Substitutional-interstitial interactions in niobium-1% zirconium-oxygen alloys

Abstract

The interaction between substitutional and interstitial atoms in single crystals of niobium-zirconiumoxygen alloys has been investigated by an internal friction technique. A digital computer was employed to show that the 50 kHz internal friction spectra of alloys with 1.0 at. %Zr and 15 to 5300 ppma oxygen could be synthesized on the basis of five Debye peaks, two corresponding to the oxygen and nitrogen Snoek peaks and three extraordinary peaks resulting from the relaxation of substitutional-interstitial (s-i) defects. The synthesis was achieved on the basis of single relaxation time (theoretical breadth) Debye peaks. Measurements on 〈100〉-, 〈110〉- and 〈111〉- orientated specimens showed that the orientation dependence of all the relaxation processes was the same as that for the Snoek peaks. The s-i defect symmetry was, thereby, concluded to be either tetragonal or 〈100〉 orthorhombic. These results and the composition dependence of the five processes showed that the defects responsible for the extraordinary peaks observed are 1. (1) an oxygen atom 2. (2) a nitrogen atom on nearest neighbor octahedral sites to a zirconium atom 3. (3) a pair of oxygen atoms on opposite nearest neighbor octahedral sites around a zirconium atom.