Single crystal structure of a layered intercalating phosphate with features of two dimensions and H-bonds

A new organic phosphate of (8-HQDH)(H₂PO₄)·H₂O has been obtained by hydrothermal reaction. The crystal structure was determined with data: triclinic, space group P , a=6.541(1) Å, b=8.5909(8) Å, c=10.769(1) Å, =98.734(7)°, β=91.20(1)°, γ=97.91(1)°, V=591.9(1) ų, and Z=2. The (H₂PO₄)⁻ groups and H₂O molecules stack into sheets and 8-HQ cations fixed parallelly with each other to form an intercalating compound by H-bonds.     

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.     

Crystal structure, thermal analysis and IR spectroscopic investigation of (C6H9N2)H2XO4 (X = As, P)

Crystals of 2-amino-4-methylpyridinium dihydrogenmonoarsenate (C₆H₉N₂)H₂AsO₄ and 2-amino-4-methylpyridinium dihydrogenmonophosphate (C₆H₉N₂)H₂PO₄ have been prepared and grown at room temperature. These materials are isotypic with the following unit cell dimensions (C₆H₉N₂)H₂AsO₄: a = 12.4415(5) Å, b = 6.8224(3) Å, c = 11.3524(5) Å, Z = 4, V = 963.60(6) Å³; (C₆H₉N₂)H₂PO₄: a = 12.4410(9) Å, b = 6.7165(3) Å, c = 11.3417(5) Å, Z = 4, V = 925.09(10) Å³. The common space group is Pnma. The structure of these compounds has been determined by X-ray data collection on single crystals of (C₆H₉N₂)H₂AsO₄ and (C₆H₉N₂)H₂PO₄. Due to the strong hydrogen-bond network connecting the H₂XO₄ groups, the anionic arrangement must be described as a linear organization. The chains composed by the macroanion spread along the b-direction, approximately centered by x = 0 and 1/2. All atoms of the structure, except one oxygen atom, are located in the mirror planes situated at y = 1/4 and 3/4, imparting an internal mirror symmetry to the anionic and the cationic entities. The linear macroanions are crossed by organic cations lying in mirrors perpendicular to the b-direction; this atomic arrangement is then described by a three-dimensional network of hydrogen bonds, built up by two types, O–HO bonds inside the chains and N–HO bonds linking adjacent chains. The thermal properties of both compounds are investigated as well as the IR properties supported by group theoretical analyses.     

Crystal structure and characterization of [2,5-(CH3O)2C6H3NH3]4P4O12·2H2O

The preparation, crystal structure, TG–DTA analysis and spectroscopy investigation are reported for the 2,5-dimethoxy phenyl ammonium cyclotetraphosphate dihydrate [2,5-(CH₃O)₂C₆H₃NH₃]₄P₄O₁₂·2H₂O. This new compound is triclinic P with unit cell dimensions: a = 7.438(5) Å, b = 11.841(7) Å, c = 12.354(4) Å,  = 96.61(4)°, β = 98.35(4)°, γ = 102.60(6)°, Z = 1 and V = 1038.0(1) Å³. Its crystal structure has been determined and refined to R = 0.049, with 5128 independant reflections. The structure can be described by rows of P₄O₁₂ ring anions along the a axis; between these rows are located the organic groups, connected to them by hydrogen bonds.     

Synthesis, structure refinement and characterization of tetrahydrated acid gadolinium diphosphate HGdP2O7·4H2O

Synthesis and single crystal structure are reported for a new gadolinium acid diphosphate tetrahydrate HGdP₂O₇·4H₂O. This salt crystallizes in the monoclinic system, space group P2₁/n, with the following unit-cell parameters: a = 6.6137(2) Å, b = 11.4954(4) Å, c = 11.377(4) Å, β = 87.53(2)° and Z = 4. Its crystal structure was refined to R = 0.0333 using 1783 reflections. The corresponding atomic arrangement can be described as an alternation of corrugated layers of monohydrogendiphosphate groups and GdO₈ polyhedra parallel to the () plane. The cohesion between the different diphosphoric groups is provided by strong hydrogen bonding involving the W4 water molecule.

IR and Raman spectra of HGdP₂O₇·4H₂O confirm the existence of the characteristic bands of diphosphate group in 980–700 cm⁻¹ area. The IR spectrum reveals also the characteristic bands of water molecules vibration (3600–3230 cm⁻¹) and acidic hydrogen ones (2340 cm⁻¹). TG and DTA investigations show that the dehydration of this salt occurs between 79 and 900 °C. It decomposes after dehydration into an amorphous phase. Gadolinium diphosphate Gd₄(P₂O₇)₃ was obtained by heating HGdP₂O₇·4H₂O in a static air furnace at 850 °C for 48 h.     

An electron diffraction study of the ZnIn2Se4 crystal structure: A novel phase

A novel layered-structure ZnIn₂Se₄ phase has been obtained. Texture electron diffraction patterns aid in the identification of a crystal structure with lattice parameters a = 4.045 Å and c = 52.29 Å, space group R m, and z = 4.5. Crystal electron diffraction patterns displayed superstructural reflection, thus indicating a √3-fold increase in the a parameter. The similirity of reflection locations and intensities both on the crystal rotation electron diffraction pattern and on texture electron diffraction patterns showed that no phase transition occurred on specimen pounding. Electrophysical and optical parameters (E_g = 1.68 eV; N = 8 × 10²² m^-3; = 0.1Ωm) are studied at 300 K. The Hall coefficient is constant (R_H = 7.2 × 10^-5m³C^-1, mobility μ = 8 × 10^-3m²V^-1s^-1 at 200–300 K.     

Three phases in the system Hg1 − xCxBa2CuOy (0.00 ≤ x ≤ 1.00)

Samples of the [Hg_{1 − x}C_x]-Ba₂CuOy system [(Hg,C)-1201] with stoichiometries within the range 0.00≤x≤1.00 were synthesized by a highpressure, high-temperature technique. The sample with X = 0.00 [HgBa₂CuO_4+δ] was non-superconducting with lattice parameters A = 3.8676(2) Å, C = 9.470(1) Å. At low ranges of substitution (0.10≤x≤0.30), the predominant phase was found to be Hg-1201 with identical lattice parameters to those found for X = 0.00. At X = 0.40 the Hg-1201 phase coexists in similar proportions with the phase of mixed [Hg_{1 − x},C_x]-1201 stoichiometry. At X = 0.50, this second phase with lattice parameters A = 3.9271(3) Å, C = 8.676(2) Å is predominant and only traces of the Hg-1201 phase were found. At X = 0.75 the [Hg_{1 − x},C_x]-1201 phase found for X = 0.50 coexists with the CO₃Ba₂CuO_y phase, which is the extreme of the substitution range. This latter was predominant at X = 1.00 with lattice parameters A = 4.0044(3) Å, C = 7.909(1) Å, but at higher pressure than the previous substitutions. This system is constituted of three main phases, HgBa₂CuO_{4 + δ}, Hg_{1 − x}C_xBa₂CuO_y (x ≈ 0.50) and CO₃Ba₂CuO_y, which appear in different proportions according to the percentage of substitution and the applied synthesis pressure.     

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.     

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.     

Synthesis and crystal structure of [2-NH2-5-CH3C5H4N]4P4O12·6H2O

Chemical preparation, crystal structure, IR absorption and thermal analysis of a new cyclotetraphosphate [2-NH₂-5-CH₃C₅H₄N]₄P₄O₁₂·6H₂O are reported. This compound is triclinic P-1 with unit-cell parameters: a = 10.206(5), b = 11.778(1), c = 9.991(4) Å,  = 110.40(6), β = 117.74(6), γ = 86.41(3)°, V = 989.1(8) Å³, Z = 1, D_x = 1.445 g cm⁻³. The structure has been determined and refined to R = 0.034 and R_w = 0.044, using 3663 independent reflections. The ring anions and water molecules form layers spreading around (a, b + c) planes via OHO hydrogen bonds. Between them are anchored 2-amino-5-methylpyridium cations, which establish H-bonds to interconnect the different adjacent layers and so contribute to the cohesion of the three-dimensional network. Tautomerization of (C₆H₉N₂)⁺ groups was evidenced in the present structure.     

Electrochemical preparation and characterisation of ruthenium bisulphide films

This paper embodies the first report on the electrochemical deposition of RuS₂ thin films. The as-deposited and heat-treated films (in argon atmosphere) were characterized by XRD, SEM and UV-VIS-NIR spectrophotometry. The polycrystalline deposits of RuS₂ obtained indicated a cubic structure with a lattice constant of 5.685 Å, an average grain size around 3 μm, and an absorption co-efficient of 5 × 10⁴ cm⁻¹. The optical band gap was found to be 1.48 eV.     

Characterization of the thorium phosphate-hydrogenphosphate hydrate (TPHPH) and study of its transformation into the thorium phosphate-diphosphate (β-TPD)

The preparation of thorium phosphate-diphosphate (Th₄(PO₄)₄P₂O₇, TPD) was developed through the precipitation of thorium phosphate-hydrogenphosphate hydrate (Th₂(PO₄)₂(HPO₄)·H₂O, TPHPH) at 150–160 °C in closed PTFE container or in autoclaves. From EPMA analyses and SEM observations, the initial precipitate was single phase and multilayered. The behaviour of TPHPH (orthorhombic system with a = 21.368(2) Å, b = 6.695(1) Å and c = 7.023(1) Å) was followed when heating up to 1250 °C. It was first dehydrated leading to the anhydrous thorium phosphate-hydrogenphosphate (TPHP, orthorhombic system with a = 21.229(2) Å, b = 6.661(1) Å and c = 7.031(1) Å at 220 °C) after heating between 180 and 200 °C. This one turned progressively into the new low-temperature variety of TPD (called -TPD, orthorhombic system with a = 21.206(2) Å, b = 6.657(1) Å and c = 7.057(1) Å at 300 °C) correlatively to the condensation of hydrogenphosphate groups into diphosphate entities. These three phases (TPHPH, TPHP and -TPD) exhibit closely related 2D layered structures, therefore different from the 3D structure of the thorium phosphate-diphosphate (high-temperature variety). This latter compound, now called β-TPD, was obtained by heating -TPD above 950 °C. All the techniques involved in this study (XRD, Raman and IR spectroscopy, ¹H and ³¹P NMR) confirmed the successive chemical reactions proposed.     

HMTTEF.C60-A 2-D close-packed layered compound of C60

The analysis of high resolution synchrotron X-ray powder diffraction data of HMTTEF.C₆₀, (HMTTEF = hexamethylenetetratellurafulvalene) gave a triclinic unit cell with a 9.9297 Å, B = 9.9359 Å, C = 13.1472 Å, = 106.966 °, β = 95.887 ° and γ = 118.252 ° in the space group P . Steric considerations suggest that there is a nearly close-packed layer of C₆₀ molecules in the plane, and HMTTEF molecules are sandwiched between layers of C₆₀. The compound is insulating and weakly paramagnetic and the charge-transfer is small.     

Synthese et etude structurale du tellurate (VI) de thallium (III) Tl2TeO6

Tl₂TeO₆ is the last reported member of the trivalent metal tellurate family with general formula M₂TeO₆. It was prepared by oxydation of intimate mixture of thallous carbonate and tellurium dioxyde. Its thermal stability was studied. Tl₂TeO₆ crystallizes with trigonal symmetry and hexagonal unit-cell parameters: a = 9,070 Å, c = 4,984 Å, Z = 3. The space group is P321. After single crystal analysis the structure was solved and refined to a final R = 0,057 for 1505 independent reflexions. Like Lu₂TeO₆ and In₂TeO₆, Tl₂TeO₆ is isostructural with sodium fluosilicate Na₂SiF₆. Each metallic-ion is octahedrally coordinated to a slightly distorded anionic hexagonal close packed array.     

Giant magnetoresistance increase in a hard–soft spin valve structure with the growth of a semiconductor layer

Magnetic and transport properties of a hard–soft spin valve structures have been investigated. A first series of sandwiches composed of an artificial antiferromagnetic (AAF) Co/Ru/Co sandwich decoupled from a soft Fe/Co buffer layer as follows: Fe_{50 Å}/Co_{5 Å}/Cu_{30 Å}/Co_{30 Å}/Ru_{5 Å}/Co_{30 Å}/Cu_{20 Å}/Cr_{20 Å} has been prepared. This sandwich presents a giant magnetoresistance (GMR) of 1.7% and an exchange coupling strength of approximately −1.73 erg/cm². Afterwards, we have grown a second series of sandwiches in which the Cu/Cr capping layer has been replaced by a 15-Å thin semiconductor layer of ZnS, covered by a soft ferromagnetic layer of Co_{5 Å}/Fe_{50 Å}. Surprisingly, the giant magnetoresistance for the last sandwiches has been increased by a factor of 2, up to 4%. To explain this non-expected result, we have performed atomic force microscope imaging at the semiconductor layer surface. The results show that the semiconductor layer is not homogeneous and contains a non-negligible density of pin-holes, that are responsible of a direct magnetic coupling between the upper 30 Å Co layer of the AAF and the Co 5 Å/Fe 50 Å bilayer. This coupling induces a strong asymmetry between the magnetic layers of the AAF and consequently an enhancement of the GMR.     

Rietveld refinement and spectroscopic studies of sodium lead fluoroapatite lacunaire synthesized by hydrothermal method

The structure of NaPb₉(PO₄)₆F(H₂O)_0.33, isostructural with apatite, was determined by X-ray powder diffraction methods and the result of Rietveld refinement is P6₃/m, a = 9.76396(8) Å and c = 7.27520(9) Å. The final refinement led to R_F = 5.4%, R_B = 6.6%. In the tunnel, the water molecule (O_w) and F⁻ ions appear to be located in 2b and 4e sites, with occupancies of 0.028(6) and 0.075(8), respectively. In the M(1) and M(2) sites the occupancies of Pb and Na are 0.282(3)/0.051(3) and 0.467(5)/0.033(5), respectively. The formula assigned to the compound is [Pb_3.38(4)Na_0.62(4)](1)[Pb_5.60(6)Na_0.40(6)](2)(PO₄)₆F_0.90(10)(H₂O)_0.33(7)□_0.77(17), where □ = vacancy. The assignment of the observed frequencies in the Raman and infrared spectra is discussed on the basis of a unit-cell group analysis and by comparison with fluor and chloroapatite analogs. The result of ³¹P and ²³Na magic angle spinning-nuclear magnetic resonance (MAS-NMR) spectroscopies confirmed the structural results.     

The effects of oxygen and copper impurities on the structure of amorphous germanium

We investigated the structural changes which occur with the incorporation of oxygen into amorphous thin films of germanium. The oxygen content of the films was from 1 at.% to a maximum of 10 at.%. The scattered electron intensity for films containing 10 at.% O is similar to that for pure films, but the first amorphous halo is shifted from |s| = 1.923Å⁻¹ to |s| = 1.88Å⁻¹, where |s| = 4π sin θ/λ and s is the momentum transfer vector. For lower oxygen concentrations this shift of the first amorphous halo is proportional to the oxygen content of the films. The radial distribution function of the oxygen-containing films has additional correlation peaks at 1.74, 2.98 and 4.83 Å which are not observed for pure films. From these results we conclude that the effect of the oxygen is to form regions in the random network structure with interatomic distances which resemble those in the tetragonal phase of GeO₂ (with some distortions), with the films remaining single-phase, homogenous and amorphous. Films which contain both 10.5 at.% O and 3.4 at.% Cu are shown to be phase separated and to contain widely spaced microcrystal up to 100 Å in diameter.     

Optical properties and energy transfer among Nd in Nd:Ca2Al2SiO7 crystals for diode pumped lasers

The energy levels of neodymium in the Nd³⁺:Ca₂Al₂SiO₇ (CAS) laser material with gehlenite structure are reported. As the Nd³⁺:Ca₂Al₂SiO₇ compound presents a broad absorption around 806 nm, it is a good candidate for diode pumped laser. The ⁴F_3/2→⁴I_9/2 and ⁴F_3/2→⁴I11/2 emission have been recorded and the fluorescence branching ratios calculated from the Judd-Ofelt analysis are 0.41 and 0.47 respectively. The emission cross section at 1.06 μm (⁴F_3/2→⁴I11/2 transition) is 5 × 10^-20 cm². The decay profiles of the Nd³⁺ emission have been analyzed for several Nd³⁺ concentrations using the kinetic microparameters related to the cross relaxation ( and R₀≈6 Å) and the energy migration probabilities ( ). In the Nd:CAS laser material, the optimal concentration corresponding to the maximum of the fluorescence intensity is determined to be around 2.7 × 10²⁰ Nd³⁺ ions cm^-3. The Nd³⁺-Nd³⁺ interactions are not very strong in this material as the optical concentration value is two times higher than in the Nd:YAG laser material.     

Fe-substituted tobermorites: Synthesis and characterization by Mössbauer spectroscopy and other techniques

The isomorphous substitution of Fe³⁺ for Si⁴⁺ in the tobermorite (Ca₅Si₆H₂O₁₈·4H₂O) structure and its effects on the cation exchange properties of tobermorites were investigated. Fe³⁺- substituted 11Å tobermorites were synthesized under hydrothermal conditions. The cation exchange capacities of these Fe³⁺-substituted tobermorites ranged between 82–122 meq/100g while specific Cs sorption ranged from 420–800 K_d. ⁵⁷Fe Mossbauer Spectroscopy, in addition to other techniques, was used to investigate the Fe-substitution in the tobermorite structure. None of the Mossbauer spectra revealed any absorption line due to Fe²⁺. The observed spectra were fitted to one or more closely overlapping quadrupole doublets. The assignment of Fe³⁺ among the available tetrahedral and octahedral sites was made based on the distinct differences in the observed isomer shifts. The extent of Fe³⁺_IV vs. Fe³⁺_VI site occupancies was determined from the corrected intensities of the respective quadrupole doublets.     

IR spectra and etch rates of plasma-enhanced chemically vapour-deposited phosphosilicate glass films

IR transmission spectra of phosphosilicate glass (PSG) films with 8 wt.% P prepared by plasma-enhanced chemical vapour deposition (PECVD) and CVD are compared. The differential IR spectrum of a PECVD PSG film differs from that of a CVD PSG film: the P=O peak has a lower intensity than the corresponding peak of the CVD film with the same phosphorus content; no peaks are evident at 980 and 500 cm⁻¹—the characteristic frequencies for P---O---P stretching and bending vibrations. The differential IR spectra of PECVD and CVD PSG films become very similar after annealing for 4 h in water vapour at 850°C. The etch rate of a PECVD film in p-etchant, which is constant throughout the film thickness, is 400 Å min⁻¹. However, the etch rate recorded after the film is subjected to annealing in water vapour at 850°C varies with the depth in the film, attaining values as high as 800 Å min⁻¹ in the region near the outer surface of the film. The results are explained as due to the oxidation of P₂O₃ to P₂O₅.