Nanocrystalline oxide (Y2O3, Dy2O3, ZrO2, NiO) coatings on BaTiO3 submicron particles by precipitation

Nanocoatings (5–20 nm) of different compounds on fine BaTiO₃ particles were obtained by means of precipitation processes. Homogeneous and smooth shells of Y(OH)CO₃ and Dy(OH)CO₃ were grown from nitrate solutions in the presence of urea. An irregular coating consisting of zirconia nanoparticles was produced from zirconyl nitrate solution using ammonia as a precipitating agent after adsorption of a polymeric polyelectrolyte on the BaTiO₃ surface. Composite particles with a peculiar morphology were obtained by inducing heterogeneous nucleation and growth of Ni(OH)₂ lamellae on the BaTiO₃ surface. The different shells can be transformed in a nanocrystalline coating of the corresponding oxide (Y₂O₃, Dy₂O₃, ZrO₂, NiO) by calcination at moderate temperatures (400–700 °C). The overall results indicate that precipitation from solution represents a versatile process to grow a second-phase layer on the surface of BaTiO₃ particles. This approach can be used as an alternative to mechanical wet mixing for controlled doping of ferroelectric materials and for the fabrication of composite materials with specific geometry of the two-phase assembly.     

Physical model of the rotation of a tropical cyclone

A physical mechanism for the intense rotation of a spiral cyclonic vortex in a laboratory model of a tropical cyclone is described on the basis of experimental results. The results obtained are compared with the equation describing the vertical component of the vorticity. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 1, 25–28 (10 January 1996)     

Electrical properties of A′Ca2Nb3O10 (A′=K, Rb, Cs) layered perovskite ceramics

The electrical conductivity properties of Dion-Jacobson type layered perovskites A′Ca₂Nb₃O₁₀ (A′=K, Rb, Cs) was investigated under different gas atmospheres. An increase in the electrical conductivity by about 2–5 orders in magnitude in both ammonia and hydrogen atmospheres is observed compared to air. Among the members of the series, the compound with the smallest size of the alkali ion, i.e. KCa₂Nb₃O₁₀, exhibits the highest conductivity. In air and hydrogen, a single activation energy value in the range 0.25 – 0.80 eV is observed, while in ammonia a sharp increase in the electrical conductivity is found at about 500 °C. The activation energy at low-temperatures (300–500 °C) is attributed to ionic motion and at higher temperatures (500–700 °C) to both defect formation and ionic motion. The unusual electrical conductivity behavior in ammonia is explained on the basis of the model developed for alkali halides. EMF measurements reveal that the layered perovskites are ionic (proton) conductors. The electrical conductivity changes as a function of the ammonia gas concentration; accordingly, layered perovskites appear to be useful solid electrolytes in galvanic cells for practical applications, e.g. for gas sensors. Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000.     

The determination of the parameters of sub- and supercritical extraction of plant raw materials

The extraction of biologically active substances by carbon dioxide from various plant raw materials (amaranth seeds, Sophora japonica flower buds, Stephania rotunda stems, and Stevia rebaudiana leaves) was studied at sub- and supercritical parameters. A laboratory unit for the extraction of plant raw materials by liquefied gases and supercritical fluids at 5–35 MPa pressures and 285–350 K temperatures was developed. The maximum yield of the extracted substances from plants specified was obtained at temperature and pressure exceeding the critical parameters of CO₂ (320–330 K, 28–30 MPa).     

Growth of monodisperse nanocrystals of cerium oxide during synthesis and annealing

Monodisperse cerium oxide nanocrystals have been successfully synthesised using simple ammonia precipitation technique from cerium(III) nitrate solution at different temperatures in the range 35–80 °C. The activation energy for growth of CeO₂ nanocrystals during the precipitation is calculated as 11.54 kJ/mol using Arrhenius plot. Average crystal diameter was obtained from XRD analysis, HR-TEM and light scattering (PCS). The analysis of size data from HR-TEM images and PCS clearly indicated the formation of highly crystalline CeO₂ particles in narrow size range. CeO₂ nanocrystals precipitated at 35 °C were further annealed at temperatures in the range 300–700 °C. The activation energy for crystal growth during annealing is also calculated and is close to the reported values. An effort is made to predict the mechanism of crystal growth during the precipitation and annealing.     

The influence of temperature on σ-phase formation and the resulting hardening of Fe–Cr–Mo-alloys

Hardening in Fe–Cr–Mo-alloys due to the formation of σ-phase, has been the subject of theoretical and experimental interest. In the present investigation Fe–Cr-alloys containing 0, 2, 4 and 6% Mo were prepared and were fully transformed to the σ-phase by isothermally annealing the samples for various periods at temperatures of 600–800oC. After each annealing cycle room temperature CEMS-spectra were recorded and micro-hardness tests were performed. The micro-hardness increases with annealing time and temperature, in accordance with the fraction of σ-phase present, and ranged from about 140 HV to 200 HV. From the measurements, activation energies were also deduced. This revised version was published online in August 2006 with corrections to the Cover Date.     

Electrochemical performances of FePO<Subscript>4</Subscript>-positive active mass prepared through a new sol–gel method

This investigation is a contribution to the research on alternative cathode materials with much more promising performances for lithium batteries. It deals with the electrochemical properties of iron phosphate compound FePO₄, chemically prepared through the so-called sol–gel Pechini process, terminated by a calcination of the product precursor at temperatures (T _c) ranging between 350°C and 650°C. A crystalline phase was obtained for temperatures ≥400°C. The particle size decreased with the decrease in T _c, giving rise to a Brunauer–Emmett–Teller (BET)-specific surface area, S _BET, as high as 28 m² g⁻¹ for the sample annealed at 400°C. The electrochemical properties of FePO₄-based composite cathodes were characterized on three-electrode laboratory cells. Charge–discharge cycling determined a maximum reversible capacity of 132 mAh g⁻¹, which fell with the increase in T _c. A direct correlation was established between the activity of the material and its active surface area.     

Planar imaging thermometry in gaseous flows using upconversion excitation of thermographic phosphors

Temperature measurement in gaseous flows is of significant practical importance for determining convection coefficients for heat transfer calculations, validating computation fluid dynamic simulations, and understanding the fundamentals of turbulent mixing and transport in flows. Here, we report on a new diagnostic technique for measuring temperature in gaseous flows which relies upon upconversion luminescence from inorganic phosphors. The phosphor used for the study consists of erbium (Er³⁺) and ytterbium (Yb³⁺) ions doped into a yttrium oxysulfide host material. The theoretical background behind the upconversion diagnostic is presented and spectral emission data taken using upconversion excitation are used to design a temperature diagnostic which is quite sensitive for temperatures ranging from approximately 300–600 K. Demonstration temperature measurements were performed in an air jet heated to temperatures ranging from 295–523 K. Single-shot images of temperature were obtained with a temperature precision of approximately ±5 K (1 standard deviation basis). This is the first known application of upconversion excitation to imaging temperatures in gaseous flows.     

Ac-conductivity and dielectric relaxations above glass transition temperature for parylene-C thin films

45% semi-crystalline parylene-C (–H₂C–C₆H₃Cl–CH₂–) _n thin films (5.8 μm) polymers have been investigated by broadband dielectric spectroscopy for temperatures above the glass transition (T _g =90°C). Good insulating properties of parylene-C were obtained until operating temperatures as high as 200°C. Thus, low-frequency conductivities from 10⁻¹⁵ to 10⁻¹² S/cm were obtained for temperatures varying from 90 to 185°C, respectively. This conductivity is at the origin of a significant increase in the dielectric constant at low frequency and at high temperature. As a consequence, Maxwell–Wagner–Sillars (MWS) polarization at the amorphous/crystalline interfaces is put in evidence with activation energy of 1.5 eV. Coupled TGA (Thermogravimetric analysis) and DTA (differential thermal analysis) revealed that the material is stable up to 400°C. This is particularly interesting to integrate this material for new applications as organic field effect transistors (OFETs). Electric conductivity measured at temperatures up to 200°C obeys to the well-known Jonscher law. The plateau observed in the low frequency part of this conductivity is temperature-dependent and follows Arrhenius behavior with activation energy of 0.97 eV (deep traps).     

Properties of reactively sputtered W–B–N thin film as a diffusion barrier for Cu metallization on Si

Thin films of W–B–N (10 nm) have been evaluated as diffusion barriers for Cu interconnects. The amorphous W–B–N thin films were prepared at room temperature via reactive magnetron sputtering using a W₂B target at various N₂/(Ar + N₂) flow ratios. Cu diffusion tests were performed after in-situ deposition of 200 nm Cu. Thermal annealing of the barrier stacks was carried out in vacuum at elevated temperatures for one hour. X-ray diffraction patterns, sheet resistance measurement, cross-section transmission electron microscopy images, and energy-dispersive spectrometer scans on the samples annealed at 500°C revealed no Cu diffusion through the barrier. The results indicate that amorphous W–B–N is a promising low resistivity diffusion barrier material for copper interconnects.     

Effect of synthesis temperature on the phase structure and electrochemical performance of nickel hydroxide

Nickel hydroxide powder is prepared by chemical precipitation method, and the effect of synthesis temperature on the phase structure and electrochemical performances of nickel hydroxide is investigated. The phase structure is characterized by X-ray diffraction (XRD), and the electrochemical performances are characterized by cyclic voltammetry, electrochemical impedance spectroscopy, and charge/discharge tests. The XRD results show that low temperatures (0–20 °C) induce the precipitation of badly crystallized nickel hydroxide while at high temperatures (40–60 °C) crystallized β-nickel hydroxide is formed. Electrochemical performance tests show that the nickel hydroxide synthesized at low temperature has better electrochemical reversibility, lower electrochemical reaction impedance, and higher discharge capacity than that of the nickel hydroxide synthesized at high temperature.     

μCF Experiments in D2 and HD Gases – Final Results

During 1994–1996, a series of μCF experiments were performed at PSI by the PSI-PNPI-IMEP-LBNL-TUM collaboration. These experiments aimed at high-precision studies of the d–μ–d fusion in D₂ and HD gases in a wide temperature range. The Gatchina ionization time projection chamber has been used to detect the dd-fusion reaction products. The main parameters of the d–μ–d fusion have been measured with high absolute precision. In this report, we present the results of the final analysis of the experimental data. The obtained results are compared with the calculations based on a recent μCF-theory. This revised version was published online in August 2006 with corrections to the Cover Date.     

Time-resolved photoluminescence and steady-state optical investigations of a Zn1−x Cd x Se/ZnSe quantum well

Il Nuovo Cimento D - We report on time-integrated and time-resolved optical experiments performed on a 26 Å thick Zn0.85Cd0.15Se/ZnSe quantum well, for temperatures in the 10–200 K...     

Optical–feedback cavity–enhanced absorption: a compact spectrometer for real–time measurement of atmospheric methane

We report on the application of the new technique of optical–feedback cavity–enhanced absorption spectroscopy to the real–time quantitative measurement of tropospheric methane traces from an airplane using a compact, low cost instrument based on a telecommunication–type diode laser operating close to room temperature. Methane concentration is obtained by fitting the absorption line centered at 1658.96 nm (6026.23 cm^-1) which belongs to the first overtone transition of the CH stretch vibration. The measurement rate is about 30 Hz, but the response time is limited to about 0.3 s by the gas flow in the measurement cell. The instrument provides the absolute ambient methane concentration accurate to ±1% (±20 ppb) without need for a periodic calibration. This is demonstrated by a hands–off comparison with a self–calibrating chromatographic setup during 10 days. The observed measurement stability can be extrapolated to much longer time periods. With respect to the short–term performance (minutes) fast concentration changes at the level of 1 ppb can be detected, and we believe this performance can be extended to the long term. Finally, a laboratory comparison with a lead–salt mid–infrared diode laser multipass spectrometer (operating close to 3028 cm^-1 at liquid nitrogen temperature) demonstrates a similar performance. PACS 07.88.+y; 42.55.Px; 42.62.Fi     

Spectral and spectral-polarization characteristics of potato leaves

The results of laboratory investigations of the spectral and spectral-polarization characteristics of radiation reflected from the leaves of potato(Solanum tuberosum) of different varieties are discussed. During the vegetation season of 1997, the angular dependence of the degree and azimuth of polarization of radiation reflected from potato leaves as well as the scattering indicatrices in the range 380–1080 nm were determined by a specially developed method with the use of a laboratory goniometric setup. The relationship between the spectral polarization characteristics of radiation and biological parameters of the potato has been obtained with the help of different methods of statistical analysis and explained on the basis of the known physical mechanisms. Translated from Zhurnal Prikladnoi Spektroskopii. Vol. 67, No. 4, pp. 524–529, July–August, 2000.     

Experimental study of thermal conductivity of refrigerant R-409A in vapor phase

Thermal conductivity of refrigerant R-409A in vapor phase was studied in the range of temperatures 306–425 K and pressures 0.12–1.33 MPa. Measurements were performed with the stationary method of coaxial cylinders. Uncertainty of experimental data on thermal conductivity was 1.5–2.5 %, and errors of temperature and pressure measurements did not exceed 0.05 K and 4 kPa, respectively. Approximating dependence of thermal conductivity on pressure and temperature was obtained. Thermal conductivity on dew line and in ideal gas state was calculated.     

Process of polarization and analysis of the water adsorption on a zeolite

We report the study of the dielectric relaxation mechanisms in the zeolite Na-X, “Faujasite”, by means of the method of Thermally Stimulated Depolarization Currents (TSDC), and polarization conductivity versus frequency. We give particular interest to the effect of adsorption on the evolution of dielectric parameters. Two distinct relaxation processes attributed to adsorbed water were found by TSDC measurements. Moreover, the polarization conductivity gives two sets of values of the potential barrier height. The evolution of the polarization conductivity as a function of the rate p/p° is comparable to the curve showing the isothermal water adsorption. Paper presented at the 1st Euroconference on Solid State Ionics, Zakynthos, Greece, 11–18 Sept. 1994     

Interactions of the Polyaniline and Nafion bilayer sensor structure with ammonia in a dry and wet air atmosphere

Presented here are the preliminary results concerning an interactions of a novel bilayer sensor structure of polyaniline and Nafion as an ammonia gas sensors in a Surface Acoustic Wave and electric planar systems. The investigations were performed with a 50 and 100 ppm concentrations of the ammonia (NH₃) in a synthetic dry (relative humidity RH∼4–5%) and wet air (RH∼50–54%) atmosphere. The prototype polyaniline and nafion bilayer structure has been manufactured by two deposition technologies: 72 nm of PANI by PVD technology and Nafion film (  nm) by spin coating technology and specific process of annealing. A good interactions with ammonia for the bilayer structure (PANI film with Nafion) has been observed especially at higher relative humidity of the atmosphere.     

345 GHZ PROTOTYPE SIS MIXER WITH INTEGRATED MMIC LNA

We report on heterodyne measurements at submillimeter wavelengths using a receiver with a Superconductor-Insulator-Superconductor (SIS) mixer device and a Microwave Monolithic Integrated Circuit (MMIC) cryogenic low noise amplifier (LNA) module integrated into the same block. The mixer characterization presented in this work demonstrates the feasibility of operating a MMIC LNA in close proximity to the SIS device without penalty in mixer performance due to heating effects. Verification of this functionality is crucial for the ongoing development of SuperCam, a 64-pixel focal plane array receiver consisting of eight, 1 × 8 integrated mixer/LNA modules. The test setup included a mixer block modified to accept a MMIC amplifier. Our tests show that the LNA can be operated over a broad range of V_drain voltages from 0.40–1.40 V, corresponding to dissipative powers of 2.6–29 mW. We observe no significant effect on the measured uncorrected receiver noise temperatures in the 345 GHz band.     

Cold atomic beam from a rubidium funnel

We report an experimental demonstration of a continuous, slow and cold beam of rubidium atoms from a two-dimensional magneto-optic trap or atomic funnel. Typically 7.3(7)×10⁸ atoms/s are ejected from the funnel with a variable velocity in the range 2–8 m/s and a temperature of 45–55 μK in the moving frame. This represents the first demonstration of sub-Doppler laser cooling in an atomic beam and temperatures as low as ≈25 μK have been observed. Received: 30 September 1999 / Published online: 5 April 2000