Studies on the structural and ionic transport properties at elevated temperatures of La1−xMnO3±δ synthesized by a wet chemical method

Structural transformation and ionic transport properties are investigated on wet-chemically synthesized La_1−xMnO₃ (x=0.0–0.18) compositions. Powders annealed in oxygen/air at 1000–1080 K exhibit cubic symmetry and transform to rhombohedral on annealing at 1173–1573 K in air/oxygen. Annealing above 1773 K in air or in argon/helium at 1473 K stabilized distorted rhombohedral or orthorhombic symmetry. Structural transformations are confirmed from XRD and TEM studies. The total conductivity of sintered disks, measured by four-probe technique, ranges from 5 S cm⁻¹ at 298 K to 105 S cm⁻¹ at 1273 K. The ionic conductivity measured by blocking electrode technique ranges from 1.0×10⁻⁶ S cm⁻¹ at 700 K to 2.0×10⁻³ S cm⁻¹ at 1273 K. The ionic transference number of these compositions ranges from 3.0×10⁻⁵ to 5.0×10⁻⁵ at 1273 K. The activation energy deduced from experimental data for ionic conduction and ionic migration is 1.03–1.10 and 0.80–1.00 eV, respectively. The activation energy of formation, association and migration of vacancies ranges from 1.07 to 1.44 eV.     

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.     

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.     

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.     

Effect of yttria concentration on low strain rate flow stress of cubic zirconia single crystals

The effects of Y₂O₃ solute concentration, strain rate, and temperature on solid-solution strengthening in single crystal yttria-stabilized cubic zirconia was investigated. Previous work was extended by studying the flow behaviour at strain rates from 1.5 × 10⁻⁵ s⁻¹ to 8 × 10⁻⁸ s⁻¹ at 1200, 1300 and 1400°C in the harder 001 orientation. Solute hardening in this system is sensitive to strain rate down to 8 × 10⁻⁸ s⁻¹, but at 1400°C there was no difference in flow stress between a 9.4 mol% alloy and 21 mol% alloy at a strain rate of 8 × 10⁻⁸ s⁻¹. The results were explained by the solute drag model.     

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.     

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.     

Utilizing the SIMS technique in the study of grain boundary diffusion along twist grain boundaries in the Cu(Ni) system

The secondary ion mass spectrometry (SIMS) technique was used to study grain boundary diffusion along (100) twist grain boundaries in the Cu(Ni) system. Concentration profiles of Ni down Cu twist grain boundaries with nominal disorientation angles of 10°, Σ5 (36.87°), and 45°, were measured using the SIMS technique. The average activation energy for grain boundary diffusion, Q_b, was found to be 245±22, 140±10, and 102±15 kJ/mol, for the 10°, Σ5, and 45° twist grain boundaries, respectively. The average grain boundary diffusion pre-exponential term, sδD_bo, was found to be 9.6±1.24×10⁻⁹, 1.1±0.17×10⁻¹⁴, and 1.3±0.36×10⁻¹⁶ m³/s, for the 10°, Σ5, and 45° twist grain boundaries, respectively.     

Improvement of high-temperature oxidation resistance of TiAl-based alloy by sol–gel method

Lithium lanthanoid silicate, a high temperature lithium ion conducting solid electrolyte, synthesized by sol–gel method, has been characterized by TGA/DTA, XRD, FTIR and SEM. Conductivity was found to be 0.847 × 10⁻⁶ Ω⁻¹ cm⁻¹ at 750 °C and activation energy was 0.5 eV.     

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.     

Crystal structure of the new ternary aluminide CeRu3−xAl10+x (x = 0.17)

A large and transparent Yb³⁺:GdYCOB crystal with dimensions up to 30 mm× 58 mm have been grown by the Czochralski method. The spectral properties of Yb³⁺:GdYCOB crystal has been investigated. The absorption cross-section (σ_a) is 1.65 × 10⁻²⁰ cm² at 977 nm. The emission cross-section (σ_e) is 0.25 × 10⁻²⁰ cm² with an FWHM of 37.2 nm at 1020 nm. The fluorescence lifetime is 3.00 ms.     

Synthesis, crystal structure and properties of the new semiconductor (EVT)4·[Pt(CN)4]

A novel radical cation salt based on of the donor (4,5-ethylenedithio-4′,5′-vinylenedithio)tetrathiafulvalene (EVT) with the square planar anion Pt(CN)₄²⁻ has been synthesized: (EVT)₄·[Pt(CN)₄] (1). According to the X-ray analysis its crystal structure includes EVT cation layers alternating with anion layers along the a-axis of the unit cell. The radical cation layer is formed by EVT stacks with β-packing type, the donors in stacks are tetramerized. The EPR spectra of a plate-like crystal of (EVT)₄·[Pt(CN)₄] salt shows a very weak signal with typical parameters of TTF derivative. The room temperature conductivity of salt 1 is 8×10⁻² Ω⁻¹ cm⁻¹ and the temperature dependence of the conductivity exhibits semiconducting character.     

Bulk and lattice thermal expansion in Ce1−xSrxO2−x (0.0≤x≤0.10)

In this communication, we report on the bulk and lattice thermal expansion studies on a number of compounds, within the homogeneity range of solid solutions, in a series with the general composition Ce_1−xSr_xO_2−x (0.0≤x≤0.10). The XRD pattern of each product was refined to determine the solid solubility of SrO into the lattice of CeO₂, and the homogeneity range. The composition with maximum solid solubility limit of SrO in CeO₂ lattice, under the slow cooled conditions, was delineated as Ce_0.91Sr_0.09O_1.91 (i.e. 9 mol.% of SrO). The bulk thermal expansion measurements from ambient to 1123 K, as investigated by a dilatometer, revealed that the _l (293 to 1123 K) values for the compositions within the homogeneity range increase from 11.58×10⁻⁶ to 12.13×10⁻⁶ K⁻¹ on increasing the Sr²⁺ content from 0 mol.% (i.e. CeO₂) to 9 mol.%, i.e. the upper solubility limit of SrO into the lattice of CeO₂. A similar trend was observed in the lattice thermal expansion coefficients _a (293 to 1473 K) as obtained by a high temperature-XRD.     

Enhancement of the wettability and solder joint reliability at the Sn–9Zn–0.5Ag lead-free solder alloy–Cu interface by Ag precoating

The enhancement of the wettability and solder joint reliability at the Sn–9Zn–0.5Ag solder alloy–Cu interface by Ag precoating has been investigated. The wettability of the Sn–9Zn–0.5Ag solder alloy–Cu interface has been improved by Ag precoating. The adhesion strength of the solder alloy–Ag precoated Cu interface increases from 4.11±0.56 to 6.92±0.85 MPa as dipped at 250 °C for 10 s. When the dipping time is prolonged from 10 to 30 s, the interfacial adhesion strength increases from 6.92±0.85 to 13.62±0.73 MPa. The interfacial adhesion strength is enhanced by the rod-like Cu–Zn intermetallic compound (IMC) formed close to the interface. The diffusion coefficients of Sn and Zn in the IMC layer are determined as 5.76×10⁻¹⁰ and 9.50×10⁻¹¹ cm²/s at the Sn–9Zn–0.5Ag–Cu and Sn–9Zn–0.5Ag–Ag precoated Cu interfaces, respectively.     

Electrical conductivity and molecular properties of organodithioheterobimetallics [PhHg]2[M(dithio)2] {M=Ni, Cu or Zn; dithio=isomaleonitriledithiolate (i-MNT) 1,1-dicarboethoxy-2,2-ethylenedithiolate (DED) or trithiocarbonate (CS3)}

Organoheterobimetallic compounds of the type, [PhHg]₂[M(dithio)₂] {M=Ni(II), Cu(II) or Zn(II); dithio=isomaleonitriledithiolate (i-MNT²⁻), 1,1-dicarboethoxy-2,2-ethylenedithiolate (DED²⁻) or trithiocarbonate (CS₃²⁻)} have been synthesized and investigated by molecular spectroscopies and conductivity techniques. Magnetic behaviour, together with electronic spectra, are compatible with square planar coordination geometry around nickel(II) in [PhHg]₂[Ni(dithio)₂]. Magnetic moments, 1.6 BM and 1.25 BM for [PhHg]₂[Cu(i-MNT)₂] and [PhHg]₂[Cu(DED)₂] showed involvement of some sort of Cu–Cu interaction. Their electronic and EPR spectra show distorted square planar geometry with tetragonal/rhombic symmetry around copper(II). Powder X-ray diffraction patterns of the complexes have been compared. All the complexes show σ_rt in 2.29×10⁻¹⁰−4.38×10⁻⁴ S cm⁻¹ range. [PhHg]₂[Ni(DED)₂] and [PhHg]₂[Cu(i-MNT)₂] show semiconducting behaviour as their conductivity increases with increase in temperature with band gaps 0.39 eV; 0.57 eV and 2.38 eV, respectively.     

Porous AlN ceramic substrates by reaction sintering

A novel approach was undertaken in producing porous AlN microelectronics tapes with high thermal conductivity and low dielectric constant. This method essentially utilised polymer micro-spherical powders that were used as a sacrificial mould to introduce controlled porosity into the green tapes during pyrolysis. The Al₂O₃-rich porous green tapes were then reaction sintered at 1680 °C for 12 h to achieve porous AlN tapes. This work builds upon the previously developed novel reaction sintering process that densified and converted Al₂O₃-rich tapes (Al₂O₃–20 wt.% AlN–5 wt.% Y₂O₃) to AlN tapes at a relatively low sintering temperature of 1680 °C. The sintering behaviour of the porous tapes was investigated, and the effects of the microspheres particle size and volume addition were studied. The microspheres successfully contributed to the significant reduction of tape density by porosity, and this contributed to lowering its dielectric constant. Dielectric constant of the AlN tapes were reduced to about 6.8–7.7 whilst thermal conductivity values were reasonable at about 46–60 W/m K. Coefficient of thermal expansion (CTE) values showed a linear trend according to phase composition, with the porous AlN tapes exhibiting CTE values of (4.4–4.8)×10⁻⁶ °C⁻¹, showing good CTE compatibility with silicon, at 4.0×10⁻⁶ °C⁻¹. The added porosity did not significantly affect the CTE values.     

The ternary system: silicon–titanium–uranium

Phase equilibria in the system Si–Ti–U were established at 1000 °C by optical microscopy, EMPA and X-ray diffraction. Two ternary compounds were observed and were characterised by X-ray powder data refinement: (1) stoichiometric U₂Ti₃Si₄ (U₂Mo₃Si₄-type) with a small homogeneity region of about 3 at.% exchange U/Ti and (2) U_2−xTi_3+xSi₄ (Zr₅Si₄-type) extending at 1000 °C for 0.7<x<1.3. Mutual solubility of U-silicides and Ti-silicides was found to be below about 1 at.%. The Ti,U-rich part of the diagram was also investigated at 850 °C establishing the tie-lines to the low temperature compounds U₂Ti and U₃Si. U₂Ti₃Si₄ is weakly paramagnetic following a Curie–Weiss law above 50 K with μ_eff.=2.67 μ_B/U, Θ_P=−150 K and χ₀=1.45×10⁻³ emu/mol (18.2×10⁻⁹ m³/mol).     

Structural, magnetic and magnetostrictive studies of Tb0.27Dy0.73(Fe1 − xAlx)2

Measurements of magnetic properties, X-ray diffraction and magnetostriction were made on Tb_0.27Dy_0.73(Fe_{1 − x}Al_x)₂ (x = 0.1, 0.2, …, 0.7) compounds. It was found that the system has the cubic MgCu₂ structure over almost the whole (Fe,Al) concentration range investigated, except for a narrow intermediate range (x = 0.4–0.6) where the hexagonal MgZn₂ structure appears. With increasing Al content x, the lattice constant a increases linearly with x. The first replacement of Fe results in a marked decrease in the Curie temperature, which is followed by a slight decrease in T_C with x. A linear decrease in magnetostriction of |λ_| − λ| at room temperature with x was also observed from 1530 × 10⁻⁶ for x=0 to 36×10⁻⁶ for x=0.3. The saturation magnetization σ_s exhibits a complex concentration dependence in the Tb_0.27Dy_0.73(Fe)_{1 − x}Al_x)₂ system: in the range x < 0.5, σ_s increases linearly with x and, for x = 0.5–0.6, σ_s decreases and then increases again. An enhancement of the magnetic ‘hardness’ in this system was also observed at low temperature.     

Fabrication and electrical and thermal properties of Ti2InC, Hf2InC and (Ti,Hf)2InC

In this paper we report on the characterization of predominantly single phase, fully dense Ti₂InC (Ti_1.96InC_1.15), Hf₂InC (Hf_1.94InC_1.26) and (Ti,Hf)₂InC ((Ti_0.47,Hf_0.56)₂InC_1.26) samples produced by reactive hot isostatic pressing of the elemental powders. The a and c lattice parameters in nm, were, respectively: 0.3134; 1.4077 for Ti₂InC; 0.322, 1.443 for (Ti,Hf)₂InC; and 0.331 and 1.472 for Hf₂InC. The heat capacities, thermal expansion coefficients, thermal and electrical conductivities were measured as a function of temperature. These ternaries are good electrical conductors with a resistivity that increases linearly with increasing temperatures. At 0.28 μΩ m, the room temperature resistivity of (Ti,Hf)₂InC is higher than the end members (0.2 μΩ m), indicating a solid solution scattering effect. In the 300 to 1273 K temperature range the thermal expansion coefficients are: 7.6×10⁻⁶ K⁻¹ for Hf₂InC, 9.5×10⁻⁶ K⁻¹ for Ti₂InC, and 8.6×10⁻⁶ K⁻¹ for (Ti,Hf)₂InC. They are all good conductors of heat (20 to 26 W/m K) with the electronic component of conductivity dominating at all temperatures. Extended exposure of Ti₂InC to vacuum (10⁻⁴ atm) at 800 °C, results in the selective sublimation of In, and the conversion of Ti₂InC to TiC_x.     

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.