Bandfilling and structural stability of trialuminides: YAl3, ZrAl3, and NbAl3

Abstract

The cohesive properties and electronic structures versus the structural stability of transition-metal trialuminides YAl3, ZrAl3, and NbAl3in their cubic L12, tetragonal DO22, and naturally stable forms (i.e., the DO19structure for YAl3and the DO23structure for ZrAl3) have been investigated using a total energy local-density approach. The variation of structural stability with transition-metal constituent can be simply understood in terms of the bandfilling of the bonding states in the rigid band sense, with the valence electrons gradually filling the bonding states on going from YAl3, ZrAl3to NbAl3. This leads to a phase transition from the cubic L12structure (for YAl3) to the tetragonal DO22structure (for NbAl3). It is argued that this criterion may also apply to explain the variation of the structural stability of other transition-metal compounds (such as transition-metal carbides, nitrides, silicides, etc.) that are dominated by covalent interactions between the transition-metaldand the metalloidpstates.