Propriedades vibracionais do HfMg(MoO4)3 e ZrMg(MoO4)3: efeito da temperatura e das condições extremas de altas pressões hidrostáticas

Abstract

This work deals with the investigation of the structural properties of Hafnium e.g., HfMg(MoO4)3 and e.g., Zirconium ZrMg(MoO4)3 molybdates, which were submitted to hydrostatic pressure variation (from 0.0 to 6.5 GPa intervals) and temperature (in the 13-300 K range), through vibrational Raman spectroscopy technique. The vibrational modes behaviour for molybdates polycrystals in function of the pressure and temperature showed correlation between the structural properties of the solids and MoO4 polyatomic group interactions. The HfMg(MoO4)3 and ZrMg(MoO4)3 solids showed orthorhombic structure, belonging to Pnma or D16 2h symetric groups at room temperature and they remained in the referred structure being stable until 1013 K. Below 298 K, the solid structure became monoclinic, belonging to P21/a or C 5 2h space group. Phase transitions were observed at 280 K for HfMg(MoO4)3 whereas the phase transitions ZrMg(MoO4)3 occurred at 160 K. Studies on varying the hydrostatic pressure revealed that HfMg(MoO4)3 possesses three phases transitions; the first one at 0.9 GPa, the second at 2.4 GPa and the third at 4.2 GPa, being the last one followed by amorphization of the material. The ZrMg(MoO4)3 solid also showed three phases transitions, being the first obtained at 0.9 GPa, the second one at 2.2 GPa while the third was evident at 3.8 GPa, followed by amorphization. Both materials did not return to their original crystalline structure under decompression, once amorphized; this indicates an irreversible process on the solids.