O3 Nanocrystals Research Articles

Structural Complexities of PbTi0.5Fe0.5O3 Nanocrystals Revealed by HRTEM

Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.

Hydrothermal processes for Tm3+ -doped GdV O4 nanocrystalline morphologies and their photoluminescence properties

Controlled reaction conditions in simple, template-free hydrothermal processes yield pure tetragonal zircon-type I41/amd TmGdV O4 nanocrystals with well-defined specific morphologies and sizes. Nitrate reagents under mild conditions (180∘C, pH=7, autogenous pressure) produce from square, hexagon and lozenge nanocrystals with sides starting in 20nm, to porous spindles, nanotubes, nanorods and nanobelts depending of the reaction times. They exhibit photoluminescence in ∼1.95μm similar to bulk single crystals. For the lowest Tm3+ concentration (0.2 % mol) in GdV O4 measured 3H4 and 3F4 fluorescence lifetimes τ are very near to their radiative values, τrad.

Hydrothermal Synthesis of Monodisperse Ce0.5Zr0.5O2 Metastable Solid Solution Nanocrystals

AbstractAn environmentally friendly and economically efficient method has been developed to synthesize monodisperse CeO2‐ZrO2 solid solution nanocrystals. In this process, the formation of oleate‐stabilized Ce0.5Zr0.5O2 nanocrystals was designed to proceed through hydrolytic sol–gel condensation of metal–oleate precursors in an aqueous solution and subsequent hydrothermal growth at 200 °C for 6 h. The results showed that the 3.0‐nm‐sized nanocrystals possess a metastable CeO2‐ZrO2 tetragonal phase with well‐designed chemical composition and are nearly monodisperse. Owing to the uniform textural and elemental properties, the products exhibit relatively high thermal stability of the metastable phase and well‐defined reduction properties.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Near-Infrared to Visible Upconversion in Er3+ and Yb3+ Codoped Lu2O3 Nanocrystals: Enhanced Red Color Upconversion and Three-Photon Process in Green Color Upconversion

The synthesis and upconversion luminescence properties upon a 980 nm pump of cubic Lu1.88Yb0.1Er0.02O3 nanocrystals with various shapes, e.g., nanorods, nanosheets, and nanoparticles, are studied. ...

Susceptibility measurements of impurity-helium condensates containing magnetic impurities

The magnetic susceptibilities of impurity-helium condensates (IHCs), containing nanocrystals of molecular oxygen and atomic nitrogen free radicals embedded in molecular N2 have been measured via a SQUID magnetometer in the temperature range between 1.1 and 2.1 K. The susceptibilities of the samples containing nitrogen atoms followed Curie-Weiss behavior with very small Weiss temperatures ranging from 0 to -0.4 K. The behavior of samples composed of O2 nanocrystals deviated sharply from results for bulk solid. The susceptibilities of the samples were 102 larger than for bulk solid O2 and showed Curie-Weiss behavior with a Weiss temperature in the range from -4.5 K to -5 K. This result is qualitatively consistent with results obtained in other laboratories for O2 confined in restricted geometries.

EELS studies of nano-precipitates in borosilicate glasses

The sequence of precipitation in five different alkali-borosilicate glasses is studied by HREM, HAADF-STEM and EELS. The glasses are doped or supersaturated with 4 mol% of CeO2, and have varying concentrations of other dopant oxides, such as Fe2O3, Nd2O3, Cr2O3, and Ag2O. The shape and distribution of precipitates range from amorphous droplet shape to dendritic crystals. Oxidation states of Ce and other cations in glass and precipitates are measured by ELNES. It is found that Ce in glass preferentially adopts +IV valence in Ce-crystal-free glasses while it adopts +III valence in glass nanocomposites that contain Ce(+IV)O2 nanocrystals.

SQUID Measurements of the Susceptibilities of Impurity-Helium Condensates

For the first time, the magnetic susceptibilities of impurity-helium condensates containing magnetic impurities have been measured via a SQUID magnetometer in the temperature range between 1.1 and 2.1 K. The impurity-helium condensates are gel-like aggregates of nanocrystallites composed of molecules and free radicals. Molecular oxygen nanocrystals and atomic nitrogen embedded in molecular N2 nanocrystals have been studied. The susceptibilities of the samples containing nitrogen atoms followed Curie-Weiss behavior with very small Weiss temperatures ranging from +0 to −0.4 K. The behavior of samples composed of O2 nanocrystals deviated sharply from the results for bulk solid O2. The susceptibility of the samples was 102 larger than for bulk solid O2 and showed Curie-Weiss behavior with a Weiss temperature in the range from −4.5 to −5 K. This result is qualitatively consistent with results obtained in other laboratories for O2 confined in restricted geometries.

Ethanol-assisted synthesis of Zn0.5Fe2.5O4 nanocrystals in thermal solvent of paraffin

Abstract In the atmosphere of N 2 , low cost paraffin slices were refined and then successfully utilized as a solvent instead of the expensive high-carbon alkanes or alkenes like 1-octadecene to synthesize Zn 0.5 Fe 2.5 O 4 nanocrystals at 320 °C. In the experiments, the precursor solutions of ferric and zinc oleates were stoichiometrically prepared and injected by two-step operations into the hot solvent, together with controlled amounts of ethanol to tailor their thermal decomposition performances. The synthesized Zn 0.5 Fe 2.5 O 4 nanocrystals were characterized by XRD and FESEM, having uniform morphology and a quasi-monodisperse size distribution with a mean value 25 nm and a standard deviation of ±12.3%. The formation and structural characteristics of Zn 0.5 Fe 2.5 O 4 nanocrystals are attributed to the catalysing function of ethanol and the effective separation of nucleation and growth of nanocrystals via the two-step injections of reactive precursors.

Shape Evolution of Pb (Zr,Ti)O3 Nanocrystals Under Hydrothermal Conditions

Pb (Zr,Ti)O3 nanocrystals with different morphologies have been prepared hydrothermally with poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAA) as surfactants. The morphology of Pb (Zr,Ti)O3 nanocrystals develops from a particle to a rod and then a wire by adjusting the ratio of PVA/PAA and reaction time in a hydrothermal system. The mixed surfactant system has been shown to promote anisotropic growth effectively and thus the formation of nanorods and single crystalline nanowires of Pb (Zr,Ti)O3. A possible mechanism for such a shape evolution of nanocrystals is simply discussed.

Concept and Realization of the Formation of Metastable Tetragonal (Zr1-xCex)O2 Nanocrystals in Aqueous Solutions

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Preparation and characterization of poled nanocrystal and polymer composite PZT/PC films

Pb(Zr0.52Ti0.48)O3 (PZT) nanocrystals and transparent polycarbonate (PC) composite thin films with useful properties for ferroelectric, piezoelectric and electro-optic devices were prepared by a spin-coating technique. Ultra-fine PZT (∼40–50 nm) nanocrystals with pure perovskite tetragonal phase were synthesized by a hydrothermal method. The structure and morphology of the composite thin films were studied by means of X-ray diffraction and scanning electron microscopy. To obtain the optimum electro-optic properties of poled composite films, the poling condition under an external electric field was optimized through the dielectric properties of PZT and PC polymer and effective field intensity theory. The electro-optic coefficient of the poled PZT/PC composite film is estimated to be 30.5 pm/V. The transparency spectra were measured and the optical band gaps of the unpoled, poled at 145 °C and poled at 165 °C composite thin films are estimated to be 4.26 eV, 4.21 eV and 4.18 eV, respectively. The measured dielectric constants of PZT/PC are in good agreement with the calculated values for the composite with a very small PZT volume fraction, based on the Onsager effective-field theory. This offers a reliable and indirect way to predict the dielectric constant of nanocrystals.

Morphologically Templated Growth of Aligned Spinel CoFe2 O4 Nanorods.

Uniaxially aligned CoFe2 O4 nanorods are obtained by coprecipitation of Co2+ , Fe2+ , and C2 O4 2- ions in a microemulsion solution, and subsequent high-temperature decomposition of CoFe2 (C2 O4 )3 . Each nanorod is made up of a "tectonic" assembly of CoFe2 O4 nanocrystals. Magnetization of such CoFe2 O4 materials may lead to their use in high-density magnetic recording media and high-performance electromagnetic and spintronic devices.

Non‐Template Hydrothermal Route Derived Mesoporous Ce0.2Zr0.8O2 Nanosized Powders with Blue‐Shifted UV Absorption and High CO Conversion Activity.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Non-template hydrothermal route derived mesoporous Ce0.2Zr0.8O2nanosized powders with blue-shifted UV absorption and high CO conversion activity

Mesoporous Ce0.2Zr0.8O2 nanosized powders were synthesized via a hydrothermal method in the presence of urea without any templates using a trivalent cerium salt as the starting material. The analyses by medium-angle powder X-ray diffraction (PXRD) and vis-Raman spectroscopy showed that the Ce0.2Zr0.8O2 powders were solid solutions of pure tetragonal phase, whether as-prepared at 160 °C or calcined at 773–1273 K. By low-angle PXRD and transmission electron microscopy, the as-prepared Ce0.2Zr0.8O2 showed a short-range ordered mesostructure probably as a result of the natural agglomeration of uniform nanoparticles upon hydrothermal treatment. The as-prepared powders had high surface areas (232–281 m2 g−1) and narrow pore size distributions (3.5–4.0 nm), according to the measurements of nitrogen adsorption. After calcining at 773 K, this mesostructure was retained to some degree with lower surface areas (66–75 m2 g−1) and larger pore sizes (5.1–7.2 nm). Determined by X-ray photoelectron spectroscopy, the numbers of oxygen vacancies (0.025–0.037) on the nanocrystalline surface was high for both as-prepared and calcined Ce0.2Zr0.8O2. UV-vis absorption measurements showed that the band gap energy of the as-prepared Ce0.2Zr0.8O2 nanocrystals was distinctly blue-shifted compared with the bulk value due to the quantum size effect. The catalytic tests demonstrated that the Ce0.2Zr0.8O2 nanosized powders synthesized at 160 °C showed higher thermal stability in terms of surface area and phase composition, and higher catalytic activity for CO conversion than that synthesized at 140 °C. Among all the catalysts tested, the mesostructured one with the highest surface area and the largest pore volume displayed the highest oxygen storage capacity of 233 μmol CO g−1 at 773 K, and the lowest 50% conversion temperature of 641 K.