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

In order to predict the stable and metastable phases of the bcc metals in the block of the Periodic Table defined by groups 5B–6B and periods 4–6, as well as the structure dependence of their transport properties, we have performed full-potential linearized augmented plane wave computations of the total energies per unit cell as functions of the unit cell volume and the c/a ratio. In all cases, a metastable body centered tetragonal (bct) phase was predicted from the calculations. The energy barrier separating the calculated stable and metastable phases ranged from 0.09 eV/cell (vanadium) to 0.38 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 the electrical resistivity and other transport properties show that bct phases derived from the early group 5B elements are more conductive than the corresponding bcc phases, while bct phases formed from the early 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 does not result from simple tetragonal distortions of bcc tantalum.