Search

The authors study the formation of crystals of Fe-Ga oxides and Fe–Ga–Cu borates in a multicomponent flux system based on Bi2Mo3O12–Na2B4O7. The Curie–Weiss temperature (θCW = 289 K) and the temperature of the ferrimagnet–paramagnet phase transition (TC = 288 K) are determined from the electron spin resonance (ESR) spectrum and the magnetization of an Fe1.1Ga0.9O3 single crystal, depending on temperature. Lines of spin-wave resonance are observed in the spectrum of magnetic resonance in the ordered phase. [ABSTRACT FROM AUTHOR]

The M-type barium hexaferrite substituted with titanium, BaFe 12 − x Ti x O 19 , was synthesized from sodium carbonate flux and the obtained single crystals with a maximum degree of substitution of up to about x = 0.9 were characterized. XPS measurements were carried out for the identification of side products and in particular in order to assign the valence states of the transition-metal constituents. Due to the aliovalent exchange of iron(III) with titanium(IV), an additional charge balance needs to occur. No titanium(III) was detected, while the amount of iron(II) increased in the same order of magnitude as the amount of titanium(IV); thus, the major charge balancing is attributed to the reduction of iron(III) to iron(II). According to the XPS data, the amount of titanium(IV) typically is slightly higher than that of iron(II). This is in line with a tendency to a minor formation of vacancies on the transition-metal sites becoming more important at higher substitution levels according to PXRD and WDS measurements, completing the picture of the charge-balance mechanism. XRD taken on single crystals indicates the distribution of titanium and vacancies over three of the five transition-metal sites. [ABSTRACT FROM AUTHOR]

We report a flux crystal growth of Ba2[(UO2)2Ti2O8] and subsequent structural and spectroscopic studies using multiple techniques. The layered crystal structure, built up with sheets of edge‐sharing dimeric uranyl pentagonal bipyramids and dimeric TiO5 square pyramids with interlayer Ba(II) ions, was revealed by synchrotron single crystal x‐ray diffraction and confirmed with electron diffraction using a transmission electron microscope. The presence of only hexavalent uranium was confirmed by both diffuse reflectance and x‐ray absorption near‐edge structure spectroscopies, consistent with the bond valence sum calculations. Its vibrational modes were revealed by Raman spectroscopy. In addition, its implications as a potential hexavalent uranium waste form for the immobilization of uranium‐rich radioactive wastes were discussed. [ABSTRACT FROM AUTHOR]

The M-type barium hexaferrite substituted with titanium, BaFe12−xTixO19, was synthesized from sodium carbonate flux and the obtained single crystals with a maximum degree of substitution of up to about x = 0.9 were characterized. XPS measurements were carried out for the identification of side products and in particular in order to assign the valence states of the transition-metal constituents. Due to the aliovalent exchange of iron(III) with titanium(IV), an additional charge balance needs to occur. No titanium(III) was detected, while the amount of iron(II) increased in the same order of magnitude as the amount of titanium(IV); thus, the major charge balancing is attributed to the reduction of iron(III) to iron(II). According to the XPS data, the amount of titanium(IV) typically is slightly higher than that of iron(II). This is in line with a tendency to a minor formation of vacancies on the transition-metal sites becoming more important at higher substitution levels according to PXRD and WDS measurements, completing the picture of the charge-balance mechanism. XRD taken on single crystals indicates the distribution of titanium and vacancies over three of the five transition-metal sites.

A new niobium-doped inorganic scintillating oxyfluoride, Rb4Ge5O9F6:Nb, was synthesized in single crystal form by high-temperature flux growth. The host structure, Rb4Ge5O9F6, crystallizes in the orthorhombic space group Pbcn with lattice parameters a = 6.98430(10) Å, b = 11.7265(2) Å, and c = 19.2732(3) Å, consisting of germanium oxyfluoride layers made up of Ge3O9 units connected by GeO3F3 octahedra. In its pure form, Rb4Ge5O9F6 shows neither luminescence nor scintillation but when doped with niobium, Rb4Ge5O9F6:Nb exhibits bright blue luminescence and scintillation. The isostructural doped structure, Rb4Ge5O9F6:Nb, crystallizes in the orthorhombic space group Pbcn with lattice parameters a = 6.9960(3) Å, b = 11.7464(6) Å, and c = 19.3341(9) Å. X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) measurements suggest that the niobium is located in an octahedral coordination environment. Optical measurements inform us that the niobium dopant acts as the activator. The synthesis, structure, and optical properties are reported, including radioluminescence (RL) measurements under X-ray irradiation. [ABSTRACT FROM AUTHOR]

Chalcogenide‐containing compounds have been widely studied as infrared nonlinear optical (NLO) materials. However, they have never been applied in the ultraviolet (UV) region owing to the high energy levels of chalcogen anions, leading to band gap narrowing. We report the synthesis of a new UV NLO oxysulfide La3Ga3Ge2S3O10 with an exceptionally wide band gap of 4.70 eV due to from the unique anion‐ordered frameworks comprising 1D 1∞[(Ga3/5Ge2/5)3S3O3] triangular tubes and 0D (Ga3/5Ge2/5)2O7 dimers of corner‐sharing (Ga/Ge)S2O2 and (Ga/Ge)O4 tetrahedra, respectively. Second harmonic generation (SHG) measurements revealed that La3Ga3Ge2S3O10 was phase matchable with twice the SHG response of KH2PO4. The results of theoretical calculations suggest that the strong SHG response is mainly attributable to the S‐3p and O‐2p orbitals in the occupied states. The anion‐directed band‐gap engineering may give insights into the application of NLO oxychalcogenides in the UV regions. [ABSTRACT FROM AUTHOR]

A new niobium-doped inorganic scintillating oxyfluoride, Rb4Ge5O9F6:Nb, was synthesized in single crystal form by high-temperature flux growth. The host structure, Rb4Ge5O9F6, crystallizes in the orthorhombic space group Pbcn with lattice parameters a = 6.98430(10) Å, b = 11.7265(2) Å, and c = 19.2732(3) Å, consisting of germanium oxyfluoride layers made up of Ge3O9 units connected by GeO3F3 octahedra. In its pure form, Rb4Ge5O9F6 shows neither luminescence nor scintillation but when doped with niobium, Rb4Ge5O9F6:Nb exhibits bright blue luminescence and scintillation. The isostructural doped structure, Rb4Ge5O9F6:Nb, crystallizes in the orthorhombic space group Pbcn with lattice parameters a = 6.9960(3) Å, b = 11.7464(6) Å, and c = 19.3341(9) Å. X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) measurements suggest that the niobium is located in an octahedral coordination environment. Optical measurements inform us that the niobium dopant acts as the activator. The synthesis, structure, and optical properties are reported, including radioluminescence (RL) measurements under X-ray irradiation.

In this review we discuss general trends in the use of alkali bromide and iodide (ABI) fluxes for exploratory crystal growth. The ABI fluxes are ionic solution fluxes at moderate to high temperatures, 207 to ~1,300°C, which offer a good degree of flexibility in the selection of the temperature profile and solubility. Although their main use is to dissolve and recrystallize “soft” species such as chalcogenides, many compositions with “hard” anions, including oxides and nitrides, have been obtained from the ABI fluxes, highlighting their unique versatility. ABI fluxes can serve to provide a reaction and crystallization medium for different types of starting materials, mostly the elemental and binary compounds. As the use of alkali halide fluxes creates an excess of the alkali cations, these fluxes are often reactive, incorporating one of its components to the final compositions, although some examples of non-reactive ABI fluxes are known.

A new germanate garnet compound, Ce2CaMg2Ge3O12, was synthesized via flux crystal growth. Truncated spherical, reddish-orange single crystals with a typical size of 0.1–0.3 mm were grown out of a BaCl2-CaCl2 melt. The single crystals were characterized by single-crystal X-ray diffraction analysis, which revealed that it adopted a cubic garnet-type structure with a = 12.5487(3) Å in the space group Ia−3d. Its composition is best described as A3B2C3O12, where Ce/Ca, Mg, and Ge occupied the A, B, and C sites, respectively. A UV–vis absorption spectroscopy measurement on the germanate garnet revealed a clear absorption edge corresponding to a band gap of 2.21 eV (λ = 561 nm). First-principle calculations indicated that the valence band maximum was composed of Ce 4f bands, whereas the conduction band minimum mainly consisted of Ce 5d bands. These findings explain the observed absorption edge through the Ce 4f → 5d absorption. Photoluminescence emission spectra exhibited a very broad peak centered at 600 nm, corresponding to transition from the lowest energy d level to the 4f levels.

Single crystals of four new layered uranyl phosphates, including three oxyfluoride-phosphates, were synthesized by molten flux methods using alkali chloride melts, and their structures were determined by single-crystal X-ray diffraction. Cs11[(UO2)12(PO4)3O13] (1) and Rb11[UO2)12(PO4)3O12F2] (2) contain uranyl phosphate layers exhibiting a new sheet topology that can be related to that of β-U3O8, while Cs4.4K0.6[(UO2)6O4F(PO4)4(UO2)] (3) and Rb4.4K0.6[(UO2)6O4F(PO4)4(UO2)] (4) contain layers of a known isomer of the prominent phosphuranylite topology. The location of the fluorine in structures 2-4 is discussed using bond valence sums. First principles calculations were used to explore why a pure oxide structure is obtained for the Cs containing phase (1) and in contrast an oxyfluoride phase for the Rb containing phase (2). Ion exchange experiments were performed on 1 and 2 and demonstrate the ability of these structures to exchange approximately half of the parent alkali cation with a target alkali cation in an aqueous concentrated salt solution. Optical measurements were performed on 1 and 2 and the UV-vis and fluorescence spectra show features characteristic of the UO22+ uranyl group.

Highlights • Well-shaped KBa R (BO 3) 2 (R = Gd, Tb, Dy, Ho, Tm and Yb) single crystals were grown by flux method. • The anisotropic magnetic properties of KBa R (BO 3) 2 (R = Gd, Tb, Dy, Ho, Tm and Yb) were studied for the first time. • A good model with R -based triangular lattice was studied here. Abstract Crystals of the KBa R (BO 3) 2 (R = Y, Gd, Tb, Dy, Ho, Tm, Yb and Lu) rare earth borates were grown by spontaneous nucleation from a KF-B 2 O 3 flux. The crystals obtained were typically well-developed hexagonal plates about 1 mm in large dimension. The crystals were used to study the anisotropic temperature and field dependent magnetization of the materials, which are based on ideal triangular planes of magnetic rare earths. All structures were refined in space group R 3 - m by single-crystal X-ray diffraction, and in addition to the equilateral triangular rare earth plane lattice, displayed K/Ba site occupancy disorder. All magnetic compounds reveal dominantly antiferromagnetic spin interactions with no magnetic ordering above 1.8 K. With the exception of KBaGd(BO 3) 2 , magnetic anisotropy was observed for other five magnetic members of the family. The results suggest that KBa R (BO 3) 2 crystals may be of further interest for investigating the magnetic properties of rare earth ions on a triangular lattice. [ABSTRACT FROM AUTHOR]

A series of lanthanide containing mixed-valent vanadium (III/IV) silicates of the type Ca x Ln 1−x VSiO 5 ( Ln = Ce–Nd, Sm–Lu, Y) was synthesized as high quality single crystals from a molten chloride eutectic flux, BaCl 2 /NaCl. Utilizing Ca metal as the reducing agent, an in-situ reduction of V 5+ to V 3+/4+ as well as of Ce 4+ to Ce 3+ was achieved. The structures of 14 reported isostructural compounds were determined by single crystal X-ray diffraction. They crystallize in the tilasite (CaMgAsO 4 F) structure type in the monoclinic space group C 2 /c . The extended structure contains 1D chains of VO 6 octahedra that are connected to each other via SiO 4 groups and (Ca/ Ln )O 7 polyhedra. The magnetic susceptibility and the field dependent magnetization data were measured for Ca x Ln 1−x VSiO 5 ( Ln = Ce–Nd, Sm, Gd–Lu, Y), and support the existence of antiferromagnetic behavior at low temperatures. [ABSTRACT FROM AUTHOR]

Single crystals of mixed valent barium titanium(III/IV) chlorosilicate, Ba 3 Ti 2 Si 4 O 14 Cl 0.91 O 0.09 , were grown in a high temperature molten chloride flux involving an in situ reduction step. The fresnoite structure related Ba 3 Ti 2 Si 4 O 14 Cl 0.91 O 0.09 crystallizes in the tetragonal space group P 4/ mbm with lattice parameters of a =8.6717(2) Å, c =18.6492(5) Å. The title compound exhibits a 3D structure consisting of 2D layers of fused Ti 2 O 9 and Si 4 O 12 groups and 2D layers of fused Ti 2 O 9 Cl 2 and Si 2 O 7 groups that are linked via barium atoms. The in situ reduction of Ti(IV) to Ti(III) is achieved via the addition of metallic Mg to the flux to function as the reducing agent. The temperature dependence of the magnetic susceptibility shows simple paramagnetism above 100 K. There is a discontinuity in the susceptibility data below 100 K, which might be due to a structural change that takes place resulting in charge ordering. [ABSTRACT FROM AUTHOR]

Single crystals of a series of rare earth borates, A 3 Ln (BO 3) (A = Na, K; Ln = Eu, Tb), were synthesized using a boric acid/hydroxide melt. The Na 3 Ln (BO 3) 2 borates crystallized in the monoclinic system with space group P2 1 /n , and the K 3 Ln (BO 3) 2 borates crystallized in the orthorhombic system with space group Pnma. The luminescence of these borates was investigated under ultraviolet and X-ray excitations for the first time. Radioluminescence (RL) measurements showed K 3 Tb(BO 3) 2 to be the brightest compound, with an integral intensity equal to 55% of the integral emission of Bi 4 Ge 3 O 12 (BGO) powder. [Display omitted] [ABSTRACT FROM AUTHOR]

Single crystals of Ba 3 Na 0.32 Nb 6 O 12 (Si 2 O 7 ) 2 were grown for the first time. The use of an alkali/alkaline earth eutectic flux facilitated the crystal growth. Ba 3 Na 0.32 Nb 6 O 12 (Si 2 O 7 ) 2 , a mixed valent Nb(V)/Nb(IV) compound, crystallizes in the noncentrosymmetric hexagonal space group P -62 m with a = 8.9998(10) Å and c = 7.8119(17) Å. The temperature dependence of the magnetic susceptibility was measured and found to be paramagnetic across the entire 2–300 K temperature range measured. Although noncentrosymmetric, Ba 3 Na 0.32 Nb 6 O 12 (Si 2 O 7 ) 2 was not found to be second harmonic generation active. Ba 3 Na 0.32 Nb 6 O 12 (Si 2 O 7 ) 2 was further characterized by IR and UV/Vis spectroscopies. [ABSTRACT FROM AUTHOR]

We have developed laser grade and highly Yb 3+ -doped cubic rare-earth sesquioxides (RE 2 O 3 , RE = Y, Gd, Lu) single crystals by means of a newly designed high-temperature solution growth method which gives them spectroscopic properties different from those obtained by high-temperature solidification methods. Absorption and emission cross sections, visible anti-Stokes emission, fluorescence decays of the new cubic Gd 2 O 3 :Yb 3+ single crystals are presented and compared to those of Y 2 O 3 :Yb 3+ and Lu 2 O 3 :Yb 3+ crystals. The case of cubic Gd 2 O 3 :Yb 3+ is particularly interesting since its basic spectroscopic properties have never been detailed and we were capable of achieving Yb-doping level as high as 20%. [ABSTRACT FROM AUTHOR]

Solid state light sources with dynamically tunable color temperature in the range of 3000–6000 K with chromaticity coordinates lying on the Planckian black body curve has been designed using mixtures of narrow emissions at 615 nm, 575 nm and 550 nm. These respective emissions lines were generated by individual phosphor crystals of trivalent rare earth (RE 3+ ) species, europium (Eu 3+ ), dysprosium (Dy 3+ ) and terbium (Tb 3+ ) activated calcium sodium molybdenum oxide (Ca 1−2 x Na x MoO 4 :RE 3+ x ), when excited by near-ultra-violet (NUV) light emitting diode (LED) with emission wavelength of 380 nm. Highly luminescent crystals of these compounds have been grown from molten solutions (flux) of molybdenum (VI) oxide. The flux grown crystals exhibit emission intensity 2–4 times more than phosphor powders of the same compounds synthesized by traditional solid-state reactions. An optimum flux to solute ratio of 2.5 and solute dissolution temperature of 1100 °C resulted in the largest size crystals. [ABSTRACT FROM AUTHOR]

InFeO3(ZnO)4 was prepared from binary oxides as starting materials at 1350 °C in sealed platinum tubes as an earth brown powder. Single crystals were grown from a K2MoO4 flux in sealed Pt-tubes using cooling rates of -0.1 K min-1. The structure of InFeO3(ZnO)4 was refined in space group P63/ mmc; No. 194 ( a = 3.211(6) Å; c = 33.032(6) Å; Z = 2; R1 = 3.68 %) from XRD data and revealed a build-up from alternate stacking of layers of edge-sharing InO6 octahedra and 5 layers of corner-sharing (Zn/Fe)O4 tetrahedra. Inversions of the (Zn/Fe)O4 tetrahedra occurs (i) at the InO6 octahedral layer and (ii) halfway in the wurtzite type region where the inversion boundary is built by cations in 4+1 trigonal bipyramidal coordination. The position of the cations in their oxygen surrounding is described by a factor t which quantifies the displacement of the cation from the center of a trigonal bipyramid towards one of the constituting tetrahedra. Refining the site occupation factors of the cations in the (Zn/Fe)O4 tetrahedra results in a clear and reasonable gradient for the distribution of iron. Refinement of the oxygen position reveals split positions for the oxygen atoms at the second inversion boundary in the center of the wurtzite type region which shows similarities to inversion domain boundaries at fivefold coordinated cations in the wurtzite type region of compounds of type ARO3(ZnO)m with m > 15. Thus, it is more likely to describe InFeO3(ZnO)4 as a closest-packed structure of cations with oxygen filling the interstices. [ABSTRACT FROM AUTHOR]

InFeO3(ZnO)4 was prepared from binary oxides as starting materials at 1350 °C in sealed platinum tubes as an earth brown powder. Single crystals were grown from a K2MoO4 flux in sealed Pt-tubes using cooling rates of -0.1 K min-1. The structure of InFeO3(ZnO)4 was refined in space group P63/ mmc; No. 194 ( a = 3.211(6) Å; c = 33.032(6) Å; Z = 2; R1 = 3.68 %) from XRD data and revealed a build-up from alternate stacking of layers of edge-sharing InO6 octahedra and 5 layers of corner-sharing (Zn/Fe)O4 tetrahedra. Inversions of the (Zn/Fe)O4 tetrahedra occurs (i) at the InO6 octahedral layer and (ii) halfway in the wurtzite type region where the inversion boundary is built by cations in 4+1 trigonal bipyramidal coordination. The position of the cations in their oxygen surrounding is described by a factor t which quantifies the displacement of the cation from the center of a trigonal bipyramid towards one of the constituting tetrahedra. Refining the site occupation factors of the cations in the (Zn/Fe)O4 tetrahedra results in a clear and reasonable gradient for the distribution of iron. Refinement of the oxygen position reveals split positions for the oxygen atoms at the second inversion boundary in the center of the wurtzite type region which shows similarities to inversion domain boundaries at fivefold coordinated cations in the wurtzite type region of compounds of type ARO3(ZnO)m with m > 15. Thus, it is more likely to describe InFeO3(ZnO)4 as a closest-packed structure of cations with oxygen filling the interstices. [ABSTRACT FROM AUTHOR]

A new tantalum silicate, Rb 4 Ta 2 Si 8 O 23 , was synthesized as high-quality single crystals by the high temperature flux growth method. Rb 4 Ta 2 Si 8 O 23 was found to exhibit intense blue luminescence and scintillation as a self-activated luminescent silicate. Rb 4 Ta 2 Si 8 O 23 crystallizes in the triclinic space group P 1 ‾ with lattice parameters of a = 6.8916(2) Å, b = 7.7669(2) Å, c = 11.0018(3) Å, α = 76.3110(10)°, β = 89.2560(10)°, and γ = 71.8090(10)°. The structure consists of corner-sharing SiO 4 tetrahedra forming infinite ribbons connected by isolated TaO 6 octahedra. The synthesis, structure, and optical properties are reported, notably, bright blue scintillation when exposed to X-rays. The scintillation of Rb 4 Ta 2 Si 8 O 23 was quantitatively evaluated by radioluminescence (RL) measurements and was determined to be ∼47% of BGO powder. [Display omitted] • Rb 4 Ta 2 Si 8 O 23 was synthesized using flux crystal growth. • The crystal structure was solved using single crystal X-ray diffraction. • Rb 4 Ta 2 Si 8 O 23 exhibits photoluminescence and scintillation. • Scintillation intensity was quantitatively determined to be 47% of BGO powder from RL measurements. [ABSTRACT FROM AUTHOR]

The new oxytelluride Ba3Yb2O5Te was obtained from an alkaline earth flux. Ba3Yb2O5Te crystallizes in the tetragonal space group P4/mmm (#123), with a=4.3615(3)Å and c=11.7596(11)Å, Z=1. The structure combines two distinct building blocks, a Ba2Yb2O5 perovskite-like double layer with square bipyramidal coordination of the ytterbium ions, and a CsCl-type BaTe layer. Short range magnetic order is apparent at below 5K, with the magnetic behavior above this temperature dominated by crystal field effects. The structure may be considered as an analog to the Ruddlesden–Popper phases, where the NaCl-type layer has been replaced by the CsCl-type layer. The two-dimensional magnetic behavior is expected based on the highly anisotropic nature of the structure. [ABSTRACT FROM AUTHOR]

Abstract: The reactions of UO3 and TeO3 with KCl, RbCl, or CsCl at 800°C for 5d yield single crystals of A2[(UO2)3(TeO3)2O2] (A=K (1), Rb (2), and Cs (3)). These compounds are isostructural with one another, and their structures consist of two-dimensional sheets arranged in a stair-like topology separated by alkali metal cations. These sheets are comprised of zigzagging uranium(VI) oxide chains bridged by corner-sharing trigonal pyramidal TeO32- anions. The chains are composed of dimeric, edge-sharing, pentagonal bipyramidal UO7 moieties joined by edge-sharing tetragonal bipyramidal UO6 units. The lone-pair of electrons from the TeO3 groups are oriented in opposite directions with respect to one another on each side of the sheets rendering each individual sheet non-polar. The alkali metal cations form contacts with nearby tellurite oxygen atoms as well as with oxygen atoms from the uranyl moieties. Crystallographic data (193K, MoKα, ): 1, triclinic, space group , , , , , , , , , for 98 parameters and 1697 reflections with ; 2, triclinic, space group , , , , , , , , , for 98 parameters and 1817 reflections with ; 3, triclinic, space group , , , , , , , , , for 98 parameters and 1965 reflections with . [Copyright &y& Elsevier]