Preparation and crystal chemistry of some rare earth vanadium (IV) pyrochlores (RE)2V2O7; RE = Lu,Yb, Tm,Lu1−xYx, Lu1−xScx

The preparation of the phases (RE)₂V₂O₇ where RE = Lu, Yb, Tm, and the solid solutions Sc_xLu_1?x (x = .10 → .50) and Y_xLu_1?x (x = .20 and .40), using a $\text{CO}\text{CO}{}_2$ buffer system are described. Precision lattice constants were determined and compared with previous work, finding good agreement with (1) but not with (2). The solid solution (Sc_xLu_1?x)₂V₂O₇ exists as a pyrochlore to x = .30, compared with x = .55 for the similar (Sc_xLu_1?x)₂ Ti₂O₇ system. Chemical analysis on the members x = .40 and x = .50 indicate significant amounts of V(III) and X-ray data show a diminishing intensity for the “ordering” reflections (h, k, l all odd). These results suggest that Lu(III), Sc(III), V(III) and V(IV) are partially disordered over both cation sites tending toward a C-type (RE)₂O₃ structure or a defect fluorite structure with increasing x.     

Ferromagnetic semiconductors: Magnetic properties of the pyrochlores, (YxLu1−x)2V2O7 and (ScxLu1−x)2V2O7

Some magnetic properties of eight members of the pyrochlore systems (Y_xLu_1?x2V₂O₇ and (Sc_xLu_1?x)₂V₂O₇ are reported. Critical temperatures are determined for Lu₂V₂O₇ (72.5K) and the other phases to about ± 1K. Trends in T_c, π_c, C_m, μ_eff, and to a lesser extent, μ_SAT., occur which can be correlated, qualitatively, with thermogravometric data. From (Y_.40Lu_.60) to (Sc_.20Lu_.80) the quantities mentioned are nearly constant and analysis indicates the presence of V⁴⁺ only. C_m (0.47 cm³K/mole) and μ_eff (1.94 μB) are significantly greater than the spin-only values of 0.36 and 1.73 respectively. From (Sc_.30Lu_.70) to (Sc_.50Lu_.50) a reduced form of vanadium is detected, probably V³⁺, which increases with Sc content. This is accompanied by a sharp decline in T_c and π_c and a sharp increase in C_m and μ_eff.     

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%.     

Shaped single crystal growth and scintillating application of Yb:(Gd,Lu)3(Ga,Al)5O12 solid solutions

Shaped single crystals of (Yb_0.05Lu_xGd_0.95−x)Ga₅O₁₂ (0.0x0.9) and Yb_0.15Gd_0.15Lu_2.7(Al_xGa_1−x)O₁₂ (0.0x1.0) were grown by the modified micro-pulling-down method. Continuous solid solutions with garnet structure and a linear compositional dependency of crystal lattice parameter in the system Yb:(Gd,Lu)₃(Ga,Al)₅O₁₂ are formed. Measured optical absorption spectra of the samples show 4f–4f transitions related to Gd³⁺ ion at 275 and 310 nm, and also an onset of charge transfer transitions from oxygen ligands to Gd³⁺ or Yb³⁺ cations below 240 nm. A complete absence of Yb³⁺ charge transfer luminescence under X-ray excitation in any of the investigated samples was explained by the overlapping of charge transfer absorption of Yb³⁺ by that of Gd³⁺ ions. For specific composition of Lu_1.5Gd_1.5Ga₅O₁₂ an intense defect––host lattice-related emission, which achieve of about 40% integrated intensity compared with Bi₄Ge₃O₁₂, was found.     

Hydrothermal synthesis and magnetic property of Cu3(OH)2V2O7·nH2O

Copper vanadium oxide hydroxide hydrate (Cu₃(OH)₂V₂O₇·nH₂O) nanoparticles with mean size of about 100 nm were successfully synthesized by a simple hydrothermal method. The structure and morphology of the as-synthesized products were characterized by X-ray diffraction (XRD), Field emission scanning electron microscopy (FE-SEM), Raman spectra, and Fourier transform infrared spectra (FTIR). The composition and purity of the as-synthesized Cu₃(OH)₂V₂O₇·nH₂O nanoparticles were characterized by Energy disperse spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The magnetic property of the as-synthesized Cu₃(OH)₂V₂O₇·nH₂O nanoparticles was characterized by vibrant sample magnetometer. Magnetic hysteresis curve indicate that the as-synthesized nanoparticles are of weak ferromagnetic property at room temperature.     

Up-conversion emission in KGd(WO4)2 single crystals triply-doped with Er/Yb/Tm, Tb/Yb/Tm and Pr/Yb/Tm ions

Triply-doped single crystals KGd(WO₄)₂:Er³⁺/Yb³⁺/Tm³⁺, KGd(WO₄)₂:Tb³⁺/Yb³⁺/Tm³⁺ and KGd(WO₄)₂:Pr³⁺/Yb³⁺/Tm³⁺ were grown by the Top Seeded Solution Growth (TSSG) method, with an aim of getting efficient up-converted multicolored luminescence, which subsequently can be used for generation of white light. Such an aim determined the choice of the triply doped compounds: excitation of the Yb³⁺ ions in the infrared spectral region is followed by red, green and blue emission from other dopants. It was shown that all these systems exhibit multicolor up-conversion fluorescence under 980 nm laser irradiation. Detailed spectroscopic studies of their absorption and luminescence spectra were performed. From the analysis of the dependence of the intensity of fluorescence on the excitation power the conclusion was made about significant role played by the host’s conduction band and other possible defects of the KGd(WO₄)₂ crystal lattice in the up-conversion processes.     

Synthesis and formation mechanism of Cu3V2O7(OH)2·2H2O nanowires

Cu₃V₂O₇(OH)₂·2H₂O nanowires have been synthesized in high yield through a simple and facile low-temperature hydrothermal approach without any template or surfactants. XRD, TG, FE-SEM, TEM and HRTEM were used to characterize the product. The results indicated that the product consisted of wirelike crystals about 80 nm in diameter and length up to several micrometers. The formation of wirelike structure of Cu₃V₂O₇(OH)₂·2H₂O depended crucially on the reaction time and pH value of the precursor suspensions. The optical absorption spectrum indicates that the Cu₃V₂O₇(OH)₂·2H₂O nanowires have a direct band gap of 1.94 eV.     

Crystal structure and cation transport properties of the ortho - diphosphates Na7(MP2O7)4PO4 (M = Al,Cr, Fe)

The isotypic ortho-diphosphates Na₇(MP₂O₇)₄PO₄ (M = Al, Cr, Fe) have been synthesized. They are tetragonal, space group P4̄2₁c. The structure of the iron member has been solved and refined to a final R = 0.037 for 577 independent reflections. It consists of (FeP₂O₇)₄PO₄ units interconnected so as to form a 3D framework into which the sodium ions are inserted. The units are made of a PO₄ tetrahedron linked to four FeO₆ octahedra; each octahedron is connected to a P₂O₇ group by two oxygens. Ion exchange experiments and conductivity measurements give evidence of some mobility of the sodium ions at high temperature. However, the σ-values ($\text{～ 10}{}^{\mathrm{?5}}\text{Ω}{}^{\mathrm{?1}}\text{cm}{}^{\mathrm{?1}}$ at 300°C) are relatively low. The narrowness of the windows between the sodium sites as well as the presence of an oxygen atom linked to only one polyhedron of the framework are unfavourable features to fast cation transport.     

New palladium phosphate complexes: K2PdP2O7 and K3.5Pd2.25(P2O7)2 synthesis, single crystal structure and conductivity

Two new diphosphate complexes containing potassium and palladium, K₂PdP₂O₇ and K_3.5Pd_2.25(P₂O₇)₂, have been synthesized and characterized by single crystal X-ray diffraction. K₂PdP₂O₇ exists with layers formed of linked PdP₂O₇ polyhedra, between which are found the potassium ions. K_3.5Pd_2.25(P₂O₇)₂ with a Pd/P₂O₇ ratio of 1.125:1 crystallizes with tunnels of various sizes in which are found the potassium ions. Conductivity measurements reveal the material to be conducting.     

Synthesis, structure and luminescent properties of Lu(PO3)3

A new structural type of rare earth metaphosphate, Lu(PO₃)₃, was prepared from high-temperature solution, of which the crystal structure was solved in S.G. of Cc (No.9) and Z = 4 with unit cell dimensions of a = 13.972(3) Å, b = 6.6710(13) Å, c = 9.958(2) Å and β = 127.36(3)°. In Lu(PO₃)₃, [LuO₆] octahedra connect with the non-bridging oxygens on (PO₃)_n infinite zigzag chains that extended along c-axis. The VUV and X-ray excited luminescent properties of undoped and Ln³⁺ (Ln = Ce, Eu, Tb) doped samples were examined, from which the optical band gap was estimated to be 8.3 eV. Besides, in the undoped sample a STE emission within 320–480 nm was observed, which probably be related to oxygen defects. However, in the Lu(PO₃)₃:Ce sample the Ce³⁺ emission was weak and STE emission was totally quenched under hard X-ray excitation.     

Hydrothermal synthesis of Cu3V2O7(OH)2·2H2O hierarchical microspheres and their electrochemical properties

Uniform Cu₃(OH)₂V₂O₇·2H₂O microspheres assembled by nanorods have been fabricated through a simple hydrothermal method for the first time employing copper hydroxide carbonate (Cu₂(OH)₂CO₃) as copper source without the assistance of any template or surfactant. The formation mechanism was proposed based on the evolution of this morphology as a function of hydrothermal time. The Electrochemical measurements revealed that the Cu₃(OH)₂V₂O₇·2H₂O microspheres displayed a high discharge capacity, which indicates that the Cu₃(OH)₂V₂O₇·2H₂O microspheres are promising cathode candidates for primary lithium batteries used in long term implantable cardioverter defibrillators (ICD).     

[NH3(CH2)2NH3][Co(SO4)2(H2O)4]: Chemical preparation, crystal structure, thermal decomposition and magnetic properties

Cobalt ethylenediammonium bis(sulfate) tetrahydrate, [NH₃(CH₂)₂NH₃][Co(SO₄)₂(H₂O)₄], has been synthesised by slow evaporation at room temperature. It crystallises in the triclinic system, space group , with the unit cell parameters: a = 6.8033(2), b = 7.0705(2), c = 7.2192(3) Å, α = 74.909(2)°, β = 72.291(2)°, γ = 79.167(2)°, Z = 1 and V = 317.16(2) Å³. The Co(II) atom is octahedrally coordinated by four water molecules and two sulfate tetrahedra leading to trimeric units [Co(SO₄)₂(H₂O)₄]. These units are linked to each other and to the ethylenediammonium cations through OW-H…O and N-H…O hydrogen bonds, respectively. The zero-dimensional structure is described as an alternation between cationic and anionic layers along the crystallographic b-axis. The dehydration of the precursor proceeds through three stages leading to crystalline intermediary hydrate phases and an anhydrous compound. The magnetic measurements show that the title compound is predominantly paramagnetic with weak antiferromagnetic interactions.     

Crystal structure and ionic conductivity of ruthenium diphosphate ARu2(P2O7)2, A=Li, Na, and Ag, with a tunnel structure

Crystal structure and ionic conductivity of ruthenium diphosphates, ARu₂(P₂O₇)₂ A=Li, Na, and Ag, were investigated. The structure of the Ag compound was determined by single crystal X-ray diffraction techniques. It crystallized in the triclinic space group P−1 with a=4.759(2) Å, b=6.843(2) Å, c=8.063(1) Å, α=90.44(2)°, β=92.80(2)°, γ=104.88(2)°, V=253.4(1) Å³. The host structure of it was composed of RuO₆ and P₂O₇ groups and formed tunnels running along the a-axis, in which Ag⁺ ions were situated. The ionic conductivities have been measured on pellets of the polycrystalline powders. The Li and Ag compounds showed the conductivities of 1.0×10⁻⁴ and 3.5×10⁻⁵ S cm⁻¹ at 150 °C, respectively. Magnetic susceptibility measurement of the Ag compound showed that it did not obey the Curie-Weiss law and the effective magnetic moment decreased as temperature decreased due to the large spin-orbital coupling effect of Ru⁴⁺ ions.     

The crystal structure of Pb8Bi2(PO4)6O2

Single crystals of Pb₈Bi₂(PO₄)₆O₂ were grown by the Czochralski technique, and the structure of this compound was determined. It was found to crystallize in Pnma orthorhombic symmetry with a = 13.313, b = 10.284 and $\text{c}\text{= 9.219}\text{A}\text{?}$. The structure was refined to an R value of 7%. Powder diffraction data are also reported.     

Hydrothermal phase equilibria in Ln2O3-H2O-CO2 systems for Tm,Yb and Lu

Phase diagrams for Tm₂O₃-H₂O-CO₂. Yb₂O₃-H₂O-CO₂ and Lu₂O₃-H₂O-CO₂ systems at 650 and 1300 bars have been investigated in the temperature range of 100–800°C. The phase diagrams are far more complex than those for the lighter lanthanides. The stable phases are Ln(OH)₃, Ln₂(CO₃)₃.3H₂O (tengerite phase), orthorhombic-LnOHCO₃, hexagonal-Ln₂O₂CO₃. LnOOH and cubic-Ln₂O₃. Ln(OH)₃ is stable only at very low partial pressures of CO₂. Additional phases stabilised are Ln₂O(OH)₂CO₃and Ln₆(OH)₄(CO₃)₇ which are absent in lighter lanthanide systems. Other phases, isolated in the presence of minor alkali impurities, are Ln₆O₂(OH)₈(CO₃)₃. Ln₄(OH)₆(CO₃)₃ and Ln₁₂O₇(OH)₁₀,(CO₃)₆. The chemical equilibria prevailing in these hydrothermal systems may be best explained on the basis of the four-fold classification of lanthanides.     

Preparation and crystal structure of a new bismuth vanadate, Bi3.33(VO4)2O2

Single crystals of a new bismuth vanadate, Bi_3.33(VO₄)₂O₂ was prepared by hydrothermal reaction using a hydrated sodium bismuthate, NaBiO₃·nH₂O as one of the starting compounds. The crystal structure was determined by using single crystal X-ray diffraction data. This compound crystallizes in the triclinic space group (#2) with a = 7.114(1), b = 7.844(2), c = 9.372(2) Å, α = 106.090(7), β = 94.468(7) and γ = 112.506(8)°, Z = 2 and the final R factors are R1 = 0.052 and wR2 = 0.14 for 2085 unique reflections. The crystal structure is composed by four bismuth atoms with the coordination number of 6 or 8 and two VO₄ tetrahedra, and one of four bismuth atoms is statistically distributed in the splitting sites with the distance of 0.83 Å. This compound exhibited photocatalytic behavior for decomposition of phenol under visible light irradiation and its activity was less than that of monoclinic BiVO₄.     

Luminescent properties of glassy and crystallized (Li2B4O7 + xB2O3)0.999(MnO2)0.001 (x = 0–16.67 mol %) materials

We have studied the thermoluminescence (TL) and roentgenoluminescence (RL) of glassy and crystallized (Li₂B₄O₇)_0.999(MnO₂)_0.001-(Li₄B₁₀O₁₇)_0.999(MnO₂)_0.001 samples. The results demonstrate that annealing influences the relative TL and RL intensities in the samples owing to crystallization processes. The TL and RL intensities of the crystalline materials are several times higher than those of the thermoluminescent material (Li₂B₄O₇)_0.999(MnO₂)_0.001 and have a maximum at B₂O₃ excesses of 7–11 mol %. Original Russian Text ? V.M. Holovey, V.I. Lyamayev, A.M. Solomon, N.N. Birov, P.P. Puga, V.T. Maslyuk, 2008, published in Neorganicheskie Materialy, 2008, Vol. 44, No. 7, pp. 841–845.     

Phase equilibria in the Zn2P2O7-M2ZnP2O7 and M′2ZnP2O7-M″2ZnP2O7 (M, M′, M″ = Li, Na, K) glass-forming systems

Data are presented on the phase relations in the Zn₂P₂O₇-M₂ZnP₂O₇ and M′₂ZnP₂O₇-M″₂ZnP₂O₇ (M, M′, M″ = Li, Na, K) systems. The stable and metastable phase equilibria in these systems have been investigated, new compounds have been identified, and wide solid-solution ranges have been found. Some of the physicochemical properties of the synthesized phases are described. Original Russian Text ? M.A. Petrova, G.A. Mikirticheva, R.G. Grebenshchikov, 2007, published in Neorganicheskie Materialy, 2007, Vol. 43, No. 9, pp. 1141–1148.     

Growth, thermal and optical properties of Yb:GdYAl3(BO3)4 crystal

Single crystal of Yb:GdYAl₃(BO₃)₄(Yb:GdYAB) has been grown by the flux method. The structure of Yb:GdYAB crystal has been determined by X-ray diffraction analysis. The experiment show that the crystal has the same structure as that of YAl₃(BO₃)₄ crystal and its unit cell constants have been measured to be a = 9.30146 Å, c = 7.24164 Å, Vol = 542.59 Å³. The absorption and fluorescence spectrum of Yb:GdYAl₃(BO₃)₄ crystal have also been measured at room temperature. In the absorption spectra, there are two absorption bands at 938 nm and 974 nm, respectively, which is suitable for InGaAs diode laser pumping. In the fluorescence spectra, there are two fluorescence peaks at 992 and 1040 nm. The thermal properties of Yb:GdYAl₃(BO₃)₄ crystal have been studied for the first time. The thermal expansion coefficient along c-axis is almost 5.4 times larger than that along a-axis. The specific heat of the crystal has been measured to be 0.77 J/g °C at room temperature. The calculated thermal conductivity is 5.26 Wm⁻¹ K⁻¹ along a-direction.