R K Singh
Articles written in Bulletin of Materials Science
Volume 17 Issue 4 August 1994 pp 389-393
We have investigated doping effects on the transition temperature (
Volume 23 Issue 4 August 2000 pp 267-272 Superconductors
The specific heats of superconducting HoBa2Cu3O7-δ (
Volume 28 Issue 2 April 2005 pp 155-171 Superconductors
We consider a two-peak model for the phonon density of states to investigate the nature of electron pairing mechanism for superconducting state in fullerides. We first study the intercage interactions between the adjacent C60 cages and expansion of lattice due to the intercalation of alkali atoms based on the spring model to estimate phonon frequencies from the dynamical matrix for the intermolecular alkali-C60 phonons. Electronic parameter as repulsive parameter and the attractive coupling strength are obtained within the random phase approximation. Transition temperature, 𝑇c, is obtained in a situation when the free electrons in lowest molecular orbital are coupled with alkali-C60 phonons as 5 K, which is much lower as compared to reported 𝑇c (≈ 20 K). The superconducting pairing is mainly driven by the high frequency intramolecular phonons and their effects enhance it to 22 K. To illustrate the usefulness of the above approach, the carbon isotope exponent and the pressure effect are also estimated. Temperature dependence of electrical resistivity is then analysed within the same model phonon spectrum. It is inferred from the two-peak model for phonon density of states that high frequency intramolecular phonon modes play a major role in pairing mechanism with possibly some contribution from alkali-C60 phonon to describe most of the superconducting and normal state properties of doped fullerides.
Volume 28 Issue 7 December 2005 pp 651-661 Semiconductors
An effective interaction potential (EIOP) is developed to invoke the pressure induced phase transition from zinc blende (𝐵3) to rocksalt (𝐵1) structure and anharmonic properties in ZnX (X = Se, S, Te) semiconductors. The effective interaction potential incorporates the long range Coulomb interaction, van der Waals interaction and short-range repulsive interaction up to second neighbour ions within the Hafemeister and Flygare approach as well as the charge transfer effects caused by the electron-shell deformation of the overlapping ions. The van der Waals coefficients are computed by the Slater Kirkwood variation method as a first step. Later on, we evaluate volume collapse, second order and third order elastic constants with pressure pointing to the systematic trends in all compounds of zinc blende structure and their thermal properties such as force constant, Gruneisen parameter, compressibility, Debye temperature etc. The vast volume discontinuity in pressure–volume (PV) phase diagram identifies the structural phase transition from zinc blende (𝐵3) to rock salt (𝐵1) structure and is consistent with those revealed from earlier reports.
Volume 42 | Issue 6
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