Abstract
A comprehensive phenomenological calculation is reported for the pressure-dependentstructural phase transition, equation of state and elastic properties ofUxLa1−xS solid solution. We develop an effective interionic interaction potential incorporating thelong-range Coulomb and the Hafemeister and Flygare form of short-range overlap repulsionextended up to the second-neighbour ions and van der Waals (vdW) multipole interactions.The overlapping of the f orbitals with the p orbitals of the nearest neighbour inUxLa1−xS that influences the effective Coulomb interactions is noticed to be apotential parameter in revealing the structural phase transition (fromNaCl type (B1) to CsCl type (B2)) as well the equations of state ofUxLa1−xS (x = 0,0.08,0.40,0.50,0.60,0.80 and 1.0) rare-earth compounds. The calculated results have revealed reasonablygood agreement with the available data on the phase transition pressures(Pt = 25.5 (LaS),30 (U0.08La0.92S),34 (U0.40La0.60S),35 (U0.50La0.50S),47 (U0.60La0.40S),59 (U0.80La0.20S) and 81 (US) GPa). The equation of state curves (plotted betweenV (P)/V (0) and pressure) for both the NaCl-type (B1) and CsCl-type (B2) structures obtained by us arein fairly good agreement with the experimental results. Deduced values of the volume collapses[ΔV (P)/V (0) ] are also closer to their observed data. Further, the variations of the second- andthird-order elastic constants with pressure have followed a systematic trend, that is almostidentical to those exhibited by the measured and observed data in other compounds ofNaCl-type structure family.
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