Sankar P. Sanyal

High pressure phase transition and elastic properties of cerium chalcogenides and pnictides

The structural properties of Cerium mono-chalcogenides and mono-pnictides have been investigated for the first time by using a modified interionic potential theory. The calculated transition pressures are in good agreement with the experimental results. The ionic bonding is found to be more pronounced in Ce-mono-chalcogenides than mono-pnictides. The calculated values of elastic constants are also predicted for the first time.

High pressure structural phase transition in alkaline earth chalcogenides

Abstract This paper reports on investigation of the pressure induced phase transition of BaSe, BaTe, SrSe and SrTe by using a three-body potential approach. The phase transition pressure and associated volume collapse obtained from this approach show a reasonably good agreement with experimental data. The variation of phase transition pressure and(−Δ v / v ol ), with Bulk modulus, and variation of phase transition pressure with ratio of cation to anion radius, follow a symmetric trend identical to that observed in other solids of this group. It is found that the present model has promise to predict the phase transition pressure for alkaline earth chalcogenides.

Plutonium chalcogenides and pnictides: pressure induced phase transition and elastic properties

Abstract We have investigated the structural and elastic properties of three plutonium mono-chalcogenides (PuX; X=S, Se, Te) and three mono-pnictides (PuY; Y=As, Sb, Bi) using an interionic potential theory with modified ionic charge, at high pressure. This method has been found quite satisfactory in the case of cerium mono-chalcogenides and mono-pnictides. The calculated equation of state, phase transition pressure, and bulk modulus agree well with the experimental findings. We have also reported the second order elastic constants (SOEC) for these Pu compounds, for the first time. A comparison of the properties of chalcogenides and pnictides of shifted homolog pair Ce–Pu, is also presented.

Structural Phase Transition and Elastic Properties of Thorium Pnictides at High Pressure

We have calculated the structural and elastic properties of thorium mono-pnictides at high pressure, for the first time, using a suitable interionic potential. This method has been found quite satisfactory in the case of uranium compounds, and describes the crystal properties in the framework of ionic model. The calculated equation of state, phase transition pressures for Bl to B2 transition and bulk modulus etc. in the case of all four ThX (X = N, P, As, Sb) compounds agree well with the experimental results. We have also reported the higher order elastic constants and discuss the dominance of various types of forces in them.

A lattice dynamical study of the role of pressure on Raman modes in high-Tc HgBa2CuO4

Abstract A lattice dynamical study has been carried out to investigate the Raman frequencies and the effect of pressure on the apical-oxygen (O A ) vibration (Raman Active) in the HgO A Cu bond in HgBa 2 CuO 4 high- T c superconductor by using an unscreened rigid ion model. The calculated Raman frequencies are, in general, in fair agreement with experimental values. The calculated values of the O A A 1g Raman mode agree reasonably well with the experimental Raman data up to 7.5 GPa and show that the O A A 1g vibrational mode increases linearly as the pressure is increased, suggesting phonons to play a dominant role in this system.

Phonon spectrum and lattice specific heat of the HgBa2CuO4 high-temperature superconductor

Abstract The phonon density of states and lattice specific heat have been calculated for the HgBa 2 CuO 4 high-temperature superconducting compound for the first time by using a simple lattice dynamical model theory, namely the rigid ion model. The obtained results show an overall consistent description of the lattice dynamics of this compound. However, we could not compare our results with experimentally measured values as they are not available so far. We emphasize that the neutron scattering and specific heat measurements justify our results. However, we expect that there will be not much difference as the present model has been quite successful in explaining the pressure dependence of the Raman active phonon modes for this compound [14,15].

Resonance photoemission studies of (111) oriented CeO2 thin film grown on Si (100) substrate by pulsed laser deposition

The electronic structure of CeO2 thin film grown by pulsed laser deposition on Si (100) substrate has been investigated using resonance photoemission spectroscopy (RPES). X-ray photoemission study on the film suggests that Ce has 3+ and 4+ valence states. Valence band spectra of the film show a feature at 2.1 eV of binding energy and a broad band at higher binding energy due to O 2p derived state. RPES measurements performed in the Ce 4d→4f photoabsorption region show maximum intensity for 2.1 eV feature at photon energy of 122 eV confirming it to be due to Ce3+ (4f1) state. RPES measurements also show maximum intensity for binding energy position of 4.4 eV in the broad band at photon energy of 125 eV, suggesting it to be due to Ce4+ (4f0) state. Constant initial state (CIS) versus photon energy plots also confirm these findings and suggest that the broad band is admixture of O 2p and Ce 4f and 5d derived states.

Electronic structure studies of Fe doped CeO2 thin films by resonance photoemission spectroscopy

We have studied the modification in the electronic properties of pulsed laser deposited CeO2 thin films due to Fe doping (2 and 6 at %), with the help of x-ray photoemission spectroscopy (XPS) and resonance photoemission spectroscopy (RPES) measurements. XPS results indicate the ionic state of Fe in the Fe doped films, ruling out the possibility of Fe metallic clusters. Valence band spectra of CeO2 show an additional feature after Fe doping, suggesting its incorporation in the CeO2 matrix. RPES studies on these films reveal the hybridization between oxygen vacancy induced Ce localized states and Fe derived states.

Structural Phase Transition in Uranium Arsenide and Telluride

We have studied the structural phase transition due to high pressure in UAs and UTe for the first time by using an interatomic potential approach based on rigid ion model formulation. The theoretically predicted phase transition pressure and other structural properties for these compounds agree reasonably well with the measured values. The relative volume change (V/V 01 ) for both compounds show that it is for UTe twice that for UAs and hence confirms that there may be more f-d hybridization mixed valence states in UTe similar to mixed valence compounds, where there is volume reduction due to f-d hybridization. We did not observe any high pressure structural phase transition for other uranium compounds such as USb, US, USe etc. up to 100 GPa. The nature of the force constants at equilibrium and high pressure is discussed.

Lattice vibrational properties of uranium chalcogenides

Abstract Lattice vibrational properties of uranium chalcogenides (UX) (X = S, Se, Te) have been investigated by using the breathing shell model (BSM) which includes breathing motion of the electrons of the U-atom due to f—d hybridization. The phonon dispersion curves of UX compounds, calculated from the present model, agree with the measured data. A comparison has been made between the present and previously reported three-body force rigid ion model (TRIM) by us [Phys. Rev. B 46 (1992) 3664]. This reveals that the short-range breathing phenomena play a dominant role in the phonon properties of UX compounds. We also report, for the first time, the two phonon density of states and specific heats of these compounds.