High Pressure and Synchrotron Radiation Physics Division

India

High Pressure and Synchrotron Radiation Physics Division

India
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Singh N.,Raja Ramanna Center for Advanced Technology | Deo M.N.,High Pressure and Synchrotron Radiation Physics Division | Roy S.B.,Raja Ramanna Center for Advanced Technology
Physica C: Superconductivity and its Applications | Year: 2017

In this paper, we report optical (reflectance) measurements and investigations of optical properties of electropolished (EP), buffered chemical polished (BCP), and as-received (AR) from vendor niobium (Nb) samples typically used for fabrication of superconducting radio frequency (SCRF) cavities. Optical conductivity (σ(0), approximated near zero frequency) of EP (σ(0) ∼ 9 × 103 Ω−1 cm−1) sample is one order of magnitude higher than that of BCP (σ(0) ∼ 7 × 102 Ω−1 cm−1) and AR (σ(0) ∼ 3 × 102 Ω−1 cm−1) niobium samples. Furthermore, physical constants of electropolished Nb-SCRF materials such as concentration of conduction electrons (∼ 1.8 × 1022 electrons/cm3), average velocity (∼ 5.9 × 107 cm/s) of the electrons on the Fermi surface, and mean free path (∼ 0.53 nm) were also found to be considerably higher than that of the BCP and the AR samples. The depth of electric field penetration (in low frequency region) in the electropolished Nb sample (∼ 80 nm) is appreciably lesser than the BCP (∼ 450 nm) and the AR (∼ 400 nm) samples. © 2017 Elsevier B.V.


Singh N.,Raja Ramanna Center for Advanced Technology | Deo M.N.,High Pressure and Synchrotron Radiation Physics Division | Nand M.,Atomic and Molecular Spectroscopy Division | Jha S.N.,Atomic and Molecular Spectroscopy Division | Roy S.B.,Raja Ramanna Center for Advanced Technology
Journal of Applied Physics | Year: 2016

We present investigations of the presence of oxides, hydrides, and hydrocarbons in high-purity (residual resistivity ratio, ∼300) niobium (Nb) materials used in fabrication of superconducting radio frequency (SRF) cavities for particle accelerators. Raman spectroscopy of Nb materials (as-received from the vendor as well as after surface chemical- and thermal processing) revealed numerous peaks, which evidently show the presence of oxides (550 cm-1), hydrides (1277 and 1385 cm-1: ∼80 K temperature), and groups of hydrocarbons (1096, 2330, 2710, 2830, 2868, and 3080 cm-1). The present work provides direct spectroscopic evidence of hydrides in the electropolished Nb materials typically used in SRF cavities. Raman spectroscopy thus can provide vital information about the near-surface chemical species in niobium materials and will help in identifying the cause for the performance degradation of SRF cavities. Furthermore, photoelectron spectroscopy was performed on the Nb samples to complement the Raman spectroscopy study. This study reveals the presence of C and O in the Nb samples. Core level spectra of Nb (doublet 3d5/2 and 3d3/2) show peaks near 206.6 and 209.4 eV, which can be attributed to the Nb5+ oxidation state. The core level spectra of C 1 s of the samples are dominated by graphitic carbon (binding energy, 284.6 eV), while the spectra of O 1 s are asymmetrically peaked near binding energy of ∼529 eV, and that indicates the presence of metal-oxide Nb2O5. The valence-band spectra of the Nb samples are dominated by a broad peak similar to O 2p states, but after sputtering (for 10 min) a peak appears at ∼1 eV, which is a feature of the elemental Nb atom. © 2016 Author(s).


Kakade M.B.,Bhabha Atomic Research Center | Bhattacharyya K.,Chemistry Division | Tewari R.,Materials Science Division | Kshirsagar R.J.,High Pressure and Synchrotron Radiation Physics Division | And 4 more authors.
Transactions of the Indian Ceramic Society | Year: 2013

Phase evolution behaviour of lanthanum strontium manganite (LSM) and nickel oxide-yttria stabilized zirconia (NiO-YSZ) composite from the respective oven dried fuel - metal nitrate gels (citrate-metal nitrate for LSM and glycine-metal nitrate for NiO-YSZ) was studied using TG-DTA, XRD and FTIR. The TG-DTA revealed sharp exotherms around 200° and 221°C attributed to the setting in of combustion of gels of LSM and NiO-YSZ respectively. The XRD results indicated formation of nanocrystalline LSM and NiO-YSZ phases above 200° and 221°C respectively. The FTIR spectra of LSM and NiO-YSZ gels heated above 200° and 221°C exhibited characteristic absorption bands corresponding to metal-oxygen vibrations in LSM and NiO-YSZ indicating formation of the respective compounds. However, chemical and phase pure LSM and NiO formed above 700°C indicate the minimum calcination temperature to be used in the processing. The role of calcination treatment on powder characteristics in the temperature range of 700° to 1350°C was studied. With increasing calcination temperature of the as-formed powders, the characteristics such as crystallite size, median particle size (D50), green density of the compacts increased while specific surface area decreased. Typical sintering studies at 1400° and 1450°C revealed that sinterability and per cent linear shrinkage decreased with increasing calcination temperature. However, the required amount of porosity for SOFC application could be obtained with incorporation of a pore former in case of LSM and varying the sintering time in case of NiO-YSZ composite. © 2013 The Indian Ceramic Society.


Maiti N.,Radiation and Photochemistry Division | Thomas S.,High Pressure and Synchrotron Radiation Physics Division | Debnath A.,Bhabha Atomic Research Center | Kapoor S.,Radiation and Photochemistry Division
RSC Advances | Year: 2016

This is the first report on the surface-enhanced Raman scattering (SERS) and X-ray photoelectron spectroscopic (XPS) studies of taurine adsorbed on the surface of silver nanoparticles. Taurine, the sulphonic acid analogue of β-alanine participates in numerous biological and physiological functions in the human body and is a potent antioxidant. The interpretation of the SERS spectrum based on the "surface selection rules", XPS studies and DFT calculations has clearly indicated that the gauche tautomer of taurine is predominant on the silver nanoparticle surface. Taurine is directly bound to the silver surface through the sulphonate group along with interactions from the NH2 group that lies in close proximity to the metal surface. The binding of taurine through the oxygen atoms of the sulphonate group is confirmed by the XPS studies which show the presence of 71% Ag-O in taurine functionalized silver nanoparticles. © 2016 The Royal Society of Chemistry.


Garg N.,High Pressure and Synchrotron Radiation Physics Division | Mishra A.K.,High Pressure and Synchrotron Radiation Physics Division | Poswal H.K.,High Pressure and Synchrotron Radiation Physics Division | Tyagi A.K.,Bhabha Atomic Research Center | Sharma S.M.,High Pressure and Synchrotron Radiation Physics Division
Journal of Solid State Chemistry | Year: 2015

Our synchrotron based angle dispersive x-ray diffraction studies on scheelite structured ErLiF4 show that it undergoes two phase transitions, at ~11.5 and ~15.5 GPa to lower symmetry monoclinic phases, before becoming (irreversibly) amorphous at ~28 GPa. The first high pressure phase transformation to the fergusonite structure (space group I2/a) is found to be of thermodynamically second order. The second high pressure phase could be fitted to the P2/c space group, but detailed analysis rules out the wolframite structure (P2/c space group), common to many scheelite compounds under high pressures. We also suggest that despite the ionic character of the LiF4 tetrahedra, the compressibility of LnLiF4 (Ln=Eu-Lu) kind of scheelites is more affected by the LnF8 dodecahedra than the LiF4 tetrahedra. © 2015 Elsevier Inc. All rights reserved.


Mishra A.K.,High Pressure and Synchrotron Radiation Physics Division | Garg N.,High Pressure and Synchrotron Radiation Physics Division | Achary S.N.,Bhabha Atomic Research Center | Sharma S.M.,High Pressure and Synchrotron Radiation Physics Division
AIP Conference Proceedings | Year: 2012

Our synchrotron based high pressure angle dispersive x-ray diffraction studies on inverse perovskite structured BaLiF3 show that this compound is structurally stable up to half a mega bar. By fitting the third order Birch-murnaghan equation of state to the observed pressure induced variation of volume, bulk modulus and its pressure derivative for BaLiF 3 is determined to be 75.9 GPa and 5.3 respectively. Our studies also show that the compressibility of perovskite and inverse perovskite fluorides is similar. © 2012 American Institute of Physics.


Ganguli N.,Indian Association for The Cultivation of Science | Ganguli N.,Indian Institute of Technology Bombay | Shanavas K.V.,High Pressure and Synchrotron Radiation Physics Division | Shanavas K.V.,University of Missouri | Dasgupta I.,Indian Association for The Cultivation of Science
Journal of Physics Condensed Matter | Year: 2012

We present a detailed study of the magnetic properties of unique cluster assembled solids, namely Mn-doped Ge46 and Ba8Ge 46 clathrates using density functional theory. We find that ferromagnetic ground states may be realized in both compounds when doped with Mn. In Mn2Ge44, ferromagnetism is driven by hybridization-induced negative exchange splitting, a generic mechanism operating in many diluted magnetic semiconductors. However, for Mn-doped Ba 8Ge46 clathrates incorporation of conduction electrons via Ba encapsulation results in RKKY-like magnetic interactions between the Mn ions. We show that our results are consistent with the major experimental observations for this system. © 2012 IOP Publishing Ltd.


Singh N.,Raja Ramanna Center for Advanced Technology | Deo M.N.,High Pressure and Synchrotron Radiation Physics Division | Roy S.B.,Raja Ramanna Center for Advanced Technology
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2016

We have investigated the possible influence of surface oxides on the optical properties of a high-purity niobium (Nb) material for fabrication of superconducting radio frequency (SCRF) cavities. Various peaks in the infrared region were identified using Fourier transform infrared and Raman spectroscopy. Optical response functions such as complex refractive index, dielectric and conductivity of niobium were compared with the existing results on oxides free Nb and Cu. It was observed that the presence of a mixture of niobium-oxides, and probably near other surface impurities, appreciably influence the conducting properties of the material causing deviation from the typical metallic characteristics. In this way, the key result of this work is the observation, identification of vibrational modes of some of surface complexes and study of its influences on the optical responses of materials. This method of spectroscopic investigation will help in understanding the origin of degradation of performance of SCRF cavities. © 2016 Elsevier B.V.All rights reserved.

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