Pressure induced structural transformations in catalytically active NH4[Eu(SO4)2] studied by light scattering

Light scattering experiments have been performed under hydrostatic pressures up to 90 kbar in NH4[Eu(SO4)2]. This material behaves as an active catalyst and presents a layered structure with two kinds of sulfate groups bonded to Eu3+ ions. Raman phonons related to the SO4 groups as well as Eu3+ photoluminescence spectra evidence the induction by pressure of two discontinuous structural transformations at around 30 and 70 kbar. No signs of pressure induced disorder is detected, on the contrary, the narrower phonons correspond to the 65 kbar phase. At low pressures the structure accommodates mainly through an anisotropic compression along the a-axis perpendicular to the Eu(SO4)2 layers.