Ashok Arya - Academia.edu (original) (raw)

Papers by Ashok Arya

Inorganic chemistry, Jan 21, 2011

A series of Mn-substituted BaMgF(4) samples have been synthesized by a hydrothermal route. X-ray ... more A series of Mn-substituted BaMgF(4) samples have been synthesized by a hydrothermal route. X-ray diffraction study reveals that the products are monophasic in nature. Scanning electron microscopy (SEM) and energy-dispersive spectrometry (EDS) studies were carried out to investigate the morphology and stoichiometry for these compounds. X-ray photoelectron spectroscoy (XPS) and electron spin resonance (ESR) studies were done to confirm the oxidation state of dopant ion. Room temperature ferromagnetism was observed on Mn substitution at the Mg site in BaMgF(4) samples. The saturation magnetization increases initially, shows a peaking effect, and then decreases with further increase in Mn concentration in BaMg(1-x)Mn(x)F(4) (0.0 ≤ x ≤ 0.15). However, ferroelectricity was found to decrease with an increase in Mn concentration in the series of investigated BaMg(1-x)Mn(x)F(4) (0.0 ≤ x ≤ 0.15) samples. First-principle calculations, using the projector augmented wave potentials on Mn-substit...

CrystEngComm, 2018

Molecular reorientations result in structural phase transition in trans-PtCl2(PEt3)2 under pressu... more Molecular reorientations result in structural phase transition in trans-PtCl2(PEt3)2 under pressure, leading to a hydrogen bond assisted supramolecular architecture.

Consiglio Nazionale delle Ricerche (CNR). Biblioteca Centrale / CNR - Consiglio Nazionale delle R... more Consiglio Nazionale delle Ricerche (CNR). Biblioteca Centrale / CNR - Consiglio Nazionale delle RichercheSIGLEITItal

EGU General Assembly Conference Abstracts, Apr 1, 2016

Journal of Nuclear Materials, 2021

Journal of Nuclear Materials, 2019

h i g h l i g h t s Ni-based alloys exposed to molten FLiNaK salt under air atmosphere develop pa... more h i g h l i g h t s Ni-based alloys exposed to molten FLiNaK salt under air atmosphere develop patches of mixed oxides at surface. Alloy 690 and Alloy 693 developed mixed oxide layers of the types NiO þCr 2 O 3 and NiO þ Al 2 O 3 þCr 2 O 3 , respectively. These oxides formed galvanic micro-couples with exposed alloy surface leading to increase in Cr depletion from the alloy. Ni-17 wt.% Mo-7wt.% Cr alloy formed MoO 3 þNiO þ Cr 2 O 3 type mixed oxide layer. A thin MoO 3 layer present on the exposed alloy surface reduces the effect of galvanic coupling thereby lowering Cr depletion.

Surface and Coatings Technology, 2013

ABSTRACT Ni-based superalloy 690 substrates were pack aluminized in a low Al-containing pack at 1... more ABSTRACT Ni-based superalloy 690 substrates were pack aluminized in a low Al-containing pack at 1273 K for 4 h in argon atmosphere. Scanning electron microscopy with energy dispersive X-ray analysis along the cross section of aluminized specimen revealed the formation of multilayer. The uppermost layer consisted of NiAl type phase (~ 45 μm), while adjoining one composed of (NiCr)Al and (NiCr)2Al types layer (~ 25 μm) and subsequently Cr-rich layer (~ 35 μm) adjacent to substrate. Al-content was found to increase while moving from Cr-rich layer towards outer layer. Cross-sectional transmission electron microscopy confirmed the formation of NiAl layer on the topmost surface and revealed the formation of nanoparticles of nickel aluminide on the uppermost surface. Microhardness was found to vary from 624 to 157 Vickers hardness number along the cross section of aluminized substrate indicating high, intermediate and low values for NiAl, Cr-rich layer and substrate, respectively. To evaluate the adherence of multilayer, scratch test was performed along the cross section of aluminized substrate at a constant load level of 2 N at ambient temperature. For aluminides, a decrease in friction coefficient with the decrease in Al-content was noticed. Cr-rich layer showed lowest friction coefficient, while its variation was little for substrate. Aluminide layers indicated lower penetration depth than the substrate, whereas no penetration was recorded for Cr-rich layer. Scratched surface did not reveal any peeling off either at the multilayer or layer/substrate interface indicating their good adherence. Aluminized specimens showed good overall oxidation resistance at 1273 K in air due to the formation of α-Al2O3. First-principle spin-polarized calculations on Ni(111)/NiAl(110) interface indicated strong adhesion (Ideal work of adhesion, Wad (ideal) = 3684 mJ/m2; lowest bound value) arising from strong metallic Ni d Ni d interaction and covalent Ni d Al p mixing of states.

Journal of Physics: Condensed Matter, 1994

Self-consistent electronic structure calculations have been performed on ordered lithium-aluminiu... more Self-consistent electronic structure calculations have been performed on ordered lithium-aluminium compounds using the tight-binding linear muffin-tin orbital (TBLMTO) method. The FCC-based ground-state superstructures (namely Ll2 and Ll0 structures) show some systematic trends in their cohesive and electronic properties, which are in reasonably good agreement with the available experimental data. We have also compared the density of states, band structures and total ground-state energies of equiatomic AlLi compounds, between the FCC-based Ll0 structure and the BCC-based B32 structure. While the former shows a two-dimensional metallic behaviour, the latter shows a resemblance to a tetrahedral-bonded covalent solid, and is more stable. After detailed comparison with some recent LAPW calculations, we conclude that the TBLMTO method can be used as an efficient and reasonably accurate first-principles tool for studying the phase stability and chemical bonding in ordered intermetallic compounds.

Journal of Alloys and Compounds, 2017

We report plane-wave based density functional theory (DFT) investigation of structural, elastic a... more We report plane-wave based density functional theory (DFT) investigation of structural, elastic and lattice dynamical properties of Fe-rich C15-Fe 2 Zr and Zr-rich FeZr 2 intermetallic compounds. These intermetallics dominantly appear in the Fe-Zr alloys which are potential candidates for immobilization of nuclear metallic waste. The calculated elastic constants and phonon dispersions show that both phases are mechanically and dynamically stable. The calculated bulk moduli as a function of temperature show that the Fe-rich C15 phase is less compressible and also less sensitive to temperature than the Zr-rich C16 phase. Furthermore, the C15-Fe 2 Zr phase has a lower thermal expansion coefficient but higher thermal conductivity as compared to the C16-FeZr 2 phase; while the heat capacities (C P and C V) of both the phases are almost identical above 450 K.

Computational Materials Science, 2016

Abstract Density functional theory (DFT) based first-principles investigation has been performed ... more Abstract Density functional theory (DFT) based first-principles investigation has been performed to study the cohesive, elastic and electronic properties of Fe–Zr binary intermetallics across the composition range. Our initial calibration of underlying DFT approximations provides good agreement of lattice parameters and bulk moduli with experimental results. Ground state stability analysis indicates C15-Fe2Zr Laves phase to be the most stable and t-FeZr2 to be more stable than c-FeZr2. All Fe–Zr intermetallics are mechanically stable as estimated from their calculated elastic constants. The calculated elastic moduli, in general, decrease with increasing Zr concentration. Anisotropies in bulk, shear and Young moduli are also presented. All the binary intermetallic phases exhibit G/B value of less than 0.57 and hence are ductile due to the presence of dominant metallic bonding arising from Fe d–Zr d interactions with a small component of covalent character.

Physical Chemistry Chemical Physics, 2020

The structural, thermodynamic, electronic, and elastic properties of Th1−xUxO2 and Th1−xPuxO2 mix... more The structural, thermodynamic, electronic, and elastic properties of Th1−xUxO2 and Th1−xPuxO2 mixed oxides (MOX) have been calculated with Hubbard corrected density functional theory (DFT+U) to account for the strong 5f electron correlations.

Journal of Alloys and Compounds, 2022

Transactions of the Indian Institute of Metals, 2019

Early stages of ordering in dilute Al-0.69(at.%)Mg-0.31(at.%)Si alloy, aged at 373 K for 120 h an... more Early stages of ordering in dilute Al-0.69(at.%)Mg-0.31(at.%)Si alloy, aged at 373 K for 120 h and 7200 h and at 453 K for 20 h, have been studied using scanning transmission electron microscopy techniques. Starting from the solute enrichment in (110)-type parallel planes, merely after 120 h of aging, isothermal growth at 373 K has been observed to lead to the formation of the small-ordered region after 7200 h of aging. Scanning transmission electron microscopy images from the aforesaid three varieties of samples and the corresponding Fourier-transformed images have been the basis to suggest the possible path of evolution of b 00 ordering in this dilute alloy. Based on this, the present study reveals the mechanism of formation of silicon pillar, which is the early stage of b 00 that transforms to a fully developed b 00. This corroborates with the concept of getting the final b 00strengthened product from an under-aged alloy by a suitable heat treatment.

Physical Chemistry Chemical Physics, 2018

Mixing enthalpies (ΔHmix) of U1−xNpxO2 and Th1−xNpxO2 solid solutions are derived from atomic sca... more Mixing enthalpies (ΔHmix) of U1−xNpxO2 and Th1−xNpxO2 solid solutions are derived from atomic scale simulations based on density functional theory (DFT) employing the generalised gradient approximation corrected with an effective Hubbard parameter (Ueff).

Journal of Nuclear Materials, 2012

Alloy melting route is currently being considered for radioactive hulls immobilization. Towards t... more Alloy melting route is currently being considered for radioactive hulls immobilization. Towards this, wide range of alloys, belonging to Zirconium–Iron binary and Zirconium–Stainless steel pseudo-binary systems have been prepared through vacuum arc melting ...

Journal of Applied Physics, 2019

The investigation of devitrification in thermally annealed nanodimensional glassy alloy thin film... more The investigation of devitrification in thermally annealed nanodimensional glassy alloy thin films provides a comprehensive understanding of their thermal stability, which can be used to explore potential applications. The amorphous to crystalline polymorphous transformation of cosputtered Ni-Zr alloy (Ni78Zr22 at. %) films, with a thickness lower than the reported critical limit of devitrification, was studied through detailed structural characterization and molecular dynamics (MD) simulations. Devitrification to a nanocrystalline state (Ni 7 Zr 2 structure) was observed at 800°C, with an increase in density (∼3.6%) much higher than that achieved in bulk alloys. Variation in the magnetic property of the films and the overall physical structure including morphology and composition were examined before and after annealing. MD simulations were employed to effectively elucidate not only the high densification but also the increased magnetic moment after annealing, which was correlated with the simulated change in the coordination number around Ni atoms. The structural relaxation process accompanying devitrification was described as a disorder-to-order transformation while highlighting the crucial role played by chemical short range order prevalent in glassy materials.

Journal of Physics: Condensed Matter

A combination of special quasi-random structure (SQS) analysis, density functional theory (DFT) b... more A combination of special quasi-random structure (SQS) analysis, density functional theory (DFT) based simulations and experimental techniques are employed in determining the transformation pathway for the disordered γ-(U, Zr) phase (bcc structure) to transform into the chemically ordered δ-UZr2 phase (C32, AlB2 type structure). A novel Monte-Carlo based strategy is developed to generate SQS structures to study the β → ω displacive phase transformation in A1−x B x binary random alloy. Structures generated with this strategy and using DFT calculations, it is determined that (222)bcc plane collapse mechanism is energetically unfavorable in chemically disordered environment at UZr2 composition. A mechanically and dynamically stable 24 atom SQS structure is derived which serves as a structural model of chemically ordered δ-UZr2 structure. Finally, a thermodynamic basis for the mechanism of the γ to δ transformation has been established which ensures chemical ordering is a precursor to th...

Journal of Nuclear Materials, 2016