Abstract
The use of pressure as a tool to modify the physical properties of materials and, thus, obtain a deeper understanding of them, has been often used during the last decades. Under pressure the interatomic bond-lengths change. This results into a modification of the physical or chemical properties of the studied material providing a unique way to obtain structural and physical correlations. One of the most interesting effects of pressure is the induction of structural phase transitions either to a new crystalline structure or to an amorphous state, resulting in both cases into abrupt changes of the physical properties. In the occurrence of a phase transition the changes that the physical properties of a material experience can only be unequivocally understood if the structure of the high-pressure phase is known. This problem is usually approached by means of high-pressure in situ x-ray diffraction (XRD) experiments in diamond anvil cells.
In this presentation I will show how we have employed single crystal XRD experiments to solve the high-pressure phase of LaPO4 at 27 GPa which transforms at 26 GPa from a monazite-type structure (S. G. P21/c) to an acentric and second harmonic generation (SHG) active phase, similar to the post-barite-type phase (S. G. P212121). Then I will show how we have used a pair distribution function (PDF) analysis to solve the controversy regarding the pressure-induced amorphization of YVO4 nanoboxes, which according to Raman spectroscopy undergo a zircon (S. G. I41/amd) to scheelite (S. G. I41/a) phase transition at 12 GPa but become amorphous at the same pressure according to powder XRD. Finally, I will present our preliminary high-pressure SHG and Raman spectroscopy results on the ferroelectric CaMnTi2O6 double perovskite (S. G. P42mc) compound, which according to our study could be the first example of pressure-induced ferroelectricity reentrance undergone in a compound with a structure different to that of a simple perovskite.