Structural and Lattice Dynamical Study of Half Heusler Alloys RuMnX (X = P, As).

In this report, we have investigated the structural and lattice dynamical properties of Half Heusler alloys RuMnX (X=P, As) under the framework of first principles calculations. The structural parameters such as lattice constants have been calculated and found to be in good agreement with the available theoretical results, while bulk modulus and pressure derivative of bulk modulus has been reported for the first time. A linear response approach of density functional perturbation theory has been employed for the calculations of lattice dynamics of these alloys. The calculated phonon dispersion curve (PDC) does not show any imaginary frequency in any symmetric directions, indicating the stability of alloys in the cubic phase. All the phonon frequencies corresponding to acoustical and optical phonon modes have been assigned. Comparison of PDC of both alloys reveal that the phonon gap has been found to be more in RuMnAs than in RuMnP. Lattice dynamical properties for these alloys has been reported for the first time. The phonon density of states for both alloys have also been calculated. Keywords: Half Heusler alloy, Crystal Structure, Lattice Dynamics, Phonons. [ABSTRACT FROM AUTHOR]