Department of Metallurgical & Materials Engineering

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IIT Jodhpur

Borophene, an elemental metallic Dirac material is predicted to have unprecedented mechanical and electronic character. Need of substrate and ultrahigh vacuum conditions for deposition of borophene restricts its large-scale applications and significantly hampers the advancement of research on borophene. Herein, a facile and large-scale synthesis of freestanding atomic sheets of borophene through a novel liquid-phase exfoliation and the reduction of borophene oxide is demonstrated. Electron microscopy confirms the presence of β12, X3, and their intermediate phases of borophene; X-ray photoelectron spectroscopy, and scanning tunneling microscopy, corroborated with density functional theory band structure calculations, validate the phase purity and the metallic nature. Borophene with excellent anchoring capabilities is used for sensing of light, gas, molecules, and strain. Hybrids of borophene as well as that of reduced borophene oxide with other 2D materials are synthesized, and the predicted superior performance in energy storage is explored. The specific capacity of borophene oxide is observed to be ≈4941 mAh g−1, which significantly exceeds that of existing 2D materials and their hybrids. These freestanding borophene materials and their hybrids will create a huge breakthrough in the field of 2D materials and could help to develop future generations of devices and emerging applications. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

World University root node

Advanced Materials

Freestanding Borophene and Its Hybrids

In the present work, Al-4 wt pct Cu/TiC composite was synthesized by the molten salt route that contains submicron-sized TiC particles in the Al-4 wt pct Cu matrix. The concentration of the TiC particle in the base alloy is 7.5 wt pct. Melt ultrasound treatment was done by remelting the as-cast composite at 1023 K (750 °C) in a view to refine the size of TiC particles to nanoscale and distribute them evenly in the matrix. The microstructure and age hardenability of the untreated and ultrasound-treated composites were investigated. The TiC particles accelerate the precipitation kinetics of CuAl2 phase in Al-4 wt pct Cu alloy. In the present study, the hardness obtained for untreated Al-4 wt pct Cu/TiC composite is 120 VHN within 5 hours of peak aging time, which is higher than the hardness of the monolithic Al-4 wt pct Cu, which is 104 VHN at 35 hours of peak aging time. Melt ultrasound treatment of Al-4 wt pct Cu/TiC composite shows no significant effect on the distribution and refinement of TiC particles in the matrix. However, it partially disintegrates the TiC into Al3Ti and Al4C3 particles. The ultrasound-treated composite showed an improved hardness of about 132 VHN at 5 hours of peak aging, in comparison to that of the untreated composite, by forming denser and homogeneous CuAl2 precipitates. © 2019, The Minerals, Metals & Materials Society and ASM International.

Metallurgical and Materials Transactions B: Process Metallurgy and Materials Processing Science

The Effect of Melt Ultrasound Treatment on the Microstructure and Age Hardenability of Al-4 Wt Pct Cu/TiC Composite

We report a comparative study of the crystal structure and magnetic properties between (001) oriented epitaxial BiFeO3films grown on NdGaO3 and SrTiO3 substrates without any magnetic parasitic phase. The 15nm BiFeO3 film deposited on a NdGaO3 substrate shows substantially high magnetization (∼250 emu/cc) as compared to an identically thick BiFeO3 film (∼100 emu/cc) deposited on a SrTiO3 substrate. Detailed structural analysis revealed that the high magnetization is associated with a monoclinic (Cm) like distortion of the BiFeO3 crystal structure. We corroborated our experimental findings with first principles density functional theory calculations which suggested a saturation magnetization (266 emu/cc) close to the experimentally obtained one and a ferromagnetic ground state with the high spin moment in the Cm phase. © 2019 Institute of Physics Publishing. All rights reserved.

EPL (Europhysics Letters)

Large intrinsic magnetization in an epitaxial BiFeO3/NdGaO3system

Acta Universitatis Upsaliensis

Materials Modelling for Energy Harvesting: From Conversion to Application Through Storage

The design of a suitable electrode is an essential and fundamental research challenge in the field of electrochemical energy storage because the electronic structures and morphologies determine the surface redox reactions. Calcium molybdate (CaMoO4) was synthesized by a combustion route at 300 °C and 500 °C. We describe new findings on the behaviour of CaMoO4 and evaluate the influence of crystallinity on energy storage performance. A wide range of characterization techniques was used to obtain detailed information about the physical and morphological characteristics of CaMoO4. The characterization results enable the phase evolution as a function of the electrode synthesis temperature to be understood. The crystallinity of the materials was found to increase with increasing temperature but with no second phases observed. Molecular dynamics simulation of electronic structures correlated well with the experimental findings. These results show that to enable faster energy storage and release for a given surface area, amorphous CaMoO4 is required, while larger energy storage can be obtained by using crystalline CaMoO4. CaMoO4 has been evaluated as a cathode material in classical lithium-ion batteries recently. However, determining the surface properties in a sodium-ion system experimentally, combined with computational modelling to understand the results has not been reported. The superior electrochemical properties of crystalline CaMoO4 are attributed to its morphology providing enhanced Na+ ion diffusivity and electron transport. However, the presence of carbon in amorphous CaMoO4 resulted in excellent rate capability, suitable for supercapacitor applications. © 2019 The Royal Society of Chemistry.

Nanoscale Advances

Phase evolution in calcium molybdate nanoparticles as a function of synthesis temperature and its electrochemical effect on energy storage

High-strength materials lack a synergistic combination of mechanical properties and corrosion resistance desired for most structural applications. Phase and grain boundary architecturing is done in the material to attain balance in these properties. A friction stir processed Fe 38.5 Mn 20 Co 20 Cr 15 Si 5 Cu 1.5 (Cu-HEA) exhibited excellent mechanical properties and high corrosion resistance in synergy. The excellent mechanical properties were attributed to the controlled transformation of ultrafine γ matrix and ε twinning; whereas good corrosion resistance was due to homogenized fine grained γ microstructure. In short, Cu-HEA design opens a new pathway towards realizing strong and ductile alloys with tunable corrosion resistance by engineering matrix metastability. © 2019 Elsevier Ltd.

Scripta Materialia

Corrosion-resistant high entropy alloy with high strength and ductility

Organic–inorganic hybrid materials are of significant interest owing to their diverse applications ranging from photovoltaics and electronics to catalysis. Control over the organic and inorganic components offers flexibility through tuning their chemical and physical properties. Herein, it is reported that a new organic–inorganic hybrid, [Mn(C 2 H 6 OS) 6 ]I 4 , with linear tetraiodide anions exhibit an ultralow thermal conductivity of 0.15 ± 0.01 W m −1 K −1 at room temperature, which is among the lowest values reported for organic–inorganic hybrid materials. Interestingly, the hybrid compound has a unique 0D structure, which extends into 3D supramolecular frameworks through nonclassical hydrogen bonding. Phonon band structure calculations reveal that low group velocities and localization of vibrational energy underlie the observed ultralow thermal conductivity, which could serve as a general principle to design novel thermal management materials. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Fulltext

Advanced Functional Materials

A 0D Lead-Free Hybrid Crystal with Ultralow Thermal Conductivity

Micromechanical deformation behaviors of E-form fine grain (EFG), E-form coarse grain (ECG), and AZ31 magnesium (Mg) alloys were investigated and compared using a mini-V-bending test. EFG and ECG Mg alloys with a weaker texture showed better bendability compared with AZ31 alloy that has a stronger texture. The evolution of the microstructure and microtexture during the mini-V-bending process was experimentally analyzed via an electron back-scattered diffraction (EBSD) technique. This study was focused on the effect that deformation twinning exerts on the strain localization and crack initiation. The twin bands (TBs) developed in the tension zone of bent specimens found to be closely related to the strain localization and crack initiation during the mini-V-bending process. A resolved shear stress (RSS) criterion and microstructure based crystal plasticity finite element method (CPFEM) were used to theoretically predict the activation of {1012} tension (TTW) and {1011} compression (CTW) twins in Mg alloys under a mini-V-bending process. RSS analysis indicated that EFG and ECG Mg alloys are more favorable for the activity of TTW and less favorable for the activity of CTW when compared with AZ31 Mg alloy during a mini-V-bending process. However, RSS analysis was not effective in quantitatively predicting twin development. The relative activities of six deformation modes, accumulated twin fractions, and accumulated plastic strains were simulated via microstructure-based CPFEM modeling. Compared with RSS analysis, CPFEM precisely explained the twin behavior that has been experimentally observed in ECG and AZ31 Mg alloys. © 2018 Elsevier Ltd.

International Journal of Plasticity

The effect of initial texture on micromechanical deformation behaviors in Mg alloys under a mini-V-bending test

This work presents the performance of the Copper (Cu) based functionally graded coatings (FGCs) when subjected to corrosion in the 3.5 wt% NaCl aqueous solution and sliding wear under the different loads (2, 5, 8 and 10 N). The Cu FGC, with three layers of Cu (each 20 μm thick), has a gradual decrement in the crystallite size from bottom to the top surface. The Cu, Cu-SiC FGC consists of three-layered Cu FGC (each Cu layer 12 μm thick) followed by two layers of Cu-SiC nanocomposite (each 12 μm thick) with a steep increase in the amount of reinforced SiC nanoparticles from 2 to 7 vol% towards the top. A comparison is made among the equally thick (60 μm) electrodeposited FGCs, i.e., Cu FGC and Cu, Cu-SiC FGC, single-layered Cu coating with the finest microstructure (smallest crystallite size) and Cu-SiC nanocomposite coating with 7 vol% SiC. A drastic reduction in the corrosion and wear rate is observed in the Cu and Cu, Cu-SiC FGCs when compared with the same of single-layered Cu and Cu-SiC nanocomposite coatings, respectively. It is also observed that the Cu, Cu-SiC FGC has higher corrosion resistance than the Cu FGC. The Cu, Cu-SiC FGC is found to be more wear resistant than the Cu FGC at high load, while the latter shows lower specific wear rate at low loads. © 2019 Elsevier B.V.