Effect of Heat Treatment Temperature on the Crystallization Behavior and Microstructural Evolution of Amorphous NbCo1.1Sn.

Heat treatment-induced nanocrystallization of amorphous precursors is a promising method for nanostructuring half-Heusler compounds as it holds significant potential in the fabrication of intricate and customizable nanostructured materials. To fully exploit these advantages, a comprehensive understanding of the crystallization behavior of amorphous precursors under different crystallization conditions is crucial. In this study, we investigated the crystallization behavior of the amorphous NbCo1.1Sn alloy at elevated temperatures (783 and 893 K) using transmission electron microscopy and atom probe tomography. As a result, heat treatment at 893 K resulted in a significantly finer grain structure than heat treatment at 783 K owing to the higher nucleation rate at 893 K. At both temperatures, the predominant phase was a half-Heusler phase, whereas the Heusler phase, associated with Co diffusion, was exclusively observed at the specimen annealed at 893 K. The Debye-Callaway model supports that the lower lattice thermal conductivity of NbCo1.1Sn annealed at 893 K is primarily attributed to the formation of Heusler nanoprecipitates rather than a finer grain size. The experimental findings of this study provide valuable insights into the nanocrystallization of amorphous alloys for enhancing thermoelectric properties.

The Effect of Boron (B) and Copper (Cu) on the Microstructure and Graphite Morphology of Spheroidal Graphite Cast Iron.

This study examines the impacts of copper and boron in parts per million (ppm) on the microstructure and mechanical properties of spheroidal graphite cast iron (SCI). Boron's inclusion increases the ferrite content whereas copper augments the stability of pearlite. The interaction between the two significantly influences the ferrite content. Differential scanning calorimetry (DSC) analysis indicates that boron alters the enthalpy change of the α + Fe3C → γ conversion and the α → γ conversion. Scanning electron microscope (SEM) analysis confirms the locations of copper and boron. Mechanical property assessments using a universal testing machine show that the inclusion of boron and copper decreases the tensile strength and yield strength of SCI, but simultaneously enhances elongation. Additionally, in SCI production, the utilization of copper-bearing scrap and trace amounts of boron-containing scrap metal, especially in the casting of ferritic nodular cast iron, offers potential for resource recycling. This highlights the importance of resource conservation and recycling in advancing sustainable manufacturing practices. These findings provide critical insights into the effects of boron and copper on SCI's behavior, contributing to the design and development of high-performance SCI materials.

Thermodynamic patterns duringin-situheating of InAs nanowires encapsulated in Al2O3shells.

Understanding the dynamic thermal behavior of nanomaterials based on their unique physical and chemical properties is critical for their applications. In this study, the thermal behavior of single-crystalline InAs nanowires in an amorphous Al2O3shell was investigated by conductingin situheating experiments in a transmission electron microscope. Two different thermodynamic patterns were observed during thein situheating experiments: (1) continuous vaporization and condensation simultaneously at temperatures lower than 838.15 K, and (2) pure evaporation at temperatures higher than 878.15 K. During the simultaneous condensation and vaporization in closer areas in a single InAs nanowire, the front edge of the vaporization was flat, while that of the condensation actively changed with time and temperature. Pure vaporization was conducted via layer-by-layer evaporation followed by three-dimensional vaporization at the final stage. The thermal behaviors of the InAs nanowires were demonstrated from a thermodynamic point of view.

Coprecipitation Temperature Effects of Morphology-Controlled Nickel Hexacyanoferrate on the Electrochemical Performance in Aqueous Sodium-Ion Batteries.

Coprecipitation effortlessly fabricated nickel hexacyanoferrate (NiHCF) with outstanding rate capability and stability for aqueous batteries. Citrate-aided coprecipitation decelerated the crystallization, assembling cubic-shaped powder based on separation between nucleation and growth. This study revealed that coprecipitation temperature determined the electrochemical performance. With lower temperatures, smaller particles with more water were formed by predominant nucleation, resulting in low crystallinity and capacity of 58 mAh g-1 . Expanded surface area reduced electrode/electrolyte interface charge-transfer resistance and showed excellent rate capability (79 % of initial capacity at 100 C-rate). However, poor cyclability was obtained. At elevated temperatures, nuclei growth and dehydration occurred, and thus highly crystalline large particles were formed. In turn, NiHCF delivered excellent capacity of 76 mAh g-1 at 1 C-rate but exhibited inferior rate performance because of longer diffusional path. Meanwhile, normal coprecipitation at 70 °C induced irregular-shaped tiny particles, presenting 93 % retention of initial capacity at 100 C-rate.

Formation of arsenic clusters in InAs nanowires with an Al2O3 shell.

An in-depth understanding of thermal behavior and phase evolution is required to apply heterostructured nanowires (NWs) in real devices. The intermediate status during the vaporization process of InAs NWs in an Al2O3 shell was studied by conducting quenching during in situ heating experiments, using a transmission electron microscope. The formation of As clusters in the amorphous Al2O3 shell was confirmed by analyzing the high-angle annular dark field images and energy-dispersive X-ray spectra. The As clusters existed independently in the shell and were also observed at the end of the InAs pieces obtained after quenching. The formation process of the As clusters was demonstrated from a theoretical perspective. Moreover, an ab initio molecular dynamics simulation (AIMD) was conducted to study the atomic and molecular behaviors.

Anisotropic atomistic evolution during the sublimation of polar InAs nanowires.

Sublimation is an interesting phenomenon that is frequently observed in nature. The thermal behavior of InAs NWs with As-face polarity and the [1[combining macron]1[combining macron]1[combining macron]] growth direction of the zinc blende structure were studied by using in situ transmission electron microscopy (TEM). In this study, the anisotropic morphological and atomistic evolution of InAs nanowires (NWs) was observed during decomposition. Two specific phenomena were observed during the continuous heating of the NWs as observed using the TEM: the decomposition of the InAs NWs around 380 °C, much lower than the melting temperature, and the formation of particular crystallographic facets during decomposition. The low decomposition temperature is related to vaporization under the vacuum conditions of the TEM. The anisotropic decomposition of the InAs NWs during heating can be explained based on the polarity and the surface energy difference of the zinc blende structure of InAs. For example, the decomposition along the [111] direction (that is, the indium-atom-terminated plane) was continuous, resulting in a few high-index planes, for example, (022), (3[combining macron]1[combining macron]1[combining macron]), and (200), whereas that in the opposite direction (the [1[combining macron]1[combining macron]1[combining macron]] direction) occurred abruptly with the formation of ledges and steps on the (1[combining macron]1[combining macron]1[combining macron]) planes, accompanied by the generation of small grooves on the surface of the NWs. Finally, density functional theory calculations were conducted to understand the sublimation of the InAs NWs from a theoretical point of view. This study is meaningful that it provides an insight into the microstructural evolution of polar nanomaterials during heating by theoretical and experimental approaches.

Electromechanical Properties and Spontaneous Response of the Current in InAsP Nanowires.

The electromechanical properties of ternary InAsP nanowires (NWs) were investigated by applying a uniaxial tensile strain in a transmission electron microscope (TEM). The electromechanical properties in our examined InAsP NWs were governed by the piezoresistive effect. We found that the electronic transport of the InAsP NWs is dominated by space-charge-limited transport, with a I ∞ V2 relation. Upon increasing the tensile strain, the electrical current in the NWs increases linearly, and the piezoresistance gradually decreases nonlinearly. By analyzing the space-charge-limited I-V curves, we show that the electromechanical response is due to a mobility that increases with strain. Finally, we use dynamical measurements to establish an upper limit on the time scale for the electromechanical response.