Zn67Mössbauer investigation of Cu-Zn alloys at high pressure

The narrow 93.3-keV Mössbauer resonance in ${}_{}{}^{67}{}_{}{}^{}\mathrm{Zn}$ was used to investigate Cu-Zn alloys (brass) containing 16.6 wt. % Zn (α phase), 50.5 wt. % Zn (β’ phase), and 44.1 wt. % Zn (α-β’ 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 α-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 β’ phase. At 4.2 K and under high pressures, β’-brass is partially transformed into a new phase which might be caused by a low-temperature martensitic transition. However, no phase transformation from the β’ to the α phase is observed.