Vibrational and cohesive properties in 4d and 5d transition metals: systematics and interrelations

Abstract

Motivated by the striking regularities between experimental quantities related to the vibrational properties of the 4d and 5d series early noted by Fernández Guillermet and Grimvall [Phys. Rev. B, 1989, 40(3), 1521], a systematic theoretical study has been made of the vibrational density of states (VDOS) of Ag, Au, Pd, Pt, Rh, Ir, Ru, Os, Tc, Re, Mo, W, Nb, Ta, Zr and Hf. The frequency moments <em>ω</em><small>_D</small>(<em>j</em>), expressed as Debye temperatures <em>θ</em><small>_D</small>(<em>j</em>) for 0 ≤ <em>j</em> ≤ 100 were evaluated. Various remarkable correlations between these quantities are reported, which have their roots in the relations of homology between the VDOS. From the <em>θ</em><small>_D</small>(<em>j</em>), several <em>k</em>(<em>j</em>) quantities with dimensions of force constants are calculated. For the elements 4d and 5d transition series, these quantities are shown to be strongly correlated, with independence of the value of <em>j</em>. It is suggested that the various interrelations between the <em>θ</em><small>_D</small>(<em>j</em>) and <em>k</em>(<em>j</em>) parameters arrived at in the current work have their roots in the homologous variations of the cohesion forces across the 4d and 5d transition series, as revealed by thermophysical properties such as the bulk modulus and the cohesive energy.