Luminescent properties of Eu, Tb or Bi activated yttrium germanates

Preliminary studies were conducted on Eu³⁺, Tb³⁺ or Bi³⁺ doped Y₂Ge₂O₇, Y₂GeO₅ and Y₄GeO₈ phosphors. Both photoluminescence and cathodoluminescent properties of the materials were measured. Among these materials, the luminescent intensities of Y₂Ge₂O₇:Eu, Y₂GeO₅:Tb and Y₂Ge₂O₇:Bi are relatively high and the luminescent colors of them are red, green and blue, respectively. In order to improve the luminescent properties for field emission display applications, further optimization is necessary. In addition, X-ray powder diffraction results indicate that Y₄GeO₈ phase forms in an orthorhombic unit cell, the parameters of which are: a=1.4976(5) nm, b=0.9357(6) nm, c=0.5885(3) nm, V_cell=0.82467(2) nm³.     

From eulytine to the ambidextrous crystal via the amorphous route: Lead & calcium bismuth germanate glasses

Lead and calcium bismuth germanate glasses containing at least 40 mole% GeO₂ were prepared. Physical properties and infrared spectra suggest that for glasses close to the PbO · Bi₂O₃ · 2GeO₂ composition: (a) packing efficiency is directly dependent upon cation size, (b) refraction is dependent upon cation type, (c) calcium can substitute for lead in nearly ideal fashion, (d) the open eulytine arrangement of a 2Bi₂O₃ · 3GeO₂ glass has collapsed, and (e) Ge₂O₇ dimers and small chains of GeO₄ tetrahedra (characteristic of Pb₅Ge₃O₁₁ and PbGeO₃ respectively) may persist. These findings offer a rationale for the limited yields of Ca₃Al₂Ge₃O₁₂ garnets obtained from such melts at high temperatures. A noncubic crystalline phase that may be Pb₃Bi₂Ge₃O₁₂ is also reported.     

Crystallization of sodium digermanate,Na2Ge2O5, from Na2O-GeO2 glasses

Na₂O-GeO₂ glasses containing 25～35 mole% Na₂O can be crystallized to give a new sodium germanate crystal together with Na₄Ge₉O₂₀, Na₂GeO₃ and/or Na₂Ge₄O₉ crystals. The new crystal is obtained as a principal crystallization product from the glass containing 33.3 mole% Na₂O, and is given a composition of Na₂Ge₂O₅. This sodium digermanate crystal is monoclinic with lattice parameters; a₀ = 8.421, b₀ = 4.962, c₀ = 12.67 Å and β = 103.5°, and isostructural with β-Na₂Si₂O₅. It is shown that the crystal is thermodynamically metastable.     

The investigation of the hydrothermal crystallization in Nd2O31bGeO21bNaOH1bH2O system

The hydrothermal crystallization in Nd₂O₃1bGeO₂1bNaOH1bH₂O system is investigated. The single crystals of NaNd₃[GeO₄]₂(OH)₂, Na_4,67[GeO₄]₃O, NaNd₃Ge₄O₁₃, Nd₂GeO₅, Nd₂Ge₂O₇, Nd(OH)₃, Na₄Ge₉O₂₀,Na₂GeO₃·H₂O are obtained. The phase diagram of the crystallization fields in the system under consideration is built. The germanates synthesized are stadied by X-Ray analysis and IR-spectroscopy.     

Structure and electrical properties of crystalline and glassy Ag2PbP2O7

Single crystals of Ag₂PbP₂O₇ have been prepared by melting of the crystalline phase under phosphate flux. Ag₂PbP₂O₇, isotype of Na₂PbP₂O₇, is of triclinic symmetry with the space group P(−1) (Z=2). The unit cell parameters are: a=5.502(6) Å, b=7.008(8) Å, c=10.018(9) Å, α=106.63(6)°, β=93.89(7)°, γ=110,68(6)°. The lattice of Ag₂PbP₂O₇ consists of corner-shared structural units {Pb₂P₄O₁₄}⁴⁻, which form ribbons parallel to the [010] direction. The {Pb₂P₄O₁₄}⁴⁻ units result from the association of corner-shared PbO₅ polyhedra and P₂O₇ pyrophosphate groups. The ribbons are interconnected by Pb–O–P bridges in the [100] direction and form lamina parallel to (001) plan. Silver atoms are located between two alternating lamina. Glasses with the same composition as the crystalline phase have been synthesized. A study of transport properties of Ag₂PbP₂O₇ in the crystalline and glassy forms is reported.     

Non-isothermal crystallization kinetics of niobium-doped BGO70 glasses

Niobium-doped BGO glass of composition 85[3Bi₂O₃–7GeO₂ (BGO70)]–Nb15 was investigated for its kinetic parameters n and activation energies E _i : i = 1, 2, g of transformations via available models. Two crystallization exothermal peaks were observed for all heating histograms exploiting 5, 10, 15, and 20 K/min heating rates following the glass transition in non-isothermal DTA curves. An exothermal shoulder prior to first crystallization peak P₁ was identified as thermally favorable crystallizing metastable phase Bi₂GeO₅. P₁ was assigned to thermally stable crystal phase Bi₄Ge₃O₁₂. T _g lied between 729 and 731 K ± 4 K; T _p1 varied from 835–855 K ± 2 K, and T _p2 had values 965–986 K ± 2 K. Independent of the model exploited, activation energies E _g, E _p1, and E _p2 were 32.89 ± 3.1, 47.33 ± 0.72, and 62.74 ± 0.72 kcal/mol, respectively. P₁ corresponds to crystalline disks of Bi₄Ge₃O₁₂, and P₂ identified stable phase BGO crystal rods growing inward from the surface imbedded in glass matrix. Niobium doping modified the transformation kinetic parameters n and E _a of the composition by providing a control on growth mechanism for BGO platelets or rods.     

Zero resistance states in modified Y-Ba-Cu-O system with transition temperatures above 135 K

Superconducting transition of minor-dispersed phase in modified YBa₂Cu₃O_7?δ samples is found to occur at around 140K. The amount of this minor phase is enough to provide zero resistivity above 135 K. The measurements of the electrical resistivity indicated that the material is stable, thermally recyclable and reproducible. X-ray analysis of the sample with the highestT _c shows a major phase with perovskite-like structure witha=3·820(1) Å;b=3·873(1) Å andc=11·659(2) Å along with several unidentified weak peaks. Magnetic measurements confirmed the mixed-phase nature with diamagnetic transition temperatures at 137,91 and 86 K. The minor phase responsible for superconductivity with zero resistivity above 135 K is about 0·4% of the bulk and its nature is still unidentified. The details of the preparation and chemical modification process and the results are presented.     

Chemical and crystallographic characterization of crystals grown by chemical vapour transport in the Fe2O3  GeO2 system

Crystal growth experiments were performed in the Fe₂O₃  GeO₂ system by chemical vapour transport. After determination of transport conditions by HCl or TeCl₄, single crystals of the following compounds were prepared : α-Fe₂O₃ (hematite), Fe₈Ge₃O₁₈ (unknown structural type), Fe₂GeO₅ (kyanite-type) and GeO₂ (rutile-type modification). Analyses of crystals by electron microprobe and neutron activation were used to check the stoichiometry and composition of the phases. Preliminary studies on crystals led to a monoclinic symmetry for Fe₈Ge₃O₁₈ (possible space group P $\text{2}\text{c}$ or P c) with a = 0.8754 nm, b = 0.5110 nm, c = 1.4280 nm and β = 101.8°. The Fe₈Ge₃O₁₈ compound was found to display structural features similar to those of Fe₂GeO₅ with the kyanite-type.     

Studies of structural and dielectric properties of Ba5BiTi3Nb7O30 ceramics

The polycrystalline samples of Ba₅BiTi₃Nb₇O₃₀ (hereafter BBTN) belonging to ferroelectric oxide family of tungsten bronze structure were prepared by high temperature solid-state reaction method. Preliminary X-ray analysis of the samples provided the lattice parametersa=11·9331 Å,b=14·9684 Å, andc=7·0193 Å, and also formation of a single-phase orthorhombic structure at room temperature (303 K). Detailed studies of dielectric constant (ε) and loss (tanδ) as a function of frequency (500 Hz to 10 KHz) at room temperature and also as a function of temperature (liquid nitrogen to 160°C) show the dielectric anomaly and structural phase transition at 16·8°C.     

Dehydration/amine intercalation in Zn(O3PR)–H2O phosphonates: the missing link,X-ray structure of Zn(O3PCH3)

The hydrothermal synthesis of colorless crystals of Zn(O₃PCH₃) was achieved using a solution of zinc nitrate and methylphosphonic acid (1:1) in water, in the presence of thiourea. The structure was determined by single crystal X-ray diffraction [monoclinic, space group P2₁/c (No. 14), a=8.7226(9) Å, b=5.2156(7) Å, c=10.847(1) Å, V=389.48(9) ų, Z=2]. From this result, the mechanism of the structure modification taking place during the dehydration of Zn(O₃PR)–H₂O phosphonates was clearly demonstrated.     

Crystal structure analysis of Y2Cu2O5

Single crystals of Y₂Cu₂O₅ were obtained in the flux growth process by controlled heating of a mixture of Y₂O₃, BaO, and CuO in a molar ratio of 1∶8∶20. These crystals were analyzed by a single-crystal X-ray diffraction analysis. The crystal contains polymeric chains of Cu₂O₅ interspersed by yttrium ions surrounded by octahedral arrangements of oxygen atoms. Crystal data: space group=Pna2₁,a=10.799(2) Å,b=3.4990(5) Å,c=12.459(2) Å,Z=4, 380 reflections,R=0.026,R _w=0.030.     

Investigation of solid solution of ZrP<Subscript>2</Subscript>O<Subscript>7</Subscript>–Sr<Subscript>2</Subscript>P<Subscript>2</Subscript>O<Subscript>7</Subscript>

In this study, ZrP₂O₇ was synthesized by the solid state reaction of ZrO₂ and NH₄H₂PO₄ at 900 °C. Then, in set 1; 10, 5, 1, 0.5, 0.1, 0.05, 0.03% previously prepared Sr₂P₂O₇ were doped into ZrP₂O₇, and Sr₂P₂O₇ slightly affect the unit cell parameter of cubic ZrP₂O₇ (a = 8.248(6)–8.233(8) Å). The reverse of this process was also applied to Sr₂P₂O₇ system (set 2). ZrP₂O₇ changes the unit cell parameters of orthorhombic Sr₂P₂O₇ in between a = 8.909(5)–8.877(5) Å, b = 13.163(3)–13.12(1) Å, and c = 5.403(2)–5.386(4) Å. Analysis of the vibrations of the P₂O ₇ ^4? ion and approximate band assignments for IR and Raman spectra are also reported in this work. Some coincidences in infrared and Raman spectra both sets were found and strong P–O–P bands were observed. Surface morphology, EDX analysis, and thermoluminescence properties of both sets were given the first time in this paper.     

A new mixed valent molybdenum monophosphate with a tunnel structure: Cs3Mo8O11(PO4)8

A new mixed valent molybdenum monophosphate, Cs₃Mo₈O₁₁(PO₄)₈, with a tunnel structure, has been synthesized. It crystallizes in the space group C2/m with a=20.203 (2) Å, b=6.370 (1) Å, c=14.379 (1) Å and β=99.827 (7)°. Its [Mo₈P₈O₄₃]_∞ 3D-framework consists of single phosphate groups, single MoO₆ octahedra, and bioctahedral units of corner-sharing octahedra Mo₂O₁₁ and of edge-sharing octahedra Mo₂O₁₀. The entire host lattice can be described by the association of [MoPO₈]_∞ chains running along b, through the corners of their octahedra and tetrahedra, and through the edges of their octahedra, forming large tunnels running along b where the Cs⁺ cations are located. Bond valence calculations show that in the bioctahedral units, the electrons are delocalized between the two Mo atoms.     

Synthesis,crystal structure and properties of a new lead fluoride borate,Pb3OBO3F

A new compound, Pb₃OBO₃F, has been grown by the high temperature solution method from the PbO–PbF₂–B₂O₃ system. It crystallizes in the orthorhombic system, space group Pbcm with unit-cell parameters a = 7.6313(14) Å, b = 6.5229(12) Å, c = 11.906(2) Å, Z = 4, volume = 592.66(19) Å³. The structure of the compound is solved by the direct methods and refined to R₁ = 0.0528 and wR₂ = 0.1400. Pb₃OBO₃F consists of Pb(1)O₃F tetrahedra, Pb(2)O₄ tetrahedra and BO₃ triangles which build up the symmetrical chains extended along the c-axis. The powder X-ray diffraction pattern of the Pb₃OBO₃F has been measured. Functional groups presented in the sample were identified by Fourier transform infrared spectrum.     

Microwave dielectric properties of a new A6B5O18-type cation deficient perovskites: Sr5LaTi2Nb3O18

A new A₆B₅O₁₈-type cation deficient perovskite Sr₅LaTi₂Nb₃O₁₈ was prepared by the conventional solid-state reaction route. The phase, microstructure, and microwave dielectric properties of the ceramic were characterized. This compound crystallizes in the trigonal system with unit cell parameter a = 5.6101(2) Å, c = 40.922(8) Å, V = 1,115.4(5) Å³, and Z = 3. It shows a high dielectric constant of 48, a high quality factors with Q _u × f of 27,806 GHz, and a small positive τ _f of +19 ppm/°C.     

Crystal structures of Ba4CaCu3O8+δ and Ba6CaCu3O10+δ

The crystal structures of the two ternary compounds, Ba₄CaCu₃O_8+δ and Ba₆CaCu₃O_10+δ, have been investigated by means of X-ray diffraction combined with Rietveld analysis. We found that the Ba₄CaCu₃O_8+δ phase has a cubic structure (Im–3m, a=8.1515(1) Å, δ=+0.8) for high oxygen content as reported in the literature but undergoes a transformation into a tetragonal structure (I4/mmm, a=8.1888(1) Å, c=8.0634(1) Å for δ=−0.3) when the oxygen content is lowered. The crystal structure of Ba₆CaCu₃O_10+δ (I4/mmm, a=4.0463(1) Å, c=21.7322(4) Å for δ=+0.2) is confirmed. Changes in the c value with sintering conditions suggest a variable oxygen content with no structure transformation.     

Hybrid open frameworks: Hydrothermal synthesis and structure determination of MIL-33: a new vanadomethylendiphosphonate intercalating potassium cations

The hydrothermal synthesis and the ab initio structure determination from powder data of K₂(V^VO₂)₄(V^IVO){O₃P–CH₂–PO₃}₂–xH₂O (x=4) or MIL-33 are presented. MIL-33 crystallizes in the monoclinic system [space group C2/m (No. 12)] with lattice parameters a=4.8716(4) Å, b=14.614(1) Å, c=15.825(1) Å, β=94.06(1) Å, V=1123.8(2) ų, Z=2. MIL-33 is a mixed valence V^IV/V^V=1/4 vanadodiphosphonate. Its layered structure shows some potassium cations located both between the hybrid layers and in the eight-membered windows of the latter.     

Crystal chemistry and redox behaviour of antimony strontium calcium perovskites

The compound Sr₂Sb_1.4Ca_0.6O₆ and their reduced forms Sr₂Sb_1.4Ca_0.6O_5.17 and Sr₂Sb_1.4Ca_0.6O_4.84 have been prepared and characterized by powder X-ray diffraction, electron diffraction, iodometric analyses and thermogravimetric analysis. The three phases with different oxygen stoichiometries are structurally related to the perovskite and show symmetry distortions from the ideal cubic structure (with cell parameter a_p). The crystal structure of Sr₂Sb_1.4Ca_0.6O₆ may be refined by the Rietveld method from powder X-ray diffraction data using the space group P2₁/n, and the cell parameters a=5.776(2), b=5.7837(2), c=8.1718(3) Å, β=90.039(3)° with the same structural model than for previously studied Sr₂Bi_1.4Ca_0.6O₆. It shows two crystallographically independent B positions with occupancies 100% Sb (site 1) and 40% Sb/60% Ca (site 2) ordered in a 3D NaCl-type arrangement. The reduced phases, Sr₂Sb_1.4Ca_0.6O_5.17 and Sr₂Sb_1.4Ca_0.6O_4.84, are obtained from Sr₂Sb_1.4Ca_0.6O₆ by treatment in Ar or Ar/H₂ at 650°C and show respectively the unit cell parameters a≈b≈5.9 Å, c≈8.4 Å (with possible space groups I2/m or Immm), and a=8.4 Å, b=6.0 Å, c=24.2 Å, β=125° (space group C2/c). The reduction process is reversible, and the initial oxidized phase can be obtained from the reduced ones by thermal treatment in oxygen or air, at temperatures close to 500°C.     

Hybrid open-frameworks: hydrothermal synthesis,structure determinations and magnetic properties of MIL-29, two copper diphosphonates (CuII(H2O))2{O3P–X–PO3} with X=C2H4, CH2–C6H4–CH2

Two copper diphosphonates were hydrothermally synthesized using ethylenediphosphonic and p-xylenediphosphonic acids, synthesized according the Arbuzov method. The structure of (Cu^II(H₂O))₂{O₃P–CH₂–CH₂–PO₃} already described from powder data, was solved from single crystal data. Its symmetry is monoclinic (space group P2₁/c (no. 14)) with lattice parameters a=8.0670(4) Å, b=7.5889(4) Å, c=7.3997(4) Å, β=116.281(2)°, V=406.18(4) ų, Z=2. The structure of (Cu^II(H₂O))₂{O₃P–CH₂–(C₆H₄)–CH₂–PO₃} was solved by powder X-ray diffraction (space group P2₁/c (no. 14)) with lattice parameters a=10.812(1) Å, b=7.577(1) Å, c=7.412(1) Å, β=92.34(1)°, V=606.7(2) ų, Z=2. Both structures are built up from identical inorganic layers covalently linked by the organic chains which act as pillars. The inorganic layers contain dimers of edge-sharing CuO₄(H₂O) square pyramids linked by the PO₃C tetrahedra. Both compounds are antiferromagnetic at 4(1) K.     

Ionic conductivity of Li4GeO4, Li2GeO3 and Li2Ge7O15

The ionic conductivity of polycrystalline samples of three lithium germanates: Li₄GeO₄, Li₂GeO₃, and Li₂Ge₇O₁₅, has been determined using a c techniques and complex plane analysis. Conductivities at 400°C are 8.7 × 10^?5, 1.5 × 10^?5, and $\text{1.4 × 10}{}^{\mathrm{?7}}\text{(Ω·}\text{cm}\text{)}{}^{\mathrm{?1}}$ respectively. The conductivity of Li₄GeO₄ rises appreciably in the range 700–750°C.