Department of Metallurgical & Materials Engineering

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IIT Jodhpur

A better understanding of the electronic structure of perovskite materials used in photovoltaic devices is essential for their development and optimization. In this investigation, synchrotron-based photoelectron spectroscopy (PES) was used to experimentally delineate the character and energy position of the valence band structures of a mixed perovskite. The valence band was measured using PES with photon energies ranging from ultraviolet photoelectron spectroscopy (21.2 eV) to hard X-rays (up to 4000 eV), and by taking the variation of the photoionization cross sections into account, we could experimentally determine the inorganic and organic contributions. The experiments were compared to theoretical calculations to further distinguish the role of the different anions in the electronic structure. This work also includes a thorough study of the valence band maximum and its position in relation to the Fermi level, which is crucial for the design and optimization of complete solar cells and their functional properties. © 2017 American Chemical Society.

World University root node

The Journal of Physical Chemistry C

Valence level character in a mixed perovskite material and determination of the valence band maximum from photoelectron spectroscopy: variation with photon energy

Ceramic composite coatings of alumina (Al2O3), alumina-micro-ceria (µ-CeO2) and alumina-micro-ceria-multiwalled carbon nanotubes (MWNTs) were processed using plasma spraying. X-ray diffraction analysis reveals evolution of new phases-namely, γ-alumina and non-stoichiometric phases of alumina. Reinforcement of 3 wt% MWNTs has been shown to restrict the degeneration of ceria and synergistically conserve the γ-phase. The catalytic ability of alumina-micro-ceria-MWNT has been confirmed from the nitric oxide (NO) oxidation reaction. An observed 25% conversion ability arises at 350°C in a 10% oxygen (O2) environment, which indicates that ceria inclusion increases the oxidation of nitric oxide. Thus, the alumina-micro-ceria-MWNT composite can serve as a potential catalyst for nitric oxide conversion. © 2017 ICE Publishing: All rights reserved.

Nanomaterials and Energy

Catalytic effects of CeO2 and carbon nanotube addition in plasma-sprayed Al2O3

Conducting polymers are being considered promising candidates for sustainable organic batteries mainly due to their fast electron transport properties and high recyclability. In this work, the key properties of polythiophene and polypyridine have been assessed through a combined theoretical and experimental study focusing on such applications. A theoretical protocol has been developed to calculate redox potentials in solution within the framework of the density functional theory and using continuous solvation models. Here, the evolution of the electrochemical properties of solvated oligomers as a function of the length of the chain is analyzed and then the polymer properties are estimated via linear regressions using ordinary least square. The predicted values were verified against our electrochemical experiments. This protocol can now be employed to screen a large database of compounds in order to identify organic electrodes with superior properties. © the Owner Societies 2017.

Physical Chemistry Chemical Physics

Assessing the electrochemical properties of polypyridine and polythiophene for prospective applications in sustainable organic batteries

ISSS Journal of Micro and Smart Systems

Sensitive and selective detection of copper ions using low cost nitrogen doped carbon quantum dots as a fluorescent sensing plateform

The potential of high-entropy alloys (HEAs) to exhibit an extraordinary combination of properties by shifting the compositional regime from the corners towards the centers of phase diagrams has led to worldwide attention by material scientists. Here we present a strong and ductile non-equiatomic HEA obtained after friction stir processing (FSP). A transformation-induced plasticity (TRIP) assisted HEA with composition Fe50Mn30Co10Cr10 (at.%) was severely deformed by FSP and evaluated for its microstructure-mechanical property relationship. The FSP-engineered microstructure of the TRIP HEA exhibited a substantially smaller grain size, and optimized fractions of face-centered cubic (f.c.c., γ) and hexagonal close-packed (h.c.p., ϵ) phases, as compared to the as-homogenized reference material. This results in synergistic strengthening via TRIP, grain boundary strengthening, and effective strain partitioning between the γ and ϵ phases during deformation, thus leading to enhanced strength and ductility of the TRIP-assisted dual-phase HEA engineered via FSP. © 2017 The Author(s).

Fulltext

Scientific Reports

Enhanced strength and ductility in a friction stir processing engineered dual phase high entropy alloy

Water splitting driven by electricity or sunlight is one of the most promising ways to address the global terawatt energy needs of future societies; however, its large-scale application is limited by the sluggish kinetics of the oxygen evolution reaction (OER). NiFe-based compounds, mainly oxides and hydroxides, are well-known OER catalysts and have been intensively studied; however, the utilization of the synergistic effect between two different NiFe-based materials to further boost the OER performance has not been achieved to date. Here, we report the rapid conversion of NiFe double hydroxide into metallic NiFeP using PH3 plasma treatment and further construction of amorphous NiFe hydroxide/NiFeP/Ni foam as efficient and stable oxygen-evolving anodes. The strong electronic interactions between NiFe hydroxide and NiFeP significantly lower the adsorption energy of H2O on the hybrid and thus lead to enhanced OER performance. As a result, the hybrid catalyst can deliver a geometrical current density of 300 mA cm-2 at an extremely low overpotential (258 mV, after ohmic-drop correction), along with a small Tafel slope of 39 mV decade-1 and outstanding long-term durability in alkaline media. © 2017 American Chemical Society.

ACS Energy Letters

Amorphous NiFe-OH/NiFeP electrocatalyst fabricated at low temperature for water oxidation applications

The effect of hydrogen on high temperature flow behavior of VT20, a near α-Ti alloy, was studied using differential strain rate compression tests. Hydrogen level was varied from 0.0015 to 0.36 wt%. Strain rate jump tests were carried out over the strain rate and temperature ranges of 10−3–10−1 s−1 and 600–947 °C, respectively. The addition of hydrogen increased the volume fraction of β phase, decreased the grain size and lowered the flow stress up to test temperature of 900 °C. The values of apparent strain rate sensitivity (m) and activation energy for deformation (Q) were found to vary from 0.03 to 0.46 and 176–382 kJ/mol, respectively, depending on strain rate, test temperature and hydrogen level. With increasing hydrogen content the peak strain rate sensitivity shifted to lower temperatures. The values obtained for m (≥0.30) and Q (~176 kJ/mol) suggested that the deformation mechanism is the grain boundary sliding accommodated by lattice diffusion. The lower values of m (0.20–0.25) suggested dislocation climb as the deformation mechanism and the further decrease in m and increase in Q suggested power law breakdown. © 2016 Elsevier B.V.

Materials Science and Engineering A

Effect of hydrogen on high temperature flow behavior of near α-Ti alloy

In this paper, we discuss the effect of potential difference and current density on the crystal morphologies of copper electrodeposits. Their individual roles have been identified by creating a passivation layer in situ at the anode during deposition, which instantaneously reduces the current density in the system while maintaining a high potential difference. It is observed that the crystal shape is decided by the potential difference and current density determines the rate at which that shape is achieved. In a copper system, at high overpotentials, coherent twin boundaries are formed due to their low formation energy as compared to high angle grain boundaries, high index surface planes, etc. Without the presence of any foreign species like H2 bubbles during the crystallization process, the slowest growth direction is identified to be &lt;1 1 1&gt;. The passivation layer is formed due to a pH distribution in the electrolyte caused by the high electric field. A new methodology to explain the formation of the passivation layer is proposed, which is performed by analyzing the current transients generated using Kirchhoff's Laws. © 2017 American Chemical Society.

Crystal Growth and Design

Effect of Anodic Passivation at High Applied Potential Difference on the Crystal Shape and Morphology of Copper Electrodeposits: Thermodynamics and Kinetics of Electrocrystallization

BT3-1 (Ti-6Al-2.5Mo-1.5Cr-0.5Fe-0.3Si) is a α+β titanium alloy that has been developed to meet the mechanical property requirements up to a temperature of 450 °C. The high temperature deformation behaviour of the material was evaluated by carrying out isothermal hot compression tests in the α+β, near β and β phase fields with a range of constant true strain rates. Using the flow behaviour data, processing map based on dynamic materials modeling was developed and the various domains in the map were correlated with microstructural mechanisms observed in the material. The material exhibits superplasticity when processed in the α+β regime while it experiences dynamic recrystallization (DRX) of β phase when processed above the β transus. When deformed close to the β transus, the material exhibits partial β recrystallization where the migrating boundaries of the β phase are pinned by the fine globular α particles distributed in the matrix. The activation energy and activation volume for deformation was evaluated to ascertain the rate controlling deformation mechanism. The results obtained are presented and discussed here © 2016 Elsevier B.V.

On the high temperature deformation behaviour of titanium alloy BT3-1

An attempt was made to develop ultrafine grained Al-Graphite composites through friction stir processing (FSP). Al-Graphite composite was initially prepared using stir casting technique and it subsequently subjected to ultrasonic treatment prior to solidification. The results showed that the ultrasonic treatment during the composite preparation reduced the porosity, graphite particles' agglomeration and the graphite particles' size in the composite. The ultrasonic treated Al-Graphite composite was subjected to a single pass FSP at a constant tool rotational speed of 1600 rpm with three different feed rates, of 20 mm/min, 40 mm/min and 60 mm/min. The microstructure of FSPed composites within the stir zone exhibited a fine recrystallized grain structure due to the combined effect of severe plastic deformation and frictional heat generation during FSP. After the single pass of FSP, the grain size of the composite was reduced from 150 μm to 14 μm, 6 μm and 0.5–1 μm for the tool transverse speeds of 20 mm/min, 40 mm/min and 60 mm/min, respectively. Distribution of graphite particles in Al matrix was significantly improved after FSP process due to the strong stirring action of the rotating tool. Most importantly, microstructural analysis suggested that a substantial reduction in graphite particles' size could be achieved with the aid of FSP process. FSPed Al-Graphite samples exhibited superior hardness as compared to the unprocessed composites due to the uniform dispersion of fine graphite particles in ultra-fine grain structure. In a nutshell, ultrafine grained Al-Graphite composites with uniform dispersion of Graphite nano particles were produced using a single pass FSP process. © 2017 Elsevier B.V.