Novel alkaline-free Er-doped fluorophosphate glasses for broadband optical fiber lasers and amplifiers

Two sets of Er³⁺-doped alkaline-free glass systems, MgF₂–BaF₂–Ba(PO₃)₂–Al(PO₃)₃ (MBBA) and Bi(PO₃)₃–Ba(PO₃)₂–BaF₂–MgF₂ (BBBM), have been prepared and investigated with the aim of using them as active media. Radiative lifetimes (τ_rad) and branching ratios (β) have been obtained for the excited states of Er³⁺. The absorption spectra were recorded to obtain the intensity parameters (Ω_t) which are found to be Ω₂ = 4.47 × 10⁻²⁰ cm², Ω₄ = 1.31 × 10⁻²⁰ cm², Ω₆ = 0.81 × 10⁻²⁰ cm² for the MBBA system and Ω₂ = 4.03 × 10⁻²⁰ cm², Ω₄ = 1.34 × 10⁻²⁰ cm², Ω₆ = 0.53 × 10⁻²⁰ for the BBBM system, respectively. The emission cross-section for the ⁴I_13/2 → ⁴I_15/2 transition is determined by the Fuchtbauer–Ladenburg method and found to be 2.35 × 10⁻²⁰ cm² and 3.54 × 10⁻²⁰ cm² for the MBBA and BBBM system, respectively. Comparison of the measured values to those of Er³⁺ transitions in other glass hosts suggests that our new glass systems are good candidates for broadband compact optical fiber and waveguide amplifier applications.     

Optical absorption and spectroscopic characteristics of Tm ions doped NaY(MoO4)2 crystal

The polarized absorption and emission spectra have been measured for the Tm³⁺ doped NaY(MoO₄)₂ crystal and spectral parameters have been estimated from the absorption data based on the Judd–Ofelt theory. The effective intensity parameters (t = 2, 4, 6) are 11.67 ×10⁻²⁰, 2.21 × 10⁻²⁰, 1.74 × 10⁻²⁰ cm², respectively. From the intensity parameters, the radiative transition probabilities, radiative lifetimes, branching ratios and the emission cross-section have been calculated. In comparison with other Tm³⁺ doped laser crystals, Tm³⁺:NaY(MoO₄)₂ crystal has potential as a promising laser crystal.     

Effect of thermal cycling through the martensitic transition on the internal friction and Young’s modulus of a Ni50.8Ti49.2 alloy

The internal friction (IF) and Young’s modulus (E) of a Ni_50.8Ti_49.2 is affected by thermal cycling. With increasing the number n of thermal cycles, the IF peak P_AM (P_MA) occurring at the austenite/martensite transition temperature decreases to disappear almost completely. Meanwhile the associated E(T) minimum at the beginning (n<250) deepens and then becomes progressively shallower and wider (3×10³≤n<18×10³). The strong sensitivity of P_AM (P_MA) to thermal cycling and to impurity (hydrogen) contents suggests that this peak is predominantly associated with stress-assisted collective motions of twin boundaries located inside the martensite platelets embedded within the austenite phase, rather than with the martensitic transition itself. However, as the high temperature tail of P_AM starts at temperatures appreciably higher than the martensite start-temperature M_s, a premartensitic contribution to damping is also present. The widening of the E(T) minimum indicates that, for n≥3×10³, the direct transformation is to some extent hindered by the dislocation network introduced by thermal cycling. A not thermally activated IF peak P_TWM, which is believed to be due to stress-assisted motions of (001) compound twin boundaries in the homogeneous martensite state, grows with increasing n.     

Effect of Sn ion implantation on electrochemical behavior of zircaloy-4

In order to study the effect of tin ion implantation on the aqueous corrosion behavior of zircaloy-4, specimens were implanted by tin ions with a dose range from 1×10¹⁶ to 5×10¹⁷ ions/cm² at an extracted voltage of 40 kV. The valence and element penetration distribution of the surface layer were analyzed by X-ray photoelectron spectroscopy (XPS) and auger electron spectroscopy (AES), respectively. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to examine the micro-morphology and microstructure of tin-implanted samples. When the dose is 5×10¹⁶ ions/cm² or higher, a large number of small tin balls are produced in the implanted surface. The potentiodynamic polarization measurement was employed to evaluate the aqueous corrosion resistance of zircaloy-4 in a 0.5 M H₂SO₄ solution. It was found that a significant improvement was achieved in the aqueous corrosion behavior of zircaloy-4 implanted with tin when the dose is 1×10¹⁶ ions/cm². When the dose is higher than 1×10¹⁶ ions/cm², the corrosion resistance of zircaloy-4 implanted with tin ions decreased compared with that of the as-received zircaloy-4. Finally, the mechanism of the corrosion behavior of the tin-implanted zircaloy-4 is discussed.     

White light electroluminescence from PSi devices capped with poly(thiophene)(s) as top contact

For the first time, electrochemically deposited poly(3-methylthiophene) and chemically produced poly(3-methylthiophene) and poly(3-phenoxymethylthiophene) have been employed as top electrical contact on porous silicon light-emitting devices. The polymer-capped devices emitted white light as opposed to the uncapped devices, which emitted orange colour. The polymer-capped devices show much higher rectification ratio (up to 1×10⁵) as opposed to 1×10³ for the uncapped devices at ±10 V. The polymer-capped devices show 10³–10⁴-fold improvement in the luminous efficiency over the uncapped devices. Electrochemically deposited poly(3-methylthiophene) top contacts give a luminous efficiency of 8×10⁻⁵ lm W⁻¹ as opposed to 3×10⁻⁹ lm W⁻¹ obtained from uncapped devices. All the devices were found to fit the space charge limited current model.     

Electrochemical properties of the MmNi3.55Mn0.4Al0.3Co0.4Fe0.35 compound

In this paper, the electrochemical properties of the MmNi_3.55Mn_0.4Al_0.3Co_0.4Fe_0.35 alloy used as a negative electrode in Ni–MH accumulators, have been investigated by different electrochemical methods such as cyclic voltammetry, chronopotentiometry, chronoamperometry and electrochemical impedance spectroscopy. The experimental results indicate that the discharge capacity reaches a maximum value of 260 mAh g⁻¹ after 12 cycles and then decreases to about 200 mAh g⁻¹ after 70 cycles. The value of the mean diffusion coefficient D_H, determined by cyclic voltammetry, is about 3.44 × 10⁻⁹ cm² s⁻¹, whereas the charge transfer coefficient , determined by the same method, is about 0.5 which allows us to conclude that the electrochemical reaction is reversible. The hydrogen diffusion coefficients in this compound, corresponding to 10 and 100% of the charge state, determined by electrochemical impedance spectroscopy, are, respectively, equal to 4.15 × 10⁻⁹ cm² s⁻¹ ( phase) and 2.15 × 10⁻⁹ cm² s⁻¹ (β phase). These values are higher, for the phase and less, for the β phase, than the mean value determined by cyclic voltammetry. We assume that this is related to the number of interstitial sites susceptible to accept the hydrogen atom, which are more numerous in the phase than in the β phase. The chronoamperometry shows that the average size of the particles involved in the electrochemical reaction is about 12 μm.     

Superplastic behavior of a 7055 aluminum alloy

It is shown that a high strength 7055 aluminum alloy with partially recrystallized initial structure exhibits superplastic behavior in the temperature interval 400–490 °C within a wide strain rate range from 8.3×10⁻⁵ to 3.3×10⁻² s⁻¹. Maximum total elongation of about 960% and strain rate sensitivity coefficient, m, of 0.6 were obtained at a temperature of 450 °C and a strain rate of 3.3×10⁻⁴ s⁻¹.     

Magnetomechanical damping in Fe–Cr alloys and effect of Al and Mo addition

The damping capacity of ferromagnetic Fe–Cr based alloys containing 0–8% Al and 0–4% Mo has been investigated over a wide range of frequencies and amplitudes using a cantilever device. The resonance curves of the flat beam samples under various driving forces were recorded from which several parameters including the damping capacity (Q⁻¹), ΔE effect, internal stress (σ_i) and magnetostriction constant (λ_s), were determined. The variation of these parameters with chemical composition and thermal treatment are analyzed. The results showed that the magnetostriction constant is the key parameter to describe variation of the damping capacity in these alloys. Lower concentration of Al and Mo enhanced the damping capacity several times but higher concentration above 4% decreased it drastically. Addition of Mo resulted in higher damping capacity than did Al.     

Thermoelectric properties of Ni- and Zn-doped Nd2CuO4

The electrical resistivity, Seebeck coefficient, and thermal conductivity of Nd₂(Cu_0.98M_0.02)O₄ (M: Ni and Zn) have been measured in the temperature range from room temperature to about 1000 K. Ni- and Zn-doping decreases the electrical resistivity and the absolute values of the Seebeck coefficient. The thermal conductivity decreases with increasing temperature, showing phonon conduction, and also decreases by doping. The power factor of Nd₂(Cu_0.98Ni_0.02)O₄ reaches 1.02×10⁻⁴ W m⁻¹ K⁻² and the figure of merit is 1.35×10⁻⁵ K⁻¹ at 320 K. The relatively low figure of merit compared with that of the state-of-the-art thermoelectric materials is due to the high thermal conductivity.     

Preparation and bulk thermal expansion studies in M1−xCexSiO4 (M = Th, Zr) system, and stabilization of tetragonal ThSiO4

Two series of compositions with the general formula M_1−xCe_xSiO₄ (M = Th, Zr; x = 0.0–0.5; 1.0) were prepared by a standard solid state route and characterized by powder XRD. About 10 mol% of ceria could be dissolved in the lattice of ThSiO₄. A striking observation was the stabilization of tetragonal modification of ThSiO₄, which is metastable, by ceria substitution. There was no solubility of ceria in zircon (ZrSiO₄) lattice. The average linear thermal expansion coefficient (293–1123 K) of ZrSiO₄, ThSiO₄ and Th_0.9Ce_0.1SiO₄ are 4.65 × 10⁻⁶, 4.97 × 10⁻⁶ and 5.14 × 10⁻⁶ K⁻¹, respectively.