.35Ge5.10O15F1.96, in a RbCl-RbF eutectic melt at 700 °C. The complex was characterized by single crystal X-ray diffraction and found to crystallize in the orthorhombic space group C2221 in the K2ZnSi2O6 structure type.

Flux Synthesis of a Metal Carbide Hydride Using Anthracene As a Reactant.

La15(FeC6)4H was synthesized from the reaction of iron and anthracene in La/Ni eutectic flux. Anthracene was the source of both the carbon and hydrogen in the product. The structure of this metal carbide hydride features hydride ions in tetrahedral interstitial sites surrounded by lanthanum ions, which was confirmed by single-crystal neutron diffraction studies. The trigonal planar FeC6 units in which the central iron atom is coordinated by three ethylenide groups are similar to those found in La3.67FeC6, a previously reported compound that is formed in the absence of a hydride source. Magnetic susceptibility data confirm that the iron sites do not have magnetic moments. Density of states calculations indicate that La15(FeC6)4H is metallic and is stabilized by the incorporation of hydride anions.

Synthesis and Crystal Structure of a 6H Hexagonal Fluoro-Perovskite: RbMgF3

RbMgF3, a perovskite halide, serendipitously crystallized from a reaction between MgCl2 and TiO2 in molten RbCl/RbF eutectic flux (melting point = 546 °C) and was characterized by single crystal X-ray diffraction. RbMgF3 crystals can also be grown directly in higher yield using a molten RbCl–RbF flux layered over MgCl2 or MgF2 contained in a silver tube at 575 °C. RbMgF3 crystallizes in the hexagonal space group P63/mmc in the 6H hexagonal perovskite structure type with lattice parameters a = 5.8368(2) A and c = 14.2087(5) A. The crystal structure exhibits face-sharing Mg2F9 octahedra connected via corner-sharing MgF6 octahedra. Elemental composition for RbMgF3 was semi-quantitatively confirmed by energy dispersive spectroscopy (EDS). X-ray diffraction quality single crystals of RbMgF3 were grown from a molten RbCl/RbF eutectic flux at 850 °C and used for structure determination using single crystal X-ray diffraction. The compound crystallizes in the hexagonal space group P63/mmc in the 6H hexagonal structure type.

Flux Crystal Growth, Structure, and Optical Properties of the New Germanium Oxysulfide La4(GeS2O2)3

Single crystals of a new germanium oxysulfide La4(GeS2O2)3 were grown out of a BaCl2-CaCl2 eutectic flux, and the crystal structure was determined via single-crystal X-ray diffraction. Ivory-white ...

New scandium borates RxLayScz(BO3)4 (x+y+z=4, R=Sm, Tb): Synthesis, growth, structure and optical properties

Herein we report the growth of new RxLayScz(BO3)4 (x + y+z = 4, R = Sm, Tb) crystals with large second-harmonic generation (SHG) responses. The obtained compounds, grown from eutectic LiBO2-LiF flux by the TSSG method, crystallize in the space group P321 with the cell parameters a = 9.800(15) Å and c = 7.9565(7) Å for Sm0.34La0.68Sc2.98(BO3)4 and a = 9.7976(7) Å and c = 7.9567(12) Å for Tb0.23La0.77Sc3(BO3)4. These crystalline materials also exhibit luminescent properties related to the optical transitions of Tb3+ and Sm3+; specifically, Tb0.23La0.77Sc3(BO3)4 shows a strong green emission that is dominated by the 5D4 to 7F5 transition. The studied crystals’ SHG intensities were higher than those of KDP crystals, revealing their potential uses in various nonlinear optics applications.

La2USe3S2: A Serendipitously Grown Lanthanide/Actinide Chalcogenide from a Eutectic Halide Flux

La2USe3S2, exact composition La2USe2.96S2.04, crystallized from a reaction between USe2 and La2S3 in a molten CsCl/KCl eutectic flux and was characterized by single crystal X-ray diffraction. La2USe3S2 crystallizes in the orthorhombic space group Pnma in the U3S5 structure type with lattice parameters a = 12.3284(3) A, b = 8.4028(2) A, and c = 7.3452(2) A. In La2USe3S2 all the anion sites have mixed S and Se occupancy and, henceforth, will be simply referred to as Q sites. The compound exhibits sigmoidal sheets built from LaQ8 (Q = S, Se) bicapped trigonal prisms that edge-share down the a-axis forming rectangular-shaped channels or tunnels. These tunnels are occupied by UQ6 (Q = S, Se) octahedra that edge-share to form infinite, one-dimensional chains running down the b-axis. X-ray diffraction quality single crystals of La2USe3S2 were grown from a molten CsCl/KCl eutectic flux at 950 °C and used for structure determination using single crystal X-ray diffraction. The compound crystallizes in the orthorhombic space group Pnma in the U3S5 structure type.

Thermodynamics of fluoride-based molten fluxes for extraction of magnesium through the low temperature solid oxide membrane (LT-SOM) process

The melt quenching experiments and thermodynamic calculations of phase diagrams were carried out to investigate potential additives for the low temperature solid oxide membrane (LT-SOM) magnesium extraction process. The solubility of MgO, which is a major source of magnesium extraction, was also measured in the molten fluoride fluxes. The solubility of MgO in the 46.5MgF2-46.5CaF2-7LiF and 45MgF2-45CaF2-10NaF (wt%) systems reached 3.4 and 1.9 wt% at 1473 K, respectively, and 1.5 wt% MgO in both fluxes at 1223 K. In addition, the 45MgF2-55CaF2 binary eutectic flux, which has been widely used in SOM process, could dissolve up to 2.3 wt% MgO at 1473 K. This value is significantly lower than the literature value, i.e. 10 wt% MgO. From the evaluation of the activity coefficient of MgO in the 46.5MgF2-46.5CaF2-7LiF and 45MgF2-45CaF2-10NaF fluxes under MgO saturation, it was confirmed that the stability of MgO in the 7LiF flux is greater than that in the 10NaF flux. Hence, the driving force of MgO dissolution into the 7LiF flux is higher than that into the 10NaF flux. The newly developed molten flux for magnesium extraction using the LT-SOM process with an operating temperature lower than 1273 K is the 46.5MgF2-46.5CaF2-7LiF system.

Facile in-situ reduction: Crystal growth and magnetic studies of reduced vanadium (III/IV) silicates CaxLn1−xVSiO5 (Ln = Ce–Nd, Sm–Lu, Y)

A series of lanthanide containing mixed-valent vanadium (III/IV) silicates of the type CaxLn1−xVSiO5 (Ln = Ce–Nd, Sm–Lu, Y) was synthesized as high quality single crystals from a molten chloride eutectic flux, BaCl2/NaCl. Utilizing Ca metal as the reducing agent, an in-situ reduction of V5+ to V3+/4+ as well as of Ce4+ to Ce3+ was achieved. The structures of 14 reported isostructural compounds were determined by single crystal X-ray diffraction. They crystallize in the tilasite (CaMgAsO4F) structure type in the monoclinic space group C2/c. The extended structure contains 1D chains of VO6 octahedra that are connected to each other via SiO4 groups and (Ca/Ln)O7 polyhedra. The magnetic susceptibility and the field dependent magnetization data were measured for CaxLn1−xVSiO5 (Ln = Ce–Nd, Sm, Gd–Lu, Y), and support the existence of antiferromagnetic behavior at low temperatures.

In Situ Neutron Diffraction Studies of the Flux Crystal Growth of the Reduced Molybdates La4Mo2O11 and Ce4Mo2O11: Revealing Unexpected Mixed-Valent Transient Intermediates and Determining the Sequence of Events during Crystal Growth

Exploratory flux-mediated crystal growth is one route to discovering novel inorganic compounds, including metastable ones; however, the method does not reveal the existence of intermediates or transient species, as only the final products are isolated at the end of the reaction. Uncovering the presence of any potential intermediates or transient species is, thus, of interest and can be achieved via in situ X-ray or neutron diffraction crystal growth studies to observe, in real time, the processes occurring, including phase formation and crystal growth. In this study we investigated the processes involved in the crystal growth of La4Mo2O11 and Ce4Mo2O11, two reduced Mo5+-containing oxides synthesized in a NaCl/CsCl eutectic flux, and studied via in situ diffraction experiments at the POWGEN beamline at the Spallation Neutron Source. These in situ studies reveal the appearance and disappearance of staring materials, intermediates, and final products. Several transient phases that formed as either single crystals or polycrystalline powders were identified and the reaction conditions (temperature and time) for their formation in single-crystals form established, enabling the use of quenching experiments to isolate these single-crystal transient species and to carry out their structural characterization. Additionally, by changing the reactants-to-flux ratio, different reaction pathways were observed to ultimately result in the same target phase. A higher flux-to-reagent ratio was shown to favor the formation of reduced molybdenum transient phases.

Clusters, Assemble: Growth of Intermetallic Compounds from Metal Flux Reactions.

Metal flux synthesis involves the reaction of metals and metalloids in a large excess of a low-melting metal that acts as a solvent. This technique makes use of an unusual temperature regime (above the temperatures used for solvothermal methods and below the temperatures used in traditional solid state synthesis) and facilitates the growth of products as large crystals. It has proven to be a fruitful method to discover new intermetallic compounds. However, little is known about the chemistry occurring within a molten metal solvent; without an understanding of the nature of precursor formation and assembly, it is difficult to predict product structures and target properties. Organic chemists have a vast toolbox of well-known reagents and reaction mechanisms to use in directing their synthesis toward a desired molecular structure. This is not yet the case for the synthesis of inorganic extended structures. We have carried out extensive explorations of the growth of new magnetic intermetallic compounds from a variety of metal fluxes. This Account presents a review of some of our results and recent reports by other groups; this work indicates that products with common building blocks and homologous series with identical structural motifs are repeatedly seen in metal flux chemistry. For instance, fluorite-type layers comprised of transition metals coordinated by eight main group metal atoms are found in the Th2(AuxSi1-x)[AuAl2]nSi2 and R[AuAl2]nAl2(AuxSi1-x)2 series grown from aluminum flux, the CenPdIn3n+2 series grown from indium flux, and CePdGa6 and Ce2PdGa10 grown from gallium flux. Similarly, our investigations of reactions of heavy main group metals, M, in rare earth/transition metal eutectic fluxes reveal that the R/T/M/M' products usually feature M-centered rare earth clusters M@R8-12, which share faces to form layers and networks that surround transition metal building blocks. These structural trends, temperature dependence of products formed in the flux, and interconversions observed by differential scanning calorimetry support the idea that these clusters likely form in the melt, existing as precursors and assembling into different crystalline products depending on time, temperature, and reaction ratio. Proof of this mechanism will require future investigations using techniques such as pair distribution function analysis of flux melts to observe cluster formation and in situ diffraction during cooling to detect various phases as they crystallize and interconvert. These data will aid in understanding the parameters that control cluster formation and assembly in metal melts, allow for prediction of products of flux reactions, and will potentially enable the tailoring of reaction conditions to promote the formation of structures with desirable properties.

New cerium cobalt borocarbide synthesized from eutectic metal flux mixture

Cerium cobalt borocarbide grown from Ce/Co eutectic flux has a partially disordered structure containing cobalt squares capped with borocarbide chains.

ChemInform Abstract: Single Crystal Growth and Characterization of NaxLn1‐xMoO4, Ln: La, Ce, Pr, Nd, Sm, and Eu (x: 0.397—0.499).

AbstractSingle crystals of the reduced lanthanoid‐containing compounds La0.516Na0.484MoO4, Ce0.512Na0.488MoO4, Pr0.502Na0.498MoO4, Nd0.501Na0.499MoO4, Sm0.509Na0.491MoO4, and Eu0.603Na0.397MoO4 are grown from a NaCl/CsCl eutectic flux by in‐situ reduction using 2:1:0.5 molar mixtures of MoO3, Ln2O3, and Mo, the latter acting as reducing agent (evacuated silica tubes, 825 °C, 24 h; cooling to 450 °C at a rate of 6 °C/h).

ChemInform Abstract: Nd8Co4‐xAlxGe2C3: A Case Study in Flux Growth of Lanthanide‐Rich Intermetallics.

AbstractNd8Co4‐xAlxGe2C3 (x ≅ 0.65) is prepared by reaction of Ge and carbon in a Nd/Co eutectic flux (alumina crucible in evacuated silica tubes, 950 °C, 12 h).

Single crystal growth and characterization of NaxLn1−xMoO4, Ln=La, Ce, Pr, Nd, Sm, and Eu (x=0.397–0.499)

Single crystals of La0.516(3)Na0.484(3)MoO4, Ce0.512(2)Na0.488(2)MoO4, Pr0.502(2)Na0.498(2)MoO4, Nd0.501(2)Na0.499(2)MoO4, Sm0.509(2)Na0.491(2)MoO4, and Eu0.603(2)Na0.397(2)MoO4 were grown for the first time out of an alkali metal halide eutectic flux. All compounds crystallize in the tetragonal space group I41/a. UV/Vis measurements show the presence of an absorption edge for all compounds except Eu0.603(2)Na0.397(2)MoO4. The temperature dependence of the magnetic susceptibility was measured for all compounds and found to be paramagnetic across the entire 2–300K temperature range measured.

Flux growth and magnetic properties of rare earth cobalt germanide, RE6Co5Ge1+xAl3−x (RE=Pr, Nd; x≈0.8)

The intermetallic compounds RE6Co5Ge1+xAl3−x (RE=Pr, Nd) were synthesized from the reaction of germanium and aluminum in RE/Co eutectic flux. These phases crystallize with the Nd6Co5Ge2.2 structure type in hexagonal space group P-6m2 (a=9.203(2)Å, c=4.202(1) Å, R1=0.0109 for Pr6Co5Ge1.80Al2.20; and a=9.170(3) Å, c=4.195(1) Å, R1=0.0129 for Nd6Co5Ge1.74Al2.26). The structure features chains of face-sharing Ge@RE9 clusters intersecting hexagonal cobalt nets linked by aluminum atoms. Magnetic susceptibility measurements indicate that both phases exhibit ferromagnetic ordering of the cobalt layers with TC in the range of 130–140K. The magnetic moments of the rare earth ions order at lower temperature (30–40K). Magnetic measurements on oriented crystals of Nd6Co5Ge1.74Al2.26 show a strong preference of the moments to order along the c-axis.