67Zn Mössbauer investigation of Cu-Zn alloys at high pressure.

Abstract

The narrow 93.3-keV M\"ossbauer resonance in $^{67}\mathrm{Zn}$ was used to investigate Cu-Zn alloys (brass) containing 16.6 wt. % Zn (\ensuremath{\alpha} phase), 50.5 wt. % Zn (\ensuremath{\beta}' phase), and 44.1 wt. % Zn (\ensuremath{\alpha}-\ensuremath{\beta}' mixed phase) under pressures up to 6.2 GPa and at 4.2 K. In the three systems the recoil-free fraction and the center shift change linearly with reduced volume. The decrease of the center shift is due to the second-order Doppler effect, which is partially compensated by the increase of the s-electron density at the $^{67}\mathrm{Zn}$ nucleus when the conduction electrons are compressed. In \ensuremath{\alpha}-brass, short-range order leads to four different Cu-Zn configurations, one of which exhibits a center shift which nearly coincides with that of the \ensuremath{\beta}' phase. At 4.2 K and under high pressures, \ensuremath{\beta}'-brass is partially transformed into a new phase which might be caused by a low-temperature martensitic transition. However, no phase transformation from the \ensuremath{\beta}' to the \ensuremath{\alpha} phase is observed.