Positron annihilation lifetime (PAL) measurements on well-characterized pellets of Bi-2212, (Bi,Pb)-2212 and (Bi,Pb)-2223 superconductors indicate the presence of a very long (around 1500 ps) third lifetime. This τ3 is attributed to positronium formation in voids even in these conducting oxides and subsequent o-Ps to p-Ps conversion. Ignoring τ3 in the fit leads to altered values of τ1 and τ2. © 1995.

D SANYAL

U DE

K MANDAL

D BANERJEE

R BHATTACHARYA

University of Calcutta (informally known as Calcutta University or CU) is a collegiate public state university located in Kolkata, West Bengal, India.&nbsp;Within India it is recognized as a &quot;Five-Star University&quot; and accredited &quot;A&quot; Grade by National Assessment and Accreditation Council.

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The University of Calcutta has secured the Fifth position among the Universities of India in the prestigious &quot;Indian University Ranking 2019&quot; list, released by the NIRF of the Ministry of Human Resource Development, Government of India.

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It was established on 24 January 1857, and was one of the first institutions in Asia to be established as a multidisciplinary and Western-style university. Its alumni and faculty include several heads of state, heads of government, social reformers, prominent artists, only academy award winner and Dirac medal winner in India, many Fellows of the Royal Society and five Nobel laureates as of 2019 which is highest in South Asia.

University Of Calcutta

Positronium formation in (Bi/BiPb)-2212 and -2223 superconductors

Physics Letters A

Concentration dependent positron annihilation lifetime (PAL) measurements on Cr doped La0.5Pb0.5Mn1-yCryO3 (y=0.075, 0.15, 0.3, 0.35, 0.45) samples showing metal-insulator transitions (MIT) between 178 and 276K (depending on y) reveal anomalous variation of average and bulk PAL, τav and τB, respectively, around y=0.35. Such anomaly has not, however, been observed from the corresponding magnetic susceptibility and resistivity data. Interestingly, the model parameters (polaron radius, number of ion sites per unit volume) obtained from fitting the high temperature (above MIT, Tp) resistivity data with small polaron hopping model show the signature of the said anomaly around the same concentration. Nonlinear variations of τav and τB support the existence of small polarons (T&gt;Tp) which act as defect centers in such rare-earth manganites. Analysis of X-ray diffraction pattern confirms a change of lattice parameters indicating a structural transformation from rhombohedral (for y≤0.30) to orthorhombic (for y≥0.35) in the present system. © 2002 Published by Elsevier Science Ltd.

Solid State Communications

Positron annihilation lifetime studies on La0.5Pb0.5Mn1-yCryO3

The black coloured polymorph of cadmium oxide, that results from its heat treatment at 800 °C, is shown to be about 1000 times more conducting than the usual yellowish brown CdO. The electrical conductivity of the 800 °C-fired CdO shows a minimum at around 88 K. It is quite interesting that its thermo-electric power shows a change of slope also at around 88 K. The X-ray diffraction pattern of the as-supplied yellowish brown CdO has extra lines with respect to the patterns taken after 400 or 800 °C firing.

Journal of Physics and Chemistry of Solids

Electrical conductivity, thermo-electric power and structure of differently heat-treated CdO

Radiation damage in Bi2Sr2CaCu2O8-δ or Bi(2 2 1 2) by 55 MeV Li3+-beam has been studied from electrical resistivity and X-ray diffraction characterizations. This irradiation increases electrical resistivity and broadens X-ray diffraction lines by generating defects in all samples. But superconducting critical temperature, Tc, is seen to increase for Bi(2 2 1 2) with excess oxygen and decrease for Bi(2 2 1 2) with O-content less than the optimum, that gives maximum Tc. This increase of the superconducting critical temperature on Li-irradiation of O-rich Bi(2 2 1 2) as well as the decrease for low-O Bi(2 2 1 2) is due to O-displacement. This is in agreement with our earlier He-irradiation results.

Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms

Enhancement and degradation of Tc in Bi-HTSC due to Li3+ irradiations

The present measurement of positron annihilation lifetimes for the high-(Formula presented) superconductor (Formula presented) or (Bi, Pb)-2223, as a function of temperature, has been inspired by our recent DBPARL (Doppler-broadened positron annihilation radiation line shape) finding of a step and minima in the region around (Formula presented) K, in the variation with temperature, of the fraction of low momentum electrons at the annihilation sites. The positron annihilation lifetime in the superconductor probes the number density of electrons at the annihilation sites. The present work observes a reduction of lifetime components in the (Formula presented) region. Significant changes in the lifetime components in other temperature regions have also been observed and discussed. © 1998 The American Physical Society.

Physical Review B - Condensed Matter and Materials Physics

Probing superconductors from 30 to 300 K by positron-lifetime measurements

Doppler-broadened positron annihilation radiation line shape (DBPARL) and electrical resistance for (Bi,Pb)-2223 oxide superconductors, with Tc(R = 0) = 104 K, have been measured from 20 to 300 K. The S-parameter, giving the fraction of low-momentum electrons of the solid involved in the annihilation process, is calculated from the DBPARL data. Both measurements indicate anomalous variations possibly due to lattice instabilities between Tc and 300 K. The variation of S with temperature T across the superconducting transition region has, in addition to abrupt changes in S and dS/dT, sharp dips in S. This new feature and its possible origin are discussed.

Journal	Physics Letters A
Publisher	-
ISSN	0375-9601