PRESSURE-INDUCED AMORPHIZATION IN NALA(MOO4)(2) - A HIGH-PRESSURE RAMAN AND IR ABSORPTION STUDY

The alkali-rare earth double molybdate NaLa(MoO4)(2) crystallizing in the orthorhombic pseudo-scheelite structure has been investigated by high pressure Raman technique up to 30 GPa. A pressure-induced amorphization is found to occur near 27 GPa at room temperature, which reverses to the original crystalline phase readily on release of pressure. This behavior is compared with the pressure-induced amorphization in Tb-2(MoO4)(3). It is proposed that structural complexity and kinetically impeded phase transition play an important role in pressure-induced amorphizations. For the observed changes to the Raman peaks near 10 GPa a disordering of the Na and La cations resulting in a statistically scheelite type lattice is suggested.