Theory of the structural phases of group 5B–6B metals and their transport properties

Abstract

In order to predict the stable and metastable phases of the bcc metals in the block of the Periodic Table defined by groups 5B to 6B and periods 4 to 6, as well as the structure dependence of their transport properties, we have performed full potential computations of the total energies per unit cell as a function of the a c ratio at constant experimental volume. In all cases, a metastable body centered tetragonal (bct) phase was predicted from the calculations. The total energy differences between the calculated stable and metastable phases ranged from 0.09 eV/cell (vanadium) to 0.39 eV/cell (tungsten). The trends in resistivity as a function of structure and atomic number are discussed in terms of a model of electron transport in metals. Theoretical calculations of 2 the electrical resistivity and other transport properties show that bct phases derived fromgroup 5B elements are more conductive than the corresponding bcc phases, while bct phases formed from group 6B elements are less conductive than the corresponding bcc phases. Special attention is paid to the phases of tantalum where we show that the frequently observed β phase is not a simple tetragonal distortion of bcc tantalum.

Kohn Anomaly and Phase Stability in Group VB Transition Metals

“…The calculations by Louis and Iyakutti [51] predicted phase transformation from the ambient pressure BCC structure to a simple cubic (SC) structure at p~1.393 Mbar with estimated T c~2 0.99 K at the transition pressure. A metastable body-centered tetragonal (BCT) phase in vanadium has been predicted by Nnolim et al [52] 2.2. Fermi Surface Nesting and Pre-Martensitic Softening in V, Nb, and Ta at High Pressures…”

Phase tailoring of Ta thin films by highly ionized pulsed magnetron sputtering

“…This is possible within a substrate-bias window, and depends on the growth conditions (target voltage and inclination angle of the substrate). For example, an increase in V T from 740 to 1000 V led to growth of bccTa at a lower V b value -a decrease from 70 V to 30 V. Many researchers have studied the growth of bcc-Ta on Si substrates [2][3][4][5][6][7][8][9] and have shown that stresses induced by ion bombardment can influence the structure of the deposited Ta film. The HIPIMS discharge is highly ionized and a large fraction of the ions bombarding the growing film consists of ions of the sputtered material [19].…”

“…The nucleation and growth conditions, i.e. the impurity levels [6] and the number of defects [7] also influence the phase formation. Face and Prober [4] and Window et al [8] used ion-beam sputtering, and showed that it is possible to obtain bcc-Ta by depositing a thin Nb layer prior to deposition of the Ta film.…”

Absence of metastable states in strained monatomic cubic crystals

“…15 Given the increased coordination near the secondary minimum in the Bain path for fcc crystals, one is tempted to conclude that this state is metastable. For example, Nnolim et al 16 considered structures along the Bain path of the Va and VIa bcc transition metals. In each case they found the secondary minimum described above, but did not consider the elastic stability of the structure.…”