Papers by Asokamani Rajamanickam
Progress in Materials Science, 2009
Physical Review Letters
Ytterbium (Yb) metal is divalent and nonmagnetic (4f 14 configuration). Under pressure its valenc... more Ytterbium (Yb) metal is divalent and nonmagnetic (4f 14 configuration). Under pressure its valence increases significantly leading to the expectation that magnetic instabilities and other highly correlated electron effects may appear before a stable trivalent state is reached (4f 13 configuration). We carried out electrical resistivity and ac magnetic susceptibility measurements to 179 GPa over the temperature range 1.4-295 K. No evidence for magnetic order is observed. However, Yb becomes a superconductor at 86 GPa with Tc ≃ 1.4 K, increasing to 4.6 K at 179 GPa. X-ray absorption spectroscopy shows that Yb remains mixed-valent to at least 125 GPa, pointing to an active role of f electrons in the emergence of superconductivity in this simple, elemental solid.
Procedia Materials Science, 2014
ABSTRACT licenses/by-nc-nd/3.0/). Selection and peer review under responsibility of the Gokaraju ... more ABSTRACT licenses/by-nc-nd/3.0/). Selection and peer review under responsibility of the Gokaraju Rangaraju Abstract This paper deals with the fabrication of WC-12wt%Co and Yttria-stabilized Zirconia coatings fabricated using Atmospheric Plasma Spraying technique.The Microstructural Characterization of the coatings was carried out using Scanning electron microscope(SEM).Potentiostat was employed to perform corrosion testing for the bare substrate and the coatings in 5 wt %Nacl solution. The adhesion between the coating and the substrate was assessed using Scratch testing machine. The results suggested that WC-12wt%Co coating offered enhanced Corrosion and Scratch resistance when compared to that of the Yttria stabilized Zirconia coatings. This enhancement could be mainly ascribed to the presence of few amounts of interconnected pores and hard tungsten carbide particles embedded in the cobalt matrix. © 2014 The Authors. Published by Elsevier Ltd. Selection and peer-review under responsibility of the Gokaraju Rangaraju Institute of Engineering and Technology (GRIET).
Journal of Physics F: Metal Physics, 1977
ABSTRACT The effect of correlation has been included in the bandstructure calculation for thorium... more ABSTRACT The effect of correlation has been included in the bandstructure calculation for thorium and osmium using the RAPW method. The complete bandstructure and Fermi surface cross sections are obtained for both the metals using the two potentials, the one (Vs) which includes only the Slater exchange and the other (VH) which includes both the exchange and correlation through Overhauser's formula (1971). A comparison of the authors' results with those of the previous calculations using the traditional approximations with regard to the exchange leads to the conclusion that VH yields results in better agreement with the experimental data than those obtained with Vs although the latter may still be considered fairly reliable without any violent disagreement.
Journal of Physics F: Metal Physics, 1978
ABSTRACT The detailed bandstructure of Mg having the HCP lattice structure has been calculated us... more ABSTRACT The detailed bandstructure of Mg having the HCP lattice structure has been calculated using the KKR method for the three different potentials Vs, VH and Vvs. The potential Vs includes only the exchange part through Slater's formula whereas the other two potentials VH and Vvs include exchange as well as correlation. The energy bands, density of states, electronic specific heat, magnetic susceptibility and Fermi surface cross sections are calculated for all the three potentials and compared with the experimental data. The results show that the potentials which include both exchange and correlation are in better agreement with the experimental values. However the results obtained with the potential Vs may still be considered reliable and do not lead to any violent disagreement with the experimental values.
International Journal of Nanomedicine, 2015
This paper presents the wear characteristics of the composite ceramic coating made with Al 2 O 3-... more This paper presents the wear characteristics of the composite ceramic coating made with Al 2 O 3-40wt%8YSZ on the biomedical grade Ti-6Al-4V alloy (grade 5) used for total joint prosthetic components, with the aim of improving their tribological behavior. The coatings were deposited using a plasma spraying technique, and optimization of plasma parameters was performed using response surface methodology to obtain dense coating. The tribological behaviors of the coated and uncoated substrates were evaluated using a ball-on-plate sliding wear tester at 37°C in simulated body-fluid conditions. The microstructure of both the titanium alloy and coated specimen were examined using an optical microscope and scanning electron microscope. The hardness of the plasma-sprayed alumina-zirconia composite coatings was 2.5 times higher than that of the Ti-6Al-4V alloy, while the wear rate of Ti-6Al-4V alloy was 253 times higher than that of the composite-coated Ti-6Al-4V alloy. The superior wear resistance of the alumina-zirconia coated alloy is attributed to its enhanced hardness and intersplat bonding strength. Wear-track examination showed that the predominant wear mechanism of Ti-6Al-4V alloy was abrasive and adhesive wear, whereas, in the case of alumina-zirconia composite coated alloy, the wear was dominated by microchipping and microcracking.
International Journal of Modern Physics B, 1997
The self-consistent scalar relativistic band structure for AgGaX 2 (X = S, Se, Te) performed in c... more The self-consistent scalar relativistic band structure for AgGaX 2 (X = S, Se, Te) performed in chalcopyrite structure using the TBLMTO method at various pressures are reported here. Empty spheres were introduced in the calculations as the chalcopyrite structure is loosely packed. From the total energy calculations, the equilibrium lattice constant and the bulk modulus at zero pressure were calculated and these values agree well with the reported experimental values. All these compounds are found to have direct energy gap at ambient pressure with the gap widening with increased pressures which are in agreement with the experimental results. The deformation potential, dE g /dP for the compounds are also reported here. The metallisation volumes are calculated and the possibility of observing superconductivity in these compounds is discussed.
Journal of Physics F: Metal Physics, 1980
ABSTRACT Results of bandstructure calculations of Tc, which has a HCP lattice structure, are used... more ABSTRACT Results of bandstructure calculations of Tc, which has a HCP lattice structure, are used to calculate the superconducting transition temperature Tc and the Fermi surface of the metal. The strong-scattering theory of Gaspari and Gyorffy (1972) is used in conjunction with McMillan's formula (1968) to calculate Tc in the spherical band approximation. As the bandstructure calculations were made for potentials constructed with and without correlation, the superconducting transition temperature is calculated for all potentials. The theoretical values of Tc are found to be very sensitive to changes in the electron-phonon enhancement factor lambda and the Coulomb pseudopotential mu *. However the theoretical value of Tc calculated for a potential which includes correlation agrees well with the experimental value for a particular choice of mu *. The Fermi surface cross sections are obtained for all the potentials and a qualitative comparison is made with the available preliminary experimental results.
Physica Status Solidi (a), 1995
... O, 25.5 K. The density of the LaBaCa,Cu,O, compound was found to be 5.4 g/cm3 and ... Acknowl... more ... O, 25.5 K. The density of the LaBaCa,Cu,O, compound was found to be 5.4 g/cm3 and ... Acknowledgements The authors wish to thank Dr. T. S. Radhakrishnan, Miss. T. Geetha Kumari, IGCAR, Kalpakkam, and Mr. V. Rao, IIT, Madras for providing their facilities and UGC India for ...
Physical Review B, 1999
The self-consistent tight-binding linear muffin-tin orbital method was employed to calculate the ... more The self-consistent tight-binding linear muffin-tin orbital method was employed to calculate the electronic structure and the total energy of Ti 2 XAl (XϭNb, V, Zr) in B2, D0 19 , and O ͑orthorhombic͒ phases and the results were used to study the phase stability and cohesive properties of these intermetallic compounds. Our theoretical calculation shows that the B2 phase is the most stable phase of Ti 2 NbAl as observed by experimentalists. However, the three phases are close in energy indicating the possibility of the presence of all these phases in equilibrium over a range of temperatures, which is in accordance with experimental observations. Our calculations predict that Ti 2 VAl is more stable in the B2 phase whereas Ti 2 ZrAl is more stable in the D0 19 phase. We also report the calculated equilibrium lattice parameters, cohesive energies, heats of formation, and bulk modulii of these systems, and a possible comparison of the calculated quantities with the available experimental data is made. From our studies we are made to conclude that the concept of pseudogaps which has been very much emphasized for binary intermetallics does not carry so much significance with respect to ternary systems. ͓S0163-1829͑99͒05047-X͔
physica status solidi (b)
The first band structures and calculated electronic properties of the compounds LaSe and LaTe are... more The first band structures and calculated electronic properties of the compounds LaSe and LaTe are reported. The energy band structure of lanthanum monochalcogenides are obtained using the self-consistent LMTO method within the atomic sphere approximation. The band structure outputs were used to calculate the physical properties such as the electronic specific heat, the Pauli paramagnetic susceptibility, and the superconducting transition temperature. The calculated results are compared with the available experimental values.Erste Bandstrukturen und berechnete elektronische Eigenschaften von LaSe and LaTe werden präsentiert. Die Bandstrukturen werden in Kugelatomnäherung mit der selbstkonsistenten LMTO-Methode erhalten und zur Berechnung der physikalischen Eigenschaften, wie der elektronischen spezifischen Wärme, der paramagnetischen Suszeptibilität und der Supraleitungssprungtemperatur, benutzt. Die Ergebnise der Rechnungen werden mit verfügbaren experimentellen Daten verglichen.
physica status solidi (a)
Synthesis of Ba,-xNdxCu,Oy (x = 0.4 and 0.5) Superconductors
Solid State Communications
The band structures of the Laves phase systems YRh2 and LaRh2 determined using the LMTO method ar... more The band structures of the Laves phase systems YRh2 and LaRh2 determined using the LMTO method are reported here. The paramagnetic band structures and the DOS curves are compared with their counterparts YCo2 and LuCo2 which exhibit anomalous variation of susceptibility with temperature, while the rhodium compounds are Pauli paramagnetic. The band structure results are used to analyse the reasons for the differences in physical properties between the cobalt and rhodium systems. Further, as the rhodium compounds are found to be superconducting, we also report their theoretically calculated values of the transition temperatures.
Physica B+C, 1986
ABSTRACT We report the effect of pressure on phonon frequency and its influence on the supercondu... more ABSTRACT We report the effect of pressure on phonon frequency and its influence on the superconducting transition temperature in the case of lanthanum. The variation of phonon frequency with pressure is calculated through the thermodynamic Grüneisen parameter γG. The calculated Tc values are found to agree very well with the experimental results.
Wear, 2011
This paper reports on the sliding wear performance of the nanostructured Al 2 O 3-13TiO 2 , ZrO 2... more This paper reports on the sliding wear performance of the nanostructured Al 2 O 3-13TiO 2 , ZrO 2 and the bilayered (ZrO 2 /Al 2 O 3-13TiO 2) coated biomedical Ti-13Nb-13Zr alloy in simulated body fluid condition. The nanopowders were sprayed using an atmospheric plasma spray technique and the reciprocatory sliding wear behavior of all the above coatings was evaluated using wear testing machine. The bilayered (ZrO 2 /Al 2 O 3-13TiO 2) coating which has not been reported hitherto exhibited two hundred and five hundred fold increase in the wear resistances when compared with that of the nanostructured Al 2 O 3-13TiO 2 (AT) and ZrO 2 (YSZ) coatings. This substantial improvement in the wear resistance of the bilayered coating is attributed to its lower porosity and higher adhesion strength when compared to the AT and YSZ coatings. This study suggests that this new type of bilayered coating may be a preferred approach to be tried for obtaining much higher wear resistant coatings.
Transactions of the Indian Institute of Metals, 2013
ABSTRACT This paper reports the wear characteristics of the ceramic coatings made with Al2O3 and ... more ABSTRACT This paper reports the wear characteristics of the ceramic coatings made with Al2O3 and also with SiC which were performed using atmospheric plasma spraying technique on the Ti-6Al-4V biomedical alloy with the aim of improving their tribological behavior. The wear behavior of the coatings was evaluated using reciprocatory wear tester with coated substrate as the flat and alumina ball as a friction partner in simulated body fluid (Hank’s solution) environment. The microstructure and phase composition of the ceramic powders and as-sprayed coatings have been characterized using scanning electron microscope and X-ray diffractometer. Porosity, microhardness, adhesion strength and roughness of the coatings were measured as they have a bearing on wear and friction behavior. The results indicate that plasma sprayed Al2O3 coating exhibits higher wear resistance compared to that of plasma sprayed SiC coating. The higher wear resistance of Al2O3 coating is attributed to the improved melting and spreading of the alumina particles onto the substrate yielding increasingly bonded splats, resulting in compact and dense microstructure with lower porosity and higher microhardness.
Wear, 2014
ABSTRACT The relative wear resistance of three candidate coatings for titanium alloy-based orthop... more ABSTRACT The relative wear resistance of three candidate coatings for titanium alloy-based orthopaedic applications was compared using a reciprocating test method. Micrometer-sized powders of the following compositions were plasma sprayed onto Ti-6Al-4V (TAV) alloy: (i) Al2O3 (AO) (ii) 8 mol% yttria stabilized Zirconia (8YSZ) and (iii) Al2O3-40 wt%8YSZ (A4Z). Deposits were characterized using x-ray diffraction (XRD), scanning electron microscopy (SEM), and porosity measurements. In addition, microindentation hardness measurements and scratch-based adhesive/cohesive strength measurements were also performed. The composite coating (A4Z) had superior wear resistance. Wear track examination suggests two reasons for this improvement. First, the A4Z coating had improved cohesive strength between splats, and second, there was a phase transition toughening mechanism associated with tetragonal zirconia. Results of contact mechanics calculations support the experimental findings.
Physical review. B, Condensed matter, 1994
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Papers by Asokamani Rajamanickam