Thermo-physical and thermal cycling properties of plasma-sprayed BaLa2Ti3O10 coating as potential thermal barrier materials

Increased turbine inlet temperature in advanced turbines has promoted the development of thermal barrier coating (TBC) materials with high-temperature capability. In this paper, BaLa₂Ti₃O₁₀ (BLT) was produced by solid-state reaction of BaCO₃, TiO₂ and La₂O₃ at 1500 °C for 48 h. BLT showed phase stability between room temperature and 1400 °C. BLT revealed a linearly increasing thermal expansion coefficient with increasing temperature up to 1200 °C and the coefficients of thermal expansion (CTEs) are in the range of 1 × 10^− 5–12.5 × 10^− 6 K^− 1, which are comparable to those of 7YSZ. BLT coatings with stoichiometric composition were produced by atmospheric plasma spraying. The coating contained segmentation cracks and had a porosity of around 13%. The microhardness for the BLT coating is 3.9–4.5 GPa. The thermo-physical properties of the sprayed coating were investigated. The thermal conductivity at 1200 °C is about 0.7 W/mK, exhibiting a very promising potential in improving the thermal insulation property of TBC. Thermal cycling result showed that the BLT TBC had a lifetime of more than 1100 cycles of about 200 h at 1100 °C. The failure of the coating occurred by cracking at the thermally grown oxide (TGO) layer due to severe oxidation of bond coat. Based on the above merits, BLT could be considered as a promising material for TBC applications.     

Synthesis and crystal structure of Ba3Si4C2

SiC powder prepared by the Na flux method at 1023 K for 24 h and Ba were used as starting materials for synthesis of tribarium tetrasilicide acetylenide, Ba₃Si₄C₂. Single crystals of the compound were obtained by heating the starting materials with Na at 1123 K for 1 h and by cooling to 573 K at a cooling rate of −5.5 K/h. The single crystal X-ray diffraction peaks were indexed with tetragonal cell dimensions of a = 8.7693(4) and c = 12.3885(6) Å, space group I4/mcm (No.140). Ba₃Si₄C₂ has the Ba₃Ge₄C₂ type structure which can be described as a cluster-replacement derivative of perovskite (CaTiO₃), and contains isolated anion groups of slightly compressed [Si₄]⁴⁻ tetrahedra and [C₂]²⁻ dumbbells. The electrical conductivity measured for a not well-sintered polycrystalline sample was 2.6 × 10⁻²–7 × 10⁻³ S cm⁻¹ in the temperature range of 370–600 K and slightly increased with increasing temperature. The Seebeck coefficient showed negative values of around −200 to −300 μV K⁻¹.     

Conductivity of a new pyrophosphate Sn0.9Sc0.1(P2O7)1−δ prepared by an aqueous solution method

New pyrophosphate Sn_0.9Sc_0.1(P₂O₇)_1−δ was prepared by an aqueous solution method. The structure and conductivity of Sn_0.9Sc_0.1(P₂O₇)_1−δ have been investigated. XRD analysis indicates that Sn_0.9Sc_0.1(P₂O₇)_1−δ exhibits a 3 × 3 × 3 super structure. It was found that Sn_0.9Sc_0.1(P₂O₇)_1−δ prepared by an aqueous method is not conductive. The total conductivity of Sn_0.9Sc_0.1(P₂O₇)_1−δ in open air is 2.35 × 10⁻⁶ and 2.82 × 10⁻⁹ S/cm at 900 and 400 °C respectively. In wet air, the total conductivity is about two orders of magnitude higher (8.1 × 10⁻⁷ S/cm at 400 °C) than in open air indicating some proton conduction. SnP₂O₇ and Sn_0.92In_0.08(P₂O₇)_1−δ prepared by an acidic method were reported fairly conductive but prepared by similar solution methods are not conductive. Therefore, the conductivity of SnP₂O₇-based materials might be related to the synthetic history. The possible conduction mechanism of SnP₂O₇-based materials has been discussed in detail.     

Improved high-Q microwave dielectric resonator using ZnO-doped La(Co1/2Ti1/2)O3 ceramics

The microwave dielectric properties and the microstructures of ZnO-doped La(Co_1/2Ti_1/2)O₃ ceramics prepared by conventional solid-state route have been studied. Doped with ZnO (up to 0.75 wt%) can effectively promote the densification of La(Co_1/2Ti_1/2)O₃ ceramics with low sintering temperature. At 1320 °C, La(Co_1/2Ti_1/2)O₃ ceramics with 0.75 wt% ZnO addition possesses a dielectric constant (_r) of 30.2, a Q × f value of 73,000 GHz (at 8 GHz) and a temperature coefficient of resonant frequency (τ_f) of −35 ppm/°C.     

Spontaneous magnetostriction of R2Fe13.6Si3.4 (R = U, Lu)

The thermal expansion of U₂Fe_13.6Si_3.4 and Lu₂Fe_13.6Si_3.4 has been measured by X-ray powder diffraction. Both compounds exhibit a large spontaneous magnetostriction. In the ground state, the volume effect 11.2 × 10⁻³ in U₂Fe_13.6Si_3.4 consists of almost equal contributions from the Fe–Fe and U–Fe exchange interactions (6 × 10⁻³ and 5 × 10⁻³, respectively). In Lu₂Fe_13.6Si_3.4, the volume effect is 8.9 × 10⁻³.     

Preparation and characteristic of spherical Li3V2(PO4)3

Spherical Li₃V₂(PO₄)₃ was synthesized by using N₂H₄ as reducer. The products were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that single-phase, spherical and well-dispersed Li₃V₂(PO₄)₃ has been successfully synthesized in our experimental process. Electrochemical behaviors have been characterized by charge/discharge measurements. The initial discharge capacities of Li₃V₂(PO₄)₃ were 123 mAh g⁻¹ in the voltage range of 3.0–4.3 V and 132 mAh g⁻¹ in the voltage range of 3.0–4.8 V.     

Structure and electrochemical performance of FeF3/V2O5 composite cathode material for lithium-ion battery

Orthorhombic structure FeF₃ was synthesized by a liquid-phase method using FeCl₃, NaOH and HF solution as starting materials, and the FeF₃/V₂O₅ composites were prepared by milling the mixture of as-prepared FeF₃ and the conductive V₂O₅ powder. The properties of FeF₃/V₂O₅ composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), galvanostatic charge/discharge and cyclic voltammetry measurements. Results showed that the FeF₃/V₂O₅ composites can be used as cathode material for lithium-ion battery. Electrochemical measurements in a voltage range of 2.0–4.5 V reveal that the addition of conductive V₂O₅ improves significantly the electrochemical performance of FeF₃, and the FeF₃/V₂O₅ composite prepared by milling for 3 h exhibits high discharge capacity and good cycle performance, and its discharge capacity maintains about 209 mAh g⁻¹ at 0.1 C (23.7 mA g⁻¹) after 30 cycles.     

Determination of the crystallization kinetic parameters of Ge22.5Te77.5 glass using model-free and model-fitting methods

Differential scanning calorimetry (DSC) technique was used to study the kinetics of amorphous to crystalline transformation for Ge_22.5Te_77.5 glass. The kinetic parameters of glassy Ge_22.5Te_77.5 under non-isothermal conditions are analyzed by the model-free and model-fitting approaches from a series of experiments at different constant heating rates (1–50 K/min). A strong heating rate dependence of the activation energy of crystallization was observed. The analysis of the present data shows that the activation energy of crystallization is not constant but varies with the degree of crystallization and hence with temperature. The crystallization mechanisms examined using the local Avrami exponents indicate that one mechanism (two-dimensional growth) is responsible for the crystallization process for heating rates 1–30 K/min and two mechanisms (one- and two-dimensional growth) are working simultaneously during the amorphous–crystalline transformation of the Ge_22.5Te_77.5 glass for a heating rate 50 K/min. The reaction model that may describe crystallization process of the Ge_22.5Te_77.5 glass is Avrami–Erofeev model (g(α) = [−ln(1 − α)]^1/n) with n = 2 for the heating range 1–30 K/min and n = 1.5 at a heating rate 50 K/min for the whole range of conversion crystallization fraction (α = 0.05–0.95). A good agreement between the experimental and the reconstructed (α − T) curves has been achieved. The transformation from amorphous to crystalline phase in glassy Ge_22.5Te_77.5 demonstrates complex multi-step involving several processes.     

Investigation of the microwave dielectric properties of Ca1−xMgxLa4Ti5O17 ceramics for application in coplanar patch antenna

In this paper, the dielectric properties of Ca_1−xMg_xLa₄Ti₅O₁₇ ceramics at microwave frequency have been studied. The diffraction peaks of Ca_(1−x)Mg_xLa₄Ti₅O₁₇ ceramics nearly unchanged with x increasing from 0 to 0.03. Similar X-ray diffraction peaks of Ca_0.99Mg_0.01La₄Ti₅O₁₇ ceramic were observed at different sintering temperatures. A maximum density of 5.3 g/cm³ can be obtained for Ca_0.99Mg_0.01La₄Ti₅O₁₇ ceramic sintered at 1500 °C for 4 h. A maximum dielectric constant (_r) and quality factor (Q × f) of Ca_0.99Mg_0.01La₄Ti₅O₁₇ ceramic sintered at 1500 °C for 4 h are 56.3 and 12,300 GHz (at 6.4 GHz), respectively. A near-zero temperature coefficient of resonant frequency (τ_f) of −9.6 ppm/°C can be obtained for Ca_0.99Mg_0.01La₄Ti₅O₁₇ ceramic sintered at 1500 °C for 4 h. The measurement results for the aperture-coupled coplanar patch antenna at 2.5 GHz are presented. With this technique, a 3.33% bandwidth (return loss <−10 dB) with a center frequency at approximately 2.5 GHz has been successfully achieved.     

Synthesis and crystal structure of a new calcium borate, CaB6O10

A new calcium borate, CaB₆O₁₀, has been prepared by solid-state reactions at temperature below 750 °C. The single-crystal X-ray structural analysis showed that CaB₆O₁₀ crystallizes in the monoclinic space group P2₁/c with a = 9.799(1) Å, b = 8.705(1) Å, c = 9.067(1) Å, β = 116.65(1)°, Z = 4. It represents a new structure type in which two [B₃O₇]⁵⁻ triborate groups are bridged by one oxygen atom to form a [B₆O₁₃]⁸⁻ group that is further condensed into a 3D network, with the shorthand notation 6: ∞³[2 × (3:2Δ + T)]. The 3D network affords intersecting open channels running parallel to three crystallographically axis directions, where Ca²⁺ cations reside. The IR spectrum further confirms the presence of both BO₃ and BO₄ groups.     

Transport anisotropy and pseudo-gap state in oxygen deficient ReBa2Cu3O7−δ (Re = Y, Ho) single crystals

The temperature dependence of the transport anisotropy of ReBa₂Cu₃O_7−δ (Re = Y, Ho) single crystals is investigated. We experimentally determine the parallel and perpendicular conductivity in oxygen deficient single crystals. It is found that, in these single crystals, oxygen deficiency results to uneven oxygen distribution within their volume that leads to the formation of superconducting phases with different critical temperatures. We present an analysis regarding the agreement of the experimental data with the predictions of different theoretical models. It is determined that, the absolute values of the energy gaps along and perpendicular to the basis plane are changed, with different signs of their derivatives. When the value of Δ_c increases, the value of the pseudo-gap decreases and vice versa, testifying that the PG regime is suppressed, with a synchronous strengthening of the localization effects. In distinction to YBa₂Cu₃O_7−δ, the temperature dependence of the anisotropy of the resistivity ρ_c/ρ_ab(T) for the HoBa₂Cu₃O_7−δ samples is well described, by the universal “law of 1/2” for the thermally activated hopping conductivity.     

Influence of thickness on the material characteristics of reactively sputtered W2N layer and electrical properties of W/W2N/SiO2/Si capacitors

The material characteristics of W₂N layer and electrical properties of W/W₂N/SiO₂/Si metal–oxide–semiconductor (MOS) capacitors with different W₂N thickness upon annealing in N₂ + H₂ ambient at 500 °C for 20 min are investigated. The nitrogen concentration of W₂N for the W/W₂N stack with thin W₂N layer (≤10 nm) is lower than that for the W/W₂N stack with thick W₂N layer (≥15 nm). In addition, the crystallinity of W₂N in the W/W₂N (15 nm) stack is better than that in the W/W₂N (10 nm) stack. For all capacitors, the oxide charges decrease significantly after annealing and the amount of oxide charges is independent of the W₂N thickness. However, the work function (Φ_m) of the W/W₂N (≤10 nm) stack (4.6 eV) is smaller than that of W/W₂N (15 nm) stack (5.0 eV). The Φ_m of W/W₂N (15 nm) stack is close to that of W₂N single layer. After annealing, the Φ_m of W/W₂N (15 nm) stack and W₂N single layer decrease, especially for the W₂N single layer. But for the W/W₂N (≤10 nm) stack, the Φ_m increases after annealing.     

Interfacial interaction of solid nickel with liquid Pb-free Sn–Bi–In–Zn–Sb soldering alloys

The dissolution process of nickel in liquid Pb-free 87.5% Sn–7.5% Bi–3% In–1% Zn–1% Sb and 80% Sn–15% Bi–3% In–1% Zn–1% Sb soldering alloys has been investigated by the rotating disc technique at 250–450 °C. The temperature dependence of the nickel solubility in soldering alloys obeys a relation of the Arrhenius type c_s = 4.94 × 10² exp(−39500/RT)% for the former alloy and c_s = 4.19 × 10² exp(−40200/RT)% for the latter, where R is in J mol⁻¹ K⁻¹ (8.314 J mol⁻¹ K⁻¹) and T is in K. Whereas the solubility values differ considerably, the dissolution rate constants are rather close for these alloys and fall in the range (1–9) × 10⁻⁵ m s⁻¹ at disc rotational speeds of 6.45–82.4 rad s⁻¹. Appropriate diffusion coefficients vary from 0.16 × 10⁻⁹ to 2.02 × 10⁻⁹ m² s⁻¹. With both alloys, the Ni₃Sn₄ intermetallic layer is formed at the interface of nickel and the saturated or undersaturated melt at dipping times of 300–2400 s. The other Ni–Sn intermetallic compounds are found to be missing. A simple mathematical equation is proposed to evaluate the Ni₃Sn₄ layer thickness in the case of undersaturated melts. The tensile strength of the nickel-to-alloy joints is 94–102 MPa, with the relative elongation being 2.0–2.5%.     

Investigations of GaN metal-oxide-semiconductor capacitors with sputtered HfO2 gate dielectrics

This work elucidates the properties of Al/HfO₂/GaN metal-oxide-semiconductor capacitors using reactively sputtered HfO₂ as a gate dielectric. The influence of GaN surface treatments and the post-annealing of HfO₂ films on the leakage current, flat-band voltage, interface trap densities, dielectric constants, and effective oxide charges of the GaN MOS capacitors are presented. The Ga oxynitride on the surface of GaN was effectively removed by chemical solutions that also slightly reduced the dielectric constant, slightly increased the flat-band voltage, eliminated the hysteresis of the capacitance–voltage measurement, and yielded a similar leakage to that without surface treatment. A highest dielectric constant of HfO₂ (17) was obtained when the sample was annealed at 600 °C for 20 min, while the lowest interface trap density (5.3 × 10¹¹ cm⁻²) was obtained when the sample was annealed at 800 °C for 40 min. The leakage mechanism was well fitted by the Schottky emission and Frenkel–Poole emission models at a lower and higher electric field.     

Growth of Mn, Co and Ni-doped near-stoichiometric LiNbO3 by Bridgman method using K2O flux

The near-stoichiometric LiNbO₃ (SLN) single crystals doped Mn²⁺, Co²⁺ and Ni²⁺ in 0.5 mol% concentration in the raw compositions were grown by the Bridgman method under the conditions of taking K₂O as flux, a high temperature gradient (90–100 °C/cm) for solid–liquid interface. The XRD, absorption spectra, excitation spectra and emission spectra have been carried out. From the absorption edges of Mn²⁺, Co²⁺ and Ni²⁺-doped SLN crystals, the molar ratio of [Li⁺]/[Nb⁵⁺] are estimated to be about 0.977. The absorption spectra of Mn²⁺:SLN have shown a broad absorption band centered at 571 nm (⁶A_1g(⁶S) → ⁴T_1g(⁴G)), three absorption peaks at 520, 549 and 612 nm (overlapping of the ⁴T₁(F)–⁴A₂(F), ⁴T₁(F)–⁴T₁(P)), and a wide absorption band at 1400 nm (⁴T₁(F) → ⁴T₂(F)) of Co²⁺:SLN, Ni²⁺:SLN, and five absorption peaks at 381 nm (³A_2g(F) → ³T_1g(P)), 733 nm (³A_2g(F) → ³T_1g(F)), 1280 nm (³A_2g(F) → ³T_2g(F)), 430 nm (³A_2g(F) → ¹T_2g(D)), and 840 nm (³A_2g(F) → ¹E(D)) of Ni²⁺:SLN were observed. A red emission at 612 nm (⁴T_1g(⁴G) → ⁶A_1g(⁶S)) for Mn²⁺:SLN, a red emission at 775 nm (⁴T₁(P) → ⁴T₁(F)) for Co²⁺:SLN, and a green emission at 577 nm (¹T_2g(D) → ³A_2g(F)) and a red emission at 820 nm (¹T_2g(D) → ³T_2g(F)) for Ni²⁺:SLN were observed under excited by 416, 520 and 550 nm lights, respectively. The concentration distribution of Mn²⁺, Co²⁺and Ni²⁺ ion in SLN crystals was investigated primarily from the absorption and emission spectra for various parts. The effective distribution coefficient for Mn²⁺ was less than 1. While, for Co²⁺ and Ni²⁺ were more than 1.     

Role of titanium valence states in optical and electronic features of PbO–Sb2O3–B2O3:TiO2 glass alloys

PbO–Sb₂O₃–B₂O₃ glasses mixed with different concentrations of TiO₂ (ranging from 0 to 1.5 mol.%) were synthesized. The samples are characterized by X-ray diffraction, scanning electron microscopy and DSC techniques. A variety of properties, i.e. optical absorption, photoluminescence, infrared, ESR spectra, magnetic susceptibility, photo-induced birefringence (PIB) and dielectric properties (constant ′, loss tan δ, a.c. conductivity σ_ac over a wide range of frequency and temperature) of these glass–ceramics have been explored. The analysis of these results indicated that Ti ion surrounding ligands play principal role in the observed PIB and the sample crystallized with 0.8 mol.% of TiO₂ is the most suitable for the applications in non-linear optical devices.     

Thermoelectric properties of hot-pressed Zn4Sb3−xTex

A series of samples have been fabricated through vacuum melting method followed by hot-pressing for Zn₄Sb_3−xTe_x (x = 0.02–0.08), XRD patterns indicated that all the samples were single-phased β-Zn₄Sb₃. Electrical conductivity and Seebeck coefficient were evaluated in the temperature range of 300–700 K, showing p-type conduction. The thermoelectric figure of merit (ZT) was increased with the increase of Te content. ZT values of 0.8 and 1.0 were obtained at 673 K for Zn_4.08Sb₃ and Zn₄Sb_2.92Te_0.08, respectively.     

Synthesis and characterization of Al2O3-Ce0.5Zr0.5O2 powders prepared by chemical coprecipitation method

Al₂O₃-Ce_0.5Zr_0.5O₂ catalytic powders were synthesized by the coprecipitation (ACZ-C) and mechanical mixing (ACZ-M) methods, respectively. As-synthesized powders were characterized by XRD, Raman spectroscopy, surface area and thermogravimetric analyses. It was found that the mixing extent of Al³⁺ ions affected the phase development, texture and oxygen storage capacity (OSC) of the Ce_0.5Zr_0.5O₂ powder. Single phase of ACZ-C could be maintained without phase separation and inhibit α-Al₂O₃ formation up to 1200 °C. The specific surface area value of ACZ-C (81.5 m²/g) was larger than that of ACZ-M (62.1 m²/g) and Ce_0.5Zr_0.5O₂ (17.1 m²/g) powders, which were calcined at 1000 °C. In comparison with ACZ-C and Al₂O₃, which were calcined at high temperature (900–1200 °C), it was found that the degradation rate of specific surface area of ACZ-C was lower than that of Al₂O₃. ACZ-C sample showed a higher thermal stability to resist phase separation and crystallite growth, which enhanced the oxygen storage capacity property for Ce_0.5Zr_0.5O₂ powders.     

Synthesis of Y2SiO5:Eu nanoparticles from a hydrothermally prepared silica sol

In this paper, a novel route for the synthesis of Y₂SiO₅ (YSO) nanoparticles doped with Eu³⁺ ions, based on the use of a hydrothermally prepared silica sol as a chemical precursor and nanostructuring template, is presented. X-ray powder diffraction revealed crystallization of nanoparticles in an X₁ monoclinic structural type (P2₁/c) with well pronounced diffraction peaks and without any sign of additional phases. Transmission electron microscopy showed that the particle diameter was around 40 nm and that the particles formed loose aggregates. The synthesized materials exhibited characteristic luminescence emission of the trivalent europium ion, with the strongest emission (⁵D₀ → ⁷F₂ transition) at 611.5 nm and a corresponding lifetime of 1.8 ms. Two site occupancy, as expected, were demonstrated.     

Solidification microstructure of laser remelted Al2O3ZrO2 eutectic

Surface resolidification experiments using a high power CO₂-laser have been performed on an Al₂O₃ZrO₂ containing 36.8 at.% ZrO₂ eutectic alloy at beam velocities between 0.3 and 8 mm·s⁻¹. The local growth rate has been measured by observation of the orientation of the microstructure using scanning electron microscopy. In the whole range of velocities, the structure is essentially a regular lamellar eutectic and the value of the growth productλ²V was found to be ≈ 9.6·10⁻¹⁷ m³·s⁻¹. The measured eutectic spacings were compared with Jackson and Hunt model. Using thermophysical properties from the literature, the measured spacings were more than four times larger than the calculated ones. Assuming all parameters of the growth relationship except the diffusion coefficient to be of the right order of magnitude or to have a negligible influence, agreement is found when using a larger liquid diffusion coefficient,D_L≈5·10⁻¹⁰m²·s⁻¹.