Structural Properties and Stability of the bcc and Omega Phases in the Zr-Nb System: Part Ⅲ. Analysis of Interatomic Distances and Chemical Bonding Effects

摘要

This work is part of a systematic investigation of the composition dependence of the structural properties and relative stability of the bcc and omega phases in the Zr-Nb system. Op the basis of our previous results on the lattice parameters of Zr-Nb alloys a detailed analysis is performed of the bonding distances in the quenched and aged omega phase. The analysis reveals striking regularities which are discussed in the light of recent first-principles calculations of the electronic structure of the omega phase in Zr. A picture of the structure bonding relations in the omega phase is proposed which accounts for the theoretical results as well as experimental data on lattice parameters, interatomic distances, and the composition dependence of the hexagonal/trigonal symmetry change in this phase. The present model is also used in discussing the possibility of atomic ordering in the Zr-Nb omega phase, and the Zr-Zr bonding distances in some AlB_2-type structure compounds of Zr.