RESUMO
Ga K-edge energy dispersive x-ray absorption spectroscopy and Raman spectroscopy measurements were employed to follow the pressure-induced semiconductor-metal phase transition of nanocrystalline GaSb produced by mechanical alloying up to 26 GPa. The results showed a slight increase of the phase transition pressures for both as-milled (8 GPa) and annealed (10 GPa) GaSb samples, as compared to that for the bulk one. The extended x-ray absorption fine structure analysis of the zinc blende (ZB) pressure domain (<10 GPa) showed that the microscopic compressibility of the bonds in the as-milled/annealed samples is higher/lower than the crystalline bulk modulus (56 GPa). The comparison between x-ray absorption near edge structure regions of the spectra and multiple scattering calculations suggests that the ZB structure evolves to a short-range chemically ordered ß-Sn structure for pressures as high as 8 GPa. Raman measurements confirm the semiconductor-metal phase transitions of ZB-GaSb between 8 and 11 GPa for both as-milled and annealed samples, showing that the semiconductor character was not recovered on releasing the pressure down to 3.9 and 1.8 GPa, indicating a very strong hysteresis effect (or even irreversible transitions). The well-known transverse effective charge reduction with pressure was also observed. Furthermore, resonance behaviour is clearly seen for transverse optical phonons and the resonance maxima peak occurs at about 1.2 GPa, corresponding to 2.11 eV in the E(1) scale, smaller by 0.3 eV than the incident photon energy.