Excellent Phase Stability Research Articles

Cs4 PbI6 -Mediated Synthesis of Thermodynamically Stable FA0.15 Cs0.85 PbI3 Perovskite Solar Cells.

The stability issue is still one of the main limitations of the commercialization of perovskite photovoltaics. The mixed cation FAx Cs1 -x PbI3 has shown great promise owing to its improved thermal and moisture stability. However, the study of FAx Cs1 -x PbI3 is concentrated on formamidine (FA)-rich perovskite, whereas cesium (Cs)-rich FAx Cs1 -x PbI3 perovskites are barely studied due to the inevitable phase separation when Cs > 30 mol%. Here, a Cs4 PbI6 -mediated method is developed to synthesize Cs-rich FAx Cs1 -x PbI3 perovskites. It is demonstrated that Cs4 PbI6 intermediate phase has a low Cs cation diffusion barrier and therefore offers a fast ion exchange with the preformed FA-rich perovskite phase to finally form the Cs-rich FAx Cs1 -x PbI3 perovskite. The results indicate that ≈15% alloying with organic FA cations can sufficiently stabilize the perovskite phase with excellent phase and UV-irradiation stability. The FA0.15 Cs0.85 PbI3 perovskite solar cells achieve a champion power conversion efficiency of 17.5%, showing the great potential of Cs-based perovskites for efficient and stable solar cells.

Microstructural characterization of modified plasma spray LZ/YSZ thermal barrier coating by laser glazing

One of the high potential material, lanthanum zirconate (LZ) is deposited on superalloy 625 due to its excellent phase stability, low thermal conductivity as well as the high melting point. However, microstructural defects were detected due to lamellar structure behaviour exhibited from the plasma-sprayed coating techniques. This paper investigated the effect of surface modification on LZ thermal barrier coating (TBC) by using laser glazing method. The double ceramic layer (DCL) TBCs are composed of NiCoCrAlYTa bond coating formed via the HVOF process while 8YSZ ceramic top coat and La2Zr2O7 as the third layer were produced by utilizing the APS technique. Nd:YAG pulsed laser has been used to modify the surface layer of plasma-sprayed LZ coatings. The microstructural morphologies of both as-sprayed and laser glazed samples were investigated using Scanning Electron Microscopy (SEM). The phases of the coatings were analysed with X-ray Diffractometry (XRD). The results showed that the laser glazing process reduced surface roughness attributed to the sealing of porosities and other structural defects of the coating. Finally, the impacts of laser energy input and laser distance on the characterization of the glazed layer are discussed.

Enhancement performance and exhaust emissions of rapeseed methyl ester by using n-hexadecane and n-hexane fuel additives

A lot of studies were conducted in recent years to improve of biodiesel performance. It has been stated that the addition of additives in biodiesel reduces emissions of unburned hydrocarbon (HC), carbon monoxide (CO) and particulate matter (PM). It makes a significant improvement in thermal efficiency (BTE) and heat dissipation rate (HRR). The additives are attractive in automotive applications due to their excellent phase stability and clean combustion ability. Engine performance and exhaust emissions are mainly based on air-fuel ratio, cetane number, oxygen content of fuel, fuel atomization and the other features. In this study, two different additives were added to the biodiesel to change the number of cetane. In addition, engine performance and emission changes were investigated experimentally. The viscosity and density of fuels were reduced by additives. Compared to R0 fuel, torque increased by 9.74% and 7.22% in RHD20 and RHX20 fuels respectively. While specific fuel consumption decreased by 9.58% and 6.50% respectively. The ignition delay and combustion times decreased due to combustion quality. Maximum cylinder pressure and heat release rate values increased after additives adding in fuels. With the increase of the additive rate, HC (RHD20 23.68%, RHX20 21.05%), CO (RHD20 16.89%, RHX20 15.81%), and soot (RHD20 34.35%, RHX20 26.19%) emissions reduced while NOx (RHD20 2.26%, RHX20 3.21%) emissions increased.

Effect of Cold Rolling and Aging on the Microstructure and Mechanical Properties of Ti-Nb-Zr Alloy

The effect of cold rolling deformation and aging treatment on the phase transformation, microstructure evolution, and mechanical properties of a new Ti-Nb-Zr metastable β-titanium alloy was investigated by x-ray diffraction, scanning electron microscopy, transmission electron microscopy, and mechanical property testing. The results show that the alloy exhibited excellent phase stability that no stress-induced α″ phase transition occurred during cold rolling and that the plastic deformation mechanism was related to dislocation slipping. Interestingly, even under the same aging treatment at 300 °C for 2 h, the aging products for the unrolled and cold-rolled alloys are β + ω and β + α, respectively. The alloy with cold deformation produces a large number of dislocation defects, and grain boundaries inhibit the nucleation of the ω phase, while the α phase tends to nucleate at the dislocations and grain boundaries and promote the precipitation of the α phase. Compared with solution treatment and aging, the aging treatment after cold deformation has high-strength matching and its ideal elastic modulus can satisfy the requirements for dental implants.

High temperature mechanical and thermal properties of CaxBa1-xZrO3 solid solutions

The excellent high temperature phase stability enables the perovskite BaZrO3 to be a promising candidate for thermal barrier coatings (TBCs). Further improvement of its thermo-physical properties is necessary to fulfill the increasing requirements for TBCs. In this work, CaxBa1-xZrO3 (x = 0.05, 0.10, 0.15, 0.20, 0.25) solid solutions are fabricated and the influence of the Ca2+ content on their mechanical/thermal properties is studied. They have moderate mechanical properties and their residual Young's moduli at 1473 K are around 80% of the values at room temperature. Compared with BaZrO3, CaxBa1-xZrO3 solid solutions have decreased thermal conductivities which are comparable to those of YSZ and other potential TBCs materials. Among these solid solutions, Ca0.25Ba0.75ZrO3 exhibits the lowest thermal conductivity that is in the range from 2.06 W⋅m-1⋅K-1 to 2.52 W⋅m-1⋅K-1. Meanwhile, CaxBa1-xZrO3 solid solutions have higher thermal expansion coefficients than that of BaZrO3. These good high temperature mechanical and thermal properties reveal their promising applications as high temperature structural ceramics including TBCs.

An Environmentally Stable Organic–Inorganic Hybrid Perovskite Containing Py Cation with Low Trap-State Density

The commonly-employed methylammonium-based perovskites are environmentally unstable, which limits their commercialization. To resolve this problem, a stable hybrid perovskite, pyrrolidinium lead iodide (PyPbI3), was synthesized successfully via a simple drop casting method. The formed PyPbI3 exhibited a hexagonal structure. It presented not only excellent phase stability, but also low trap-state density, as confirmed via the X-ray diffraction and space-charge-limited currents measurements. This novel perovskite may be applicable to perovskite photovoltaics to improve their environmental stability.

Influence of Y2O3 and Ta2O5 Co-doping on Microstructure and Thermal Conductivity of Gd2Zr2O7 Ceramics

Rare earth zirconates (RE2Zr2O7) are considered as a class of potential high-temperature structural materials. In this paper, a series of Y2O3 and Ta2O5 co-doped Gd2Zr2O7 [(Gd1−xYx)2(Zr1−xTax)2O7+x, x = 0, 0.1, 0.2, 0.3, 0.4] ceramics were prepared by solid-state reaction sintering in order to clarify the influence of Y2O3 and Ta2O5 co-doped on microstructure, Young’s modulus and thermal conductivity. The results showed that Y2O3 and Ta2O5 co-doped Gd2Zr2O7 exhibited a single pyrochlore structure, and a small amount of Y3+ ions were doped into the Zr4+ ions lattice. The Young’s moduli of doped Gd2Zr2O7 ceramics slightly change with the increase in Y2O3 and Ta2O5 doping concentration. The minimum thermal conductivities of the specimens were obtained at 800 °C. The thermal conductivity of doped Gd2Zr2O7 with x = 0.3 is lower than that of others among the doped specimens, which is around 1.41 W m−1 K−1 at 800 °C. In addition, (Gd0.7Y0.3)2(Zr0.7Ta0.3)2O7.3 ceramic exhibits excellent phase stability from room temperature to 1550 °C.

Subcycle mid-infrared coherent transients at 4 MHz repetition rate applicable to light-wave-driven scanning tunneling microscopy.

We produce subcycle mid-infrared (MIR) pulses at a 4MHz repetition rate via the optical rectification (OR) of sub-10fs near-infrared pulses delivered by an optical parametric chirped pulse amplifier. The coherent MIR pulses generated in a GaSe crystal under an ultrabroadband phase-matching condition contain only 0.58-0.85 oscillation cycles within the full width at half-maximum of the intensity envelope. The use of OR enables excellent phase stability of 56mrad over 5.6h, which is confirmed by field-resolved detection using electro-optic sampling. An electromagnetic simulation using a finite integration technique reveals that the peak field strength can easily exceed 10V/nm owing to the field enhancement resulting from focusing MIR pulses onto a tunnel junction.

Crystal growth behavior and phase stability of rare earth oxides (4 mol.% GdO1.5-4 mol.% SmO1.5) doped zirconia nanopowders

Nanocrystalline powders of 4mol.% GdO1.5-4mol.% SmO1.5 doped ZrO2 (4Gd4SmSZ) has been synthesized by co-precipitation process. Their phase transformation and crystalline growth behavior was investigated by Thermo gravimetric-Differential Thermal Analysis (TG-DTA), X-ray Diffraction (XRD), Raman spectroscopy and High-Resolution Transmission Electron Microscopy (HR-TEM) after calcinations at different temperatures. The XRD, Raman spectra and HRTEM results confirm the nature of tetragonal zirconia (t-ZrO2). The prepared 4Gd4SmSZ powders, remains in the single metastable tetragonal phase over the whole calcination temperature ranging from 873K to 1273K for 2h. The crystallite size varies from 11.98nm to 18.90nm with increase of temperature from 873K to 1273K. The activation energy of the prepared powders at low temperature is considerably lesser than that at a higher temperature. The annealed 4Gd4SmSZ powders had shown excellent phase stability at 1573K for 100h.

High-Rubidium–Formamidinium-Ratio Perovskites for High-Performance Photodetection with Enhanced Stability

Formamidinium lead trihalide perovskites have emerged as promising photovoltaic materials owing to their superior absorption coefficient properties. However, one big challenge is the material phase stability and thermal stability at high temperature. In this work, a large quantity of rubidium (Rb) ions is incorporated into formamidinium (FA) perovskite thin films to improve the material phase stability and thermal stability. Photodiodes based on optimized FA0.7Rb0.3PbI3 perovskites deliver a high responsivity of 0.43 A W-1, a detectivity of >1012 Jones, a relatively large linear dynamic range of 125 dB, and an ultrafast response speed of approximately 300 ns. Moreover, these photodiodes present lower dark current and higher photocurrent after baking at high temperature. These results are very promising for photodetection at high operational temperature. In addition, the high-ratio rubidium-incorporated perovskite films may have great potential in fabricating other high-performance optoelectronic devices, i.e., light-emitting diodes and solar cells with excellent phase stability and high temperature thermostability.

Proof-of-Principle Experimental Demonstration of Twin-Field Type Quantum Key Distribution.

The twin-field (TF) quantum key distribution (QKD) protocol and its variants are highly attractive because they can beat the well-known fundamental limit of the secret key rate for point-to-point QKD without quantum repeaters (repeaterless bound). In this Letter, we perform a proof-of-principle experimental demonstration of TFQKD based on the protocol proposed by Curty, Azuma, and Lo, which removes the need for postselection on the matching of a global phase from the original TFQKD scheme and can deliver a high secret key rate. Furthermore, we employ a Sagnac loop structure to help overcome the major difficulty in the practical implementation of TFQKD, namely, the need to stabilize the phase of the quantum state over kilometers of fiber. As a proof-of-principle demonstration, the estimated secure key rate from our experimental TFQKD data at the high loss region surpasses the repeaterless bound of QKD with current technology.

High CO2-tolerance oxygen permeation dual-phase membranes Ce0.9Pr0.1O2-δ-Pr0.6Sr0.4Fe0.8Al0.2O3-δ

High stability and oxygen permeability are two prominent requirements for the oxygen transport membrane candidates used as industrialization. Herein, we report several composite membranes based on xwt.%Ce0.9Pr0.1O2-δ (CPO)-(100-x)wt.%Pr0.6Sr0.4Fe0.8Al0.2O3-δ (PSFAO) (x = 50, 60 and 75) prepared via a modified Pechini method. Oxygen permeability test reveals that the 60CPO-40PSFAO composition exhibits the highest oxygen permeability. The oxygen permeation flux through the optimal uncoated 0.33 mm-thickness 60CPO-40PSFAO composite can reach 1.03 mL cm-2 min-1 (over the general requirement value of 1 mL cm-2 min-1) in air/He atmosphere at 1000 °C. In situ XRD performance confirms the optimal 60CPO-40PSFAO sample shows excellent stability in CO2-containing atmospheres. The 60CPO-40PSFAO membrane still exhibits simultaneously excellent oxygen permeability and phase stability after operating for over 100 h at air/CO2 condition at 1000 °C, which further indicates that the 60CPO-40PSFAO composite is likely to be used for oxygen supply in CO2 capture.

La2Hf2O7 ceramics as potential top-coat materials for thermal/environmental barrier coatings

La2Hf2O7 (LH) ceramics with pyrochlore structure have excellent phase stability up to 1600 °C, and far superior sintering resistance as well as comparable mechanical properties to typical 8 wt% yttria-stabilized zirconia (8YSZ). More importantly, they have the coefficients of thermal expansion (CTEs) of 8.76 × 10−6 K−1, lower than that of 8YSZ (10.38 × 10−6 K−1), and thermal conductivities of 1.34 W/m·K at 1000 °C, approximately 40% lower than that of 8YSZ (2.1–2.22 W/m·K). These comprehensive properties promote them as thermal insulation top-coats in thermal/environmental barrier coatings (T/EBCs) on ceramic-matrix composites (CMCs) or top-coats of double-ceramic-layered thermal barrier coatings (DCL-TBCs) on superalloys.

Design of extended surfactant-only EOR formulations for an ultrahigh salinity oil field by using hydrophilic lipophilic deviation (HLD) approach: From laboratory screening to simulation

To address harsh brine issues of mature fields, extended surfactants with outstanding hardness tolerance were selected in this research. The involved surfactant and site crude oil were characterized against the hydrophilic-lipophilic deviation (HLD) theory (i.e., K, Cc and EACN values of the system). A surfactant-only formulation was successfully developed with a predictive tool of the HLD theory based on the microemulsion phase behaviors. The developed surfactant slug can be easily prepared in harsh formation brine of 161,860 mg/L total dissolved solids (TDS) without any water pre-treatment with fast coalescence rate (<30 min) and excellent phase stability. The static IFT between the optimal surfactant brine mixture and site crude oil is 0.004 mN/m at reservoir temperature of 115 °F. The optimal surfactant formulations were further explored in one-dimensional sand pack tests under a representative condition. For further optimization, varying pore volumes of the chosen surfactant slugs were injected after water flooding and sand pack results showed tertiary oil recovery ranging from 52% to 66% of the residual oil (Sor). In addition, to better capture the transport properties of the developed surfactant formulations, the performances of sand packs were theoretically simulated with good match using the software package of UTCHEM in conjunction with the HLD theory. These results show that the correct determined HLD parameters predict the phase behavior in a good accuracy range under ultra-high salinity conditions with extended surfactants. Additionally, the phase behavior tests designed for targeted reservoir salinity could be readily used in salinity scan based simulation packages.

Preparation of monoclinic celsian glass-ceramic by a solid-state reaction of the BaO–Al2O3–SiO2 eutectic glass, BaAl2O4 and SrAl2O4

Abstract A simple, rapid and efficient approach for the monoclinic celsian glass-ceramic fabrication is proposed here. The first step was preparing the amorphous BaO–Al 2 O 3 –SiO 2 glass powder (BAS, with a eutectic temperature of 1400 °C). The second step was fabricating glass-ceramics by the solid-state reaction of the amorphous BAS glass, BaAl 2 O 4 and SrAl 2 O 4 powders. The formation mechanism of monolithic celsian is analyzed via differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The monolithic celsian rapidly formed at 1350 °C with 1.5 h due to the presence of SrAl 2 O 4 . And the complete monolithic celsian glass-ceramic is obtained as soon as the content of SrAl 2 O 4 exceed 0.2 mol. The coefficient of thermal expansion (CTE) is determined from ambient temperature to 1200 °C, and the result indicates that with an increase in the SrAl 2 O 4 content, the CTE of glass-ceramic decreases first and then increases. And the monolithic celsian glass-ceramic containing 0.2 mol SrAl 2 O 4 has the lowest CTE of 4.927 × 10 −6 / o C (20–1200 °C). Besides, the prepared monolithic celsian glass-ceramic has an excellent phase stability at 1600 °C, which is higher than the temperature of the phase transition from monolithic into hexagonal occurring.

Phase structures and thermophysical properties of ZrO2-doped SmTaO4 ceramics

The [Formula: see text] ceramics have excellent high-temperature phase stability and mechanical properties and show great potential for use as next-generation thermal barrier coating (TBC) materials. However, the thermophysical properties of [Formula: see text], especially [Formula: see text]-doped, were not clearly established. The [Formula: see text] ceramics doped with different contents of [Formula: see text] (0%, 2%, 4%, 6%, and 8%) by high-temperature solid-state reaction were studied in this paper. The phase structures and microstructures of the samples were characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and EDS. The thermophysical properties of the samples including specific heat, thermal diffusivity, and thermal conductivity were measured systematically. The results show that [Formula: see text]-doped [Formula: see text] ceramics have a single monoclinic phase, and that [Formula: see text] ion doping does not change the crystal structure. The bandgap of 2% [Formula: see text]-doped [Formula: see text] ceramics was narrow (4.48 eV), indicating that heat is conducted by phonons in ceramics. The [Formula: see text] doped with 2% of [Formula: see text] had lower thermal conductivity [Formula: see text] at [Formula: see text] than [Formula: see text] [Formula: see text] at [Formula: see text]. This indicates that 2% [Formula: see text]-doped [Formula: see text] ceramics have the potential to be employed as TBCs in next-generation gas turbines.

Postsynthesis Spontaneous Coalescence of Mixed-Halide Perovskite Nanocubes into Phase-Stable Single-Crystalline Uniform Luminescent Nanowires.

All inorganic mixed-halide perovskite, CsPb(Br xI1- x)3 (0 ≤ x ≤ 1), nanocrystals possess tunable photoluminescence with high quantum yield in the visible window. However, the photoluminescence degrades rapidly with postsynthetic aging due to the spontaneous ion separation and phase instability. Here we show that the postsynthetic aging of CsPb(Br xI1- x)3 nanocubes spontaneously forms highly uniform single-crystalline nanowires with a diameter of 9 ± 0.5 nm and length of up to several micrometers. The nanowires show bright photoluminescence with an absolute photoluminescence quantum yield of 41%. Rietveld refinement identifies the stable orthorhombic phase of the nanowires, implying a phase transition from the cubic crystallographic phase of the nanocubes during the morphology evolution. Transient absorption spectroscopy reveals a faster excited-state decay dynamic with a large exciton delocalization length in 1D nanowires. Our findings elucidate the insights into the postsynthesis morphology evolution of mixed-halide perovskite nanocrystals leading to luminescent nanowires with excellent crystal phase stability for potential optoelectronic applications.

Outdoor to Indoor Propagation Channel Measurements at 28 GHz

Outdoor to indoor penetration loss is one of the crucial challenges faced at millimeter-wave frequencies. This paper presents the results from 28-GHz channel sounding campaigns performed to investigate the impact of this phenomenon on the wireless propagation channel characteristics in small cell and fixed wireless access scenarios. The measurements are performed with a real-time channel sounder equipped with phased array antennas that allow beam-forming and electronic beam steering for directionally resolved measurements. Thanks to the short measurement time and the excellent phase stability of the system, we obtain both directional and omnidirectional channel power delay profiles without any delay uncertainty. We compare the measured path loss, delay spread, and angular spread for indoor and outdoor receiver locations for two different types of buildings. We find that the penetration loss strongly depends on the angle of incidence, and the scatterers on the outside of the building strongly impact how much power is coupled into the building. Based on the results, we provide statistical models for path loss, delay spread, and angular spread.

Thermophysical properties of Er3Ce7Ta2O23.5 and Dy3Ce7Ta2O23.5 oxides

In this study, two types of rare-earth tantalum oxides, Er3Ce7Ta2O23.5 and Dy3Ce7Ta2O23.5, are synthesised by sintering at 1873 K for 10 h. Their phase composition, microstructure, thermal conductivity, and thermal expansion coefficients are investigated. The obtained oxides exhibit a single-crystal fluorite-type lattice and dense microstructure. Owing to phonon scattering by the complex lattice framework, the large number of oxygen vacancies and substituting atoms, the obtained oxides have lower thermal conductivities than that of YSZ. The thermal expansion coefficient of Dy3Ce7Ta2O23.5 at 1473 K is slightly higher than that of Er3Ce7Ta2O23.5 owing to the larger lattice parameter of Dy3Ce7Ta2O23.5 than that of Er3Ce7Ta2O23.5. Both ceramics have excellent phase stability up to 1473 K.

Phase stabilization design for radio-frequency system of the IMP HIRFL-SSC

Abstract The Radio Frequency (RF) system at the Heavy Ion Research Facility in Lanzhou of the Institute of Modern Physics was upgraded to a digital low-level radio frequency system. The key part is the phase and amplitude negative feedback system based on Digital Signal Processing (DSP) and a Field Programmable Gate Array (FPGA). This paper mainly introduces the design of the phase stabilization loop, including the principle designs for phase stabilization, loop filter design, parameter calculation, and hardware. In order to improve the performance and stability of the system, the loop filter was designed by means of zero-pole cancellation. In this paper, the derivation of the “zero pole cancellation method” is introduced in detail. The implementation structure of the loop filter in the FPGA is an ingenious design that can be applied to RF systems with different cavity loaded quality factor ( Q L ) values. For different RF systems, the parameters of proportional integral (PI) algorithm are fixed, and only one parameter Q L needs to be set. An economical compensation method for the temperature drift in the pick-up cables was designed to improve the control accuracy of the system. The phase control system was tested in long-term stability experiments, and the results show that the system has excellent phase stability over the long term, as well as parasitic phase modulation suppression.