Role of rf power on the properties of undoped SnOx films deposited by rf-PERTE at low substrate temperature

Transparent and conductive undoped tin oxide (SnO_x) thin films were deposited at low substrate temperature (< 140 °C) by radio frequency (rf) plasma enhanced reactive thermal evaporation (rf-PERTE) of tin (Sn) in the presence of oxygen The undoped SnO_x films were not submitted to any post-annealing treatments. The influence of rf power variation on the optical, electrical and structural properties of the as-grown films is presented. A variation in the films' structure was verified with the increase of rf power. Undoped SnO_x films, 90 nm average thick, deposited at rf power range of 60–70 W are nanocrystalline, show a conductive behaviour, an average visible transmittance of ≥ 80% and a maximum electrical conductivity of about 34.6 (Ω cm)^− 1. Films deposited at lower values of rf power (40 W) are amorphous and exhibit a semiconductive behaviour, showing an electrical conductivity of about 7.54 × 10^− 1 (Ω cm)^− 1. As a low substrate temperature deposition process is used, SnO_x thin films can be obtained on a wide range of substrates.     

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.     

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.     

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.     

Fabrication of anatase-type TiO2 films by reactive pulsed laser deposition for photocatalyst application

TiO₂ films having anatase crystal structure were prepared on glass substrates by reactive pulsed laser deposition using a metallic Ti target in an O₂ gas ambient. At a fixed substrate temperature of 400 °C, the crystalline structure, surface morphology, optical properties and photocatalytic activity of the TiO₂ films were greatly affected by the O₂ gas pressure. It was found that nearly pure anatase-phase TiO₂ film can be obtained under an O₂ pressure of 15 Pa, which had smallest grain size among the films deposited under various O₂ gas pressure from 5 to 30 Pa. This film also showed good optical transmittance between the wavelength of 200 and 800 nm and high photocatalytic efficiency on the decomposition of methylene blue in aqueous solution. Discussions were given to explain the experimental phenomena.     

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.     

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.     

Synthesis, crystal structure, oxygen stoichiometry, and electrical conductivity of La1−aCaaCr0.8Ti0.2O3−δ solid solutions

Series of perovskite-type compounds La_1−aCa_aCr_0.8Ti_0.2O_3−δ (a=0–1.0) were synthesized by the ceramic technique in air (final heating 1350 °C). The crystal structure of the compounds after cooling in air to room temperature was characterized as orthorhombic in space group Pbnm. Analysis of the lattice constants shows a noticeable decrease with increasing Ca content. All compounds prepared were stable in air and in a stream of Ar/1 Pa O₂ at 20–1400 °C, as also in Ar/5% H₂ (pH₂O/pH₂=0.01) at 850–1000 °C. Oxygen stoichiometry and electrical conductivity of the solid solutions with a=0.0–1.0 are investigated. Increasing Ca contents decrease the stability of the oxides in respect to the thermal dissociation of oxygen. All compounds are p-type semiconductors in the temperature range 20–1000 °C at oxygen partial pressures of 10⁻¹⁵ to 0.21×10⁵ Pa. A maximum conductivity of about 30 S/cm in air at 1000 °C is observed for the composition with a=0.6 corresponding to a ratio of Cr³⁺/Cr⁴⁺=1 at an oxygen stoichiometry near 3.0, and oxidation states of La, Ca, Ti, and O ions of 3+, 2+, 4+, and 2−, respectively.     

Influence of Al- and Cu-doping on the thermodynamic properties of the LaNiIn–H system

The Pressure–Composition–Temperature (P–C–T) relations for the LaNiIn, LaNi_0.95Cu_0.05In and LaNiIn_0.98Al_0.02–H systems were measured by a volumetric Sieverts’ method at 398–423 K. All isotherms show plateau pressure regions indicating equilibria between two hydride phases. The replacements of Ni by Cu and In by Al affect the P–C–T diagrams, stability of the hydrides, homogeneity regions of the hydrides formed, slope of the isotherms and critical temperatures of the β–γ transition. In addition, the Cu-doping induces a significant hysteresis between the hydrogen absorption and desorption processes. The relative partial molar thermodynamic properties for the studied systems are: ΔH_H = −34.6 ± 2.1 kJ (mol_H)⁻¹, ΔS_H = −70.7 ± 3.6 J (K·mol_H)⁻¹ for LaNiIn–H; ΔH_H = −34.1 ± 0.5 kJ (mol_H)⁻¹, ΔS_H = −74.9 ± 1.0 J (K·mol_H)⁻¹ for LaNi_0.95Cu_0.05In–H; ΔH_H = −33.2 ± 0.8 kJ (mol_H)⁻¹, ΔS_H = −68.3 ± 1.2 J(K·mol_H)⁻¹ for LaNiIn_0.98Al_0.02–H.     

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).     

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.     

Sm0.5Sr0.5CoO3 cathode material from glycine-nitrate process: Formation, characterization, and application in LaGaO3-based solid oxide fuel cells

Cathode material Sm_0.5Sr_0.5CoO₃ (SSC) with perovskite structure for intermediate temperature solid oxide fuel cell was synthesized using glycine-nitrate process (GNP). The phase evolution and the properties of Sm_0.5Sr_0.5CoO₃ were investigated. The single cell performance was also tested using La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ (LSGM) as electrolyte and SSC as cathode. The results show that the formation of perovskite phase from synthesized precursor obtained by GNP begins at a calcining temperature of 600 °C. The single perovskite phase is formed completely after sintering at a temperature of 1000 °C. The phase formation temperature for SSC with complete single perovskite phase is from 1000 to 1100 °C. The SrSm₂O₄ phase appeared in the sample sintered at 1200 °C. It is also found that the sample sintered at 1200 °C has a higher conductivity. The electrical conductivity of sample is higher than 1000 S/cm at all temperature examined from 250 to 850 °C, and the highest conductivity reaches 2514 S/cm at 250 °C. The thermal expansion coefficient of sample SSC is 22.8 × 10⁻⁶ K⁻¹ from 30 to 1000 °C in air. The maximum output power density of LSGM electrolyte single cell attains 222 and 293 mW/cm² at 800 and 850 °C, respectively.     

Standard enthalpies of formation of some carbides, silicides and germanides of cerium and praseodymium

The standard enthalpies of formation of some congruent-melting compounds in the binary systems Re---X, where Re Ce, Pr or La and X C, Si or Ge have been determined by direct-synthesis calorimetry at 1473 ± 2 K. The following values of ΔH_f^o are reported: CeC₂, −25.4 ± 1.4 kJ (mol atom)⁻¹; CeSi₂, −60.5 ± 2.0 kJ (mol atom)⁻¹; CeSi, −71.1 ± 3.3 kJ (mol atom)⁻¹; Ce₅Ge₃, −73.4 ± 2.3 kJ (mol atom)⁻¹; CeGe_1.6, −75.6 ± 1.9 kJ (mol atom)⁻¹; PrC₂, −29.4 ± 1.6 kJ (mol atom)⁻¹; PrSi₂, −61.5 ± 1.7 kJ (mol atom)⁻¹; PrSi, −78.1 ± 1.9 kJ (mol atom)⁻¹; Pr₅Ge₃, −70.4 ± 2.3 kJ (mol atom)⁻¹; PrGe_1.6, −81.7 ± 1.7 kJ (mol atom)⁻¹; LaSi₂, −56.8 ± 2.5 kJ (mol atom)⁻¹. The results are compared with earlier experimental data, with predicted values from Miedema's semiempirical model, and with available data obtained for Sn and Pb compounds by Borzone et al., by Palenzona and by Palenzona and Cirafici.     

Internal friction of Cu–CuAlO alloys

Polycrystalline internal oxidize copper alloy with CuAlO particles has been studied by isothermal mechanical spectrometry, above room temperature. The frequency range was 10⁻⁴ to 30 Hz and the maximum strain 2×10⁻⁵. Experiments were carried out on a sample after 18% cold-rolling and successive annealings at various temperatures. The internal friction spectra obtained between 290 and 400 K exhibit only a low frequency background superimposed to a non thermally activated maximum. After annealing at 400 K, the background decreases, a relaxation peak appears and its maximum rises progressively as temperature increases. The relaxation parameters, obtained from the frequency shift of the maximum with temperature, leads to E_a=0.9 eV, and τ₀=6.9×10⁻¹⁰ s. These values are similar to those described in the literature for a relaxation peak assigned to dislocation motion inside grains.     

Power factor of La1−xSrxFeO3 and LaFe1−yNiyO3

The electrical conductivity (σ), Seebeck coefficient (S), and power factor (σS²) of perovskite-type LaFeO₃, La_1−xSr_xFeO₃ [0.1 ≤ x ≤ 0.4] and LaFe_1−yNi_yO₃ [0.1 ≤ y ≤ 0.6] were investigated in the temperature range of 300–1100 K to explore their possibility as thermoelectric materials. The electrical conductivity of LaFeO₃ showed semiconducting behavior, and its Seebeck coefficient changed from positive to negative around 650 K with increasing temperature. The electrical conductivity of LaFeO₃ increased with the substitutions of Sr and Ni atoms, while its Seebeck coefficient decreased. The Seebeck coefficient of La_1−xSr_xFeO₃ was positive, whereas that of LaFe_1−yNi_yO₃ changed from positive to negative with increasing Ni content. The substitutions of Sr and Ni were effective in increasing the power factor of LaFeO₃; 0.0053 × 10⁻⁴ Wm⁻¹ K⁻² for LaFeO₃ (1050 K), 1.1 × 10⁻⁴ Wm⁻¹ K⁻² for La_1−xSr_xFeO₃ (x = 0.1 at 1100 K) and 0.63 × 10⁻⁴ Wm⁻¹ K⁻² for LaFe_1−yNi_yO₃ (y = 0.1 at 1100 K).     

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.     

Achieving tensile superplasticity in 8 mol% Y2O3 cubic stabilized ZrO2 through the addition of intergranular silica

The addition of 5 wt.% SiO₂, a viscous second phase, to 8 mol% Y₂O₃ cubic stabilized ZrO₂ (8Y-CSZ) made superplastic 8Y-CSZ. This material had a fine grain size of 0.4 μm and exhibited deformations in tension as large as 520% at 1430 °C with a strain rate of 1.0 × 10⁻⁴ s⁻¹.     

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.     

Ni-BaTiO3 interface phenomenon of Co-fired PTCR by aqueous tape casting

The green sheets with Ni paste as inner electrodes were sintered at 1 320 ℃ for 1 h under a N2/H2 mixing gas at an oxygen partial pressure p（O2）=10-8-10-12 MPa, and then reoxided at 900-1 000 ℃ to form multilayer positive temperature coefficient of resistance（PTCR）. During the experiments, electronic characteristic effects of PTC with different thicknesses were contrasted. A certain extending of Ni diffusion is beneficial to the ohmic contact of multilayer PTCR but excessive diffusion is harmful to PTCR. The diffusion was studied by scanning electron microscopy（SEM） and energy-dispersive X-ray spectrometry（EDS）. Inter-diffusion of element takes place along the Ni-BaTiO3 interface, especially Ni diffusion to BaTiO3 dominated the process. Furthermore, the degree of Ni diffusion is very severe as ceramic layers are very thin.