Interatomic distances in the stable and metastable bcc and omega structures of the transition metals: analysis of experimental and theoretical trendsand correlations with Pauling's bond lengths

The name omega (Omega) phase refers to a high-pressure modification of the transition metals (TMs) Ti, Zr, and Hf. in alloys of Ti, Zr and Hf with oth er TMs, the Omega phase can be formed and retained metastably at room tempe rature by quenching the bcc structure, which is usually the stable high-tem perature phase in these alloy systems. As a part of a long-term research pr ogram on the structural and bonding properties of TM phases, we present in this paper a detailed analysis of the shortest interatomic distances (SIDs) of the stable and metastable bcc and Omega structures of the 3d, 4d and 5d TMs, as well as the connections between these and the single-bond length D (1) entering into Pauling's classical bond length vs, bond number relation (BLBNR). The analysis involves an extensive database including experimental data, very recent ab initio calculations, and new predictions based on the BLBNR for the bcc phase of the TMs. Our results lend support to early sugg estions by Jamieson of the existence of a correlation between D(1) and the SID of the Omega phase of Ti and Zr. We also find that. for most TMs, D(1) and the SID of the Omega structure differ by less than about 2%, which impl ies that the Jamieson correlation might be considered as a reasonably accur ate first approximation in estimating IDs and lattice parameters for unknow n Omega phases of the TMs. (C) 1999 Published by Elsevier Science S.A. All rights reserved.