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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Nano-Hydroxyapatite/Fluoridated and Unfluoridated Bioactive Glass Composites: Structural Analysis and Bioactivity Evaluation

Biphasic bioceramic composites containing nano-hydroxyapatite (HAP) and nanosized bioactive glasses have been prepared in the form of pellets and have been examined for the effects of bioglass concentrations and sintering temperature on the structural transformations and bioactivity behavior. Pure stoichiometric nano-HAP was synthesized using sol-gel technique. Two bioglasses synthesized in this work--fluoridated bioglass (Cao-P{sub 2}O{sub 5}-Na{sub 2}O{sub 3}-CaF{sub 2}) and unfluoridated bioglass (Cao-P{sub 2}O{sub 5}-Na{sub 2}O{sub 3}) designated as FBG and UFBG respectively, were added to nano-HAP with concentrations of 5, 10, 12 and 15%. The average particle sizes of synthesized HAP and bioglasses were 23 nm and 35 nm, respectively. The pellets were sintered at four different temperatures i.e. 1000 deg. C, 1150 deg. C, 1250 deg. C and 1350 deg. C. The investigations involved study of structural and bioactivity behavior of green and sintered pellets and their deviations from original materials i.e. HAP, FBG and UFBG, using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The phase composition of the sintered pellets was found to be non-stoichiometric HAP with {alpha}-TCP (tricalcium phosphate) and {beta}-TCP. It was revealed from SEM images that bonding mechanism was mainly solid state sintering for all pellets sintered at 1000 deg. C and 1150 deg. C and also for pellets with lower concentrations of bioglass i.e. 5% and 10% sintered at 1250 deg. C. Partly liquid phase sintering was observed for pellets with higher bioglass concentrations of 12% and 15% sintered at 1250 deg. C and same behaviour was noted for pellets at all concentrations of bioglasses at 1350 deg. C. The sintered density, hardness and compression strength of pellets have been influenced both by the concentration of the bioglasses and sintering temperature. It was observed that the biological HAP layer formation was faster on the green pellets surface than on pure HAP and sintered pellets, showing higher bioactivity in the green pellets.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Boron and nitrogen-codoped TiO{sub 2} nanorods: Synthesis, characterization, and photoelectrochemical properties

Boron and nitrogen codoped TiO{sub 2} nanorods (BNTRs) were synthesized via two-step hydrothermal reactions using TiN as a starting material. The as-prepared samples were characterized by X-ray diffraction, field-emission scanning electron microscope (SEM), transmission electron microscopy and X-ray photoelectron spectroscopy techniques. The results showed that TiO{sub 2} nanorods with the diameter of approximately 50-100 nm and the length of several micrometers were doped by the interstitial N and B. The nanorods were firstly formed in the hydrothermal synthesis of nitrogen doped TiO{sub 2}. The growing process of nanorods was observed by SEM and a most probable formation mechanism of the trititanate nanorods was proposed. The BNTRs showed a higher photocatalytic activity and a bigger photocurrent response than N-TiO{sub 2} nanorods under visible light irradiation. - Graphical abstract: Boron and nitrogen codoped TiO{sub 2} nanorods (BNTRs) were synthesized using TiN. The BNTRs showed a higher photocatalytic activity and a bigger photocurrent than N-TiO{sub 2} nanorods (NTRs) under visible light irradiation. Highlights: > Novel B- and N-codoped TiO{sub 2} nanorods (BNTRs) are designed and synthesized. > A most probable formation mechanism of the trititanate nanorods is proposed. > The BNTRs show an outstanding photocurrent response under visible light. > The BNTRs exhibit an improved visible light photocatalytic activity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

Topotactic synthesis of Co{sub 3}O{sub 4} nanoboxes from Co(OH){sub 2} nanoflakes

Hollow nanocubes of spinel Co{sub 3}O{sub 4} with the dimension of 20 nm were successfully prepared via a facile and reproducible solvothermal route. The structure and morphology of Co{sub 3}O{sub 4} nanoboxes were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscope (HRTEM) techniques. And a possible growth mechanism of Co{sub 3}O{sub 4} nanoboxes were suggested that solid Co{sub 3}O{sub 4} nanocubes nucleate in-situ and grow epitaxially from hexagonal {beta}-Co(OH){sub 2} precursors with the structural matching relationship of [0 0 1] {beta}-Co(OH){sub 2}//[1 1 1] Co{sub 3}O{sub 4}, and then solid Co{sub 3}O{sub 4} nanocubes gradually hollow and convert to single-crystal nanoboxes owing to Ostwald ripening. - Graphical abstract: The formation mechanism of Co{sub 3}O{sub 4} nanoboxes can be expressed as epitaxial growth of Co{sub 3}O{sub 4} nanocubes from {beta}-Co(OH){sub 2} nanoflakes due to a topotactic transformation and hollowing process owing to Ostwald ripening. Highlights: > Co{sub 3}O{sub 4} nanoboxes were prepared by a convenient, economical and controllable hydrothermal route. > Morphology and structure of Co{sub 3}O{sub 4} nanoboxes were characterized by XRD, SEM, and TEM techniques. > Co{sub 3}O{sub 4} nanoboxes grow epitaxially from Co(OH){sub 2} by topotactic transformation was suggested.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Large-scale controllable synthesis of dumbbell-like BiVO{sub 4} photocatalysts with enhanced visible-light photocatalytic activity

The controllable synthesis of novel dumbbell-like BiVO{sub 4} hierarchical nanostructures has been successfully obtained via a simple hydrothermal route. The as-synthesized products were studied by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy and UV-vis absorption spectroscopy. The results showed that the nucleation and growth of the nanodumbbells were governed by an oriented aggregation growth mechanism. It is noteworthy that the concentration of poly(vinyl pyrrolidone) and the volume ratio of H{sub 2}O to CH{sub 3}COOH were crucial to the growth of the final nanoarchitectures. Control experiments were also carried out to investigate the factors which impact on the morphology of the products. Furthermore, the as-prepared BiVO{sub 4} hierarchical nanostructures demonstrated the superior visible-light-driven photocatalytic efficiency, which is helpful for the separation and recycle considering their promising applications in harmful pollutants disposal. - Graphical Abstract: The controllable synthesis of novel dumbbell-like BiVO{sub 4} hierarchical nanostructures has been successfully obtained via a simple hydrothermal route; the as-prepared BiVO{sub 4} hierarchical nanostructures demonstrated the superior visible-light-driven photocatalytic efficiency. Highlights: Black-Right-Pointing-Pointer Dumbbell-like BiVO{sub 4} structures were synthesized and characterized for the first time. Black-Right-Pointing-Pointer The volume ratios of H{sub 2}O to CH{sub 3}COOH were crucial to the final morphologies. Black-Right-Pointing-Pointer Their photocatalytic activity was up to 90% under visible-light irradiation. Black-Right-Pointing-Pointer Dumbbell-like BiVO{sub 4} structures may utilize the pollutant disposal.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

Simple synthesis of mesoporous boron nitride with strong cathodoluminescence emission

Mesoporous BN was prepared at 550 {sup o}C for 10 h or so via a simple reaction between NaBH{sub 4} and CO(NH{sub 2}){sub 2}. X-ray diffraction demonstrates the formation of t-BN with lattice constants a=2.46 and c=6.67 A. High-resolution transmission electron microscopy displays a lot of porous films in the product, which possesses a high surface area of 219 m{sup 2} g{sup -1} and a pore size primarily around 3.8 nm tested by nitrogen adsorption-desorption method. The mesoporous BN exhibits a strong luminescence emission around 3.41 eV in the cathodoluminescence spectra, a high stability in both morphology and structure, and good oxidation resistance up to 800 {sup o}C. The byproducts generated during the reaction are responsible for the formation of the mesoporous BN. -- Graphical abstract: The mesoporous BN with a high specific surface area of 219 m{sup 2} g{sup -1} exhibits a strong luminescence emission around 3.41 eV in the CL spectra, high thermal stability in both morphology and structure, and good oxidation resistance up to 800 {sup o}C. Display Omitted Research highlights: Mesoporous BN was prepared by a simple reaction between NaBH{sub 4} and CO(NH{sub 2}){sub 2} at 550 {sup o}C. The mesoporous BN possesses a high surface area of 219 m{sup 2} g{sup -1}. The mesoporous BN exhibits a strong luminescence emission around 3.41 eV. The mesoporous BN has high stability and good oxidation resistance up to 800 {sup o}C.

36 MATERIALS SCIENCE↗
DOE OSTI2011

TiO{sub 2}/carbon nanotube hybrid nanostructures: Solvothermal synthesis and their visible light photocatalytic activity

MWCNT/TiO{sub 2} hybrid nanostructures were prepared via solvothermal synthesis and sol-gel method with benzyl alcohol as a surfactant. As-prepared hybrid materials were characterized by X-ray diffraction, transmission electron microscopy, UV-vis diffuse reflectance spectra and X-ray photoelectron spectroscopy. The results showed that MWCNTs were uniformly decorated with anatase nanocrystals in solvothermal condition, but MWCNTs were embedded in a majority of TiO{sub 2} nanoparticles by sol-gel method. When the weight ratio of MWCNTs to TiO{sub 2} was 20%, MWCNT/TiO{sub 2} hybrid nanostructures prepared by solvothermal synthesis exhibited higher visible-light-driven photocatalytic activity than that prepared by sol-gel method. Post-annealing of MWCNT/TiO{sub 2} nanostructures at 400 deg. C resulted in the formation of the carbonaceous Ti-C bonds on the interface between TiO{sub 2} and MWCNTs, which enhanced the photoabsorbance of the hybrid materials in the visible light region and improved the visible-light degradation efficiency of methylene blue. - Graphical abstract: MWCNT/TiO{sub 2} nanostructures have been prepared by solvothermal method, which exhibited higher visible-light-driven photocatalytic activity than that prepared by sol-gel method. The carbonaceous Ti-C bonds on the interface between TiO{sub 2} and MWCNTs enhanced the photoabsorbance of the hybrid materials in the visible light region. Highlights: > Anatase TiO{sub 2} nanoparticles were anchored on CNTs surface uniformly via solvothermal method {yields} The morphology facilitated the electron transfer between CNTs and TiO{sub 2} {yields} Ti-C bonds extended the absorption of MWCNT/TiO{sub 2} to the whole visible light region. > The hybrid nanostructures showed enhanced visible-light induced photocatalytic activity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

InN/InGaN multiple quantum wells emitting at 1.5 {mu}m grown by molecular beam epitaxy

This work reports on the growth by molecular beam epitaxy and characterization of InN/InGaN multiple quantum wells (MQWs) emitting at 1.5 {mu}m. X-ray diffraction (XRD) spectra show satellite peaks up to the second order. Estimated values of well (3 nm) and barrier (9 nm) thicknesses were derived from transmission electron microscopy and the fit between experimental data and simulated XRD spectra. Transmission electron microscopy and XRD simulations also confirmed that the InGaN barriers are relaxed with respect to the GaN template, while the InN MQWs grew under biaxial compression on the InGaN barriers. Low temperature (14 K) photoluminescence measurements reveal an emission from the InN MQWs at 1.5 {mu}m. Measurements as a function of temperature indicate the existence of localized states, probably due to InN quantum wells' thickness fluctuations as observed by transmission electron microscopy.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Titania-lanthanum phosphate photoactive and hydrophobic new generation catalyst

Titania-lanthanum phosphate nanocomposites with multifunctional properties have been synthesized by aqueous sol-gel method. The precursor sols with varying TiO{sub 2}:LaPO{sub 4} ratios were applied as thin coating on glass substrates in order to be transparent, hydrophobic, photocatalytically active coatings. The phase compositions of the composite powders were identified by powder X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM). The anatase phase of TiO{sub 2} in TiO{sub 2}-LaPO{sub 4} composite precursors was found to be stable even on annealing at 800 deg. C. The glass substrates, coated with TL1 (TiO{sub 2}-LaPO{sub 4} composition with 1 mol% LaPO{sub 4}) and TL50 (composite precursor containing TiO{sub 2} and LaPO{sub 4} with molar ratio 1:1) sols and annealed at 400 deg. C, produced contact angles of 74 deg. and 92 deg., respectively, though it is only 62 deg. for pure TiO{sub 2} coating. The glass substrates, coated with TL50 sol, produced surfaces with relatively high roughness and uneven morphology. The TL1 material, annealed at 800 deg. C, has shown the highest UV photoactivity with an apparent rate constant, k{sub app}=24x10{sup -3} min{sup -1}, which is over five times higher than that observed with standard Hombikat UV 100 (k{sub app}=4x10{sup -3} min{sup -1}). The photoactivity combined with a moderate contact angle (85.3 deg.) shows that this material has a promise as an efficient self-cleaning precursor. - Graphical abstract: Multifunctional TiO{sub 2}-LaPO{sub 4} composite stabilizes anatase phase with enhanced photocatalytic activity, and moderately higher hydrophobicity is a promising material for self-cleaning application. Highlights: > Titania-lanthanum phosphate nanocomposites were synthesized by aqueous sol-gel method. > Transparent, hydrophobic, photoactive coatings were developed on glass substrates. > The glass substrates, coated with TL1 annealed at 400 deg. C, produced a contact angle of 74 deg. > The TL1 material at 800 deg. C has shown the highest UV photoactivity (k{sub app}=24x10{sup -3} min{sup -1}). > Photoactivity and moderate contact angle show that this is an efficient self-cleaning precursor.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

Pb{sub 2.85}Ba{sub 2.15}Fe{sub 4}SnO{sub 13}: A new member of the A{sub n}B{sub n}O{sub 3n-2} anion-deficient perovskite-based homologous series

Pb{sub 2.85}Ba{sub 2.15}Fe{sub 4}SnO{sub 13}, a new n=5 member of the anion-deficient perovskite based A{sub n}B{sub n}O{sub 3n-2} (A=Pb, Ba, B=Fe, Sn) homologous series, was synthesized by the solid state method. The crystal structure of Pb{sub 2.85}Ba{sub 2.15}Fe{sub 4}SnO{sub 13} was investigated using a combination of neutron powder diffraction, electron diffraction, high angle annular dark field scanning transmission electron microscopy and Moessbauer spectroscopy. It crystallizes in the Ammm space group with unit cell parameters a=5.7990(1) A, b=4.04293(7) A and c=26.9561(5) A. The Pb{sub 2.85}Ba{sub 2.15}Fe{sub 4}SnO{sub 13} structure consists of quasi two-dimensional perovskite blocks separated by 1/2[110](1-bar 01){sub p} crystallographic shear (CS) planes. The corner-sharing FeO{sub 6} octahedra at the CS planes are transformed into edge-sharing FeO{sub 5} distorted tetragonal pyramids. The octahedral positions in the perovskite blocks between the CS planes are jointly taken up by Fe and Sn, with a preference of Sn towards the position at the center of the perovskite block. The chains of FeO{sub 5} pyramids and (Fe,Sn)O{sub 6} octahedra of the perovskite blocks delimit six-sided tunnels at the CS planes occupied by double chains of Pb atoms. The compound is antiferromagnetically ordered below T{sub N}=368{+-}15 K. Highlights: Black-Right-Pointing-Pointer Compound Pb{sub 2.85}Ba{sub 2.15}Fe{sub 4}SnO{sub 13} was synthesized and characterized for the first time. Black-Right-Pointing-Pointer It is a new member of the anion-deficient perovskite based homologous series A{sub n}B{sub n}O{sub 3n-2} with n=5. Black-Right-Pointing-Pointer Its structure consists of quasi two-dimensional perovskite blocks separated by interfaces. Black-Right-Pointing-Pointer Interfaces are made up of edge-sharing FeO{sub 5} distorted tetragonal pyramids. Black-Right-Pointing-Pointer Pb{sub 2.85}Ba{sub 2.15}Fe{sub 4}SnO{sub 13} is antiferromagnetically ordered below T{sub N}=368{+-}15 K.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Critical shell thickness for InAs-Al{sub x}In{sub 1-x}As(P) core-shell nanowires

InAs nanowires with Al{sub x}In{sub 1-x}P or Al{sub x}In{sub 1-x}As shells were grown on GaAs substrates by the Au-assisted vapour-liquid-solid method in a gas source molecular beam epitaxy system. Core diameters and shell thicknesses were measured by transmission electron microscopy (TEM). These measurements were then related to selected area diffraction patterns to verify either interface coherency or relaxation through misfit dislocations. A theoretical strain model is presented to determine the critical shell thickness for given core diameters. Zincblende stiffness parameters are transformed to their wurtzite counterparts via a well known tensor transformation. An energy criterion is then given to determine the shell thickness, at which coherency is lost and dislocations become favourable. Our model only considers axial strain relieved by edge dislocations since they were the only type of dislocation observed directly by TEM.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2011

Special fractal growth of dendrite copper using a hydrothermal method

Special fractal dendrite Cu nanostructures have been synthesized through a simple hydrothermal method, and the effects of the volume ratio between glycerol and water and the concentration of H{sub 3}PO{sub 3} on the morphologies of dendrite Cu have been studied in detail. The Field emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM) and X-ray diffraction (XRD) have been used to characterize these Cu products. The results indicate that rhombic diamond and different morphologies of fractal dendrite were prepared because of the accumulation of Cu nuclei based on the diffusion-limited aggregation (DLA) and the nucleation-limited aggregation (NLA) model. Fortunately, symmetrical leaf-like dendrite Cu nanostructures different from Cu dendrites reported before have been obtained. Additionally, an explanation for the growth of fractal dendrite Cu has been discussed carefully. - Graphical abstract: Uniform dendritic Cu are grown through controlling V{sub glycerol/water} in range of 0.6-1.2 and the concentration of H{sub 3}PO{sub 3} in range of 0.06-0.3 M. The rhombic cluster Cu are obtained by decreasing the amount of glycerol. Highlights: > Volume ratio of glycerol/water and concentration of H{sub 3}PO{sub 3} were varied, respectively. > Morphologies of dendritic Cu have some changes. > Leaf-like and rhombic cluster Cu were obtained. > The concentration changes affect the aggregation of Cu crystallites. > The aggregation and crystallographic orientation cause leaf-like Cu nanostructures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

SiO{sub 2} nanospheres with tailorable interiors by directly controlling Zn{sup 2+} and NH{sub 3}.H{sub 2}O species in an emulsion process

SiO{sub 2} nanospheres with tailorable interiors were synthesized by a facile one-spot microemulsion process using TEOS as silica source, wherein cyclohexane including triton X-100 and n-octanol as oil phase and Zn{sup 2+} or NH{sub 3}.H{sub 2}O aqueous solution as dispersive phase, respectively. The products were characterized by Scanning Electron Microscopy, Transmission Electron Microscopy and X-ray Powder Diffraction. It was suggested that the as-synthesized silica nanospheres possessed grape-stone-like porous or single hollow interior, and also found that the ammonia dosage and aging time played key roles in controlling the size and structure of silica nanospheres. Furthermore, the comparative results confirmed that in-situ zinc species [ZnO/Zn(OH){sub 2}] acted as the temporary templates to construct grape-stone-like interior, and a simultaneously competing etching process occurred owing to the soluble Zn(NH{sub 3}){sub 4}{sup 2+} complex formation while the additional excessive ammonia was introduced. With the aging time being extended, the in-situ nanocrystals tended to grow into bigger ones by Ostwald Ripening, producing single hollow interior. - Graphical Abstract: Formation process of SiO{sub 2} nanospheres with porous and single hollow interior. Highlights: > ZnO/Zn(OH){sub 2} nanocrystals as the temporary templates shape the interior structures of SiO{sub 2} nanospheres. > Fabrication of porous and single hollow interiors needs no additional processes such as roasting or dissolving. > Tailorable interiors can be easily obtained through adjusting the aging time of temporary templates.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2010

Graphene growth by molecular beam epitaxy on the carbon-face of SiC

Graphene layers have been grown by molecular beam epitaxy (MBE) on the (0001) C-face of SiC and have been characterized by atomic force microscopy, low energy electron diffraction (LEED), and UV photoelectron spectroscopy. Contrary to the graphitization process, the step-terrace structure of SiC is fully preserved during the MBE growth. LEED patterns show multiple orientation domains which are characteristic of graphene on SiC (0001), indicating non-Bernal rotated graphene planes. Well-defined Dirac cones, typical of single-layer graphene, have been observed in the valence band for few graphene layers by synchrotron spectroscopy, confirming the electronic decoupling of graphene layers.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Transport of intensity equation: a tutorial

When it comes to “phase measurement” or “quantitative phase imaging”, many people will automatically connect them with “laser” and “interferometry”. Indeed, conventional quantitative phase imaging and phase measurement techniques generally rely on the superposition of two beams with a high degree of coherence: complex interferometric configurations, stringent requirements on the environmental stabilities, and associated laser speckle noise severely limit their applications in optical imaging and microscopy. On a different note, as one of the most well-known phase retrieval approaches, the transport of intensity equation (TIE) provides a new non-interferometric way to access quantitative phase information through intensity only measurement. Despite the insufficiency for interferometry, TIE is applicable under partially coherent illuminations (like the Köhler’s illumination in a conventional microscope), permitting optimum spatial resolution, higher signal-to-noise ratio, and better image quality. In this tutorial, we give an overview of the basic principle, research fields, and representative applications of TIE, focus particularly on optical imaging, metrology, and microscopy. The purpose of this tutorial is twofold. It should serve as a self-contained introduction to TIE for readers with little or no knowledge of TIE. On the other hand, it attempts to give an overview of recent developments in this field. These results highlight a new era in which strict coherence and interferometry are no longer prerequisites for quantitative phase imaging and diffraction tomography, paving the way toward new generation label-free three-dimensional microscopy, with applications in all branches of biomedicine.

42 ENGINEERING↗
DOE OSTI2017

Correlative cellular ptychography with functionalized nanoparticles at the Fe L-edge

Precise localization of nanoparticles within a cell is crucial to the understanding of cell-particle interactions and has broad applications in nanomedicine. Here in this paper, we report a proof-of-principle experiment for imaging individual functionalized nanoparticles within a mammalian cell by correlative microscopy. Using a chemically-fixed HeLa cell labeled with fluorescent core-shell nanoparticles as a model system, we implemented a graphene-oxide layer as a substrate to significantly reduce background scattering. We identified cellular features of interest by fluorescence microscopy, followed by scanning transmission X-ray tomography to localize the particles in 3D, and ptychographic coherent diffractive imaging of the fine features in the region at high resolution. By tuning the X-ray energy to the Fe L-edge, we demonstrated sensitive detection of nanoparticles composed of a 22 nm magnetic Fe 3 O 4 core encased by a 25-nm-thick fluorescent silica (SiO 2 ) shell. These fluorescent core-shell nanoparticles act as landmarks and offer clarity in a cellular context. Our correlative microscopy results confirmed a subset of particles to be fully internalized, and high-contrast ptychographic images showed two oxidation states of individual nanoparticles with a resolution of ~16.5 nm. The ability to precisely localize individual fluorescent nanoparticles within mammalian cells will expand our understanding of the structure/function relationships for functionalized nanoparticles.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Preparation and Characterization of Niobium Doped Lead-Telluride Glass Ceramics

Niobium-lead-telluride glass ceramics of composition xNb{sub 2}O{sub 5}-(20-x) pbO-80TeO{sub 2}(where x = 0.1 mol% to 0.5 mol%) were prepared by using conventional melt quenching method. The prepared glass samples were initially amorphous in nature after annealed at 400 deg. c all samples were crystallized. This was confined by X-ray diffraction and scanning electron microscopy. The particle size of these glass ceramics have been calculated by using Debye-Scherer formula and the particle size is in the order of 15 nm to 60 nm. The scanning electron microscopy (SEM) photograph shows the presence of needle-like crystals in these samples.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Molecular beam epitaxial growth of BaTiO{sub 3} single crystal on Ge-on-Si(001) substrates

Thin films of perovskite type BaTiO{sub 3} (BTO) oxide have been grown epitaxially directly on Ge(001) surface at high temperature using molecular beam epitaxy. A stable (2x1) BaGe{sub x} surface periodicity is the critical enabling template for subsequent BTO heteroepitaxy on Ge(001). Reflection high energy electron diffraction (RHEED) and transmission electron microscopy indicate that high quality heteroepitaxy on Ge-on-Si(001) take place with <100>BTO(001)||<110>Ge(001) confirming a 45 deg. rotation epitaxial relationship. X-ray diffraction has been used to study the BTO lattice parameters and we evidenced that both tetragonal and cubic phases of BTO are present in the epilayer.

36 MATERIALS SCIENCE↗
DOE OSTI2010

Novel microporous zirconium silicate (K{sub 2}ZrSi{sub 3}O{sub 9}.2H{sub 2}O) from high temperature phase transformation

A new microporous zirconosilicate K{sub 2}ZrSi{sub 3}O{sub 9}.2H{sub 2}O (AV-15) has been prepared by high-temperature phase transformation at 910 {sup o}C. Its structure has been determined ab initio from powder X-ray diffraction data. The unit cell is orthorhombic, space group C222{sub 1} (no. 20), Z=4 with cell dimensions: a=8.105(3), b=10.684(5), c=12.030(5) A, V=1041.76(7) A{sup 3}. The framework connection of AV-15 is essentially the same as the previously reported sodium stannosilicate AV-10 while the locations of potassium and water molecules in the former are quite different from those of the sodium and water molecules in AV-10. In AV-10 sodium and water molecules form a sinucoidal chain, while potassium and water molecules build up a linear chain in AV-15. The water molecules in AV-15 are lost on heating with a typical zeolitic behaviour. SEM shows that the particle sizes and habits of AV-15 and parent umbite material are the same. The {sup 29}Si MAS NMR spectrum of AV-15 displays two resonances at ca. -89.4 and -90.1 ppm in a 1:2 intensity ratio. Thermogravimetry analysis confirms the existence of water in this material. -- Graphical abstract: A new microporous zirconosilicate has been prepared by high temperature phase transformation at 910 {sup o}C. Its structure has been determined ab initio from powder X-ray diffraction data. The water molecules in this material are lost below 125 {sup o}C in a way typical of zeolites and molecular sieves. Display Omitted

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗