Department of Metallurgical & Materials Engineering

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IIT Jodhpur

We demonstrate the use of dispersed graphene oxide (DGO) as dye adsorbents for the degradation of methylene blue (MB) dye. Reduction in absorbance of MB solution in the presence of DGO is studied using optical spectroscopy. A threshold concentration of 0.125 ppm of DGO is found to be required for effective degradation of 1ppm MB solution in water.

World University root node

Materials Today: Proceedings

Dye adsorption behavior of graphene oxide

The inherent spin-orbit coupling (SOC) effect in non-centrosymmetric crystal structure has laid the foundation of Rashba splitting phenomena. This Rashba splitting directly governs the charge carrier recombination, which eventually controls the carrier lifetime and diffusion length and therefore the solar cell efficiency for such hybrid perovskite materials. In this work, we have performed a rigorous structural search prediction of the mixed cation-mixed halide hybrid perovskites FA0.83MA0.17Pb(I0.83Br0.17)3 and FA0.875MA0.125Pb(I0.875Br0.125)3, which are the two nearest neighbor structures of record efficiency (22.1%) holder FA0.85MA0.15Pb(I0.85Br0.15)3 in the structural composition phase space. We have found the prediction routes for a structural search such as the mixed perovskite structure govern the Rashba splitting energy value, depending on whether it has been predicted from FPI (FAPbI3) or MPB (MAPbBr3) as parent structure, which are leading to the mixed phase FA0.83MA0.17Pb(I0.83Br0.17)3 and FA0.875MA0.125Pb(I0.875Br,0.125)3 respectively. The strong dependency of the splitting energy on the structural phase evolution along with the stoichiometry and space group is also observed, where in the mixed phase, 0.045 difference in concentration could lead to a remarkable difference in the splitting energy, which is more pronounced in the valence band as compared to the conduction band. We have also determined the Goldschmidt tolerance factor to envisage structural stability of the newly predicted crystal structures based on the corresponding chemical route in the composition phase space. Copyright © 2019 American Chemical Society.

ACS Applied Energy Materials

Rashba Triggered Electronic and Optical Properties Tuning in Mixed Cation–Mixed Halide Hybrid Perovskites

We investigated Li-doped carbon nanotubes (CNTs) as a promising hydrogen storage media. In this computational model, we considered isolated lithium atom adsorbed on a CNT wall as an adsorption site for hydrogen. We focused on the influence of size effects on the structural and energetic characteristics of CNT(n,n)@Li+kH2 complexes where n = 5, 7, 9; k = 1,..., 6; Nc = 4, 5, 6 (Nc is translation length of CNT, expressed in terms of a number of CNT unit cells). We proved that modeled CNT length substantially influences internal sorption of Li and hydrogen on the narrow tube (5,5), which subsequently alters the adsorption energies of H2 molecules and causes the deformation of the carbon framework. Moreover, the size effects are not pronounced in the case of external sorption for all considered CNT translation lengths and diameters. We have not observed any noticeable qualitative difference between internal and external hydrogen sorption in the nanotube wider than CNT(5,5). In the case of external adsorption on all considered nanotubes, doping with Li increases hydrogen adsorption energies of up to four H2 molecules by 100 meV in comparison with pure CNTs. And the local density approximation estimations (-250 meV/H2) of adsorption energy on Li-decorated CNTs exceed the lowest requirement proposed by the U.S. Department of Energy (200 meV/H2). In the case of internal sorption on Li-functionalized tubes, the generalized gradient approximation also gives hydrogen adsorption energies in the desired range of 200-600 meV/H2. However, steric hindrances could prevent sufficient hydrogen uptakes (less than 2 wt % inside CNT(5,5)). We believe that our findings on the size effects are important for estimation of CNT's hydrogen storage properties. © 2019 American Chemical Society.

ACS Applied Nano Materials

Li-functionalized carbon nanotubes for hydrogen storage: importance of size effects

Li-ion batteries are key electric energy storage devices due to high energy density and long cycling lifetime, being widely used in portable electronic devices and large scale systems. In spite of stable cycling performance, the graphite electrode suffers from a low capacity. It is demonstrated in this context that oxygen doping makes MgCl2 electrochemically active. Importantly, the doped structure delivers a high capacity of 941 mAh g−1 for the bulk and 1098 mAh g−1 for the monolayer. The diffusion barrier is calculated to be lower than 0.6 eV. Hexagons and octahedrons composed of Li and Cl atoms are gradually formed with increasing Li coverage, breaking the Mg–Cl bonds. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Physica Status Solidi (B) Basic Research

Oxygen Doping Enhanced Lithiation in MgCl2 for Battery Applications

Near-α (VT 20) and α + β (Ti–6Al–4V) Ti alloys having similar initial grain morphology with equiaxed α in transformed β were subjected to microstructure refinement processes by thermohydrogen processing (THP) and caliber rolling (CR), respectively. The microstructure analysis after THP and CR of the alloys revealed the change in morphology and refinement of microstructure. The microstructure analysis after initial constant strain rate tests at 850 °C exhibited needle-like morphology for THP alloy, whereas it was equiaxed for as-received VT 20 and CR 750 alloy. An additional attempt was made on the CR alloy towards determining the magnitudes of strain rate sensitivity index (m) through differential strain rate test conducted over a number of strain rate change cycles at 850 °C and 927 °C. Both THP and CR processes resulted in grain refinement and the change in morphology of microstructure. © 2019, The Indian Institute of Metals - IIM.

Transactions of the Indian Institute of Metals

Effects of Temporary Alloying and Severe Plastic Deformation on Microstructure Evolution and Mechanical Properties of Ti-Alloys: A Comparative Study

The mechanical properties of titanium alloys are highly sensitive to the morphology, topology, and dimensions of the α and β phases present in the material. An attempt has been made here to systematically evaluate the effect of heat treatment parameters, that is, solution treatment temperature and cooling rate, on the microstructure and room temperature tensile properties of a near-α titanium alloy IMI 834. Seven important microstructural features that affect the mechanical properties of a near-α titanium alloy IMI 834 processed in the α + β regime were quantified and used to establish a direct microstructure-mechanical property correlation with the aid of artificial neural network. The established neural network has been used to evaluate and understand the effect of each individual microstructural feature on the tensile property of the material. The results obtained are presented and discussed here. © 2019 by ASTM.

Materials Performance and Characterization

Correlation between microstructural features and tensile properties in near-α titanium alloy IMI 834 processed in the α + β regime

The study has examined the work hardening characteristics and damage mechanisms of a newly developed carbide-free bainitic steel. These are correlated with the microstructural constituents using the established empirical equations and the experimental findings. Carbide-free bainitic steel has shown primarily three stages of deformation in modified Crussard-Jaoul analysis, which best describes the work hardening behaviour. Plastic deformation of retained austenite precedes the deformation of bainitic ferrite. The blocks of retained austenite transform to strain induced martensite at lower strain levels than the films of retained austenite. With increasing strain, cross slip assisted dynamic recovery, and sub-grain formation become predominant in bainitic ferrite. Although early void initiation occurs at the non-metallic inclusions, these do not play a significant role in the final fracture. Void initiation and splitting of phase boundaries due to strain incompatibility, decohesion of prior austenite grain boundaries and cracking of martensitic-austenitic constituents are the main damaging mechanisms. © 2019 Elsevier B.V.

Materials Science and Engineering: A

Work hardening behaviour and damage mechanisms in carbide-free bainitic steel during uni-axial tensile deformation

Physical Review B

Spin-entropy induced thermopower and spin-blockade effect in CoO

We demonstrate the use of graphene oxide (GO) in making p-n junctions. Two variants of p-n junctions made using GO are reported. In one of the variant, we deposit a layer of GO on aluminium zinc oxide (AZO) and study the junction properties using current-voltage (I-V) characteristics. In the other variant, we reduce the GO deposited on a glass substrate to obtain reduced graphene oxide (rGO) and make a GO-rGO bilayer p-n junction. The photovoltaic response of this GO-rGO bilayer is reported. These two approaches provide an inexpensive route to make p-n junctions for realizing GO based electronic devices.

Graphene Oxide based p-n junctions

In this study, we investigated the detwinning phenomenon of in-plane compressed E-form magnesium (Mg) alloy sheet systematically using in situ tensile test combined with electron backscattered diffraction (EBSD) technique. Microstructure and microtexture evolutions were analyzed at different tensile strains during the in situ tensile test. The detwinning phenomenon in E-form Mg alloy was found to be linked to both twin boundary mobility and the interaction of their boundaries with dislocations. The pre-compressed sheet of E-form Mg alloy effectively accommodated the thickness direction strains generated during the in situ tensile test. The effect of detwinning on formability and mechanical behavior of the E-form Mg alloy was also examined. EBSD results indicate that most of the deformation twins formed during in-plane compression were removed when the load is reversed during the in situ tensile test. © 2019, The Minerals, Metals & Materials Society.