Electrical conducting properties of proton-conducting terbium-doped strontium cerate membrane

The electrical conduction behavior of SrCe_0.95Tb_0.05O_3−δ (SCTb) was investigated in different gases at high temperatures. In air, oxygen or nitrogen SCTb shows small electronic-hole conduction below 800°C and oxygen ionic conduction over 800°C with activation energy about 30 kJ/mol and 164–181 kJ/mol respectively. SCTb becomes a protonic conductor in hydrogen or methane in 500–900°C, with the proton conductivity in the range of 10⁻³–10⁻² S/cm, two to three orders of magnitude higher than electronic or oxygen ionic conductivity of SCTb in air or oxygen. The activation energy for protonic conduction in SCTb is 49 kJ/mol in methane and 54 kJ/mol in hydrogen. The electrical conductivity of SCTb in water vapor-saturated nitrogen, air or oxygen is higher than in corresponding gas without water vapor. Presence of water vapor does not affect the electrical conduction of SCTb in hydrogen or methane. Gas permeation measurements show that SCTb membrane is impermeable to hydrogen when the membrane is exposed to hydrogen or methane upstream and nitrogen or oxygen downstream. These results confirm that SCTb is a pure protonic conductor with very low electronic and oxygen ionic conductivity. SCTb will find applications as a high temperature electrolyte in fuel cells or hydrogen sensors.     

Hydroxyl ion conduction in ytterbium-doped strontium cerate at T<580 K in H2O/air atmosphere

Open circuit voltage (OCV) measurements in H₂O/air concentration cells at T<580 K using Yb-doped SrCeO₃ electrolyte indicate that under these conditions, protons are transported through the electrolyte as -ve ions, possibly as hydroxyl (OH⁻) ions. The H⁺ ionic transport, which is generally reported, becomes the dominant mode for H₂O/air concentration cells at temperatures greater than 750 K or when H₂O/air electrodes are replaced by H₂/Ar, and the anomalous OCV sign disappears. The combination of low temperature and the presence of hydrogen and oxygen as provided by the H₂O/air system appears to be necessary for the postulated hydroxyl ion electrode reactions to take place. In addition to OCV measurements, results from impedance spectroscopy are used to provide evidence in support of the suggested hydroxyl ion mode of protonic transport under the specified conditions. These findings are directly relevant in the development of novel humidity sensors in the temperature range 450–580K and is reported in a separate paper in this conference. Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Italy, Sept. 15–22, 1996     

Increased strontium uptake in trabecular bone of ovariectomized calcium‐deficient rats treated with strontium ranelate or strontium chloride

Based on clinical trials showing the efficacy to reduce vertebral and non‐vertebral fractures, strontium ranelate (SrR) has been approved in several countries for the treatment of postmenopausal osteoporosis. Hence, it is of special clinical interest to elucidate how the Sr uptake is influenced by dietary Ca deficiency as well as by the formula of Sr administration, SrR versus strontium chloride (SrCl₂). Three‐month‐old ovariectomized rats were treated for 90 days with doses of 25 mg kg^?1 d^?1 and 150 mg kg^?1 d^?1 of SrR or SrCl₂ at low (0.1% Ca) or normal (1.19% Ca) Ca diet. Vertebral bone tissue was analysed by confocal synchrotron‐radiation‐induced micro X‐ray fluorescence and by backscattered electron imaging. Principal component analysis and k‐means clustering of the acquired elemental maps of Ca and Sr revealed that the newly formed bone exhibited the highest Sr fractions and that low Ca diet increased the Sr uptake by a factor of three to four. Furthermore, Sr uptake in bone of the SrCl₂‐treated animals was generally lower compared with SrR. The study clearly shows that inadequate nutritional calcium intake significantly increases uptake of Sr in serum as well as in trabecular bone matrix. This indicates that nutritional calcium intake as well as serum Ca levels are important regulators of any Sr treatment.     

Measurements and simulation of hysteresis loops of donor-doped strontium bismuth tantalate ceramics

Wolframium ions doped SrBi₂Ta₂O₉ ceramics have been synthesized by the conventional mixed-oxide method. A sawtooth-like hysteresis loop was observed at low measuring-frequency. This phenomenon was thought to be related with the perturbation of the defect-dipole polarization under an external electrical field. A developed physical-model was derived on the basis of simplifying such perturbation to a simple harmonic pendulum oscillator, which combines physical considerations with the well-known Preisach model. On the hypothesis of the simple harmonic pendulum oscillator, the included-angle between the defect-dipole polarization and the elementary-dipole polarization can be expressed as the product of the defect-dipole relaxation velocity and permitted relaxation time. Simulation result was excellently agreed with the observed measurement.     

Measurements of collisional quenching of hydrogen atoms in an atmospheric-pressure hydrogen oxygen flame by picosecond laser-induced fluorescence

Atomic hydrogen has been probed in a hydrogen/oxygen flame at atmospheric pressure by use of two-photon, picosecond Laser-Induced Fluorescence (LIF). The fluorescence was detected and temporally resolved by a streak camera with a temporal resolution of a few ps which allowed determination of the collisionally quenched lifetime of then = 3 level of atomic hydrogen. The measurements were performed for three flame stoichiometries, = 1.4, 2.0 and 3.5, and were spatially resolved with respect to the reaction zone. The evaluated lifetime was found to vary rapidly in the reaction zone from 60 to 105 ps just above and then levelled out at 90 ps throughout the post-flame region. Power dependence measurements of the fluorescence signal indicated the presence of other phenomena, such as saturation, ionization and photodissociation. Since an inverted population is created between then = 3 and then = 2 level, Stimulated Emission (SE) of considerable magnitude occurred and was studied temporally resolved using the streak camera. The LIF and SE signal strengths for individual laser pulses were recorded in order to analyse a possible anti-correlation between the LIF and the SE.     

Comparison of the hydrogen uptake of different high temperature proton conductors

The water uptake of several high temperature proton conductors was studied in situ by thermogravimetry. These materials were SrCe_0.95Yb_0.05O_3-α, SrZr_0.95Yb_0.05O_3-α and BaCa_0.39Nb_0.61O_3-α. At different temperatures, the weights were recorded as a function of the applied water vapour pressures. From the observed mass changes, the proton contents were calculated. For all of the three systems, the water uptake could be described by an ideal solution process. Each individual system was characterized by two parameters: 1. The solution limit which is the maximum proton concentration that can be incorporated 2. The solution enthalphy which determines the pressure and temperature dependence of the uptake. The solution limits were compared with those expected from stoichiometric considerations. The enthalphies were considered with regard to a possible application as high temperature proton conductor. Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Italy, Sept. 15–22, 1996     

Frequency tuning and doubling in Yb-doped fiber lasers

A compact Yb-doped fiber laser (YDFL) based on a tunable fiber Bragg grating (FBG) with ～6 W output power and ～45 nm tuning around 1080 nm has been developed. The laser output power and its spectral width (～0.15 nm) do not change significantly at the tuning, while the FBG reflection coefficient increases with an increase in FBG compression. It has been shown that this increase is due to stress-induced changes in the FBG’s refractive-index modulation amplitude. Intracavity frequency doubling in the YDFL has also been performed. About 0.4 W of green radiation with tuning in the range 540–548 nm has been achieved with a KTP nonlinear crystal.     

Longitudinal relaxation of Fe nuclei in Yb-doped YIG

Measurements of T₁ for ⁵⁷Fe nuclei in Yb-doped YIG are reported for the temperature range 0·7–140 K, with the magnetization along the [111], [100], [110], and [112] crystallographic directions respectively. The dependence of T₁ on Yb concentration and on the magnitude of the applied field was also studied. These results are interpreted in terms of the ‘slow relaxation theory’, and are correlated with the ferrimagnetic resonance work of Clarke, Tweedale, and Teale, whose data have been reanalyzed by us. Both sets of data can be represented fairly well by the theory, with a consistent set of relevant parameters. However, the tensor G which describes the splitting of the Yb ground-state doublet must be modified somewhat from that deduced by Clarke et al., the new principal values being G₁ = 29·0 cm⁻¹, G₂ = 20·4 cm⁻¹ and G₃ = 8·5 cm⁻¹ respectively. Below approximately 10 K, when the magnetization is in the [110] or [112] direction, the nuclear relaxation rate is higher than predicted. These anomalies correspond to those observed in ferrimagnetic resonance line width, which have been attributed to Yb ions on the octahedral lattice sites normally occupied by iron. Anomalously large values of T⁻¹₁ are also observed below approximately 4 K in the [111] and [100] directions, and these remain to be accounted for.     

Formation of a magnetic composite by reduction of Co-Nd doped strontium hexaferrite in a hydrogen gas flow

Co-Nd strontium hexaferrite nanoparticles synthesized by the self-combustion method were treated in a hydrogen flow at different temperatures and times. The samples were characterized structurally by scanning electron microscopy and X-ray diffraction and magnetically with a vibrating sample magnetometer. Phase identification showed decomposition of the hexaferrite structure into Fe₃O₄ and different strontium mixed oxides. The sample treated at 500 °C for 30 minutes shows good magnetic properties due to the formation of a magnetite/hexaferrite composite. In this case magnetization is very close to the original sample while the coercivity slightly diminishes. The hexagonal phase is almost completely transformed into different oxides at a reducing temperature of 500 °C for 120 minutes. The obtained results are analyzed in terms of the phase composition and of the magnetic susceptibility of the studied samples.     

Measurements of the cross-sections for the photoproduction of positive pions on hydrogen in the region of the first resonance

In this paper the properties and the dependence upon parameters of those quantities are investigated, which are characteristic for the gas-heating process in electric arcs with axial gas flow. Starting with the equations of the one-fluid-model of plasma physics three various methods are derived, to calculate analytically or numerically the thermal and electrical entities of the inlet region of the arc. With these results expressions can be given for the thermal and electrical inlet length. Further the azimuthal component of the velocity and its inlet length are determined. A discussion of the results will be outlined in a later paper (part II).     

Femtosecond pulse generation and amplification in Yb-doped fibre oscillator-amplifier system

In recent times ytterbium (Yb) doped fibre-based mode-locked master oscillator and power amplifier have attracted a great deal of interest because of their inherent advantages like flexibility, reliability, compactness, high power handling capability and diffraction limited output beam quality as compared to the solid-state counterpart. But, to successfully develope of high-power femtosecond oscillator-amplifier system based on Ybdoped fibre, an appropriate choice of the mode-locking regime and the amplifier geometry are required. Development of an all-fibre integrated high-power Yb-doped fibre oscillator-amplifier system in which the advantages of a fibre-based system can be fully exploited remained a challenge as it requires the careful optimization of dispersion, nonlinearity, gain and ASE contribution.     

Effect of co-dopant addition on the properties of yttrium and neodymium doped barium cerate electrolyte

The paper discusses the Y and Nd doped barium cerate perovskites prepared by a modified Pechini method. The series prepared is described by the formula BaCe_0.80Y_xNd_0.2−x O_3−δ. The BaCeO₃ based powders, about 10–20 nm sized and uniformly shaped, were obtained through the calcination of the gel at 500 °C for 2 h. Their structures and ionic conductivities were characterized by X-ray diffraction and AC impedance spectroscopy. All the electrolytes were found to be barium cerate based solid solutions of perovskite type structures. Impedance spectra indicate that the grain boundary resistance of the specimen synthesized by this method is smaller than that of the samples prepared by a conventional solid-state method. The ionic conductivities of co-doped barium cerate were a factor of several times than that of the single-doped one at 673–1073 K. Among the electrolytes examined, the one co-doped with 5 mol% Nd and 15 mol% Y shows the best improvement in performance. These co-doped barium cerate are more ideal intermediate temperature (IT) electrolyte materials.     

Measurements of the total neutron cross sections of hydrogen and carbon at 0.5, 1.0 and 2.0 MeV

The total neutron cross sections of carbon and hydrogen were measured at 0.5, 1.0 and 2.0 MeV. The determination of the H(n, n) cross section often used as a standard was the major objective of the present measurements and values were obtained with accuracies of ～0.2 %, 0.2 % and 0.4 % respectively. A parameter set for the shape-independent effective-range approximation of the H(n, n) cross section was obtained with the present and other recent data indicating lower crosssection values than given in the Hopkins-Breit analysis.     

Radiation-induced change of OH content in Yb-doped silica glass

Yb-doped silica glasses containing low, medium, and high content of OH are prepared through nanoporous glass sintering technology. High-OH sample exhibits better X-ray irradiation resistivity than low- and medium-OH samples. After irradiation, OH content of low- and medium-OH samples increases 37.5% and 11%, respectively;in contrast, OH content of high-OH sample decreases dramatically. The different OH content changes among the samples are discussed regarding the proposed inter-conversion reactions involving Si-H and Si-OH during the irradiation.     

掺Yb硼硅酸盐玻璃的光学特性及其双光子合作上转换荧光

采用高温固相反应方法制备了不同掺Yb浓度的硼硅酸盐玻璃．通过室温吸收光谱、光致荧光光谱及Raman光谱的测量，系统地研究了掺Yb激光玻璃近红外的光致荧光特性．给出了硼硅酸盐玻璃中的Yb^3＋的吸收和发射截面，计算了Yb^3＋-^2F5/2能级的自发辐射寿命，并对Yb离子对的团簇上转换荧光进行了测量和分析，给出了Yb离子团簇上转换荧光光子能量与红外荧光光子能量以及声子振动能量的关系．     

Temperature dependence of photoluminescence and magnetic properties in Yb-doped ZnS nanocrystals

Zinc sul?de semiconductor nanocrystals doped with Yb³⁺ ions have been prepared through a chemical precipitation method using PVP (polyvinylpyrrolidone) as a capping agent. The structure of the nanoparticles has been analyzed by X-ray diffraction (XRD). The average size of the nanoparticles is found to be 3.7±0.4 nm. Photoluminescence spectra were recorded for doped ZnS nanoparticles as a function of temperature between 9 and 300 K. The results suggest that two emission bands have been observed at different temperatures. The width of 1.269 eV peak increases as temperature is raised. A shift of lower energy emission band has been observed with the change of temperature. Moreover, the magnetic measurement showed that the sample exhibits paramagnetic behavior.     

Theoretical and experimental study of transient response of the Yb-doped fiber amplifier

Some analysis of the transient response of the Yb-doped fiber amplifier are performed by solving a set of time-dependent rate and power transfer equations based on finite-difference method.Meanwhile,the variation of time to reach the steady state for upper level population distribution,the forward and backward amplified spontaneous emissions(ASEs)and stored energy on the system parameters including pump power,fiber length,Yb-doped concentration,and core area are numerically simulated,respectively.The results show that,by optimizing pump pulse width,stored energy can reach or even exceed the steady state value of continuous wave(CW)pump.By increasing Yb-doped concentration and core area,stored energy is increased,the ASE is suppressed and the ASE built-up time is postponed.In addition,the experimental results show the validity of the theoretical ASE built-up time.The obtained results can provide important guiding for the optimization of pump pulse width and fiber parameters.     

EPR and optical spectra of cupric ions doped in powder strontium maleate tetrahydrate and magnesium Bis (hydrogen maleate) hexahydrate

Abstract

EPR spectra of Cu²⁺ ions doped in a strontium maleate tetrahydrate and magnesium bis (hydrogen maleate) hexahydrate have been studied in X-band at room temperature and at liquid nitrogen temperature. Spin-Hamiltonian parameters have been calculated. Molecular orbital coefficients are obtained by correlating optical absorption data with EPR results.