Ultralow lattice thermal transport and considerable wave-like phonon tunneling in chalcogenide perovskite BaZrS3_3

Chalcogenide perovskites provide a promising avenue for non-toxic, stable thermoelectric materials. Here, thermal transport and thermoelectric properties of BaZrS$_3$ as a typical orthorhombic perovskite are investigated. An extremely low lattice thermal conductivity $\kappa_L$ of 1.84 W/mK at 300 K is revealed for BaZrS$_3$, due to the softening effect of Ba atoms on the lattice and the strong anharmonicity caused by the twisted structure. We demonstrate that coherence contributions to $\kappa_L$, arising from wave-like phonon tunneling, leading to a 18 \% thermal transport contribution at 300 K. The increasing temperature softens the phonons, thus reducing the group velocity of materials and increasing the scattering phase space. However, it simultaneously reduces the anharmonicity, which is dominant in BaZrS$_3$ and ultimately improves the particle-like thermal transport. Further, by replacing S atom with Se and Ti-alloying strategy, $ZT$ value of BaZrS$_3$ is significantly increased from 0.58 to 0.91 at 500 K, making it an important candidate for thermoelectric applications

Band Structure Engineering of Interfacial Semiconductors Based on Atomically Thin Lead Iodide Crystals

To explore new constituents in two-dimensional materials and to combine their best in van der Waals heterostructures, are in great demand as being unique platform to discover new physical phenomena and to design novel functionalities in interface-based devices. Herein, PbI2 crystals as thin as few-layers are first synthesized, particularly through a facile low-temperature solution approach with the crystals of large size, regular shape, different thicknesses and high-yields. As a prototypical demonstration of flexible band engineering of PbI2-based interfacial semiconductors, these PbI2 crystals are subsequently assembled with several transition metal dichalcogenide monolayers. The photoluminescence of MoS2 is strongly enhanced in MoS2/PbI2 stacks, while a dramatic photoluminescence quenching of WS2 and WSe2 is revealed in WS2/PbI2 and WSe2/PbI2 stacks. This is attributed to the effective heterojunction formation between PbI2 and these monolayers, but type I band alignment in MoS2/PbI2 stacks where fast-transferred charge carriers accumulate in MoS2 with high emission efficiency, and type II in WS2/PbI2 and WSe2/PbI2 stacks with separated electrons and holes suitable for light harvesting. Our results demonstrate that MoS2, WS2, WSe2 monolayers with very similar electronic structures themselves, show completely distinct light-matter interactions when interfacing with PbI2, providing unprecedent capabilities to engineer the device performance of two-dimensional heterostructures.Comment: 36 pages, 5 figure

Advanced Bifunctional Oxygen Reduction and Evolution Electrocatalyst Derived from Surface-Mounted Metal-Organic Frameworks

Metal‐organic frameworks (MOFs) and their derivatives are considered as promising catalysts for the oxygen reduction (ORR) and oxygen evolution reaction (OER), which are important for many energy provision technologies, such as electrolyzers, fuel cells and some types of advanced batteries. In this work, a “strain modulation” approach has been applied through the use of surface‐mounted NiFe‐MOFs in order to design an advanced bifunctional ORR/OER electrocatalyst. The material exhibits an excellent OER activity in alkaline media, reaching an industrially relevant current density of 200 mA·cm ‐2 at an overpotential of just ~210 mV. It demonstrates operational long‐term stability even at a high current density of 500 mA·cm ‐2 and exhibits the so far narrowest “overpotential window” ΔE ORR‐OER : 0.69 V in 0.1 M KOH with a mass loading being two orders of magnitude lower than that of benchmark electrocatalysts

Bus driver scheduling enhancement: a derandomizing approach for uncertain bus trip times

The bus driver scheduling problems aim to optimally deploy drivers to fulfil published timetables for bus services subject to drivers’ contractual working rules. In this study, we first develop an integer linear programming model for a practical driver scheduling problem. We proceed to formulate another integer linear programming model for the driver scheduling enhancement to incorporate with uncertain bus travel times, which are addressed by an effective derandomizing approach. Moreover, the lower and upper bounds of the developed models are investigated by using the Lagrangian problems with which the solution quality can be evaluated. To assess the efficiency and applicability of the developed models, we conduct a case study based on historical operational data of the bus route #95 in Singapore. Finally, we perform a necessary sensitivity analysis of the bus fleet size and driver workload on the bus driver scheduling problems to identify some valuable managerial insights

Bus driver scheduling enhancement: A derandomizing approach for uncertain bus trip times

Transportmetrica B: Transport Dynamics801200-21

Tunable magnetic flux avalanches triggered by a focalized laser spot

peer reviewedAbstract Magnetic flux avalanches caused by thermomagnetic instabilities are a common phenomenon occuring in type II superconducting films. The unpredictability of these catastrophic events threaten the application of superconducting thin film equipment, such as high-temperature superconducting magnets. In the present work, through the fast Fourier transform method, we numerically investigate artificially triggered flux avalanches in superconducting films by a focalized laser, unveiling new features beyond naturally occurring avalanches. The numerical modeling is validated by reproducing previous experimental results. We investigate the effects of laser irradiation on the nucleation and evolution of flux avalanches for different cases, namely varying the laser irradiation position, laser power, laser-spot size, ramping rate of applied magnetic field and working temperature. We find that the laser irradiation can control and guide the position of flux avalanche at applied magnetic fields with small ramping rate, while the similar guidance effect cannot be observed at high ramping field. We demonstrate that such phenomenon can be tuned by environmental temperature, and the mechanism can be revealed by current crowding and local temperature around the laser spot. Furthermore, by considering a pair of laser spots, we observe two tunable scenarios by the laser power, (i) single flux avalanche triggered at one of laser spots and (ii) double flux avalanches triggered at both laser spots

Tuning the Polaronic Properties of Hybrid Organic-Inorganic Perovskites CH3NH3PbI3 by Mixing Cation

International audienc

Geometry Distortion and Small Polaron Binding Energy Changes with Ionic Substitution in Halide Perovskites

International audienceSolution-processed organometallic perovskites have demonstrated remarkable performances in optoelectronic devices and applications. Despite the extraordinary progress associated with perovskite materials, many questions about the fundamental photophysical processes taking place in these devices, remain open. Here we report the results from an in-depth computational study of small polaron formation, electronic structure, charge density, and reorganization energies using isolated structures. Local lattice symmetry, electronic structure, and electron phonon coupling are interrelated in polaron formation in hybrid halide perovskites. To illustrate these aspects, first principles calculations are performed on CsPbI3, CsSnI3, CsPbBr3, MAPbI3, FAPbI3, MAPbBr3, FAPbBr3, MASnI3, and FASnBr3. This study will focus on how ionic substitution changes the polaron binding energy in the material. It is found that in all cases that hole polaron formation is associated with lattice contraction, while electron polaron formation is associated with lattice expansion