Vipul Srivastava

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.

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.

Study of high pressure behavior and elastic properties of praseodymium monochalcogenides and monopnictides

The structural and elastic properties of praseodymium monochalcogenides (PrX: X = S, Se, Te) and monopnictides (PrY: Y = P, As, Sb, Bi) with NaCl-type structure have been investigated by using an interionic potential theory with necessary modification to include the effect of Coulomb screening due to the delocalized f-electrons of rare earth ion. The calculations are done at ambient as well as at high pressure. The structure of the high pressure phase of PrX compounds is CsCl-type while all the PrY compounds have been found to undergo from their initial NaCl-type structure to high pressure body centered tetragonal (BCT) structure, which can be seen as the distorted CsCl-type with c/a ratio ≈ 0.82–0.87. The calculated transition pressures are in good agreement with the experimental results. The elastic properties like second-order elastic constants for PrX, Y compounds are calculated for the first time. The nature of the bonding is also predicted by calculating the distance between the ions with the increasing pressure.

Pressure-induced phase transitions in some AnS (An = Th, U, Np, Pu) Compounds

Pressure-induced structural phase transitions at high-pressure in monosulfides of thorium, uranium, neptunium and plutonium (AnS) have been studied theoretically by an inter-ionic potential theory with modified ionic charge introduced to include the Coulomb screening effect due to localized ‘f’ electrons. These AnS compounds undergo a phase transition from sodium chloride (NaCl) to cesium chloride (CsCl) structure at a very high-pressure. The present theoretical investigation carried out up to 120 GPa reveals that these compounds undergo NaCl–CsCl phase transitions at 100, 81, 75 and 105 GPa for ThS, US, NpS and PuS, respectively. The first-order pressure derivatives calculated from the present theory agree well with observed data.

High pressure behaviour of heavy rare earth mono antimonides

We have investigated theoretically the high-pressure structural phase transition and cohesive properties of two heavy rare earth mono antimonides (RESb; RE = Dy and Lu) by using two body interionic potential with necessary modifications to include the effect of Coulomb screening by the delocalized 4f electrons of the RE ion. The peculiar properties of these compounds have been interpreted in terms of the hybridization of f electrons with the conduction band and strong mixing of f states of RE ion with the p orbital of neighboring pnictogen ion. These compounds exhibit first order crystallographic phase transition from their NaCl (B1) phase to CsCl (B2) phase at 23.6 GPa and 25.4 GPa respectively. The bulk modulii of RESb compounds are obtained from the P-V curve fitted by the Birch equation of state. We also calculated the RE-RE distance as a function of pressure. Elastic properties of these compounds have also been studied and their second order elastic constants are calculated.

High pressure effect on structural, elastic and thermal properties of DyP and DyAs

We have performed an inter-ionic potential theory with modified ionic charge to investigate the structural, elastic and thermal properties of DyP and DyAs theoretically, at high pressure. We found a structural phase transition from NaCl (B1) - to CsCl (B2)-type structure at 57 GPa for DyP and 51 GPa for DyAs and other properties, such as lattice constant, bulk modulus, cohesive energy and second-order elastic constants were also calculated and compared with the available theoretical data. In order to gain further information, we have also predicted the Youngs modulus (E), Poissons ratio (v), anisotropy factor (A) and Debye temperature (θD). Our results are in good agreement with theoretical data where available and provide predictions where they are not.

Structural and electronic properties of Cd-rich lanthanide intermetallics

The structural and electronic properties of B2-cadmium lanthanide (RE), CdLn (Ln=La, Ce and Pr) intermetallics have been calculated at T=0K at ambient and at high pressure by using tight binding linear muffin tin orbital method. We have estimated lattice parameter, bulk modulus, density of states for the three CdLn intermetallics. The f-electrons present in the -Ln, play important role. The variation in density of states under compression is calculated due to Pr-f effect in CdPr, which opens a possibility of structural instability.

Study of electronic and structural properties of half metallic rare earth mononitrides

In the present work we investigated theoretically the electronic, magnetic and structural properties of two rare-earth nitrides (REN: RE = Sm, Eu) by using self- consistent tight-binding linear muffin tin orbital (TBLMTO) method. Magnetically, both the rare earth nitrides (RENs) are stable in ferromagnetic (FM) state, while its ambient structure is found to be stable in NaCl-type (B1) structure. From the present study we predict the pressure induced structural phase transition in both RENs from the relatively open NaCl-type structure into more dense CsCl-type structure at 8.6 GPa and 14.6 GPa respectively. They form a new class of half-metallic magnets with high magnetic moments and are strong candidates for applications in spintronics and spinfiltering devices. We have therefore, calculated electronic band structures, equilibrium lattice constants, cohesive energies, bulk moduli and magnetic moments for REN compounds in both B1 and B2 phases.

Mechanical and thermal properties of praseodymium monochalcogenides and monopnictides under pressure

The mechanical and thermal properties of praseodymium monochalcogenides and monopnictides are calculated using elastic constants, those have been derived from two body inter- ionic potential theory. We have calculated the Youngs modulus (E), Poissons ratio (v), anisotropy factors (A), sound velocities and Debye temperature (θD) for these compounds. The bulk modulus to shear modulus ratio (B/G) lies between 1.75-1.92 for all these compounds, which shows that all compounds are ductile in nature. Youngs modulus shows that PrS and PrAs are stiffer than the other monochalcogenides and monopnictides of praseodymium. The variation of elastic constants (C11, C44) with pressure and the variation of Debye temperature with pressure are also presented for these compounds.

Electronic and thermal properties of spin polarised MgPr intermetallic

The B2-type MgPr intermetallic was studied with respect to its electronic and thermal properties by using spin polarized self-consistent tight binding linear muffin tin orbital method for the first time at ambient pressure. Interestingly, it was observed from the calculations that one of the spins was metallic, while other spin was not completely metallic under ambient conditions. Thermal properties like Debye temperature and Gruneisen constant are predicted at T=0K within the Debye-Gruneisen model.