Good Phase Stability Research Articles

Highly Conducting p-Type Transparent LnCuOS (Ln = La and Nd) and p–n Junction by Using Ink

The development of high performance p-type transparent conducting oxides (TCOs) remains as the greatest challenge to the achievement of advanced future optoelectronics including transparent electronics. In this work, we proposed and succeeded in designing a novel chemical solution method to prepare highly conducting p-type oxychalcogenides LnCuOS (Ln = La and Nd). Not only is our proposed chemical solution process much more economically efficient, versatile, and safer than all the currently available methods, but also the synthesized NdCuOS demonstrates the record high intrinsic p-type conductivity of 11.4 S cm–1 for oxychalcogenides. The large improvement in the electrical conductivity is attributed to our synthesis process, leading to high Cu vacancies. The good phase stability of our highly Cu-deficient film was also proven by our computational calculation. At the same time, thin films of LnCuOS were also prepared via spin-coating methods for the first time. As the nanoparticles were used for spin-coating, the fabricated thin films are rather dense and smooth. Moreover, the strong photoluminescence (PL) peaks also indicate its great potential to be used in many future optoelectronics. The great performance demonstrated by the fabricated p–n junctions indicates the good opportunity to be integrated in devices like transparent electronics.

A study of phase evolution and crystal growth for nano-sized monoclinic Y4Al2O9 as a novel thermal barrier coatings

Nano-sized monoclinic Y4Al2O9 was produced by sol-gel process as a novel potential candidate material for thermal barrier coatings. The thermal behavior, structural evolution of the products and the morphological characteristics of the compacted bodies were investigated by Thermogravimetric analysis and differential scanning calorimeter (TG-DSC), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and Field emission scanning electron microscopy (FESEM). Qualitative analyses indicate that monoclinic Y4Al2O9 was formed at about 1000 °C, and exhibited good phase stability throughout the annealing temperature ranging from 1000 °C to 1400 °C. The thermophysical properties of Y4Al2O9 ceramics were also evaluated compared with 8YSZ and La2Zr2O7. The determined activation energy of crystal growth is about 72.71 ± 0.31 kJ mol−1. Meanwhile, Y4Al2O9 represents low thermal conductivity (1.71 W m−1 K−1), moderate thermal expansion coefficient (8.73 × 10−6 K−1), and high sintering-resistance ability. Such results reveal that nano-sized Y4Al2O9 is favorable for the application of TBCs.

Computation‐Guided Design of LiTaSiO5, a New Lithium Ionic Conductor with Sphene Structure

AbstractThe development of all‐solid‐state Li‐ion batteries requires solid electrolyte materials with many desired properties, such as ionic conductivity, chemical and electrochemical stability, and mechanical durability. Computation‐guided materials design techniques are advantageous in designing and identifying new solid electrolytes that can simultaneously meet these requirements. In this joint computational and experimental study, a new family of fast lithium ion conductors, namely, LiTaSiO5 with sphene structure, are successfully identified, synthesized, and demonstrated using a novel computational design strategy. First‐principles computation predicts that Zr‐doped LiTaSiO5 sphene materials have fast Li diffusion, good phase stability, and poor electronic conductivity, which are ideal for solid electrolytes. Experiments confirm that Zr‐doped LiTaSiO5 sphene structure indeed exhibits encouraging ionic conductivity. The lithium diffusion mechanisms in this material are also investigated, indicating the sphene materials are 3D conductors with facile 1D diffusion along the [101] direction and additional cross‐channel migration. This study demonstrates a novel design strategy of activating fast Li ionic diffusion in lithium sphenes, a new materials family of superionic conductors.

Phase stability and oxygen permeability of Fe-based BaFe0.9Mg0.05X0.05O3 (X = Zr, Ce, Ca) membranes for air separation

The effects of various dopants including Zr4+, Ce4+ and Ca2+ on the structure and oxygen permeability of B-site doped BaFe0.9Mg0.05X0.05O3−δ (BFM-X) perovskite-type oxygen transport membranes were studied. Slight X cation doping could stabilize the cubic structure of BFM-X perovskite down to room temperature. XRD, SEM and thermogravimetric results revealed that all the cubic BFM-X oxides exhibited good phase stability under argon atmosphere without any phase changes. The weight loss of BFM-Ce from TG analysis suggests the reduction of cerium ions at high temperatures, which may account for its larger electrical conductivity and higher oxygen permeability comparing to BFM-Zr and BFM-Ca membranes. X-ray photoelectron spectroscopy (XPS) data revealed that Ca dopant with larger size caused the mismatch with Fe ions and led to the substitution of Ca ions at both Fe and Ba site in BFM-Ca oxide, being detrimental to electrical conductivity and oxygen permeation. Among these membranes, BFM-Ce has the highest oxygen permeability and good long term permeation stability under air/argon gradient, thus it was recommended as a potential and promising material for air separation.

High-entropy environmental barrier coating for the ceramic matrix composites

A novel high-entropy material, (Yb0.2Y0.2Lu0.2Sc0.2Gd0.2)2Si2O7 ((5RE0.2)2Si2O7) was prepared by the sol-gel method and investigated as a promising environmental barrier coating (EBC) for SiC-based composites. The results of X-ray diffraction and transmission electron microscopy indicated that rare-earth elements were distributed homogeneously in the single monoclinic phase. Moreover, it was found that the new material (5RE0.2)2Si2O7 had good phase stability, well-matched coefficient of thermal expansion with SiC-based composite, and excellent resistance to water-vapor corrosion. The water-vapor corrosion test of (5RE0.2)2Si2O7 coated Cf/SiC composites further confirmed that (5RE0.2)2Si2O7 was suitable for application as EBC material and could provide effective protection to Cf/SiC composites from water-vapor damage.

Mg2SiO4 as a novel thermal barrier coating material for gas turbine applications

Forsterite-type Mg2SiO4 was investigated systematically for thermal barrier coating (TBC) applications. Results showed that Mg2SiO4 synthesized by solid-state reaction possessed the good phase stability up to 1573 K. The thermal conductivity of Mg2SiO4 at 1273 K was lower ˜20% than that of yttria stabilized zirconia (8YSZ). Mg2SiO4 also presented moderate thermal expansion coefficients, which increased from 8.6 × 10−6 K−1 to 11.3 × 10−6 K−1 (473˜1623 K). Mechanical properties including hardness, fracture toughness, and Young’s modulus of Mg2SiO4 were comparable to those of 8YSZ. The sintering results indicated a promising low-sintering activity of Mg2SiO4. Mg2SiO4 samples were subjected to water quenching test at 1573 K and showed a superior thermal shock resistance compared to 8YSZ. Mg2SiO4 coating with stoichiometric composition was produced by atmospheric plasma spraying. The thermal cycling test result showed that Mg2SiO4 coating had a lifetime more than 830 cycles at 1273 K, which is desirable for TBC applications.

Modulating the Surface Atomic Arrangement of Perovskite LaMnO3/C Towards Superior Electrocatalytic Activity and High Performance for Li-O2 Batteries.

A composite of Lanthanum manganese oxide-carbon (LaMnO3/C) has been also synthesized by a facile electrospinning approach followed by controlled heat treatment, in which the carbon form a continuous conductive network connecting the electrocatalyst LaMnO3 nanoparticles together to facilitate good electrochemical performance. Based on a correlation between theoretical (DFT) and experimental analysis on the effect of the surface atomic arrangement, the electrocatalyst (Mn-terminated LaMnO3) with uniform Mn surface termination show favourable rechargeability, and good phase and morphology stability in lithium oxygen batteries compared to La rich surface termination. Excellent cycling performance is also demonstrated, in which the terminal voltage is higher than 2.4 V after 100 cycles at limited capacity of 1000 mAh g-1 (based on composite). Figure 1

Structural evolution of Al-modified PS-PVD 7YSZ TBCs in thermal cycling

Feather-like columnar 7YSZ thermal barrier coatings (TBCs) were prepared by plasma spray-physical vapor deposition (PS-PVD). In order to improve the thermal cycle performance of TBCs, Al-modification was carried out with the as-sprayed TBCs. Al film was deposited on the surface of TBCs. Subsequently, the Al-deposited TBCs were conducted with vacuum heat treatment. After that, a dense overlay consisting of α-Al2O3, Al3Zr phases was generated on the TBCs surface due to the reactions of Al and O2, Al and ZrO2. The Al-modified TBCs show a better thermal cycle performance than the as-sprayed TBCs because of the overlay generation. Moreover, the structural evolution of overlay was investigated emphatically before and after thermal cycle testing, showing good phase stability. No crack and spallation were observed in the Al-modified TBCs.

Yttrium dependent space charge effect on modulating the conductivity of barium zirconate electrolyte for solid oxide fuel cell

Development of high proton conducting, chemically stable electrolyte for solid oxide fuel cell application still remains as a major challenge. In this work, yttrium (0, 5, 10, 15 and 20 mol%) doped barium zirconate synthesised by hydrothermal assisted coprecipitation exhibited highly crystalline cubic perovskite. The results demonstrate that the proton conductivity is higher than oxygen ion conductivity measured in the temperature range of 200–600 °C. The 20 mol% Y doped BaZrO3 exhibited higher protonic conductivity (6.1 mScm−1) with an activation energy 0.64 eV under the reducing atmosphere. The Mott–Schottky analysis carried out in hydrogen atmosphere at 200 °C revealed that the barrier height of doped BaZrO3 reduced from 0.6 to 0.2 V. The Schottky depletion layer width also decreased from 4 to 2 nm with the increase in yttrium concentration and the boiling water test showed good phase stability. Our study highlights the critical role of space charge in the grain boundary and its suppression with the increase in dopant concentration. The results demonstrate that Y doped BaZrO3 sintered at low temperature is a promising candidate as the electrolyte material for the intermediate temperature proton conducting solid oxide fuel cells.

Investigation on microstructures and thermo-physical properties of ferroelastic (Y1-xDyx)TaO4 ceramics

A series of ceramics of (Y1-xDyx)TaO4 monoclinic phases (space group: I2 (5)) are prepared by the solid-state reaction method. The high-resolution transmission electron microscopy (HRTEM) suggest the (Y1-xDyx)TaO4 ceramics possess ferroelastic domain, which is derived from reversible second-order ferroelastic transformation between the high-temperature tetragonal (t) and low-temperature monoclinic (m) phase. Similar to metastable tetragonal YSZ ceramics, the ferroelastic toughening mechanism may exist in m-phase (Y1-xDyx)TaO4 ceramics through the shift or reorientation of ferroelastic domain under the stress field of a crack. The energy dispersive spectroscopy reveals that the elements of Y and Dy are inhomogeneous in the grain of (Y1-xDyx)TaO4 ceramics, which breaks down the relationship of concave parabola between thermal conductivity and composition parameter (x). Moreover, the thermal conductivities (1.7–2.0 W/m/k at 900 ̊C) and thermal expansion coefficients (TECs) (10–11 × 10−6 K−1) of (Y1-xDyx)TaO4 ceramics are comparable to that of YSZ (yttria-stabilized zirconia). In view of the low thermal conductivity, high thermal expansion coefficients, good high-temperature phase stability and ferroelastic transformation, the (Y1-xDyx)TaO4 ceramics show great potentials in the application of high-temperature thermal insulator materials, particularly as thermal barrier coatings.

Phase stability and thermodynamic database validation in a set of non-equiatomic Al-Co-Cr-Fe-Nb-Ni high-entropy alloys

A series of six high-entropy alloys in non-equiatomic proportions were produced to study the phase stability across a range of compositions within the Al-Co-Cr-Fe-Nb-Ni system. Phase identification was performed using SEM, TEM, and XRD and computational tools were employed for comparison to the experimental findings. Complex microstructures were obtained following exposure at 900 °C with precipitation of Laves, NiAl, γ′ and δ phases. Primary and secondary Laves populations were identified and found to become more stable with increasing Fe and Nb content. Additions of Nb promoted the formation of thin, plate-like, δ phase at the expense of the secondary Laves. The NiAl phase was observed to precipitate in the alloys with high Fe content, above the γ′ solvus temperature. Overall, the thermodynamic predictions using Thermo-Calc with the TCNi8 database were accurate with respect to identifying the phase composition, while TTNi8 provided good phase stability results. However, significant differences were observed with respect to the solvus temperatures of the precipitate phases.

Predictive modeling and design rules for solid electrolytes

Abstract

Microstructure and Thermophysical Properties of SrZrO3 Thermal Barrier Coating Prepared by Solution Precursor Plasma Spray

Strontium zirconate (SrZrO3) thermal barrier coatings were deposited by solution precursor plasma spray (SPPS) using an aqueous precursor solution. The phase transition of the SrZrO3 coating and the influence of the aging time at 1400 °C on the microstructure, phase stability, thermal expansion coefficient, and thermal conductivity of the coating were investigated. The unique features of SPPS coatings, such as interpass boundary (IPB) structures, nano- and micrometer porosity, and through-thickness vertical cracks, were clearly observed evidently in the coatings. The vertical cracks of the coatings remained substantially unchanged while the IPB structures gradually diminished with prolonged heat treatment time. t-ZrO2 developed in the coatings transformed completely to m-ZrO2 phase after heat treatment for 100 h. Meanwhile, the SrZrO3 phase in the coatings exhibited good phase stability upon heat treatment. Three phase transitions in the SrZrO3 coatings were revealed by thermal expansion measurements. The thermal conductivity of the as-sprayed SrZrO3 coating was ~1.25 W m−1 K−1 at 1000 °C and remained stable after heat treatment at 1400 °C for 360 h, revealing good sintering resistance.

Performance of the Castor Oil in Methanol-Gasoline as a Bi-Functional Additive

In this paper, the castor oil, as additives, has been investigated on the phase separation temperature of M15, M30, M50 and M65 methanol gasoline at-25.0°C to 40.0°C, respectively. The effect of the additives on the phase stability and saturation vapour pressure was discussed. It was found that castor oil derivatives have good phase stability to various ratio methanol gasoline blends. Introducing water in the methanol gasoline blends need much amount of methyl castor oil to realize phase mixable. Besides, the castor oil can depress the saturation vapour pressure of methanol gasoline effective as well. With these data, it can be concluded that the castor oil have the great potential to be used gasoline-methanol additives.

Influence of Ca Doping on the Performance of Ruddlesden-Popper Oxides Sr3.2-XCaxLn0.8Fe1.5Co1.5O10-δ as Cathode Materials for It-SOFCs

Solid oxide fuel cell (SOFC) is an attractive electrochemical device for energy conversion with high efficiency and fuel flexibility at high operating temperatures (~1000 °C). Current operating temperatures of SOFC technology limit its wide commercialization due to the selection of materials used and degradation of cell components. This challenge has generated enormous interest in SOFCs operating at intermediate temperatures (600 – 800 oC). However, the catalytic activity of the conventional La1-xSrxMnO3 perovskite cathode drops significantly at temperatures < 800 °C. Mixed ionic-electronic conducting perovskites are widely investigated as cathodes for SOFCs due to their high catalytic activity for oxygen reduction reaction (ORR) at intermediate operating temperatures. Cobalt-based perovskite oxides exhibit good mixed ionic-electronic conductivity and catalytic activity at 600 – 800 oC, but they suffer from a huge thermal expansion mismatch between the electrolyte and electrode. Another class of materials with mixed ionic and electronic conducting property and catalytic activity for ORR is the perovskite-related intergrowth oxides belong to the Ruddlesden-Popper (R-P) series. Here we present R-P oxides of the n = 3 series Sr3.2-xCaxLn0.8Fe1.5Co1.5O10-δ with x = 0 and 0.4 and Ln = La, Pr, and Nd as potential cathodes for intermediate temperature SOFCs. Specifically, the effects of Ca substitution for Sr on the crystal chemistry, oxygen content, thermal expansion coefficient (TEC), and electrocatalytic activity in SOFC are presented. The substitution of Ca for Sr in Sr3.2-xCaxLn0.8Fe1.5Co1.5O10-δ enhances the stability of phase at the operating temperatures and decreases the amount of oxygen loss on heating. Comparing different lanthanides with and without Ca in Sr3.2-xCaxLn0.8Fe1.5Co1.5O10-δ, the Ln = Nd samples exhibit superior cathode performance which is ascribed to the high concentration of oxygen vacancies. Among the different compositions studied, the composite cathode Sr2.8Ca0.4Nd0.8Fe1.5Co1.5O10-δ + GDC exhibits an enhanced performance with good phase stability due to high oxygen vacancy concentration and enhanced oxide-ion transport.

Effect of Y doping on microstructure and thermophysical properties of yttria stabilized hafnia ceramics

A series of Y2O3-doped HfO2 ceramics (Hf1-xYxO2-0.5×, x = 0, 0.04, 0.08, 0.12, 0.16 and 0.2) were synthesized by solid-state reaction at 1600 °C. The microstructure, thermophysical properties and phase stability were investigated. Hf1-xYxO2–0.5x ceramics were comprised of monoclinic (M) phase and cubic (C) phase when Y3+ ion concentration ranged from 0.04 to 0.16. The thermal conductivity of Hf1-xYxO2–0.5x ceramic decreased as Y3+ ion concentration increased and Hf0.8Y0.2O1.9 ceramic revealed the lowest thermal conductivity of ~ 1.8 W/m*K at 1200 °C. The average thermal expansion coefficient (TEC) of Hf1-xYxO2–0.5x between 200 °C and 1300 °C increased with the Y3+ ion concentration. Hf0.8Y0.2O1.9 yielded the highest TEC of ~ 10.4 × 10−6 K−1 while keeping good phase stability between room temperature and 1600 °C.

Effect of Co and Gd Additions on Microstructures and Properties of FeSiBAlNi High Entropy Alloys.

FeSiBAlNi (W5), FeSiBAlNiCo (W6-Co), and FeSiBAlNiGd (W6-Gd) high entropy alloys (HEAs) were prepared using a copper-mold casting method. Effects of Co and Gd additions combined with subsequent annealing on microstructures and magnetism were investigated. The as-cast W5 consists of BCC solid solution and FeSi-rich phase. The Gd addition induces the formation of body-centered cubic (BCC) and face-centered cubic (FCC) solid solutions for W6-Gd HEAs. Whereas, the as-cast W6-Co is composed of the FeSi-rich phase. During annealing, no new phases arise in the W6-Co HEA, indicating a good phase stability. The as-cast W5 has the highest hardness (1210 HV), which is mainly attributed to the strengthening effect of FeSi-rich phase evenly distributed in the solid solution matrix. The tested FeSiBAlNi-based HEAs possess soft magnetism. The saturated magnetization and remanence ratio of W6-Gd are distinctly enhanced from 10.93 emu/g to 62.78 emu/g and from 1.44% to 15.50% after the annealing treatment, respectively. The good magnetism of the as-annealed W6-Gd can be ascribed to the formation of Gd-oxides.

Microstructure and Thermomechanical Properties of Atmospheric Plasma-Sprayed Yb2O3 Coating

In this study, a Yb2O3 coating was fabricated by the atmospheric plasma spray technique. The phase composition, microstructure, and thermal stability of the coating were examined. The thermal conductivity and thermal expansion behavior were also investigated. Some of the mechanical properties (elastic modulus, hardness, fracture toughness, and flexural strength) were characterized. The results reveal that the Yb2O3 coating is predominantly composed of the cubic Yb2O3 phase, and it has a dense lamellar microstructure containing defects. No mass change and exothermic phenomena are observed in the thermogravimetry and differential thermal analysis curves. The high-temperature x-ray diffraction results indicate that no phase transformation occurs from room temperature to 1500 °C, revealing the good phase stability of the Yb2O3 coating. The coefficient of thermal expansion of the Yb2O3 coating is (7.50-8.67) × 10−6 K−1 in the range of 200-1400 °C. The thermal conductivity is about 1.5 W m−1 K−1 at 1200 °C. The Yb2O3 coating has excellent mechanical properties and good damage tolerant. The unique combination of these properties implies that the Yb2O3 coating might be a promising candidate for T/EBCs applications.

Hot corrosion behavior of BaLa2Ti3O10 exposed to calcium-magnesium-alumina-silicate at elevated temperatures

Calcium-magnesium-alumina-silicate (CMAS) attack has been regarded as one of the significant failure mechanisms for thermal barrier coatings (TBCs). In this study, CMAS corrosion behavior of BaLa2Ti3O10, a novel TBC material, is investigated at 1300 °C and 1350 °C for 0.5 h, 4 h, 12 h and 24 h. Results reveal that BaLa2Ti3O10 has high resistance to molten CMAS infiltration, attributable to the formation of a dense reaction layer. X-ray diffraction, scanning electron microscope, energy dispersive spectroscope, transmission electron microscope confirm that the layer consists of apatite, celsian and perovskite phases. With increased corrosion duration, the layer retains good phase stability and the thickness increases. The formation of corrosion products and the reaction layer are discussed according to a dissolution-reprecipitation mechanism and the optical basicity theory.

Holographic line field en-face OCT with digital adaptive optics in the retina in vivo.

We demonstrate a high-resolution line field en-face time domain optical coherence tomography (OCT) system using an off-axis holography configuration. Line field en-face OCT produces high speed en-face images at rates of up to 100 Hz. The high frame rate favors good phase stability across the lateral field-of-view which is indispensable for digital adaptive optics (DAO). Human retinal structures are acquired in-vivo with a broadband light source at 840 nm, and line rates of 10 kHz to 100 kHz. Structures of different retinal layers, such as photoreceptors, capillaries, and nerve fibers are visualized with high resolution of 2.8 µm and 5.5 µm in lateral directions. Subaperture based DAO is successfully applied to increase the visibility of cone-photoreceptors and nerve fibers. Furthermore, en-face Doppler OCT maps are generated based on calculating the differential phase shifts between recorded lines.