STRUCTURAL-PROPERTIES AND STABILITY OF THE BCC AND OMEGA-PHASE IN THEZR-NB SYSTEM .3. ANALYSIS OF INTERATOMIC DISTANCES AND CHEMICAL BONDING EFFECTS

This work is part of a systematic investigation of the composition dep endence of the structural properties and relative stability of the bcc and omega phases in the Zr-Nb system. On the basis of our previous re sults on the lattice parameters of Zr-Nb alloys a detailed analysis is performed of the bonding distances in the quenched and aged omega pha se. The analysis reveals striking regularities which are discussed in the light of recent first-principles calculations of the electronic st ructure of the omega phase in Zr. A picture of the structure bonding r elations in the omega phase is proposed which accounts for the theoret ical results as well as experimental data on lattice parameters, inter atomic distances, and the composition dependence of the hexagonal/trig onal 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 AlB2-type structure compound s of Zr.