Rational Electronic and Structural Designs Advance BiCuSeO Thermoelectrics

In this work, a record high thermoelectric figure-of-merit ZT of 1.6 ± 0.2 at 873 K in p-type polycrystalline Bi_0.94Pb_0.06CuSe_1.01O_0.99 by a synergy of rational band manipulation and novel nanostructural design is reported. First-principles density functional theory calculation results indicate that the density of state at the Fermi level that crosses the valence band can be significantly reduced and the measured optical bandgap can be enlarged from 0.70 to 0.74 eV by simply replacing 1% O with 1% Se, both indicating a potentially reduced carrier concentration and in turn, an improved carrier mobility and a boosted power factor up to 9.0 µW cm⁻¹ K⁻². Meanwhile, comprehensive characterizations reveal that under Se-rich condition, Cu₂Se secondary microphases and significant lattice distortions triggered by Pb-doping and Se-substitution can be simultaneously achieved, contributing to a reduced lattice thermal conductivity of 0.4 W m⁻¹ K⁻¹. Furthermore, a unique shear exfoliation technique enables an effective grain refinement with higher anisotropy of the polycrystalline pellet, leading to a further improved power factor up to 10.9 µW cm⁻¹ K⁻² and a further reduced lattice thermal conductivity of 0.30 W m⁻¹ K⁻¹, which gives rise to record high ZT.     

Simultaneous growth of well-aligned diamond and graphitic carbon nanostructures through graphite etching

A hot filament chemical vapor deposition process based on hydrogen etching of graphite has been developed to synthesize diamond and graphitic carbon nanostructures. Well-aligned diamond and graphitic carbon nanostructured thin films have been synthesized simultaneously on differently pretreated silicon substrates in a pure hydrogen plasma. Graphitic nanocones, diamond nanocones and carbon nanotubes were selectively grown on uncoated, diamond and nickel pre-coated silicon substrates, respectively, in a single deposition process. The nanocones are solid cones with submicron scale roots and nanometer-size sharp tips. The nanotubes are hollow tubes with outer diameter of approximately 50 nm. The orientation of the well-aligned carbon nanostructures depends on the direction of the electric field at the samples surface. Nucleation and growth of diamond on the nanocones were further investigated under similar conditions without plasma. Diamond nanocomposite films have been obtained by depositing a nanocrystalline diamond film on the layer of diamond nanocones.     

Nanoscale origins of small hysteresis and remnant strain in Bi0.5Na0.5TiO3-based lead-free ceramics

BiAlO₃-doped Bi_0.5Na_0.5TiO₃-Bi_0.5K_0.5TiO₃ (BA-doped BNT-BKT) ceramics are greatly concerned due to their sufficient electric-field-induced strain with small hysteresis and remnant strain for high precision positioning devices and other actuators. In this paper, the structural analysis especially the high-resolution transmission electron microscope (HRTEM) is used to reveal the origin of excellent properties obtained in 0.96(0.75BNT-0.25BKT)-0.04BA, which exhibits a large strain of 0.21% at ～70 kV/cm, a small strain hysteresis of only 24% and a near-zero remnant strain. Using HRTEM, the antiferroelectric nano-domains composited by three variants of in-phase a⁰a⁰c⁺ octahedral tilting coexisted with the remnant ferroelectric nano-domains of anti-phase a^?a^?a^? octahedral tilting are directly identified. Then a continuous tilting model is proposed to interpret the gradually transitional tilting involving nano-domains leading to the small hysteresis and near-zero remnant strain. The findings may pave a way for further optimizing the properties through creating stable antiferroelectric nano-domains in BNT-based ceramics and the analogues.     

Nano‐engineered nickel catalysts supported on 4‐channel α‐Al2O3 hollow fibers for dry reforming of methane

A nickel (Ni) nanoparticle catalyst, supported on 4‐channel α‐Al₂O₃ hollow fibers, was synthesized by atomic layer deposition (ALD). Highly dispersed Ni nanoparticles were successfully deposited on the outside surfaces and the inside porous structures of hollow fibers. The catalyst was employed to catalyze the dry reforming of methane (DRM) reaction and showed a methane reforming rate of 2040 Lh^?1gNi^?1 at 800°C. NiAl₂O₄ spinel was formed when Ni nanoparticles were deposited on alpha‐alumina substrates by ALD, which enhanced the Ni‐support interaction. Different cycles (two, five, and ten) of Al₂O₃ ALD films were applied on the Ni/hollow fiber catalysts to further improve the interaction between the Ni nanoparticles and the hollow fiber support. Both the catalyst activity and stability were improved with the deposition of Al₂O₃ ALD films. Among the Al₂O₃ ALD coated catalysts, the catalyst with five cycles of Al₂O₃ ALD showed the best performance. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2625–2631, 2018     

Reducing Pb concentration in α-CsPbI3 based perovskite solar cell materials via alkaline-earth metal doping: A DFT computational study

Full inorganic perovskite solar cell materials have shown significantly improved performance in recent years. To reduce their reliance on Pb, alkaline-earth metal ions (Ba, Sr, Ca, and Mg) have been employed for the exchange of Pb in α-CsPbI₃. In this study, density functional theory calculations were used to study the structures, band structures, and optical absorption properties of these alkaline-earth-metal doped α-CsPbI₃ materials with CASTEP (2017) and Dmol³ (2017). The calculation also investigated the effect of spin-orbit coupling. Alkaline-earth metal doping can enlarge the band gap of α-CsPbI₃ and convert α-CsPbI₃ from a direct gap semiconductor to an indirect gap semiconductor. After alkaline-earth metal doping, the sun-light absorption increased. Among all the alkaline-earth metals studied here, Mg-doped α-CsPbI₃ showed the most improved indirect gap band structure, ideal band gap (compared to α-CsPbI₃), and sun-light absorption.     

Fabrication of a high-performance film based borosilicate glass/Al2O3 ceramics for LTCC application

The present work was initiated aiming at developing a high-performance film for LTCC application using a kind of polymeric dispersant in tape casting process of borosilicate-based glass/Al₂O₃ ceramics. The dispersion mechanism of the polymeric dispersant with the powders was analyzed in detail and the optimal amount of the dispersant addition was also determined through the sedimentation experiment. Its effects on the compactness, tensile strength and surface roughness of the films were analyzed. In addition, the sintering and microwave properties of the composite fired at 850 °C were also determined. For the application of tape technology, the co-firing compatibility between the composite and Ag electrodes at 850 °C was also verified. After testing and verification with different qualitative and quantitative instruments, a flexible film optimized by 1.5 wt% polymeric dispersant achieved the best overall performance.     

Preparation,thermal and phase evolution and functional properties of non-stoichiometric strontium-doped lanthanum manganite perovskite ceramics

Powders of (La_0.85Sr_0.15)_0.98MnO_3-δ (LSM85) and (La_0.80Sr_0.20)_0.98MnO_3-δ (LSM80) perovskites have been synthesized and characterized in detail, and then sintered to evaluate their electrical and magnetic properties at low temperatures and at near room temperature. Microstructural observations/analyses after the dilatometric essays show that the perovskites have compositions that deviate from the nominal ones. Furthermore, magnetic characterization of both samples reveals a ferromagnetic behavior with a Curie temperature above 300 K for LSM80 and of 260 K for LSM85. In addition, LSM85 is insulator from 15 up to 300 K, whereas LSM80 is metallic up to 160 K and insulator up to 300 K. This significant discrepancy of behaviour is attributable to structural and compositional differences between the two perovskites.     

REACTKIN—a program for modelling the chemical reactions in electrolytes solutions

In this paper, REACTKIN, the new computer program for modelling the kinetics of complex homogeneous chemical reactions in electrolyte and non-electrolyte solutions has been presented. This program makes possible the creation of a model of a reaction in the convenient form of a graph as well as simulating the course of a reaction on the basis of the model created. REACTKIN allows the determination of the rate constants of elementary reactions using experimental kinetic data concerning the influence of the ionic strength of the solution. The program REACTKIN can be of importance in the studies of multi-step chemical reactions in electrolyte solutions as well as in chemistry education.     

Calculation of phase diagrams for the metastable Al-Fe phases forming in direct-chill (DC)-cast aluminum alloy ingots

In direct-chill (DC)-cast 1xxx-and 5xxx-series Al sheet-ingots, the presence of mainly Fe and some Si, and cooling rates increasing from ≤1 °C/s in the ingot center to ~20 °C/s near the surface cause the formation of metastable intermetallic Al₆Fe and Al_mFe compounds in addition to the stable Al₃Fe, and hence the fir-tree defect. Since the Al-Fe and Al-Fe-Si phase diagrams are not useful in predicting the metastable phase formation, a binary phase diagram study was conducted to calculate the Al-Al₆Fe and Al-Al_mFe metastable phase equilibria using a thermodynamic software and an Al-alloy database. The Al-Al₃Fe phase diagram was calculated using the existing Gibbs energy data which gives the eutectic point at 1.85wt% Fe and the eutectic temperature as 654 °C. The missing Gibbs energy data for the metastable phases were estimated using substitutional and graphical methods and the phase diagrams were calculated. In the Al-Al₆Fe phase diagram, the eutectic temperature is depressed from 654 °C (equilibrium) to 648 °C and the eutectic point is shifted from 1.85wt% Fe to 3.4wt% Fe. In the Al-Al_mFe phase diagram, the eutectic temperature is 643 °C and the eutectic point is at 4.6wt% Fe. The verification of the calculated eutectic temperatures was carried out by DSC measurements which were conducted on samples removed from Al-Fe alloy rods directionally grown in a Bridgman-type solidification furnace. A good agreement is observed between the calculated and measured values.