Crystal structure and spectroscopic studies of NaGd(PO3)4

Single crystals of gadolinium–sodium polyphosphate NaGd(PO₃)₄ were grown for the first time using a flux method and characterized by X-ray diffraction. This phosphate crystallizes in a monoclinic system with P2₁/n space group and with the following unit-cell dimensions: a = 9.767(3) Å, b = 13.017(1) Å, c = 7.160(2) Å, β = 90.564(5)°, V = 910.3(4) Å³ and Z = 4. The crystal structure was solved from 3451 X-ray independent reflections with final R(F²) = 0.0219 and R_w(F²) = 0.056 refined with 164 parameters (). The atomic arrangement can be described as a long chain polyphosphate organization. Two infinite (PO₃)∝ chains with a period of eight tetrahedra run along the [0 1 1] direction. The structure of NaGd(PO₃)₄ consists of GdO₈ polyhedra sharing oxygen atoms with phosphoric group PO₄. Each Na⁺ ion is bonded to eight oxygen atoms.     

Spectral properties of Tm:NaGd(MoO4)2 crystal

The Tm³⁺:NaGd(MoO₄)₂ crystal with dimensions of Φ 15 × 38 mm² was grown by Czochralski method. Polarized absorption and fluorescence spectra at room temperature were investigated. The absorption bands attributed to ³H₆ → ³H₄ transition have large absorption cross-sections, which are 3.99 × 10⁻²⁰ and 2.36 × 10⁻²⁰ cm² for σ- and π-polarization, respectively. The emission bands corresponding to the ³H₄ → ³H₆ transition are strong and broad with emission cross-sections of 1.33 × 10⁻²⁰ and 1.20 × 10⁻²⁰ cm² for σ- and π-polarization, respectively. The correlative full widths at half maximum are 35 nm for σ-polarization and 36 nm for π-polarization. The fluorescence lifetime for the ³H₄ → ³F₄ transition is 146 μs and the luminescent quantum efficiency is 76.8%.     

Growth and characterization of non-linear optical crystal Cd3Zn3B4O12

Cd₃Zn₃B₄O₁₂ polycrystals were synthesized by solid-state and wet chemical reaction methods. Cd₃Zn₃B₄O₁₂ single crystals with millimeter grade were grown from the self-flux B₂O₃ (Cd:Zn:B = 1:1:1.5); and larger crystals were obtained from the PbO-0.85PbF₂ fluxes easily. As-grown crystals were characterized by differential scanning calorimetry and thermogravimetric, X-ray diffraction, infrared and Raman spectral analysis, respectively. The non-linear optical coefficient of the Cd₃Zn₃B₄O₁₂ crystal is 2.6 times as large as that of KH₂PO₄ crystal. Chemical etching shows that this crystal is very stable in neutral solution and not hygroscopic in air at room temperature.     

Preparation, structure and luminescent properties of a new potassium yttrium borate K3Y3(BO3)4

A new yttrium borate compound K₃Y₃(BO₃)₄ has been obtained in the K₂O-Y₂O₃-B₂O₃ ternary system. Its structure, determined from single crystal X-ray diffraction data, shows that it belongs to space group P2₁/c with unit cell dimensions of a = 10.4667(16) Å, b = 17.361(3) Å, c = 13.781(2) Å and β = 110.548(8)°. The structure consists sheets of [Y₈B₈O₂₄]_∞ linked by out of sheet BO₃ groups and Y ions to form a three-dimensional framework. The luminescent properties of Eu³⁺ and Tb³⁺ doped K₃Y₃(BO₃)₄ materials have also been studied.     

Phase relations of the Li2O-Ta2O5-B2O3 and Li2O-WO3-B2O3 systems and promising nonlinear optical compounds in K2O-Ta2O5-B2O3 system

The subsolidus phase equilibria of the Li₂O-Ta₂O₅-B₂O₃, K₂O-Ta₂O₅-B₂O₃ and Li₂O-WO₃-B₂O₃ systems have been investigated mainly by means of the powder X-ray diffraction method. Two ternary compounds, KTaB₂O₆ and K₃Ta₃B₂O₁₂ were confirmed in the system K₂O-Ta₂O₅-B₂O₃. Crystal structure of compound KTaB₂O₆ has been refined from X-ray powder diffraction data using the Rietveld method. The compound crystallizes in the orthorhombic, space group Pmn2₁ (No. 31), with lattice parameters a = 7.3253(4) Å, b = 3.8402(2) Å, c = 9.3040(5) Å, z = 2 and D_calc = 4.283 g/cm³. The powder second harmonic generation (SHG) coefficients of KTaB₂O₆ and K₃Ta₃B₂O₁₂ were five times and two times as large as that of KH₂PO₄ (KDP), respectively.     

Synthesis of shape-controlled Nb3O7F/NbB2 heterostructure: A new idea to synthesize binary hybrid materials by incomplete reaction

Niobium oxide fluoride/niobium diboride (Nb₃O₇F/NbB₂) heterostructures with urchin-like and nanowall-like morphologies were synthesized by a facile hydrothermal approach. The high-density one-dimensional Nb₃O₇F nanoneedle arrays and two-dimensional Nb₃O₇F nanosheets stand on the surface of NbB₂ cores. Here a new idea is proposed to synthesize binary heterostructure by in situ “incomplete reaction”. Ultraviolet-visible spectra showed that such heterostructure has a wide absorption peak at around 270 nm and the absorption edge of the products synthesized at higher temperature shifts to longer wavelength because of stronger nanometric effect.     

Synthesis and characterization of the colossal magnetoresistance manganite La1.2(Sr1.4Ca0.4)Mn2O7 by citrate gel

Single-phase La_1.2(Sr_1.4Ca_0.4)Mn₂O₇ has been synthesized from the aqueous solution of metal nitrates and citric acid by the sol-gel technique. Small particle size with high homogeneity of the powder was obtained. The valence of Mn is determined to be 3.45±0.05 by chemical titration. The MR ratio [ρ−ρ(H)]/ρ(H), is 115% (102 K, 1.5 T) for the composition prepared by the citrate route, and is nearly three times larger than that of the sample prepared by solid state reaction.     

Luminescent properties of long lasting phosphor Ca2MgSi2O7:Eu

Long afterglow phosphors (Ca_1−xEu_x)₂MgSi₂O₇ (0.002 ≤ x ≤ 0.02) were prepared by solid-state reactions under a weak reductive atmosphere. X-ray diffraction pattern, photoluminescence spectra, decay curve, afterglow spectra and thermoluminescence curves were investigated. The phosphors showed two emission peaks when they were excited by 343 nm, due to two types of Eu²⁺ centers existing in the Ca₂MgSi₂O₇ lattice. However, only one emission peak can be found in their afterglow spectra. Energy transfer between Eu²⁺ ions in inequivalent sites was found. A possible mechanism was presented and discussed. The afterglow decay time of Ca_1.998MgSi₂O₇:Eu_0.002 was nearly 12.5 h which means it was a good long lasting phosphor.     

Hydrothermal synthesis, characterization and magnetic properties of NaVGe2O6 and LiVGe2O6

Supercritical fluids are shown to be an excellent reaction media for the synthesis of novel solid state phases at intermediate temperatures. LiVGe₂O₆ and NaVGe₂O₆ have the common pyroxene structure composed of VO₆ linear chains. NaVGe₂O₆ crystallizes in the monoclinic space group C2/c with four formula units having cell dimensions a = 9.960(4) Å, b = 8.853(10) Å, c = 5.4861(10) Å, β = 106.403(3)°. The structure was refined until R = 0.0290 and R_w = 0.0370. For LiVGe₂O₆ in space group P2₁/c: a = 9.8508(7) Å, b = 8.754(3) Å, c = 5.3948(13) Å, β = 108(3)°, R = 0.0240 and R_w = 0.0250. The compounds contain edge-shared VO₆ octahedral chains and corner-shared GeO₄ tetrahedral chains. The presence of these VO₆ chains results in spin-Peierls distortion. Structural and physical characterization of the compounds are reported.     

Crystal growth and spectral properties of Pr:La2(WO4)3

Pr³⁺-doped La₂(WO₄)₃ single crystal with dimensions up to Ø 20 mm × 35 mm has been grown by the Czochralski method. The structure of the Pr³⁺:La₂(WO₄)₃ crystal was determined by the X-ray powder diffraction and the Pr³⁺ concentration in this crystal was determined. The absorption and fluorescence spectra of Pr³⁺:La₂(WO₄)₃ crystal were measured at room temperature, and the fluorescence lifetime of main emission multiplets were estimated from the recorded decay curves. The spectral properties related to laser performance of the crystal were evaluated.     

Y2O3:Eu microstructures: Hydrothermal synthesis and photoluminescence properties

Hexagonal microprisms of yttrium hydroxide (Y(OH)₃) with tuned diameter and height have been successfully prepared for the first time via a facile hydrothermal process using sodium citrate as the shape modifying agent. Y(OH)₃ microspheres with diameter of ca. 2.5 μm and microtubes with an average length about 13 μm, outer diameter about 3 μm and tube thickness about 800 nm were also obtained in current reaction systems. The possible formation mechanism for the Y(OH)₃ microstructures was briefly proposed. Y₂O₃:Eu³⁺ (5%) microstructures with similar morphologies was obtained after thermal treatment of the as-prepared Y(OH)₃:Eu³⁺ microstructures at 700 °C for 4 h. Results show that the relative emission intensity of the Y₂O₃:Eu³⁺ microprisms is about 8 times as those of the Y₂O₃:Eu³⁺ microtubes and microspheres under excitation of 259 nm ultraviolet light. The products were characterized by XRD, SEM, and EDS.     

Growth and optical properties of Er,Yb:YAl3(BO3)4 crystal

Single crystal of erbium, ytterbium-codoped yttrium aluminum tetraborate Er,Yb:YAl₃(BO₃)₄(Er,Yb:YAB) has been grown by the flux method. The absorption spectrum in the visible and NIR regions of Er,Yb:YAl₃(BO₃)₄ crystal are measured at room temperature and fluorescence spectrum of Er,Yb:YAl₃(BO₃)₄ crystal are also measured at room temperature, excited by 976 nm laser. Not only the strong NIR emission peaks located at 1548 nm was observed, but also the visible up-conversion luminescence has been found. The specific heat of the Er/Yb:YAB crystal at room temperature is 0.81 J/g °C.     

Crystal structure and spectroscopic properties of a new oxyarsenate Li0.5Ni0.25TiOAsO4

The new oxyarsenate Li_0.5Ni_0.25TiOAsO₄ has been synthesized and studied by a combination of X-ray powder diffraction, neutrons powder diffraction and vibrational spectroscopy. Li_0.5Ni_0.25TiOAsO₄ crystallizes in the monoclinic P2₁/c space group with the unit cell parameters: a = 6.5854(3) Å, b = 7.4665(4) Å, c = 7.4969(4) Å, β = 89.884(6)°, V = 368.62(1) Å³ and Z = 4. The structure has been determined at room temperature from neutrons diffraction by the Rietveld method analysis. It is formed by a 3D network of TiO₆ octahedra and AsO₄ tetrahedra sharing corners. Structural refinement shows a partial and a statistical occupancy of 2a and 2b sites by Li⁺ and Ni²⁺ ions. TiO₆ octahedra are linked together by corners and form infinite chains along c-axis. Raman and infrared studies confirm the existence of -TiOTi- chains. Diffuse reflectance spectrum indicates the presence of octahedrally coordinated Ni²⁺ ions.     

Formation of NiFe2O4 nanoparticles by mechanochemical reaction

Preparation of nanosized NiFe₂O₄ particles by mechanochemical reaction(NiO+α-Fe₂O₃) and subsequent thermal treatment was investigated using X-ray diffraction (XRD). Thermal treatment of the as-milled powder at 700 °C for 1 h led to the formation of NiFe₂O₄ nanoparticles with an average crystal size of about 23 nm. Effect of thermal treatment temperature on the crystal size of the nanoparticles was studied. The mechanism of nanoparticles growth was primarily discussed. The activation energy of NiFe₂O₄ nanoparticle formation during calcination was calculated to be 16.6 kJ/mol.     

Chemical preparation, crystal structure and characterization of the new sodium ytterbium cyclotriphosphate Na3Yb(P3O9)2·9H2O

Chemical preparation and crystal structure are reported for a new lanthanide cyclotriphosphate Na₃Yb(P₃O₉)₂·9H₂O. This salt crystallizes in the trigonal system, space group with the following parameters: a = 30.933(2), c = 12.8282(5) Å. The crystal structure was refined to R₁ = 0.0432 using 1782 reflections with I > 2 σ(I). In the Na₃Yb(P₃O₉)₂·9H₂O structure, the phosphoric ring anions, located around the axis are interconnected by YbO₈ dodecahedra and NaO₆ and NaO₇ polyhedra to build, around the threefold axis, large channels parallel to the c axis. All the nine water molecules in the present arrangement participate in the coordination spheres of the associated cations. The thermogravimetric analysis shows that the removal of these water molecules occurs in three stages between 305 and 736 K.The vibrational study by IR absorption spectroscopy of Na₃Yb(P₃O₉)₂·9H₂O is also reported.     

Structural characterization and AC conductivity of bis tetrapropylammonium hexachlorado-dicadmate, [N(C3H7)4]2Cd2Cl6

Synthesis, crystal structure, vibrational study, ¹³C, ¹¹¹Cd CP-MAS-NMR analysis and electrical properties of the compound [N(C₃H₇)₄]₂Cd₂Cl₆, are reported. The latter crystallizes in the triclinic system (space group , Z = 2) with the following unit cell dimensions: a = 9.530(1) Å, b = 11.744(1) Å, c = 17.433(1) Å, α = 79.31(1)°, β = 84.00(1)° and γ = 80.32(1)°. Besides, its structure was solved using 6445 independent reflections down to R = 0.037. The atomic arrangement can be described by alternating organic and inorganic layers parallel to the plan, made up of tetrapropylammonium groups and Cd₂Cl₆ dimers, respectively. In crystal structure, the inorganic layer, built up by Cd₂Cl₆ dimers, is connected to the organic ones through van der Waals interaction in order to build cation-anion-cation cohesion. Impedance spectroscopy study, reported in the sample, reveals that the conduction in the material is due to a hopping process. The temperature and frequency dependence of dielectric constants of the single crystal sample has been investigated to determine some related parameters to the dielectric relaxation.     

Single crystalline Co3O4: Synthesis and optical properties

Crystals of Co₃O₄ have been prepared from thermal decomposition of molecular precursors derived from salicylic acid and cobalt (II) acetate or chloride at 500 °C. A cubic phase Co₃O₄ micro- and nanocrystals have been obtained. The as-synthesized products were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). The images of electron microscopes showed octahedral crystals of Co₃O₄. The volume and polarizability of the optimized structures of molecular precursors have been calculated and related to the particle size. The optical band gap of the obtained crystals has been measured. The results indicated two optical band gaps with values 2.65 and 2.95 eV for (E_g1) (E_g2), respectively.     

Optical, magnetic and electronic properties of Ln2O2Te (Ln = La, Sm and Gd)

The synthesis, the optical and magnetic properties and the electronic structure of the rare-earth oxytellurides of formula Ln₂O₂Te (Ln = La, Sm and Gd) are reported. The magnetic measurements show that La₂O₂Te exhibit a diamagnetic behavior. The value of the magnetization M of Gd₂TeO₂ at our highest available field (50 kOe) is about 5.5μ_B, well below the expected value for two independent Gd ions (2gJ = 14μ_B) confirming the antiferromagnetic character of this compound. The magnetic properties of Sm₂TeO₂ reveal that Sm is in its 3+ oxidation state with a large Van Vleck contribution. The electronic structure calculations, studied by means of a first principles DFT approach, are consistent with the optical measurements and suggest an indirect band gap semiconductor behavior.     

Larger Ba(NO3)2/Sr(NO3)2 crystal growth and solubility determination

The solubility of Ba(NO₃)₂ and Sr(NO₃)₂ crystals in aqueous solution from 25 to 65 °C has been determined by both an optical interferometer and a weight technique. A Mach-Zehnder interferometer was used for measuring the concentration distribution of Ba(NO₃)₂ and Sr(NO₃)₂ near the solid/liquid interface during crystal growth and dissolution. A fringe carrier technique was introduced to visualize more clearly the boundary layer and to solve the concentration distribution. Crystals were successfully grown with sizes larger than  mm by a temperature cooling method. The Ba_xSr_1−x(NO₃)₂ crystal was also nucleated and grown. The Raman spectra of Ba_xSr_1−x(NO₃)₂ indicate that the barium ions probably degrade the properties of Sr(NO₃)₂.     

Cu5Sb2O8SiO4, an open framework structure with copper uncommon coordination modes: CuO6 and CuO8

Cu₅Sb₂O₈SiO₄ is orthorhombic, space group Pcca, with a = 19.031 (2), b = 9.3944 (6), c = 9.602 (2) Å, and z = 8. Its crystal structure was determined using single crystal X-ray diffraction (R₁ = 0.0432 and wR₂ = 0.1146). The compound presents a parwelite-like structure. Its anionic three-dimensional framework is built up of corner-sharing SbO₆ octahedra and SiO₄ tetrahedra, delimiting interconnected channels wherein Cu²⁺ with different coordination modes, are located. The χ_M and χ_MT product versus T plots, showed the Cu₅Sb₂O₈SiO₄ material to exhibit an anti-ferromagnetic character with a Neel temperature of about 27 K.