Positron annihilation in Zr, Ti, and aZr0.53Ti0.47alloy

Abstract

The temperature dependence of the Doppler-broadened linewidth of annihilation photons from an integral ${}_{}{}^{68}{}_{}{}^{}\mathrm{Ge}$ positron source has been studied in Zr, Ti, and a ${\mathrm{Zr}}_{0.53}$ ${\mathrm{Ti}}_{0.47}$ alloy in the temperature range $20<T<\mathrm{}1500\mathrm{}$°C. The results are discussed in terms of a normalized peak fraction $L$ of the annihilation photopeak area. Both Ti and the alloy show a predominantly linear increase of $L$ with $T$ below their respective hcp → bcc transformation temperatures $T_{\theta }$. For $T>\mathrm{}{T}_{\theta }$, a second linear, but more pronounced, dependence of $L$ on $T$ is observed, the onset of which, in Ti, is marked by a discontinuous increase in $L$ at $T_{\theta }$. A further feature, common to the Ti and Zr data, is an apparent tendency at $T<\mathrm{}400\mathrm{}$°C for a third region with a reduced temperature dependence of $L$ to develop with increasing high-temperature exposure. Aside from data associated with this latter region, the Zr results indicate a rather linear increase of $L$ with $T$ below 750°C. At higher temperatures, the response of $L$ to $T$ increases before showing evidence of a decline near the upper temperature limit of the experiment.