High pressure behavior of manganites by infrared and Raman spectroscopy

The effect of hydrostatic pressure on the properties of the La0.75Ca0.25MnO 3 manganite have been studied by means of spectroscopic techniques. Raman a nd infrared (IR) spectra of this pseudocubic manganese perovskite have been collected fur the first time over a wide pressure range (0-14 GPa) using a diamond anvil cell. Preliminary results have been obtained also in the cas e of the Sr1.5La0.5MnO4 layered perovskite. The Raman measurements allow us to follow the pressure evolution of the phonon spectrum of the MnO6 octahe dron vibrational modes. Through the TR measurements we study the pressure d ependence of the high-frequency octahedron stretching mode and of the broad background associated to polaronic absorption. Raman results show an abrup t discontinuity at P* - 7.5 GPa in both frequency and width of some of the observed phonons. The infrared absorption measurements shows a remarkable i ncrease of the polaronic absorption which do not completely screen the phon on peak even at the maximum pressure. Our results, which are in agreement w ith recent high pressure diffraction data, do not support the possibility o f obtaining a metallization transition in the La0.75Ca0.25MnO3 manganite at high pressure.